SELF-SUSTAINABLE SERVICE FACILITY Charlene Nothnagel

SELF-SUSTAINABLE SERVICE FACILITY Charlene Nothnagel
SELF-SUSTAINABLE SERVICE
FACILITY
Charlene Nothnagel
Bachelor’s thesis
October 2014
Environmental Engineering
ABSTRACT
Tampereen ammattikorkeakoulu
Tampere University of Applied Sciences
Environmental Engineering
CHARLENE NOTHNAGEL
Self-sustainable service facility.
Bachelor's thesis 114 pages, appendices 4 pages
October 2014
The objective of this study was to collect and analyze information in producing a selfsustainable service facility. The service facility can be utilized for various reasons,
constructed from a shipping/cargo container.
The data researched and analyzed was done by taking into account a rainwater
harvesting system and alternative energy options such as solar, wind, and passive
energy.
A rainwater harvesting system was found to be a definite viable option, especially in
water scarce countries. The system required few skills, little supervision to operate, with
minimal maintenance. Another definite viable option was the container modification in
a passive solar design for thermal comfort. It is far more available, affordable, and earth
friendly than any other traditional energy sources available. A passive solar design can
be used throughout the world and can also be implemented to a certain degree according
to comfort. On the other hand, energy generating systems such as solar and wind turbine
systems were found to be a very expensive investment. Many factors were taken into
consideration but these systems are very site specific. Therefore it was inconclusive
whether these system would be advisable or not, and other alternative energy forms may
be considered.
Key words: passive; solar; wind; energy; rainwater
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CONTENTS
1 INTRODUCTION (CONFIDENTIAL) ...................................................................... 5
2 PASSIVE SOLAR ENERGY ..................................................................................... 7
2.1. Passive heating and cooling ................................................................................. 7
2.2. Passive solar building design ............................................................................... 9
2.2.1 Orientation............................................................................................... 11
2.2.2 Shading.................................................................................................... 13
2.2.3 Ventilation ............................................................................................... 16
2.2.4 Thermal mass .......................................................................................... 18
2.2.5 Insulation ................................................................................................. 19
3 ENERGY GENERATING SYSTEMS ..................................................................... 21
3.1. Solar energy system ........................................................................................... 22
3.1.1 Photovoltaic technologies ....................................................................... 22
3.1.2 Mounting structure .................................................................................. 24
3.1.3 Tilt angle ................................................................................................. 25
3.1.4 Factors affecting the output of a solar system ......................................... 27
3.1.5 Site evaluation ......................................................................................... 28
3.2. Wind energy system ........................................................................................... 30
3.2.1 Wind turbine technologies ...................................................................... 31
3.2.2 Mounting structure .................................................................................. 32
3.2.3 Minimum tower height consideration ..................................................... 33
3.2.4 Factors affecting the output of a wind turbine ........................................ 36
3.2.5 Site evaluation ......................................................................................... 38
3.3. System connection ............................................................................................. 40
3.4. System components ........................................................................................... 42
3.4.1 Inverter .................................................................................................... 42
3.4.2 Batteries................................................................................................... 43
3.4.3 Charge controller ..................................................................................... 45
3.4.4 Other BOS equipment ............................................................................. 46
3.5. Energy generating system sizing ....................................................................... 48
3.5.1 Estimating the energy consumption demand .......................................... 48
3.5.2 Solar array sizing..................................................................................... 49
3.5.3 Wind turbine sizing ................................................................................. 50
3.5.4 BOS equipment sizing ............................................................................ 52
3.6. General system estimation ................................................................................. 56
4 RAINWATER HARVESTING................................................................................. 58
4.1. A roof rainwater harvesting system ................................................................... 59
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4.2. Rainwater collected ............................................................................................ 61
4.3. Estimating the size of a system .......................................................................... 62
5 SUSTAINABLE SERVICE FACILITY CASE STUDY: JOHANNESBURG,
SOUTH AFRICA ...................................................................................................... 64
5.1. Passive solar energy ........................................................................................... 64
5.1.1 Orientation............................................................................................... 67
5.1.2 Shading.................................................................................................... 68
5.1.3 Ventilation ............................................................................................... 71
5.1.4 Thermal Mass .......................................................................................... 73
5.1.5 Insulation ................................................................................................. 73
5.2. Energy generating systems ................................................................................ 75
5.2.1 Estimating the power consumption demand ........................................... 75
5.2.2 Solar array sizing..................................................................................... 80
5.2.3 Wind turbine sizing ................................................................................. 84
5.2.4 Battery sizing .......................................................................................... 88
5.2.5 Charge controller sizing .......................................................................... 93
5.2.6 Inverter sizing.......................................................................................... 96
5.2.7 System connection types ......................................................................... 97
5.3. Rainwater harvesting system ........................................................................... 102
6 CONCLUSION ....................................................................................................... 105
REFERENCES.............................................................................................................. 108
APPENDICES .............................................................................................................. 115
Appendix 1. Service facility specifications (CONFIDENTIAL) ............................ 115
Appendix 2. Grinding machine specifications (CONFICENTIAL)........................ 117
Appendix 3. Online Links ....................................................................................... 118
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1
INTRODUCTION (CONFIDENTIAL)
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7
2
PASSIVE SOLAR ENERGY
Solar energy is a radiant heat source which can be utilized in a manner to help heat and
cool a building through a thorough managed building design. The use of the sun's energy for heating and cooling structures or living spaces is known as passive solar energy.
Passive solar energy means that mechanical means are not employed and as a consequence, the basic natural process of heat transfer is exploited. (Sustainable Sources,
2014) Passive solar energy is far more available, affordable, and earth friendly than traditional energy sources, and it can also be used directly or in combination with other
energy generating systems. This form of energy can be used for heating, lighting, cooling, etc., thus a properly designed home in a temperate (moderate) climate can use passive solar designs without adding any mechanical assistance. (Findley, D.S., 2010)
2.1. Passive heating and cooling
Passive solar heating is when the sun is used for maximum effect. This happens when
sunlight strikes an object and the heat are absorbed (Alternative Energy, 2008.). Passive
solar heating can be classified in 3 different approaches; direct gain, indirect gain, and
isolated gain. These design approaches utilizes the installation of construction materials
which absorbs solar energy easily, then slowly releases the heat throughout the day or
night to heat a living space. This is known as thermal mass and will be discussed in
more detail in section 2.2.4. (Solar Town, 2009.)

Direct solar gain is where the sun strikes thermal mass materials such as the
floors and walls through a window, and heat is radiated throughout the living
space (figure 1). (Sustainable Sources, 2014)

Indirect solar gain is where the thermal mass material is located between the sun
and the living space, thus the thermal mass absorbs thermal heat and conducts it
to the living space (figure 2). (Sustainable Sources, 2014).

Isolated gain designs are where the usage of these heat absorbing materials are
remote to the rest of the living space, for example where the sun may warm a
sun-room and then naturally funnels the heated air to the living space. Isolated
gain is illustrated by figure 3. (Solar Town, 2009.)
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Direct and indirect solar gains are important for any site that needs heating, because this
is the simplest and least costly way of passively heating a building (Sustainable Workshop, 2011). When heat is inside a building, various techniques can be utilized to spread
it and avoid heat loss (Alternative Energy, 2008).
Figure 1: Direct solar gain. During the day the floor of a living space absorbs solar
heat directly through a window, and during the night this heat is radiated back to keep
the living space warm. (Sustainable Sources, 2014)
Figure 2: Indirect solar gain. During the day the sun heats the thermal mass wall, the
vents are open to let heat in and ventilate the living space. During night time the vents
are closed where the heat is then conducted into the living space through the thermal
mass wall to keep the living space warm. (Sustainable Sources, 2014)
Figure 3: Isolated gain (Sustainable Sources, 2014)
Opposite techniques are applied to passive solar cooling than in passive solar heating
(Alternative Energy, 2008). The main objective is to keep the sun out by shading techniques and moving cool air in through ventilation techniques (SEED, 2014). When con-
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sidering a building design and ventilation techniques, attention should be paid to crossventilation, direction of prevailing winds, and the source of cooling night breezes. Shading devices can be fixed or adjustable to control the amount of solar radiation entering a
living space. (Alternative Energy, 2008) Shading is used to prevent as much direct sunlight as possible from reaching walls and floors with thermal mass, so they do not retain
heat and can keep the cool air inside. Shading techniques can be in the form of overhangs over windows or on the roof. (SEED, 2014) Buildings can also be shaded by natural vegetation and specialized window glazing. These “shading devices can reduce
solar gains by up to 90%, while still admitting a significant amount of indirect light”
(Alternative Energy, 2008). It also has to be kept in mind that external solar heat gain
can be minimized by good insulation, and reflective materials in the walls and roof for
hot sunny climates. (Alternative Energy, 2008)
2.2. Passive solar building design
A building erected with a passive design is practiced throughout the world and has exhibited low energy costs, reduced maintenance, and superior comfort (Sustainable
Sources, 2014). Passive solar designs can be used to accommodate average and severe
climates. When planning to utilize passive solar energy, the first two considerations that
need to be taken into account are the climate and solar elevation (altitude) of the area.
The solar elevation (altitude) concerns with angles of the sun as it affects how much
light and energy passively enters the home (figure 5 & 6). (Findley, D.S., 2010)
The next consideration to be taken into account in the design approach is the five design
elements as illustrated in figure 5. The five elements for a passive solar design are:

thermal mass is material used to reflect light and collect heat during the day;

absorber, an absorbing material to hold and store the heat;

aperture, is an opening to allow the light energy to enter;

control, to vary the amount of sunlight that is passed; and

distribution, a method for distributing energy during the evening.
If these elements are present and designed correctly, the building might function without mechanical assistance or intervention (Findley, D.S., 2010).
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Figure 5: The five elements of a passive solar design and solar altitude
(Findley, D.S., 2010).
In conjunction with these elements, the five major passive design principles should be
taken into account. The five major passive design principles are orientation, glazing or
shading, ventilation, thermal mass, and insulation. These may include important factors
such as, solar exposure, terrain and vegetation, wind patterns, appropriate ventilation
and window placement, roof and window overhangs, etc. A passive solar design can
take many forms as a design approach where it can be integrated to greater or lesser
degrees. (Sustainable Sources, 2014)
Solar elevation calculation
The solar elevation (altitude) angle is the angular height of the sun from the ground surface or horizon. Solstice is an astronomical event that occurs twice a year as the Sun
reaches its highest or lowest point in the sky. Throughout the year the path of the sun
changes between summer and winter, and therefore the sun is higher in the sky in summer than in winter. (Cairns Regional Council, n.d.) The maximum and minimum elevation angles at solar noon are a function of latitude and the declination angle. The declination angle varies seasonally due to the tilt of the earth on its axis of ration and the
rotation of the earth around the sun. (Honsberg, C., and Bowen, S., n.d.) The elevation
angles at solar noon can easily be calculated for the solstices and equinoxes as follow:
Equinox = 90º - Latitude
Summer solstice = 90º – Latitude + 23.5° (Declination angle)
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Winter solstice = 90º – Latitude – 23.5° (Declination angle)
(McGee, C., 2013)
Summer Solstice
Equinox
21 March & September
Winter Solstice
Latitude
Figure 6: Illustrates the solar elevation variations according to seasons.
Around 21 December the Northern hemisphere of the earth is tilted 23.45 degrees away
from the sun. This is the winter solstice for the Northern hemisphere and the summer
solstice for the Southern hemisphere. Around 21 June the Southern hemisphere is tilted
23.45 degrees away from the sun. This is the summer solstice for the Northern hemisphere and winter solstice for the Southern hemisphere. Around 21 March and September are the fall and spring equinoxes when the sun is passing directly over the equator
and the day and night times are equal in duration. (Gronbeck, C., 2009)
If more elevation angles are required, an online solar elevation calculator can be used to
calculate these angles for the specified location according to the respective dates and
times, depending on the calculator settings.
Keisan Online Calculator: http://keisan.casio.com/exec/system/1224682277
2.2.1
Orientation
The placement of a structure or building in a right orientation is an important element to
consider. Sometimes it is restricted by the aspect of land chosen, but the orientation can
reduce or increase heat load of a building. This in turn can reduce the need for costly
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artificial cooling or heating and maximize free energy from the sun and wind. (Cairns
Regional Council, n.d.)
The sun's path changes throughout the day and due to this phenomenon, advantage can
be taken from the most sunlight between 9:00 A.M. And 3:00 P.M. (sun time). This is
done by positioning the building with the long axis of the building running on the eastwest axes so that the longest wall faces true north or true south (facing the equator). The
side of the building facing the equator needs windows to allow solar energy to enter the
building. In the Southern Hemisphere the longest wall faces true north to receive the
most sunlight (figure 7), and in the Northern Hemisphere the longest wall faces true
south. (Cairns Regional Council, n.d.; SEED, 2014)
Figure 7: Orientation of a building in the Southern Hemisphere
(Sustainability Institute, 2009. p.14).
A factor to consider when taking into account a building's orientation is prevailing wind
patterns. The orientation of a building can maximize the benefits from cooling breezes
in hot weather conditions and shelter from undesirable winds in cold weather. Buildings
do not have to face directly into the wind to achieve good cross-ventilation. Internal
spaces and structural elements can be designed to channel air through the building. Local site obstructions such as trees and other buildings can obscure prevailing wind directions listed by weather data. “The right strategy depends on the climate.” (Sustainable
Workshop, 2011)
The orientation of the building should be decided together with building massing early
in the design process. Neither can be truly optimized without the other. 'Massing' is taking into account the overall shape and size of the building to maximize the free energy
from the sun and wind. (Sustainable Workshop, 2011)
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2.2.2
Shading
Shading is a method used to allow solar gain in cold weather conditions and block excess sun in warmer weather conditions. Shading is mainly used to keep a building cool
because heat entering through windows is the largest source of unwanted heat gain.
(Cairns Regional Council, n.d.) The sun's path changes throughout the year and therefore the sun is higher in the sky during summer than during winter. Shading devices
may be:

eaves such as overhangs illustrated in figure 8,

louvered, shutters or blinds illustrated in figure 9,

vegetation-supporting such as deciduous trees or bushes illustrated in figure 10,
or

a combination of these aspects.
Shading devices may also be fixed, operable, and/or removable. Fixed overhangs are
durable and low maintenance at the expense of flexibility. Adjustable devices allow the
user to fine tune the amount of shade or direct sunlight desired, but these require more
maintenance. (InspectApedia, 2014)
Figure 8: Roof overhang
Figure 9: Louvers or blinds
(Blankenbehler, B., 2013).
(Blankenbehler, B., 2013).
Figure 10: Deciduous trees used to filter sunlight (McGee, C., 2013).
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In the form of a window or roof overhang, sunlight can be kept off windows and walls
during warm weather when the sun is at a high angle (SEED, 2014). If the building element bears more than about 30º of true south or north, the effectiveness of an overhang
(as with any solar feature) begins to decrease. Overheating may occur unless the overhang provides enough shade; therefore the physical dimension of an overhang is important. An overhang that might work well in some locations can be completely inappropriate for other locations. Many variables such as latitude, climate, solar radiation
transmittance, illuminance levels, and window size and type need consideration for
properly sizing an overhang in a specific location. Since there is not yet a universally
simple formula available for sizing overhangs, it is best to have an experienced solar
designer or builder to calculate a proper overhang dimension. (InspectApedia, 2014)
There are general guidelines and methods that may be useful in estimating a suitable
overhang design.
Guidelines
The following guidelines may be useful in overhang design. These guidelines are listed
by climate type and solar noon when the sun reaches its maximum altitude for a given
day. It has to take into account that solar noon is very rarely the same as noon in local
standard time.

Cold Climates: above 6 000 heating degree days (HDD)* (at base 18ºC (65ºF))
Locate the shadow line at mid-window using the summer solstice sun angle.

Moderate Climates: below 6 000 heating degree days (HDD)* (at base 18ºC
(65ºF)) and below 2 600 cooling degree days (CDD)* (at base 22ºC (75ºF))
Locate shadow line at window sill using the summer solstice sun angle.

Hot Climates: above 2 600 cooling degree days (CDD)* (base 22ºC (75ºF))
Locate shadow line at window sill using the vernal equinox sun angle.
(HDD and CDD data is available from local weather services) (InspectApedia, 2014)
HDD – Heating Degree Days
CDD – Cooling Degree Days
Solar elevation angles
Roof or window overhangs is useful so that the summer sun is blocked but the lower
winter sun is let through. Thus the height of the sun (solar elevation) in summer and
winter should be considered for the length of the overhang. (Blankenbehler, B., 2013)
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The solar elevation angle estimates were explained in section 2.2, and can be used in a
simple sketch to estimate the overhang width.
Overhang rule of thumb
The simplest calculation for a roof overhang with is according to a roof overhang rule of
thumb:
W=½H
where W is the width of the overhang, and H is the height from the window sill of the
window to the roof. The equation is illustrated by figure 11 below. (eXtension, 2013)
Figure 11: Rule of Thumb: w = ½ H
Eave online calculator
The following is an online calculator to help calculate the required eave depth for ideal
passive solar benefit for a North facing (Southern Hemisphere) or South facing (Northern Hemisphere) window. It has to be kept in mind that the values calculated on the
website should be taken as a rough guide; it does not take into account other effects
such as trees, other buildings, etc.
Website Link: http://www.ecowho.com/tools/passive_solar_eaves_calculator.php
Values required by the online calculator:

Values for the window – Height in meters.

Values for the location of the window – Either the latitude or site location such
as the country, state and city. (EcoWho, 2014)
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2.2.3
Ventilation
An excellent means to naturally cooling a home is by natural ventilation. This is also
called passive ventilation which involves the use of natural air movement and pressure
differences to both passively cool and ventilate a building. For effective area ventilation,
windows should be able to open wide or designed in a way to capture, deflect, or scoop
breezes. The opening size of the window or louver can also affect the amount of air and
its speed. Pairing a smaller inlet with a larger outlet opening, the cooling effectiveness
can be increased (figure 12). As the same amount of air must pass through both the bigger and smaller openings in the same period of time, the air must pass through the
smaller opening more quickly and thus the inlet air can have a higher velocity. (Sustainability Workshop, 2011)
Figure 12: Pairing a smaller inlet with a larger outlet opening increases air velocity
(Sustainability Workshop, 2011).
Cross ventilation is air entering through an inlet and exiting through an outlet to optimize the path air follows through the building. Openings such as windows or vents
placed on opposite sides of the building create a funnel effective which aids air movement. Generally it is not recommended to place openings exactly across from each other, as it can cause some parts of the room to be well-cooled and ventilated while other
parts are not. Placing openings not directly opposite each other causes the air to mix,
better distributing the cooling and fresh air, and also increase cross-ventilation. (Sustainability Workshop, 2011)
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Figure 13: Cross-ventilation. The bottom images are more effective than ventilation
that does not pass through the whole space such in the top images. (Sustainability
Workshop, 2011)
To cool spaces more effectively, inlets can be placed low in the room and outlets high in
the room. These placements of openings leverage the natural convection of air. As a rule
of thumb, cooler air sinks while hot air rises. Thus, by locating the opening down low
helps push air cooler air through the space, while locating the exhaust up high helps pull
warmer air out of the space. (Sustainability Workshop, 2011)
Figure 14: Opening heights affect passive ventilation. (Sustainability Workshop, 2011)
Not all parts of buildings can be oriented for cross-ventilation, but wind can be steered
by architectural features. Examples of these architectural features are casement windows, wing walls, fences, or even strategically planted vegetation. These features can
scoop the air into a building. (Sustainability Workshop, 2011)
Figure 15: Building structures can redirect prevailing winds to cross-ventilation
(Sustainability Workshop, 2011).
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Night-purge ventilation is when windows and other passive ventilation openings are
kept closed during the day, but open at night. This is to flush the warm air out of the
building and to cool thermal mass for the next day. This type of ventilation is especially
useful when daytime temperatures are so high that bringing unconditioned air into the
building would not be cool enough, but the night time air is cool or cold. (Sustainability
Workshop, 2011)
Figure 16: During the day the thermal mass soaks up heat, and at night it is cooled by
outside air. (Sustainability Workshop, 2011)
2.2.4
Thermal mass
“Thermal mass refers to the ability of a material to absorb heat energy.” Thermal mass
is a design principal, but it can also be used to refer to a type of building material. The
basic principal is that materials with a high thermal mass act like a battery, which is
advantageous in cool climates. (Cairns Regional Council, n.d. Sheet 2) Thermal mass is
crucial for thermal comfort and the correct application of thermal mass can moderate
internal temperatures by averaging the day/night extremes. It can also exacerbate the
worst extremes of the climate when not carefully utilized. For effective thermal comfort,
appropriate areas of glazing facing appropriate directions with appropriate levels of
shading, insulation, and thermal mass should be incorporated into building design. (Sustainability Institute, 2009) “Correct use of thermal mass can delay heat flow through the
building envelope by as much as 10 – 12 hours, producing a warmer house at night in
winter and a cooler house during the summer.” (McGee, C., 2013)
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High thermal mass materials absorb and retain heat, thus “slowing the rate at which the
sun heats the space and the rate at which the space loses heat when the sun is gone.”
(Sustainability Workshop, 2011) High thermal mass materials are for example bricks,
concrete, and masonry which absorbs heat during the day and when the temperature
drops, these materials releases the stored heat. (Cairns Regional Council, n.d. Sheet 2)
This phenomenon is illustrated in figure 17.
Winter
Summer
Thermal mass absorb and store heat form
the sun during the day, and re-radiates the
heat back into the living space during the
night
Heat absorbed during the day can be
flushed out of the house with passive ventilation, and protect thermal mass during the
day from excess summer sun with shading
and insulation.
Figure 17: Effect of thermal mass on building inner air temperature. (Sustainability
Institute, 2009. p.14)
Low thermal mass materials for the tropics are ideal since these materials reacts well to
cooling breezes. Low thermal mass materials do not store heat but react quickly to external conditions. Timber, corrugated iron, and brick veneer are examples of some low
thermal mass materials. However, it is possible to couple well insulated and thermal
mass (shaded/unshaded) in innovative ways to achieve thermal comfort. “Good integrated design is the key.” (Cairns Regional Council, n.d. Sheet 2)
2.2.5
Insulation
Thermal energy travels from hot to cold, therefore heat is lost from inside to outside in
winter and cool air is lost in summer as heat tries to move indoors. (RSCP, n.d. 2013)
When a passive building is well insulated, warm air is kept inside during the winter and
cool air is kept inside during the summer (SEED, 2014). To be fully effective, insulation
should be used in conjunction with other passive design techniques. “Insulation is an
extremely cost effective measure and can pay itself back within a few years from the
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savings on energy bills.” (Cairns Regional Council, n.d., Sheet 2) Figure 18 illustrates
the typical heat losses during winter and heat gains during summer without insulation in
a temperate climate. (Mosher, M., and McGee, C., 2013) Insulation effectiveness is
measured by R-values which measure the resistance to heat flow (Cairns Regional
Council, n.d., Sheet 2). When choosing insulation, consideration should be given to the
R-Value, the price per square meter, and whether it can be installed DIY or it must be
done professionally. Some types of insulation should be installed with safety equipment
such as masks and protective clothing. The insulation chosen should ensure that it suits
the particular application and fits within the space available. The appropriate degree of
insulation depends on the climate and building type. (Mosher, M., and McGee, C.,
2013)
Figure 18: Typical heat losses and gains without insulation.
(Mosher, M., and McGee, C., 2013)
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3
ENERGY GENERATING SYSTEMS
Renewable energy sources are obtained from different natural sources, and can be considered as a 'free' energy source with lower carbon emissions. Renewable energy
sources such as wind and solar energy are constantly replenished and will never run out.
Most renewable energy comes either directly or indirectly from the sun in the form of
solar radiation. Solar radiation can be used for heating and lighting homes or buildings
(known as passive solar discussed above), and generating electricity. The sun's heat also
drives wind, whose energy is captured by wind turbines to generate electricity. The sun
radiates a huge amount of energy towards the Earth, thus the sun can provide in about
an hour the present energy requirements of the entire human population for a whole
year. Renewable energy producing technologies are more effective when it is combined
with other factors in an energy efficient structure such as adding passive solar techniques, appropriate insulation, and energy-efficient appliances. (Alternative Energy,
2014; Renewable Energy World, 2014)
The advantages of renewable energy sources are:

these sources are renewable and easily regenerated, unlike fossil fuels which are
perishable once used;

energy such as solar produce clean energy that does not pollute the environment
as no burning is required during energy usage;

renewable energy are available everywhere throughout the world;

renewable sources of energy boost economic growth and increase job opportunities.
The disadvantages of renewable energy sources are:

the technology is costly and some have high maintenance costs;

most sources are affected by weather and thus reduces their reliability;

these technologies has difficulty in producing energy quantity that is equivalent
to that produced by nonrenewable fuels. (Alternative Energy, 2014; Renewable
Energy World, 2014)
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3.1. Solar energy system
The sun radiates a huge amount of energy towards the Earth, thus the sun can provide in
about an hour the present energy requirements of the entire human population for a
whole year (Lynn, P.A., 2010). A PV solar system can be more effective when it is
combined with other factors in an energy-efficient structure such as adding passive solar, appropriate insulation, and energy-efficient appliances. Photovoltaic solar systems
can be and is used almost everywhere. These systems are stable, reliable, pollution-free,
affordable, and it can be profitable in places where the excess power can be sold to a
utility company. Solar is a sporadic power source which only functions when the sun is
shining. Even with this limitation, PV power can be utilized successfully in cloudy parts
of the world. (Findley, D.S., 2010)
3.1.1
Photovoltaic technologies
Photovoltaic (PV) cells or solar cells are the building blocks for a PV system, converting sunlight directly into electricity. PV cells are produced from materials called semiconductors. Semiconductor material is a substance which has electrical conductivity
such as silicon. For many years silicon has been and still is the most common used material for solar cells in the PV industry. Silicon is an extremely common component of
the Earth's crust but creating the semiconductor layer of the solar cell is expensive. The
type of materials used and how these are formed is very important because any impurities will affect performance. (Lynn, P.A., 2010; Findley, D.S., 2010)
The crystallinity of materials indicates how perfectly the atoms in the crystal structure
are ordered. Silicon and other semiconductor materials come in these main forms:

Mono-crystalline or single-crystalline - are crystals that are repeated in a regular
pattern from layer to layer. Solar panels produced from mono-crystalline are the
most expensive to produce but also offers the highest efficiency, are long lasting, and degrade slowly. (Findley, D.S., 2010)

Polycrystalline or multi-crystalline – are small crystals that are arranged randomly which is similar to shattered glass. These panels are made from pure molten silicon or silicon offcuts, using a casting process which creates a cell made
up of several bits of pure crystal. Polycrystalline panels are slightly less effi-
23
cient than mono-crystalline panels, as the individual crystals are not necessarily
all perfectly aligned together and therefore are losses at the joints between them.
Because of the miss-alignment of the individual crystals the cells work better
from light at all angels. (C Changes, n.d.) Polycrystalline silicon is utilized in an
attempt to cut manufacturing cost; they are not as efficient as single-crystalline
silicon but are in performance and degradation. (Findley, D.S., 2010; Toothman,
J., and Aldous, S., n.d.)

Thin-film or amorphous silicon – which is materials in these panels that have no
crystalline structure (Findley, D.S., 2010). Thin-film panels can be made flexible
and light weight (Wholesale Solar, 2013). This technology does not depend on
the long expensive process of creating silicon crystals, it still does depend on silicon which has high levels of impurities and in turn reduces efficiency of the
product. Due to the low efficiency more space and mounting hardware is required to produce the same power output as the crystalline silicone cells. (Findley, D.S., 2010)
Mono-crystalline and polycrystalline are the 'traditional' or 'first generation' technologies for solar panels and these are grouped into the category 'crystalline silicon'.
Both, mono-crystalline and polycrystalline are the two major types of crystalline silicon solar cells currently in high volume production. (Wholesale Solar, 2013; Lynn,
P.A., 2010)
Figure 19: Main forms of solar cell technology (Pak Agro Tech, 2014).
Figure 20: Thin-film PV cell (Electronics Lab, 2014)
24
The basic element of a PV system is the solar cell. Multiple solar cells are connected to
form a module (a panel) where these modules are wired together in series to form
strings. Multiple modules are connected to form a solar array (figure 21). (Endecon Engineering, 2001)
Figure 21: Photovoltaic cells, modules, array (Varkie, C.T., 2013).
The continuous change in module cost and efficiencies due to improved technology and
manufacturing methods makes it difficult to provide a general recommendation. Although there are a number of different commercially available solar panel types, they all
function in a similar way. The choice of panel to be purchased will depend on how
much power is required, where the panels will be mounted, and how much space is
available. (Findley, D.S, 2010) In the end it is the efficiency of any solar cell or module
(the percentage of solar radiation it converts into electricity) which is considered one of
the most important properties. This is especially important when space is limited and
additional costs of PV systems such as mounting and fixing module are area related.
(Lynn, P.A., 2010) According to Findley, the following numbers are the advertised percentages of efficiency for each of the different types of solar panels: monocrystalline
19%, polycrystalline 15 %, and thin-film 10%.
3.1.2
Mounting structure
PV modules and arrays need a secure mounting whether these are roof pole-mounted,
ground-mounted, wall-mounted, or installed as part of a shade structure (Roos, C.,
2009). A variety of static mounting structures are available and each has their own pros
and cons (Lynn, P.A., 2010). Take for example: roof mount structures typically keep the
wire length between the solar array and battery bank or inverter to a minimum but they
25
may require roof penetrations in multiple locations and expensive ground fault protection devices, ground mounted solar arrays require a fairly precise foundation setup and
more susceptible to theft/vandalism and excessive snow accumulation at the bottom,
pole mounts are relatively easy to install are a better choice for cold climates because
snow slides off easily and it reduces the risk of theft/vandalism. (Wholesale Solar,
2013)
When considering mounting structures, space should be left at the back of the PV modules for air circulation (Lynn, P.A., 2010). To maximize daily energy output, PV panels
should face true South in the Northern hemisphere, or true North in the Southern hemisphere. PV panels are also mounted and oriented at an angle for optimum solar collection, as more electricity is produced when the sunlight is more intense and/or strikes the
PV panels directly at a perpendicular angle. Solar panels installed at an angle assist in
keeping the panels clean by shedding rain or snow. (Roos, C., 2009)
3.1.3
Tilt angle
The angle at which a PV system is installed depends on the latitude of the area. A factor that needs to be taken into account is the season as the sun is in different portions or
elevations in the sky throughout the year. (Findley, D.S., 2010) The tilt and orientation
does not need to be perfect as PV modules produce 95% of their full power when within
20 degrees of the sun's direction. An optimum tilt of a solar array can achieve yearly
maximum output of power. In the winter months an increased tilt favors power output
where in the summer months a decreased tilt favors output. (Roos, C., 2009) Tilted PV
panels can be fixed or adjustable seasonally. A tracking system can be installed to track
the movement of the sun throughout the day but this will increase the cost of a solar
system. By adjusting the tilt twice or four times a year can give a meaningful boos in
energy as illustrated in table 1. (Landau, C.R., 2014)
Table 1: The effect of adjusting the angle of a solar panel.
Fixed
Adj. 2 seasons Adj. 4 seasons 2-axis tracker
% of optimum 71.1% 75.2%
(Landau, C.R., 2014)
75.7%
100%
26
A tilt angle rule of thumb
A simple tilt angle calculation that can be used for adjusting the tilt angle twice a year is
the tilt angle rule of thumb. The rule of thumb is: the latitude of the location, plus 15
degrees in the winter and minus 15 degrees in the summer. It has to be kept in mind that
this calculation is only an estimate and the sun angles differs during the year and can
affect the output of the solar array. (Landau, C.R., 2014)
Online tilt angle calculator
The tilt angle can also be calculated by an online solar angle calculator. The calculator
presents the optimum tilt angle for each month according to the country and city. It also
illustrates the optimum tilt angle for winter, summer, and spring/autumn. The figures
and values are shown in degrees from a vertical axis. These values can be utilized directly if the solar panels are pole-mounted or mounted on the side of a building. When
the tilt angle is needed from a horizontal axis, such as with roof-mount or groundmounts, a simple formula can be utilized:
Angle from horizontal axis = 90° – Angle from vertical axis
Link: http://solarelectricityhandbook.com/solar-angle-calculator.html
Table 2 below supplies a schedule which indicates when the angle can be adjusted according to season.
Table 2: Estimated time-line for adjusting the tilt angle accordingly.
Northern hemisphere Southern hemisphere
Adjust to summer angle on April 18
October 18
Adjust to autumn angle on August 24
February 23
Adjust to winter angle on
October 7
April 8
Adjust to spring angle on
March 5
September 4
(Landau, C.R., 2014)
27
3.1.4
Factors affecting the output of a solar system
The output of PV panel is rated and tested at the factory under Standard Testing Conditions (STC). These conditions are easily recreated in a factory but do not include factors
such as ambient and cell temperature and irradiance that affect the output of modules in
the real world. Actual conditions will rarely match rated conditions and thus actual
power output will almost always be less. STC ratings provide a basis for comparisons of
products. The STC conditions are: solar cell temperature = 25ºC; solar irradiance (intensity) = 1 000 W/m²; and solar spectrum as filtered by passing through 1.5 thickness of
atmosphere. The output of a PV panel is also affected by battery efficiency, inverter
efficiency, and wiring losses due to resistance. Module mismatch also affects the output
and is due to slight inconsistencies in performance from one module to the next. (Roos,
C., 2009; Davidson, J., and Orner, F., 2008.)
Photovoltaic panels are affected by shading, thus a well-designed system needs clear
and unobstructed access to the sun. According to Roos, C., 2009, even a small shadow
can reduce the power output of a solar module. A shadowed cell still carry string current
as it is part of a series with all the other operating sell, but without internally generated
voltage, the shadowed cell cannot produce power (acts as a load instead) and the remaining cells in the string must work at a higher voltage to make up for the loss (Patel,
M.R., 2006). It also has to be kept in mind that an area may be unshaded during one part
of the day may be shaded at another part of the day, and a site that is unshaded during
summer time may be shaded in the winter due to longer winter shadows. (Ross, C.,
2009)
Another factor to consider is the temperature of a solar panel. It is ironic but the hotter
the panels gets, less energy can be produced. When a solar panel temperature increases,
its output current increases exponentially, the voltage output in turn reduced linearly as
power is equal to voltage times current. In some cases the heat factor can reduce output
by 10 – 25% depending on the location. Not all solar panels are affected by heat equally
as the power loss due to temperature is also dependent on the type of solar panel being
used. The recommended operating use is 25ºC. When acquiring a solar panel, the manufacturer's data sheet should display the 'temperature coefficient Pmax'. This means that
for each degree over 25ºC, the maximum power of the panel is reduced by that value.
(Solar facts and advice, 2013)
28
Dirt and dust that accumulate on solar array surface can block some of the sunlight. Certain airborne particles may be abrasive and scratch the surface of the solar modules
which can cause permanent damage when not removed. Other organic deposits can become wet and cause potential corrosion. Allowing build-up can lead to overheating inside solar modules, called hot spots. Hot spots cause the same effects as shading. Although dirt and dust is cleaned off during the rainy season, rainfall alone does not suffice
to properly clean and maintain solar modules. In addition, rain may itself leave mineral
deposits on solar models after evaporation. Thus solar panels should be cleaned frequently, but the frequency by which it should be cleaned depends on the location and
environment in which they are placed. (Sol Clean, 2011; Endecon Engineering, 2001)
3.1.5
Site evaluation
Solar is universal and will work virtually anywhere, but some areas are more suitable
for solar panels than others. Irradiance is a measure of the sun's power available at the
surface of the earth (peaks at 1000 w/m²), and insolation is a measure of the available
energy from the sun which is expressed in terms of 'full sun hours'. Take for example, 4
full sun hours equals 4 hours of sunlight at an irradiance level of 1000 w/m². Different
parts of the world receive more 'full sun hours' per day than others. By utilizing a solar
insolation zone map (figure 22) will give a general idea of the 'full sun hours' per day at
a location. (Wholesale Solar, 2013)
Figure 22: Solar insolation map - The amount of solar radiation throughout the world
with color-tone shading. (Ember LED, n.d.)
29
Even though the sun is up for 12 hours a day at certain locations, all these hours are not
considered as full sun hours. Early morning and late afternoon sunlight shines through
more atmosphere than at midday and also the angle of the sun is too sharp relative to the
surface of the solar panels. (Roos, C., 2009; Wholesale Solar, 2013) It has to be noted, a
solar module can produce up to 80% of its full sun power on partly cloudy days, and
even with heavy clouds on an extremely overcast day it can produce about 30% power.
(Roos, C., 2009)
The online links supplied below can be used to find peak sun hour charts for more accurate data according to a specific location:
World Climate and Temperatures - http://www.climatemps.com/
World Weather and Climate Information - http://www.weather-and-climate.com
Solar Irradiance Calculator - http://solarelectricityhandbook.com/solar-irradiance.html
30
3.2. Wind energy system
The terms 'wind energy' or 'wind power' describes the process by which natural wind in
the atmosphere is captured and converts the wind's kinetic energy into mechanical/rotational energy and then electricity (Wind Energy Development, n.d.). Wind turbines are mounted on a tower to take advantage of faster and less turbulent wind and
capture the most energy. When the wind blows past a turbine it catches the wind's energy with its propeller-like blades and rotates. There are usually two or three blades
mounted on a shaft to form a rotor. As the wind blows, a pocket of low-pressure air is
formed on the downwind side of the blade, the low-pressure air pocket pulls the blade
toward it which causes the rotor to turn, and this is called lift. The force of the lift is
much stronger than the wind's force against the front side of the blade, called drag. Thus
the combination of lift and drag causes the rotor to spin like a propeller (figure 23). The
rotation triggers an internal shaft to spin, connected to a gearbox, connected to a generator that ultimately produces electricity. Wind energy has become the least expensive
source of new electric power that is also compatible with environment preservation programs (Patel, M.R., 2006). But since wind energy is affordable the greatest disadvantage is that is not accessible everywhere. (American Wind Energy Association,
2013; Renewable Energy World, 2014; Sautter, E., n.d)
Figure 23: Pressure difference (Clean Energy Brands, 2014).
31
3.2.1
Wind turbine technologies
Wind turbines are available in an assortment of types and sizes. Basically small homesized or distributed wind turbines are used to directly power a home, farm, or small
business as its primary use. Small home-sized turbines have rotors between 2,5 and 8
meters in diameter, can stand 9 meters tall, and are 50 kilowatts or smaller. (American
Wind Energy Association, 2013; Wind Energy Development, n.d.) Wind turbines can
further be classified according to their type of design. There are various small-scale
wind turbine types in operation today. They all operate on similar principles but fall into
two basic groups; horizontal-axis turbines and vertical-axis turbines (figure 24):

Horizontal-axis turbines - are the most common turbine used today and most of
these are two-or three-bladed. The blades are typically made of fiberglass, glass
polypropylene, or some other composite material. The turbine consists of a tall
tower, rotor, generator, controller, and other components. These turbines utilizes a fan-like rotor that faces into or away from the wind and are placed high atop
a tower to take advantage of stronger and less turbulent wind The amount of
power these turbines will produce is determined by the diameter of the rotor, in
other words, the 'swept' are or the quantity of wind intercepted by the turbine.

Vertical-axis turbines have blades that go from top to bottom. These turbines
make up only a very small share of the wind turbines today. Vertical-axis turbines are available in two types, Savonius and Darrieus. (Wagner, HJ. & Mathur, J., 2009; U.S. Department of Energy, 2013)
Figure 24: Horizontal-axis and Vertical-axis wind turbines
(The Scottish Government, 2006).
32
The basic theoretical advantages of a vertical-axis turbine are that the generator, gearbox, etc. can be placed on the ground and that a yaw mechanism is not needed to turn
the rotor against the wind. But the basic disadvantages of vertical-axis turbine are:

the need of a tower is eliminated, but the wind speed will be very low on the
lower part of the rotor;

the overall efficiency of the vertical-axis turbine is less than that of a horizontalaxis turbine;

it is not self-starting. For example a Darrieus machine will need a 'push' before it
starts. When the turbine is grid connected this is only a minor inconvenience
since the generator may be used as a motor drawing current from the grid to start
the machine

the machine may need guy wires to hold it up (Wagner, H.J. & Mathur, J.,
2009).
3.2.2
Mounting structure
There are two types of domestic-sized or home-sized wind turbines:

Pole mounted/mast-mounted/free-standing – these turbines are free standing and
are erected in a suitable exposed position.

Building-mounted/roof-mounted – these turbines are smaller than mast-mounted
systems which can be installed on the roof. Often these types are around 1kW to
2kW in size. (Energy Savings Trust, 2014)
It should be noted that wind turbines mounted to structures vibrate and transmit vibrations to the structures. This can lead to noise disturbances within the building. When a
wind turbine is roof-mounted, it is an area of increased turbulence which can shorten the
life of the turbine and reduce energy production. Additional costs to mitigate these concerns can lead to increased total cost of the installation. (OpenEI, 2013)
There are two types of towers; self-supporting (free-standing) and guyed (anchored)
towers (figure 25). Most home wind power systems use guy towers. Guyed towers are
less expensive than self-supporting towers and they are easier to install. These towers
consist of lattice sections, pipes, or tubing (depending on the design); support guy wires;
and the foundation. Guyed towers require space to accommodate them because the radi-
33
us must be one-half to three-quarters of the tower height. There are also tilt-down towers available but these are more expensive. They offer an easy way to perform maintenance and it is useful during hurricanes and other hazardous weather conditions when it
necessary to lower the turbine. A lot of manufacturers provide wind energy system
packages that include a range of tower options. (OpenEI, 2013; U.S. Department of Energy, 2012)
Figure 25: Types of towers (Wind Power Systems, n.d.; Clean Energy Brands, 2014).
The tower needs to be as tall as possible as the wind speed increases with height
(OpenEI, 2013). When siting the wind turbine, it should also be erected as far away
from local turbulence causing obstructions such as large trees, buildings, and hills. Extreme turbulence or 'bad winds' can cause fatigue damage and can shorten the turbine's
working life. If erecting the wind turbine far away from obstructions is not possible, the
other option is to use a taller tower to ensure that the turbine is well above these obstructions which gives the turbine access to cleaner and stronger wind resource. Therefore it is advisable to erect the turbine as high as the zoning laws and the initial investment allow. Since taller towers increases the cost of a wind turbine system, it is best to
evaluate the overall energy and cost payback before investing in taller towers. (Energy
Matters, 2012)
3.2.3
Minimum tower height consideration
It is recommended to site the wind turbine at least 6 m (20 feet) above any surrounding
obstacles such as trees or buildings in a 76 m (250 feet) radius (illustrated by figure 26).
34
Trees and taller structures can be down-wind from the wind generator. The result is an
entry level tower height that should be considered and not seen as the optimal height.
This gives an indication of the minimum tower height that might be needed to overcome
the effect of obstacles and the turbulence they create. (Energy Matters, 2012)
Figure 26: Siting wind turbine (Energy Matters, 2012)
Take into consideration a few invariable complications. The following situations include:

The largest obstacles that usually pose a problem are trees. Not just the current
height of the surrounding trees needs to be known, but also the mature height for
these trees. Or the growth of these trees over the 20 – 30 year life of the wind
turbines system.

If the specific are has a prevailing tree line or the area consists of 50% tree cover, the tree line becomes the effective ground level for the tower and should be
sized accordingly.

The strongest seasonal winds in most locations come from one to several prevailing wind directions. The wind turbine can be sited upwind of obstacles towards the prevailing wind directions. This may compromise occasional winds
from other directions, but it reduces the effect of turbulence from trees and
buildings. (Sagrillo, M., 2009) Tower height always is “site specific.”
Velocity at different height estimation
Wind resources are measured at certain height and the measured height might not be at
the same height as where the wind turbine is going to be located. Wind is strongly affected by obstacles on the ground and the surface roughness. Higher above the ground
the wind is no longer influenced by the surface, approximately 5 km above ground.
35
Wind speed changes between these two extremes and this phenomenon is called vertical
wind shear. (The Swiss Wind Power Data Website, n.d.)
The formula below can be used to estimate the velocity at different heights and by estimating the wind velocity at a different height, the power output at that height can be
estimated. Since a taller tower will increase the productivity of any wind turbine by giving it access to higher wind speeds as shown in the Wind Speeds increase with Height
graph. Estimating the power outputs at different heights, such as the minimum tower
height rule of thumb, a bit taller or a bit shorter, can give some indication on the tower
height which will fit the bank.
where v2 is the wind speed at a certain height (h2), and v1 is the wind speed at a measured height (h1). Z0 is the roughness length that can be selected according to a roughness class supplied in the table 3 below. (The Swiss Wind Power Data Website, n.d.)
Table 3: Roughness Classes and Lengths
Roughness Roughness
Land cover types
class
length (Z0)
0
0.0002 m
Water surfaces: seas and lakes
0.5
0.0024 m
Open terrain with smooth surfaces, e.g. concrete, airport runways, mown grass, etc.
1
0.03 m
Open agricultural land without fences and hedges; maybe some
far apart buildings and very gentle hills.
1.5
0.055 m
Agricultural land with a few buildings and 8 m high hedges
separated by more than 1 km.
2
0.1 m
Agricultural land with a few buildings and 8 m high hedges
separated by approx. 500 m.
2.5
0.2 m
Agricultural land with many trees, bushes and plants, or 8 m
high hedges separated by approx. 250 m.
3
0.4 m
Towns, villages, agricultural land with many or high hedges,
forests and very rough and uneven terrain.
3.5
0.6 m
Large towns with high buildings.
4
1.6 m
Large cities with high buildings and skyscrapers.
(The Swiss Wind Power Data Website, n.d.)
Wind Profile Calculator - http://wind-data.ch/tools/profile.php?lng=en
36
3.2.4
Factors affecting the output of a wind turbine
The earth's surface roughness and obstacles slow winds down and therefore decrease
wind energy efficiency. The earth surface roughness affects wind speed due to the friction against the surface of the earth. Obstacles affect wind speed due to the occurrence
of turbulence and also impose more wear and tear on the wind turbine. The slowdown
effect on wind from an obstacle increases with the height and length of the obstacle.
Generally the slowdown effect is more pronounced close to the obstacle and close to the
ground. This is why towers for wind turbines are usually made tall enough to avoid turbulence. (Wagner, HJ. & Mathur, J., 2009)
There is also the difference in wind directions near the surface. Sea breezes, mountain
breezes and 'tunnel effects' influence the flow of wind patterns close to the surface of
the earth. A tunnel effect occurs when air becomes compressed on the windy side of
buildings or mountains, and the speed increases considerably between the obstacles to
the wind. By placing a wind turbine in such a tunnel is one way of obtaining higher
wind speeds than in the surrounding areas. But to obtain a good tunnel effect the tunnel
should be 'softly' embedded in the landscape, as turbulence may negate the wind speed
advantage completely. (Wagner, HJ. & Mathur, J., 2009)
The amount of energy which the wind transfers to the rotor depends on the density of
the air, the rotor area, and the wind speed. The figure below illustrates a formula showing the variables that determine the power in the wind going into the wind turbine.
Figure 27: Variables determining the power in the wind (Watson, D., 2010).
Density of air
Air density changes slightly with air temperature and elevation. Air density increases
the colder it gets and it decreases the warmer it gets, thus the denser or 'heavier' the air,
the more energy is received by the turbine. (Wagner, HJ. & Mathur, J., 2009) Ratings
for wind turbines are based on standard conditions of 15°C at sea level and a density
37
correction can be made. According to the International Standard Atmosphere (ISA), air
has a density of approximately 1.225 kg/m³ at sea level and at 15°C.
Turbine blade diameter / Rotor swept area
The rotor area determines how much energy a wind turbine is able to harvest from the
wind. If the swept area is doubled, the power it produces is also doubled. Thus the basic
idea is when the rotor area increases it might increase the energy output. (Carbon Trust,
2008; Wagner, HJ. & Mathur, J., 2009)
Velocity of wind / Wind speed
Wind speed is always fluctuating and due to this phenomenon the energy content of the
wind is always changing, in other words, the energy output from a wind turbine varies
as the wind vary. The wind speed is illustrated as a function to the power of 3, thus if
the wind speed doubles the power is increased eightfold (2³=8). This demonstrates how
sensitive power is to wind speed and why it is of utmost importance to understand the
wind conditions in the site location when considering wind turbines. (Carbon Trust,
2008; Wagner, HJ. & Mathur, J., 2009)
A constant (Betz limit) / Efficiency
Wind energy is generated by the flow of air over the blades and through the rotor area.
The wind turbine extracts the kinetic energy in the wind by slowing it down. If a wind
turbine was 100% efficient by converting all the wind's kinetic energy to mechanical
energy, the velocity leaving the turbine would be zero. In other words there is no kinetic
energy left in the wind and there is no wind. Therefore a wind turbine would not work.
The theoretical maximum amount of energy that a wind turbine can collect from the
wind is approximately 59%, otherwise known as the Betz limit. (EnergyBible, 2012;
Watson, D., 2010)
The collection efficiency of a turbine in practice is not as high as 59%. A specific wind
turbine has a 'design point'. It is the peak efficiency at a wind speed for which the system is designed. The efficiency is the same or less at wind speeds above and below the
design speed. At all other wind speeds the efficiency will be worse. Generally wind turbines operate at lower than best efficiency, as wind speeds are never constant or average. The efficiency decreases even more when taking into account the energy losses in a
complete wind energy system. (EnergyBible, 2012; Watson, D., 2010) The system
38
components has less than perfect efficiencies and according to the Carbon Trust, anecdotal evidence suggests that the capacity factor for a small-scale wind turbine generally
ranges between 12 – 20% or less than 25%. (Carbon Trust, 2008)
3.2.5
Site evaluation
Wind turbines can be an effective source of renewable power in many areas across the
world. Before considering a small wind turbine system for a specific site, the following
conditions should be determined beforehand: there is at least a 4.5 m/s average wind
speed (best at 5.4 m/s or more), the property is unobstructed from tall buildings and
trees, the property has enough space for erecting the tower, and the local zoning allows
a structure that is at least 12 m tall. A proper site for a small wind turbine system is critical to its performance and longevity. (Energy Matters, 2012)
Determining the wind resource can be done by utilizing Meteorology data. Ideally in
terms of a wind rose which was calculated over 20 – 25 years would probably be the
best guide, but care should be taken when using meteorology data. The wind data collected by meteorologists is for weather forecasts and aviation, where this information is
often used to assess the general wind conditions for wind energy in a specific location.
Therefore it is difficult to estimate wind conditions at a nearby site and should be used
as an indication of what the wind resource is at the specific location. According to
Wagner and Mathur, in most cases using meteorology data directly underestimate the
true wind energy potential in an area. (Wagner, H.J. & Mathur, J., 2009)
Wind resource data can also be obtained from local weather stations or universities. It is
recommended not to use airport data as a source, since airports are generally located in
lower wind areas such as valleys and their measurement techniques do not produce
good data. Another method that can be used collectively with wind maps or local data is
by looking around and observing the deformation of vegetation and trees on and around
the specific site. The Griggs-Puttnam Index was a scientific study, where the wind resource at a particular site can be determined by looking at how wind deforms the vegetation (figure 28). Conducting an actual wind resource assessment at the specific site
would by far be the most accurate strategy, but it is also the most expensive and time
consuming (hiring someone or DIY). (Energy Matters, 2012)
39
Figure 28: The Griggs-Puttnam Index deformity chart
(Silverford Renewable Blog, 2012)
A wind turbine should be erected in the most optimum place. The ideal position would
be (figure 29):

a flat open space with good wind from at least one direction known as the prevailing
wind direction. Winds running off a cliff may be very turbulent, causing wind
shears, therefore it is very important to site the generator far enough from a cliff to
avoid turbulent wind;

a coastline, typically very strong prevailing winds blow from the ocean and for this
reason it is important to install the wind turbine as close to the coastline as possible;
or

a smooth hill top with an open area in the prevailing wind. Near the top of a hill, the
wind compresses as it blow over the top and the wind speeds up significantly. With
proper placement the air flow should be reasonably smooth and free from excessive
turbulence and a shorter tower can be used. (Energy Matters, 2012)
Figure 29: Three typical siting considerations (Energy Matters, 2012).
40
3.3. System connection
The electricity generated by solar panels or wind turbines can be stored, used directly,
fed back into the grid line, or combine with other electricity generators. Energy generating systems includes different components (explained in section 3.4), that should be
selected according to the system type, location, and application. (Roos, C., 2009) These
systems can generally be divided into two major categories: grid-connected and standalone systems. A grid-connected system is interfaced to an electricity grid and a standalone system is self-contained. (Lynn, P.A., 2010)
The grid-connected or grid-tied systems are the most common type of PV and wind turbine systems (figure 30). The PV or wind turbine system and the grid acts in harmony
and there is an automatic, seamless back and forth flow of electricity according to sunlight/wind conditions and the electricity demand. With this type of system connection
the PV array or wind turbine does not need to produce 100% of the electricity demand
and allows users to utilize energy from the electricity grid when required. The excess
output from these renewable sources can be fed into the grid when it is not required.
(Lynn, P.A., 2010) Thus a net metering agreement with the utility company can be
completed where this agreement allows utility customers to receive credit for their excess energy generated. Net metering policies and agreements are different for each
country and utility. (Roos, C., 2009)
Figure 30: A grid-connected solar system (Wholesale Solar, n.d.)
Grid-tied systems without battery backup are the simplest, most reliable, and least expensive configuration. But this type of system will shut down when a utility power outage occurs, where on the other hand, a system with battery back-up can maintain power
to some or all of the electric equipment. Adding batteries to a system comes with several disadvantages such as: batteries consume energy during charging and discharging
which reduce the efficiency and output of the system; batteries increases the complexity
41
of the system and the cost; batteries require maintenance; and batteries will usually need
to be replaced before other parts of the system. For this reason the disadvantages must
be weighed against the advantage of power back-up. (Roos, C., 2009)
Stand-alone systems (figure 31) can be more cost-effective in remote locations than
extending a power line to the electricity grid, but can also be used to obtain independence from the power provider or demonstrate a commitment to non-polluting energy
sources.
Figure 31: Stand-alone solar system (Wholesale Solar, n.d.).
Another type of stand-alone system is known as a hybrid system (figure 32). The main
purpose of a hybrid power system is to combine multiple electricity generating sources
to generate 100% of the electricity demand. PV and wind turbine systems can be connected with each other, or it can be connected with another source of power, and are
more likely to produce power when required. When neither the PV and wind turbine
produce electricity, power can be provided through batteries and/or an engine-generator
powered by fossil-fuel like diesel. Adding an engine generator makes the system more
complex. Modern electronic controller can operate these systems automatically and adding an engine generator can also reduce the size of the other components needed. Hybrid systems can also be connected to the utility grid. (Wagner, HJ. & Mathur, J., 2009)
Figure 32: Hybrid system, grid-tied with a battery bank (Wholesale Solar, n.d.).
42
3.4. System components
As mentioned before, energy generating system includes different components that
should be selected according to the system type. Additional items are required to complete a system which is essential to a properly engineered installation. These are generally referred to as Balance-OF-System (BOS) equipment. The BOS equipment can include an inverter, charge controller, batteries, etc.). BOS equipment are also the additional costs to the energy generating equipment and mounting structures, including parts
and labor which will depend on the specific application. Some manufacturers do supply
system packages that include all the parts necessary for specific applications.
(Lynn, P.A., 2010)
3.4.1
Inverter
Inverts are used to convert direct current (DC) to alternative current (AC). PV modules,
some wind turbines, and batteries produce DC power, where appliances use AC power.
For this reason, an inverter is one of the most important equipment in a system connection. Inverters used in a grid-connected system are not suitable for stand-alone systems.
Stand-alone system inverters are not as constrained as grid-connected inverters, for the
basic reason that the inverter receives power from the battery bank which has more or
less constant DC voltage. Grid-connected inverters are designed to connect to the utility
grid. Thus grid-connected inverters can also be divided into two types, inverters designed to be used with batteries and inverters designed for a system without batteries.
(Lynn, P.A., 2010)
Grid-tied inverters receive energy from the utility grid, receives energy from the renewable energy sources or a battery bank, and it can also feed the excess energy generated
back into the utility grid. Grid-tied inverters not only convert DC to AC, but also generate AC at precisely the right frequency and phase to match the grid supply and for the
use in appliances. These types of inverters must be able to handle a wide range of energy output from PV modules and/or wind turbines, in other words, fluctuating power
output according to the sunlight and wind conditions. This is done by using maximum
power point tracking (MPPT) to optimize the energy yield.(Lynn, P.A., 2010) The
MPPT automatically adjust the system voltage and when selecting an inverter the
43
MPPT capability should be considered. Sizing and selecting grid-tied inverters entail
different considerations, but it is easier since the system does not have to provide 100%
of the energy demand and peak energy demand and surge capacity does not need to be
taken into account. (Roos, C., 2009)
Micro inverters are also available which is directly attached to the individual panels in a
PV array making each module its own AC power source. Micro-inverters have several
advantages over conventional central inverters. The main advantage of micro-inverters
is that it can be used to get the most power from a PV system. Shading, debris, snow
lines, or malfunctions from one panel will not affect the output of the entire PV array.
Thus each inverter harvest its optimum power by performing MPPT for its individual
connected panel. Another advantage is that instead of sizing an inverter to a specific
number and overall wattage of solar panels, the size of the solar electric system can be
increased and panels of different wattages and manufacturers can be added. Since a micro-inverter is installed on each solar panel, the total cost for these micro-inverters can
be more than for a central inverter. Another disadvantage can be life reduction due to
high temperatures when a PV array is installed on the roof. (AMECO Solar, 2014)
3.4.2
Batteries
Stand-alone systems need a battery bank to provide power at night and cloudy or windless days. If a system is grid-connected, a battery bank is not necessary unless it is used
as a back-up emergency power. Batteries is an electrical storage device and come in
many shapes and sizes, but they all have one thing in common, they store direct current
energy for later use. (Davidson, J. & Orner, F., 2008) This energy storage comes at a
cost, it reduces the efficiency output (about 10%), it increases the complexity of the
system, and it also increases the cost. In general, battery backup in grid-tied systems can
be smaller since it is only used when there is a power outage. The types of batteries
used are:

Lead-acid batteries
o Flooded or liquid vented (FLA), unsealed with liquid electrolyte
o Sealed or valve-regulated lead acid
o Absorbent Glass Mat (AGM), sealed with electrolyte held captive by
glass mat
44
o Gel cell (VRLA), sealed with gel electrolyte

Alkaline batteries
o Nickel-cadmium
o Nickel-iron
Each type of battery has its own benefits, drawbacks and requirements. The most common batteries used in the systems in general are lead-acid batteries. The comparisons
between the three different lead acid batteries are summarized in table 4. (Solar Town,
2012; Roos, C., 2009)
Table 4: Comparison Chart – Lead acid batteries
Lifespan
(if well
cared for)
Minimal
Gassing
Spill
Flexibil-
Proof
ity in
Rating
Mounting
Charging
Voltage
Sensitivi-
Maintenance Price
ty
Flooded
3
1
1
1
3
1
3
Gelled
2
3
3
2
1
3
2
AGM
2
3
3
2
2
3
1
Rating:
1 – Poor;
2 – Good;
3 - Excellent
(Solar Town, 2012)
Alkaline batteries are more expensive, but they are only recommended in extremely
cold temperatures (-45°C or less) or for certain commercial or industrial applications.
Their advantages over lead-acid batteries include tolerance of freezing or high temperatures, low maintenance requirements, and the ability to be fully discharged or overcharged without harm. (Roos, C., 2009)
High-quality lead-acid batteries should be utilized for stand-alone systems. These batteries must have long working lives under frequent conditions of charge and discharge.
During long cloudy periods or winter months, the batteries must also display low selfdischarge rates and high efficiency. A rule of thumb, the faster the discharge the lower
the capacity. The most energy derived form a battery is by discharging it as slowly as
possible. The capacity of a battery also depends on the temperature, where the rated
capacity normally applies to 20ºC and reduces by about 1% for every degree drop in
temperature. (Lynn, P.A., 2010)
45
When sizing a battery bank for an off-the-grid system, it is usually sized for one to three
cloudy days. In the other hand, battery bank sizing for grid-connected systems, it is for
relatively short periods of time such as 8 hours being typical. Depending on the particular needs of a facility and the length of power outages expected, sizing may vary. In a
PV system the solar array must have a higher voltage than the battery bank in order to
fully charge the batteries. Another consideration is the wiring distance between the
modules, the charge controller and the battery bank, since higher voltages may be required for long wiring distances. (Roos, C., 2009)
An ideal battery storage area has the following characteristics:

good ventilation, even in a plastic storage box,

not near any open flames,

no possibility for electrical sparks,

easy to maintain and inspect,

tidy and easy to clean, kept at 15,5 to 21.1ºC,

out of reach of non-authorized personnel, and

has an up-to-date fire extinguisher handy. (Davidson, J., and Orner, F., 2008)
3.4.3
Charge controller
A charge controller is also sometimes referred to as regulators or a battery charger. A
charge controller is only necessary in a system with battery back-up as it protects batteries from damage and prolongs its working life. The primary function of a charge controller is to prevent the overcharging batteries when the electricity supply exceeds demand, and over discharging when demand exceeds supply. Charge controllers also prevent charge from draining back to solar modules and wind turbine when these components do not produce electricity. Depending on the price and sophistication of the
charge controller, various subsidiary control and display functions are included to protect the batteries and ensure an operating regime that maximizes the performance and
length of life. Since batteries are an expensive part of a system, especially in stand-alone
systems, the modest cost of a good charge controller is money well spent. (Lynn, P.A.,
2010; Roos, C., 2009)
46
There are four types of charge controllers: shunt, series, pulse, and maximum power
point tracking.

A shunt controller is a solid-state device with a transistor in parallel to the array.
It directs the excess current produced to an earth ground, a power dissipating
heat sink, or another load. Shunt controllers are simple, inexpensive, and are only designed for very small systems (Roos, C., 2009).

Series controllers usually have a relay or switch transistor in series between the
PV array and the battery. This device switches array current on and off.

Pulse controllers also connect in series like the series controller but this device
rapidly switch or pulse the array current on and off.

Maximum power point tracking (MPPT) controllers are also connected in series.
But these controllers use a microprocessor-based algorithm to repeatedly find
the highest solar array voltage and current output. MPPT controllers are most effective in cold weather. According to Davidson and Orner, manufacturers claim
that their devices increase power production up to 25% but, the typical annual
increase is 15% or less. Davidson and Orner also state that with this production
increase, it is enough to justify the two- to four-times higher price of a MPPT
charge controller. MPPT controllers should not be confused with solar array
trackers that physically move the the array to follow the sun, and most grid-tie
inverters have MPPT electronics but these inverters do not regulate the charge
from to a battery bank. (Davidson, J., and Orner, F., 2008)
Charge controllers selected for off-grid systems, their default setting may not be appropriate for grid-connected systems. A charge controller should not interfere with proper
operation of the inverter when it is set up, and the controller must be set up so that the
charging of batteries from the PV array takes precedence over charging from the grid.
Also, the charge controller must be selected to deliver the charging current appropriate
for the type of batteries used in the system. (Roos, C., 2009)
3.4.4
Other BOS equipment
Grounding equipment
This equipment provides a well-defined, low resistance path from the system to the
ground. It protects the system from current surges from lightning strikes or equipment
47
malfunctions, it also stabilizes voltages and provides a common reference point.
Equipment grounding provides protection from shock caused by a ground fault which
occurs when a current-carrying conductor comes into contact with the frame or chassis
of an appliance or electrical box. Any exposed metal and all system components should
be grounded. (Roos, C., 2009)
Meters and instruments
Installing a PV or wind turbine system, it might be required to install a new electrical
meter. The meter allows for a measurement of net energy consumptions in both entering
and leaving the system. (Findley, D.S., 2010) Essentially there are two types of meters
used in the systems, a utility kilowatt-hour meter and a system meter. A utility kilowatthour meter measures energy delivered to or from the grid, where a system meter
measures and displays system performance and status. (Roos, C., 2009)
Disconnects
A disconnect is needed for each source of power or energy storage device in a system.
Automatic and manual safety disconnects protect the wiring and components from power surges and other equipment malfunctions where they also ensure safe system shut
down and removal of components for maintenance and repair. When a system is gridconnected, the safety disconnects ensure that the generating equipment is isolated from
the grid as it is very important for the safety of utility personnel. It is not always necessary to provide a separate disconnect, but before omitting a separate disconnect, a result
for unsafe conditions in performing maintenance on any component should be considered. Another consideration is the convenience of the disconnect location, where an
inconveniently located disconnect may lead to the tendency to leave the power on during maintenance which can result in a safety hazard. (Roos, C., 2009)
48
3.5. Energy generating system sizing
3.5.1
Estimating the energy consumption demand
To calculate the daily energy consumption of each appliance, the following formula can
be used:
Watt-hours per day consumption = Quantity x Rated watts x Hours used per day
Add up all the watt-hours per day consumption for each appliance to calculate the total
energy consumption demand. The estimated power consumption demand per day calculation can easily be calculated by utilizing the power consumption demand worksheet
below.
Total Power Consumption Demand Worksheet
Appliance
Watts
(volts x amps)
Qty
Total
Watts
Average
Watt-hours
per day
Hours per
day used
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
x
=
Total Watt consumption at one time
Total Watt-hours consumed per day
(Wagner, HJ. & Mathur, J., 2009)
=
=
49
3.5.2
Solar array sizing
Sizing the solar array needed to produce the total watt-hours needed per day depends
mostly on energy consumption demand. The amount of solar panels needed in the array
also depends on: the derating factors, weather the system includes a battery bank or not,
the peak sun hours, and the module wattage rating. The solar array size needed can easily be calculated by utilizing the following formula:
Number of Modules =Total Watt-hours per day ÷ Derating Factors ÷ Peak Sun Hours ÷
Module Wattage Rating (STC)
The derating factors
The derating factors take into account the efficiency losses. The derating factors are
supplied in table format below.
Table 5: Typical Derating and Efficiency Factors
Derate Factor
Derate Range
Typical Deratings
Temperature
0.95 – 0.80
0.90 for single-crystal Si
0.88 for polycrystalline Si
0.95 for amorphous Si
Dust and Dirt
0.98 – 0.90
Keep array clean for less than 5% loss
Module Mismatch
0.98 – 0.96
0.98 to 0.96 (2% to 4%)
DC Wire Loss
0.99 – 0.97
0.98 (2% or less)
Battery Conversion
Efficiency
0.90 – 0.80
0.90 (90% coulombic efficiency)
Inverter Efficiency
0.90 – 0.80
0.90 for batteryless type
0.85 for battery type
or manufacturer's rating at 75% load
AC Wire Loss
0.99 – 0.98
0.995 (1.5% or less)
Keep total DC + AC wire loss below 3%
(Davidson, J., and Orner, F., 2008.)
This table can be used to calculate the efficiency loss for each system components separately or an alternative method for an approximate calculation is to divide the amount of
electricity demand by an overall efficiency of a PV system:

65% for a system with batteries or

75% for a system without batteries
50
Assuming the PV array is placed in the correct orientation and tilt angles according to
the specific location for optimum energy output. PV Array Azimuth Derating Factor
and PV Array Tilt Derating Factor = 1. (Wagner, HJ. & Mathur, J., 2009)
Peak sun hours
The actual watt-hours demand from the PV array is calculated by taking into account
the solar insolation, irradiance or peak sun hours of a specific location. Solar insolation
or peak sun hours can be found or calculated by utilizing an insolation map, peak sun
hour charts, or the solar irradiance calculator as explained in the site evaluation in section 3.1.5. The value chosen as the peak sun hours should be the lowest winter value, as
not to size the solar array too small. (Wagner, HJ. & Mathur, J., 2009)
Module wattage ratings
There are different PV modules and sizes available and each will produce different
amount of power. The result from this calculation is the minimum number of PV panels,
if more models are installed, the system will perform better and battery life will improve. The total power needed per day from the PV array is divided by the rated output
Watt-peak of the PV modules available. The result should be rounded off the next highest full number. This will be the number of PV modules required. (Leonics, 2013)

For 24-volt DC systems using 12-volt modules round up to the nearest number
divisible by two.

For 48-volt DC system using 12-volt modules round up to the nearest number
divisible by four. (Wagner, HJ. & Mathur, J., 2009)
3.5.3
Wind turbine sizing
There is no universal formula to size a wind turbine, but the energy that a wind turbine
needs to produce depends mostly on energy consumption demand from the appliances
or devices at one time. This value gives an idea of the size wind turbine that is needed
and it is advisable to acquire a bit bigger turbine to take into account efficiency losses. It
is also recommended that if appliances are used with inductive motors which require
more power to start, a wind turbine at least 3 times bigger should be considered.
51
A recommended minimum wind speed of at a site for a wind turbine is 5 m/s. It is generally accepted that wind speed measurements are based on readings at 10 m above
ground (Energy Savings Trust, 2014), but the wind resource should rather be measured
at the top of the tower where the wind turbine will be living and working. (Energy Matters, 2012)
The power output of a wind turbine can be estimated according to a selected wind turbine power curve. The turbine manufacturer should be able to supply the power curve
and some common terms associated with wind speed are explained below:

Start-up Speed – The speed at which rotor and blade assembly begins to rotate.

Cut-in Speed – Is the minimum wind speed at which the wind turbine will generate usable power. Usually between 3 – 4.5 m/s (7 – 10 mph) for most turbines.

Rated Speed – Is the minimum wind speed at which the wind turbine will generate its designated power. Usually between 11 – 15.5 m/s (25 – 35 mph) for most
machines. A wind turbine power output increases as the wind increases. The
power output according to wind speed can be seen in the 'power curve', supplied
by most manufacturers for the specific wind turbine.

Cut-out Speed -Is the wind speed where the turbine cease power generation and
shut down due to very high wind speeds. This is a safety feature which protects
the wind turbine from damage. (EnergyBible, 2012)
In addition to wind speed terms mentioned above, the relationship between wind speed
and power for a wind turbine can be considered. This can be presented as a power
curve, presented in figure 33. A site's wind characteristics and a turbine's power curve
can be used in conjunction to determine how much energy the selected turbine will generate. (Carbon Trust, 2008)
Figure 33: Wind turbine power curve. (an illustrative example, not a particular make
and model) (Carbon Trust, 2008).
52
OR
In theory it is possible to estimate the maximum power a wind turbine can extract in a
free stream. This is due to the wind power (P) governed by the relationship: P ~ v³Aρ.
The the following formula can be used to calculate the maximum power that can be
extracted from a free stream:
Maximum power in a free stream = (16/27) (v³Aρ ÷ 2)
where:

16/27 is a constant known as the Bertz limit,

v is the wind speed (m/s),

A is the swept area (m²) calculated: A = πr², and

ρ is the density in air (kg/m³). (Carbon Trust, 2008)
3.5.4
BOS equipment sizing
Batteries
Batteries should be large enough to store efficient energy to operate appliances when
energy is not generated by the energy generating equipment. The following is used to
calculate the size of batteries:
i.
The watt-hours of storage needed:
Watt-Hours of Storage Needed = Total Watt-hours per day
x Autonomy Multiplier
x Battery Temperature Correction Factor (Table 6)
÷ 0.5 (correction for 50% depth of discharge)
Where:

the autonomy multiplier for battery storage is the number of days needed to operate a system when there is no power production. Usually a standard of 3 days
are used, but this value can also be found for certain countries from a battery
storage requirements map.

a battery temperature correction factor table is supplied below. (Commonly select the correction factor that corresponds to the average winter time ambient
temperature that the battery bank will experience)
53

the 50% depth of discharge for the battery provides a safety factor so that overdischarging the battery bank can be avoided.
ii.
The battery watt-hours for chosen batteries (The ampere-hour is the battery’s
rated storage capacity)
Battery Watt-Hours = Battery Ampere-Hours x Battery Voltage
iii.
The number of batteries needed
Number of Batteries Needed = Watt-hours of storage Needed / Battery Watt-hours
*Round up to the nearest even number of batteries in series string to equal the system
voltage. (Wagner, HJ. & Mathur, J., 2009)
Table 6: Battery Temperature Correction Factor for Vented Lead-Acid Cells
(Integrated Publishing Inc., 2010)
54
Charge controller
Charge controllers are rated and sized depending on the current and voltage. “Ampere
ratings can be between 1 – 100 amps and voltage ratings from 6 – 60 volts.” (King Solar, 2009) It is important to make sure the charge controller has enough capacity to handle the current (amps) from the PV array or wind turbine feeding into the controller
(Leonics, 2013). An additional 25%-30% needs to be factored in due to factors that
cause a sporadic increase in current levels. It can be advantageous if a higher amps
charge controller is acquired, as it can be used if there are plans to increase the size of
the energy system in the future. (King Solar, 2009)
Charge controller rating (A) = (Input Wattage ÷ Battery Voltage) x 1.3
where:

the input wattage is the total watts produced by the energy generating equipment,

the battery voltage is the battery voltage of the battery bank. (Most systems today are 24 or 48 VDC and most grid-connected systems operate at 48 volts or
higher (Wholesale Solar, n.d.).), and

1.3 is an additional 30% factored in due to factors that can cause a sporadic increase in current levels.
Sizing a charge controller for a solar system depends on the total PV input current
which is delivered to the controller and also depends on PV panel configuration (*series
or parallel configuration).” (Leonics, 2013) Thus the following equation can be utilized:
Charge controller rating (A) = Total short circuit current (Isc) x 1.3
MPPT (Maximum Power Point Tracking) charge controller: commonly used when the
voltage differs from the battery bank's voltage (the lower voltage). This charge controller also works well with systems that have panels with odd voltage ratings. MPPT
charge controllers automatically and efficiently convert higher voltage to lower voltage.
(King Solar, 2009)
55
Inverter
The inverter input rating should never be lower than the total watt of the appliances. It
should also have the same nominal voltage of the battery if a battery is acquired. When
it is a stand-alone system, the inverter must be large enough to handle the total amount
of watts used at one time. The best is to use an inverter size 25%-30% bigger than the
total watts of the appliances. Another factor to take into account is when an appliance
type is a motor or compressor. The inverter size should be minimum 3 times the capacity of these appliances because a surge current during starting must be added to the inverter capacity. When the system is grid-connected, the input rating of the inverter
should be the same as the PV array or wind turbine rating to allow for safe and efficient
operation. (Leonics, 2013)
Inverter rated power (W) = Total watts of the appliances x 1.3
where:

the total watts of the appliances is the total watts consumed at one time, and
1.3 is an additional 30% factored in due to factors that can cause a sporadic increase in
current levels.
56
3.6. General system estimation
Considering an energy generating system require planning to determine if there is
enough sun/wind resources on a consistent basis in the specified area, if there is enough
space, if zoning codes or covenants allow the systems in the area, and if the system will
be economical with all of the elements taken into consideration including installation
and maintenance considerations (Energy.Gov,2012). To help determine the suitability
and the size for an alternative electric system, the following factors need to be taken into
account.
Estimate the resources available
This can be done by a site evaluation and to take into account the factors affecting the
output of the renewable energy system. Estimating the resources available can vary significantly over an area. (Energy.Gov,2012)
System sizing
The size of the system required for energy production will depend on energy consumption demand according to the appliances that needs to be powered. Estimating the size
of a system involves taking into account the energy generating equipment such as the
solar panels or wind turbine, including the balance-of-system equipment. This will also
depend on whether the system is grid-connected, stand-alone, or a hybrid system. (Energy.Gov,2012)
Investment and space required by the system and additions
When a general idea of the systems size and the required equipment is known, the cost
of the system and space available for all the equipment needed should be taken into
consideration. The investment and space needed for the respective renewable energy
system need to take into account the following:

Solar system – Solar array, mounting racks and hardware, wiring, and the BOS
equipment.

Wind generating system – Wind turbine, tower and foundation, wiring, and the
BOS equipment. (Energy.Gov,2012)
57
Zoning codes, permits and other considerations
Zoning regulations, codes, and permits vary dramatically across states, countries, and
municipalities. Before investing in a renewable energy system, it is advisable to acquire
information on the zoning regulations, codes, or permits needed. (Energy.Gov,2012)
Deciding to invest in a renewable energy system, a professional installer should be contacted for a more accurate estimation. A credible installer may also be able to provide
additional information on all these considerations. (Energy.Gov,2012)
58
4
RAINWATER HARVESTING
Harvesting rainwater is a method used to capture and use rainwater. Rainwater harvesting is especially useful locations where water is a scarce resource and water supply is
limited. It can reduce the need and demand for water transport systems which threatens
the health of the water cycle and the environment. Even areas with low rainfall still have
an enormous potential for harvesting rainwater. There are many potential sources for
harvesting rainwater, but for the purpose of this paper, roof harvesting and their necessary components will be reviewed. (Greywater Action, n.d.) Rainwater harvesting can
also provide water needed for fire protection in regions where water is either scarce or
not connected to a municipal water supply.
The following are the pros and cons of harvesting rainwater.
Pros:

Most useful in arid and semi-arid areas where other sources of water are scarce.

Provides a source of water at the point where it is needed and it is owner operated and managed.

It is an essential reserve in times of emergency and/or breakdowns of public water supply systems.

Construction of a rooftop harvesting system is simple, and local people can easily be trained to build one which minimizes cost.

The technology is flexible as the system can be built to meet almost any requirements.

The properties, physical and chemical, of rainwater may be superior to groundwater or surface water that may have been subject to pollution, especially from
unknown sources.

The running costs are low.

The construction, operation, and maintenance are not labour intensive.
Cons:

It is not a dependable water source in times of dry weather or prolong drought.
The success of rainwater harvesting depends on the frequency and amount of
rainfall.
59

Low storage capacities limit rainwater harvesting. The system may not be able
to provide water in a low rainfall period. Increased storage capacities add to construction and operating costs.

Possible contamination of water from animal wastes and vegetable matter.

The system increases construction cost. (Organization of American States, n.d.)
4.1. A roof rainwater harvesting system
A roof rainwater harvesting system is simple and can store water for later use. A basic
rainwater harvesting system consists of three elements: a collection or catchments area,
a conveyance system, and a storage tank.
Catchment area
The catchment area is the surface which directly receives the rainfall. This would be the
roof area of the shipping container. The roof material is not as important as the contaminants that may be on the roof. Since the container is a metal roof, it can easily shed
contaminants. The slope of the roof affects how quickly water will runoff, and a steep
roof will shed runoff quickly and more easily cleaning the roof of contamination. A
less-steep or flatter roof will cause the water to move more slowly which raise the potential for contamination to remain on the catchments surface. The size of the catchment
area will determine how much rainwater can be harvested. (AgricLife Extension, n.d.)
Conveyance
The conveyance system consists of the gutters and/or pipes that is attached to the building to deliver rainwater from the roof to the storage tanks. Gutters attached to the edge
of a roof gathers water from the catchment area and are connected to a downspout
which transports the rainwater to a covered storage tank. Gutters can be semi-circular or
rectangular. Using locally available material such as plain galvanized iron sheet, folded
to the required shape, a rectangular gutter can be produced. A semi-circular PVC gutters
can be prepared by cutting PVC pipes into two equal semi-circular channels. The size of
the gutter should be according to the flow during the highest intensity rain and oversized by 10-15%. Gutters need to support the load when filled with water, thus they
need to be supported so they do not sag or fall off. It is possible to fix iron or timber
brackets into the walls for gutter support. Downspouts can be of any material like pol-
60
yvinyl chloride (PVC), galvanized iron (GI) or fiberglass, materials that are commonly
available.

A 'first flush device' can be connected to direct the first rain of the year away
from the tank and the subsequent water continues to flow to the tank (figure 34).
The 'first flush system' is utilized because the first rain of the year is the most
dirty as it cleans the roof and due to pollutants.

Screens such as coarse mesh are attached over the downspout connected to the
gutter or to the inlet of the storage tank. This is utilized to remove leaves and
debris from the rainwater collected on the roof. (Greywater Action, n.d.; Center
for Science and Environment, n.d.)
Figure 34: First-flush device (Aquabarrel, 2014)
Storage tank
The storage tank can be located next to the building, leveled, and on a raised platform.
Each tank should have an excess water overflow system. More than one storage tank
can be connected to the same system if one storage tank is not sufficient. The storage
tank can be dark which prevent algae from growing, and covered to prevent leaves, debris, and mosquitoes from entering. Large storage tanks can be made from plastic, Ferro
cement, metal or fiberglass, available in a range of sizes. Rain barrels are a popular
choice for rainwater harvesting as they are low in cost and can be installed along buildings. (Greywater Action, n.d.; Center for Science and Environment, n.d.)
61
4.2. Rainwater collected
A rainwater harvesting system require few skills and a little supervision to operate, but
the major concern is the prevention of contamination during construction and while it is
replenished. Contamination with certain materials such as oil can be avoided by the use
of proper materials during the construction phase. (Organization of American States,
n.d.) Rainwater is naturally very clean, having been naturally distilled by the sun and its
heating action causing evaporation from the surface of the earth and water sources. But
rainwater collects pollutants through the atmosphere and is usually slightly acidic in
nature. It also dissolves or physically carries dirt, debris, insects, and bird and animal
droppings on the roof surface down to the gutters. Thus, the end result is that a large
collection of organic and fecal material on the roof finds its way into the rainwater collection system. The best strategy is to remove as much of this contaminating material as
possible, by physically cleaning the roof surface and drains during the year. Screens and
a first flush system can also be put in place to eliminate some contaminating material.
Screens and first flush devices have a very large sieve size and are not capable of removing small bacteria, viruses, and parasites. For this reason the water should not be
used as drinking water, unless it is properly filtered or disinfected by other means such
as boiling. (One House Green, 2014)
62
4.3. Estimating the size of a system
Estimated rainwater resource available
The estimated amount of rainwater (net runoff) that can be harvested can be calculated
by the following formula:
Net Runoff (liters) = Catchment area x Rainfall x 0.95
where:

the catchment area is the roof area measured in square meters (m²),

the rainfall measured in millimeters or liters per square meter (1 mm = 1 L/m²),
and

0.95 is the runoff coefficient for a pitched metal roof.
(Lancaster, B., 2006)
Collection capacity needed
The collection capacity needed (size of the storage tank) can be estimated by using the
same equation as above but the rainfall in the equation can be according to a large storm
event:
Capacity needed (liters) = Catchment area x Rainfall expected in a local high volume
storm x 0.95
This is a rough estimate of the tank size that will be needed to capture the roof runoff
for this size storm. It will reduce the water loss to overflow from the tank and extend the
availability of a lot of rainfall long after the rain event. (Lancaster, B., 2006)
Estimated pipe size
If too small pipes are utilized in the system, it will restrict the water flowing through the
system fast enough. A rule of thumb that can be utilized is: 1 cm² of gutter cross section
per 1 m² of roof area. To calculate the pipe diameter, the equation used to calculate the
area of a circle can be converted to the following equation:
(Appropedia, 2012)
63
Table 7 can be used if the rainfall intensity can be found. The following table supplies
some indication of the diameter pipe required for draining out water based on rainfall
intensity and roof area
Table 7: Sizing of rainwater pipe for roof drainage.
Diameter
Of pipe
Average rate of rainfall in mm/h
(mm)
50
75
100
125
150
200
50
13.4
8.9
6.6
5.3
4.4
3.3
65
24.1
16.0
12.0
9.6
8.0
6.0
75
40.8
27.0
20.4
16.3
13.6
10.2
100
85.4
57.0
42.7
34.2
28.5
21.3
125
-
-
80.5
64.3
53.5
40.0
150
-
-
-
-
83.6
62.7
(Appropedia, 2012)
64
5
SUSTAINABLE SERVICE FACILITY CASE STUDY: JOHANNESBURG,
SOUTH AFRICA
The methods or modifications that can be used to construct a self-sustainable service
facility were applied, evaluated, and discussed. Each method was applied hypothetically
if a self-sustainable service facility would be constructed at a specified location. Passive
solar energy, energy generating systems, and rainwater harvesting system all has one
thing in common, they all are 'site specific'. Therefore all values calculated, information
examined, and discussed were based on the consideration of a service facility constructed in Johannesburg, South Africa.
5.1. Passive solar energy
The passive solar design discussed below is an illustrative example if a service facility
would be placed on a site in Johannesburg, South Africa. First the climate, wind direction, and solar altitude of the location were considered.
Climate
Johannesburg has a mild temperate climate with dry winters and warm summers (climatemps, 2014). According to Reardon, C. (2013), the main characteristics for a mild temperate climate zone is:

Low day–night temperature range near coast, high range inland

Four distinct seasons: summer and winter exceed human comfort range; spring
and autumn are ideal for human comfort

Mild to cool winters with low humidity

Hot to very hot summers, moderate humidity. ( Reardon, C., 2013)
The temperature averages were illustrated in table 8. Temperature averages can be
found by various sources on the internet. Some internet sources that can be utilized were
supplied in appendix 3.
65
Table 8: Temperatures in Johannesburg, South Africa
Temperature
Max
Avg
Min
Max Temperature
31ºC 22ºC 11ºC
Mean Temperature
24ºC 16ºC 5ºC
Min Temperature
19ºC 10ºC -2ºC
(Weather Underground, 2014)
Wind directions
Figures 35 and 36 illustrate the wind directions over the year in Johannesburg, South
Africa. The figure shows that most often the wind blows from the north and NorthWest.
Figure 35: Wind direction percentage over a year (WeatherSpark, n.d.).
Figure 36: Monthly wind directions over a year (WeatherSpark, n.d.).
* “The fraction of time spent with the wind blowing from the various directions over the
entire year. Values do not sum to 100% because the wind direction is undefined when
the wind speed is zero” (WeatherSpark, n.d.)
66
Solar elevation
The solar elevation angles were calculated as explained previously. The latitude for Johannesburg, South Africa is 26º10'S (Maps of the World, 2014).

Equinox = 90 degrees – Latitude
= 90º – 26.10º
= 63.9°

Summer solstice = 90 degrees – Latitude + 23.5 degrees
= 90º – 26.10º + 23.5º
= 87.40º

Winter solstice = 90 degrees – Latitude – 23.5 degrees
= 90º – 26.10º – 23.5º
= 40.40º
To confirm these values, an online link which calculates the elevation angle for a location according to its respective dates and times were utilized (figure 37).
Figure 37: The summer and winter solstice for Johannesburg, South Africa
(Keisan, 2014; modified).
After the climate, wind direction, and solar elevation were known, the passive solar design elements were considered in conjunction with the passive design principals. Thus
some design considerations that were taken into account for a mild temperate climate
with dry winters and warm summers while designing a passive service facility was:

Individual site analysis and location within the region determine whether heating
or cooling is the predominant need.

Minimize external wall areas (especially east and west-facing).

Passive solar heating is essential when heat is needed and simply achieved
where solar access is available. (Solar access require north-facing with the majority of glazing.)

Reducing heat gain though appropriate use of window shading and glazing (size,
location and type) as it is a critical design consideration.
67

Cooling comfort is simply achieved with adequate cross-ventilation and minimizing solar and ambient heat gains with shading and insulation.

Use convective ventilation and heat circulation.

Lower thermal mass requirements allow for low embodied energy solutions. (
Reardon, C., 2013)
5.1.1
Orientation
SA is located in the Southern Hemisphere of the world and according to the shape and
window placement of the container; the container should be oriented with its long axis
on the East-West axes with the window facing true North. Facing the window North
allows solar energy to enter the container. Solar gain through the window will be very
beneficial during the winter as the low temperature can range between 19 to -2°C. At
this point the wind directions were also taken into consideration, since the window is
specifically placed where the rod rack will be stacked in the container and the container
doors can either face East or West. As mentioned above, the wind direction is most often from the North and North-West and due to this phenomenon; the container doors
should face to the west side to take advantage of the north-west winds. Generally the
optimum orientation would be that the shorter axis align with prevailing winds to provide the most ventilation (Sustainable Workshop, 2011), but structures such as the container doors and window can be used to direct winds. Figure 38 below illustrates the
orientation of the shipping container as discussed above.
Figure 38: Container orientation
68
5.1.2
Shading
Shading can be used to regulate the solar heat gain in container. The basic idea of the
shading structures are to keep the sun out in the summer and let the sun through in the
winter. The container can either be shaded with a window overhang to shade the window or a roof overhang to shade the window and the wall facing the sun. The choice
will depend on the customer and the degree of thermal comfort he/she is comfortable
with. The roof and window overhang were utilized in the example.
South Africa has a moderate climate and according to the weather history (see table 9
below), Johannesburg has HDD below 6 000 and CDD below 2 600. According to the
guidelines for overhang design provided by InspectApedia, the shadow line should be
located at the window sill using the summer solstice sun angle.
Table 9: Degree days in Johannesburg, South Africa
Degree Days
Max
Avg
Sum
Heating Degree Days
24
6
1 744
Cooling Degree Days
10
1
375
(Weather Underground, 2014)
By utilizing the guideline and the solar elevation angles calculated above, a sketch was
drawn according to scale (1 m = 50 mm) to estimate the width of the overhang (roof or
window). This principle was illustrated in figure 39 below. As seen from the sketch, the
width can be drawn and estimated to any length for a comfortable fit. Since summer, the
beginning of autumn, and the end of spring can get very hot, the overhang was drawn
through the summer solstice elevation angle line to the equinox elevation angle line.
The roof overhang was measured and estimated to be 0.97 – 1.0 m wide, where it is
supposed to shade the wall during the whole summer and only half of the time during
spring and autumn. The window overhang was measured and estimated to be 0.6 m
wide, where it is supposed to shade the window during the whole summer and half of
the time during spring and autumn. The same principle can be used to estimate the roof
overhang to shade the whole wall during summer. The only difference is that the solar
elevation angles should be measured from the ground surface and not the bottom of the
window sill.
69
87.4°
North
Figure 39: Roof and window overhang according to solar elevation.
The roof overhang rule of thumb and the window eave online calculator were also utilized to estimate the roof and window overhang for the container. These methods were
also used to confirm the values estimated above, since there is no universal formula to
easily calculate the roof and window overhang.
The roof overhang rule of thumb: W = ½ H
The total height of the shipping container = 2.896 m
The window height = 1.2 m
Height from the ground to the window sill = 0.9 m
Thus the height from the window sill to the roof top was calculated as follow:
H = Total height of the shipping container - Height from the ground to the window sill
= 2.896 m - 0.9 m
= 1.996 m
By utilizing the rule of thumb formula:
W = ½H
= 0.5 (1.996 m)
= 0.998 m
70
According to this method the roof overhang should be 0.9 – 1.0 m wide. The rule of
thumb was illustrated by the figure below.
W = ½H
= 0.998 m
m
H = 1.996 m
1.896 m
North
0.9 m
Figure 40: Overhang rule of thumb illustrated.
Window overhang online calculator
According to the online calculator, the window overhang width should be 0.53 m and
the overhang would produce a 0.33 m top window winter shade if the overhang would
be placed right above the window. The online calculator also supplied information such
as:

The width includes everything that contributes to shade across the window (i.e.
gutters).

The top window winter shade is the space at the top of the window to the overhang itself which will always be in shade throughout the year.

The algorithm works on the principal that complete summer sun shade during
the hottest part of the day during the whole of summer is wanted. (Eco Who,
2014)
The figure below illustrates the results generated by the online calculator according to
the values supplied.
71
Figure 41: Results from online calculator (EcoWho, 2014; Modified).
As seen from the two methods used above, the rule of thumb and online calculator, the
values calculated for a roof and window overhang is quite accurate when using the solar
elevation sketch. The only difference (and advantage) between the solar elevation
sketch method and the other two methods, are that the sketch can be used to estimate the
overhang width according to the solar gain wanted during the equinox (spring and autumn).
The window can also be installed with adjustable blinds or fixed horizontal louvers to
shade the window. Adjustable shading can be very beneficial during spring and autumn
to allow viable solar access. Adjustable shading also makes it easier to control heat gain
according to comfort. Window efficiency can also be considered, as the window choice
will affect the heat gain and the light transfer. The basic consideration for a temperate
climate would be a window with a high SHGC and low U-value glazing. (Reardon, C.,
2013) Other considerations would be deciduous trees or bushes, but these should already be available at the right place and size to function as an effective shading method/device.
5.1.3
Ventilation
The container can be ventilated passively by utilizing the window and container doors
to direct the wind from the different wind directions. Since most of the wind comes
from the North, the North facing window should be able to open to let the wind pass
through. The container door can also be opened at an angle to direct the Northern wind
to enter the container. The second highest wind direction is from the North-West which
can let the wind through by the west facing doors and a window opening that opens to
72
the east to direct the wind inside (figure 42). The same principle but opposite openings
can be used to deflect the wind when it is unwanted in the winter or cooler days.
North
North-West
Winds
Figure 42: Door and window openings used to scoop the wind inside.
These are just simple examples that can be used to scoop or deflect the wind to or from
the inside of the container. If blinds and louvers were to be used for shading, it should
not hinder the opening of the window since not all parts of the building can be oriented
for effective cross-ventilation. Using the door and window opening, which is adjacent
from each other, creates a funnel effect which aids the air movement and increases the
cross-ventilation. A vent can also be cut from the east side wall of the container. The
vent should be placed high in the wall, which can be used as an outlet for hot air as hot
air rises. The vent should also be adjustable since the heat needs to be kept inside during
the winter and therefore the vent will be closed. Figure 43 illustrates the crossventilation created by the window and door openings, where figure 44 illustrates the
cross-ventilation created by the door and a vent opening.
Figure 43: Two openings – Adjacent
(Sustainability Workshop, 2011)
Figure 44: Two openings – Opposite
(Sustainability Workshop, 2011)
73
5.1.4
Thermal Mass
The container is constructed out of corrugated iron which is a low thermal mass material. This kind of material reacts quickly to external conditions, which means it will
heighten the climate extremes. This can be avoided by the insulating options discussed
below. The amount of sunlight absorbed by building material also depends on its color.
The container would be spray-painted white which is beneficial for reflecting the sun
and keeping the inside cool. Adding an overhang to the container can either be constructed out of wood or corrugated iron. This is due to the fact that lower thermal mass
requirements allow for low embodied energy.
Taking thermal mass into consideration, care should be taken when choosing a window.
It was noticed that metal equipment will be stacked by the window. This means that
when the sun strikes these equipment, the metal would heat up and radiate heat into the
container. Letting the sun through the window and heating the metal equipment will be
beneficial in the winter, but it must be shaded during the summer. Blinds can be used to
control the solar gain to the metal equipment, but it has to be kept in mind that blinds
will also radiate heat from the sun to the inside of the container. Therefore it might be
more beneficial if a roof or window overhang is utilized to shade the window during the
summer. If there is some unwanted solar gain through the window during the winter,
adjustable blinds can be used to protect the metal equipment from heating up.
5.1.5
Insulation
There are several different ways to insulate the interior of a shipping container and there
are more coatings on the market that offer insulation qualities. Although the more
commonly used materials are fiberglass, rigid polystyrene foam panels and closed cell
spray foam (figure 45). (Gregorio, R., 2012)
Fiberglass insulation has a standard thickness of about 90 mm and provides an insulating value of R-13. Sections are cut and fitted inside of a wood framed interior. Since the
walls of a storage container are corrugated there will be gaps between the insulation and
the outside corrugation. Depending on where the storage container is going to be placed,
74
it might be advisable to consider a moisture barrier between the container wall and the
insulation. (Gregorio, R., 2012)
Rigid polystyrene foam panels are available in varying thickness as well as size. These
panels are also available in varying densities. The application of the container will dictate the type of panel utilized. An approximated insulating value of R-5 per inch is provided by foam panels. A major benefit in using foam panels instead of fiberglass is interior space can be saved. Space is saved because foam panels do not need wood frames
as in fiberglass insulation, thus saving several inches on the sidewalls and ceilings.
Foam panels can either be glued directly to the wall or it can be screwed into flat bar
mounted to the walls. (It is recommended that the flat bar method should be utilized
opposed to gluing the panels to the wall. Since the container walls are corrugated, the
panels do not come in constant contact with the walls.) (Gregorio, R., 2012)
Closed cell spray foam is of the opinion that it is the most efficient insulation. It can
offer the highest insulation value of approximately R-6 per inch. The spray foam completely covers the surface of the corrugated shipping container wall, thus there are no
gaps between the insulation and the container wall. There is also much less risk of condensation or moisture developing with closed cell spray foam, there is no need to frame
out the interior as the spray foam adheres directly to the walls and ceiling, it can be
sprayed as thick as necessary to achieve the required insulating value. The major disadvantage of this type of insulation is its cost. (Gregorio, R., 2012)
Any of these methods are very effective and it is recommended that a wall covering,
such as plywood, installed over the insulation to finish out the interior. (Gregorio, R.,
2012)
Figure 45: Fiberglass, rigid polystyrene foam panels, and closed cell spray foam respectively (Gregorio, R., 2012).
75
5.2. Energy generating systems
A solar system and wind turbine system were sized and evaluated according to different
system connection options. The energy generating systems were sized and evaluated
accordingly, if these systems were to be used in a service facility placed in Johannesburg, South Africa. First the major components to complete an energy generating system were sized and discussed separately. After the size of these components needed
were known, the different system connection options were compiled and discussed as a
whole.
During the course of sizing the major components to complete an energy generating
system, tables were compiled to illustrate the price and equipment specifications. The
information compiled in these tables was derived from two South African online eco
stores which produces equipment specifications and their prices freely. The tables were
used as a basis for evaluation and discussion purposes, but it has to be kept in mind that
there would be a lot more choices available in the market from different manufacturers
at different ratings and at different prices. Each component's specifications supplied
according to the component being sized and discussed were as follow:
•
Solar module specifications (table 13),
•
Wind turbine specifications (table 15),
•
Battery specifications (table 18),
•
Charge controller specifications (table 22), and
•
Inverter specifications (table 25)
(Sustainable.co.za, 2014 & Alternagy.co.za, n.d.)
5.2.1
Estimating the power consumption demand
The power consumption demand was calculated by using the total power consumption
demand worksheet. First the appliances that need to be powered in the service facility
(as specified) were listed and their respective values used to complete the worksheet
were explained below.
The appliances in this instance that need to be powered are:

Grinding machine, compressor, lights, laptop, room air conditioner (optional)
76
The power each appliance consume were estimated values as approximate values for
these devices were not supplied, except for the grinding machine. The approximate values should be used that is supplied on the appliance label, or specified by the manufacturer as this will give a more realistic estimation on the total power consumption demand. The values used in the power consumption estimation were explained by appliance:
Grinding machine: 2 400 W
Watts = Amps x Volts
= 10 Amps x 240 Volts
= 2 400 Watts
Information according to the grinding machine specs supplied in appendix 2.
Compressor (8 – 10 bar): 2 000 Watt
This value is an estimate for an 8 to 10 bar compressor according to some compressor
specifications. The energy consumption will depend on which type of compressor is
utilized such as an oil less, lubricated, silent, etc. compressor. The torque power (starting power) consumed should also be taken into account, as this power consumption can
be three times more than the running consumption. The starting and running power consumption information can be supplied by the compressor manufacturer. A 2 000 W value for simplicity sake was used, but when determining the amount of power consumption for a system, it is advisable to use the values supplied by the manufacturer according to the specific compressor utilized.
Laptop: 60 W
The power consumption of a laptop depends on the screen size. Typically the power
consumption for a laptop when running off the battery is as low as 20 watts, but can go
up to 100 watts. When charging a laptop battery, the power consumption will increase
10% - 20%, thus it is estimated that 60 watts is the average power consumption for a 14
– 15 inch laptop when plugged in. (Energy Use Calculator, 2014)
Lights (CFL 60W): 14 W (CFL light bulbs were chosen for the calculations.)
77
LED
CFL
Incandescent
Watts per bulb (equiv. 60 watts)
10
14
60
Light bulb projected lifespan
50 000 hours
10 000 hours
1 200 hours
Cost per bulb
$ 35.95
$ 3.95
$ 1.25
(Eartheasy, 2012)
Room air conditioner (optional): 1 000W
Single room air conditioners come in different sizes and can use from 500 W to 1 500
W per hour. (Energy Use Calculator, 2014)
Next the time each device can be used per day were estimated and explained:
Device/Appliance (Qty)
Hours used per day
Grinding machine (1)
4 hours in the morning and 4 hours in the evening
Compressor (1)
4 hours in the morning and 4 hours in the evening
Laptop (1)
8 hours during day and 8 hours during night
Lights* (3)
12 hours
Air Conditioner* (1)
8 hours
The estimated hours used for these devices are including day shift (6:00 – 15:00) and
night shift (20:00 – 5:00). When estimating the times used for each device or appliance,
the maximum value were used to avoid sizing the system too small.
*Lights – Johannesburg (South Africa) receives a minimum of 10:30 hours of daylight
during mid-winter. Thus the lights might be used one or two hours extra in the winter
during the day, 3 hours for day shift + 9 hours for night shift.
*Air Conditioner - The temperatures in Johannesburg (South Africa) were already supplied in table 8.
Thus assuming the service facility is not passively designed, the summer will have day
extremes and the winter will have night extremes. For this reason an 8 hour air conditioning use were estimated, for the day extremes during summer and night extremes
during the winter.
78
System sizing scenario 1: Day and night shift including an air conditioning unit
Appliance
Qty
Watts
(volts x amps)
Total
Watts
Hours
per day
used
Average
Watthours/day
Grinding machine
1
x 2 400
= 2 400
x 8
= 19 200
Compressor
1
x 2 000
= 2 000
x 8
= 16 000
Laptop
1
x 60
= 60
x 16
= 960
Lights
3
x 14
= 36
x 12
= 504
Air Conditioner
1
x 1 000
= 1 000
x 8
= 8 000
= 5 502 W
Total Watts at one time
= 44 664 W
Total Watt-hours per day
The total watts and total watt-hours per day consumption demand value calculated
above is a rough estimate. The actual power consumption demand may vary substantially depending on the location of the service facility, type of devices or appliances used,
and the hours used per day. For this reason, each customer need to supply values that is
as exact as possible according to their situation for a more accurate estimate of their
power consumption demand. To illustrate the importance for exact values used, two
more scenarios were taken into account and therefore two more system sizing worksheets were supplied. Worksheet 2 is where the service station is located, modified, and
designed to utilize passive solar energy and no air conditioning unit is needed. Worksheet 3 is where the service station is only used during the day shift.
System sizing scenario 2: Day and night shift excluding air conditioning unit
Appliance
Qty
Watts
(volts x amps)
Total
Watts
Hours
per day
used
Average
Watthours/day
Grinding machine
1
x 2 400
= 2 400
x 8
= 19 200
Compressor
1
x 2 000
= 2 000
x 8
= 16 000
Laptop
1
x 60
= 60
x 16
= 960
Lights
3
x 14
= 36
x 12
= 504
Total Watts at one time
Total Watt-hours per day
= 4 502 W
= 34 664 W
79
System sizing scenario 3: Only day shift including air conditioning unit
Appliance
Qty
Watts
(volts x amps)
Hours
per day
used
Total
Watts
Average
Watthours/day
Grinding machine
1
x 2 400
= 2 400
x 4
= 9 600
Compressor
1
x 2 000
= 2 000
x 4
= 8 000
Laptop
1
x 60
= 60
x 8
= 480
Lights
3
x 14
= 36
x 3
= 42
Air Conditioner
1
x 1 000
= 1 000
x 8
= 8 000
= 5 502 W
Total Watts at one time
= 26 122 W
Total Watt-hours per day
The table blow illustrates the results from the estimated power consumption demand
calculated according to three scenarios. The three scenarios were taken into account for
comparison purposes and to illustrate the importance for utilizing accurate values.
Table 10: Results of the total watt consumption at one time and the total watt-hour consumption per day according to their different scenarios.
Total Watts at one time
Total Watt-hours per day
Scenario 1
Scenario 2
Scenario 3
5 502 W
4 502 W
5 502 W
~ 5 500 W
~ 4 500 W
~ 5 500 W
44 664 Wh
36 664 Wh
26 122 Wh
~ 45 000 Wh
~ 37 000 Wh
~ 26 000 Wh
It can already be seen from table 10 that by eliminating an air-conditioning unit lowers
the power demand with 1 kW, as scenario 1 and scenario 2 were calculated using the
exact same values but eliminating the air-conditioning unit from scenario 2. Power consumption demand also differs in the time each appliance is used per day. This was illustrated in the difference between scenario 1 and scenario 3. All the values used were the
same, except that the appliances were used less per day in scenario 3 than in scenario 1.
All the values used in the calculation were estimated values and not approximate values.
80
5.2.2
Solar array sizing
The estimate solar array size was calculated by using the following formula:
Number of Modules =Total Watt-hours per day ÷ Derating Factors ÷ Peak Sun Hours ÷
Module Wattage Rating (STC)
Thus the estimated number of modules needed according to scenario 1 (table 10) for a
system with batteries and using a 300 W module was calculated as follow:
Number of Modules =44 664 Wh ÷ 0.65 ÷ 3.96 hours ÷ 300 W
= 57.84 ≈ 58 modules
where:

the total watt-hours per day used was 44 664 Wh supplied in table 5,

the derating factors used were the alternative method for an approximate calculation of a system with batteries (65%),

the peak sun hours used were according to the solar irradiance calculator (figure
41), and

module wattage rating used were a 300W solar module.
Figure 41: Result from the solar irradiance calculator
(Solar Electricity Handbook, 2014; modified).
The solar irradiance calculator measures the average solar insolation in kWh/m2 per
day. As seen in June the average solar insolation is 3.96 kWh/m2/day, thus Johannesburg receives 3.96 peak sun hours per day during June. This value was used during the
calculations as the rule of thumb is to apply the lowest winter value of sun hours.
81
Table 11 was compiled to illustrate the total number of modules needed according to the
different total watt-hours per day (supplied in table 10). The table also illustrates the
difference in the total number of modules needed for a system with batteries and a system without batteries. The only difference in the calculation for a system without batteries was the derating factor, which was 75% according to the alternative method for an
approximate calculation.
Table 11: The total number of modules needed in a solar array
System with batteries
Total Watt-hours
(Wh) per day
System without batteries
Scenario 1
Scenario 2
Scenario 3
Scenario 1
Scenario 2
Scenario 3
45 000
37 000
26 000
45 000
37 000
26 000
Overall efficiency
adjustment
÷ 0.65
÷ 0.75
Peak Sun Hours
(h)
÷ 3.96
÷ 3.96
Module Wattage
Rating (W)
÷ 300 W
÷ 300 W
Number of Modules
58
48
34
51
41
30
Solar is universal and will work virtually anywhere, but some areas are more suitable
for solar panels than others as it depends on the solar irradiance available at the surface
of the earth (Wholesale Solar, 2013). Two different cities in their respective countries
were chosen to illustrate the effect solar irradiance has on the solar array size in these
cities. The two cities chosen were Tampere, Finland and Kitwe, Zambia. Their peak sun
hours were calculated using the solar irradiance calculator (figure 47). The results were
compiled in table 12.
Table 12: Solar array needed in different cities
System with batteries
Johannesburg, SA
Peak sun hours: 3.96
Number of Modules
Tampere, Finland
Peak sun hours: 0.14
System without batteries
Scenario 1
Scenario 2
Scenario 3
Scenario 1
Scenario 2
Scenario 3
58
48
34
51
41
30
1 637
1 336
957
1 418
1 158
830
82
Number of Modules
Kitwe, Zambia
Peak sun hours: 4.91
Number of Modules
47
39
28
41
33
24
Figure 47: Result from the solar irradiance calculator for Tampere and Kitwe (Solar
Electricity Handbook, 2014; modified).
As seen from the values calculated above, the number of modules needed in a system
depends on how much sun hours is available in a location, the power the array should
provide and whether the system includes a battery bank or not. These dependent factors
have a huge impact on array investment and space needed to mount the array. The alternative derating factor method was used to calculate the array size, but this value is not
an exact value of the efficiency loss that can occur. By utilizing specific derating factors
as supplied in the derating factor table or efficiency values supplied by the manufacturer
specifications for each component used in the system, the array size needed to produce
the power demand might be smaller as calculated above. This in turn will also have an
impact on the investment and space needed for the array size.
Table 13: Solar module specifications
Short cirArea (m²) Weight cuit curLxW
(kg)
rent (Isc =
A)
Manufacturer
Module
Power
Rating
Cell type
Price
ReneSola
300 W
PolyCrystalline
R3 300
(€ 230)
1.94
29
7.02
300 W
MonoCrystalline
R4140.00
(€ 290)
1.96
22.5
8.7
Tenesol
83
Solaire
250 W
PolyCrystalline
R2990
(€ 210)
MonoR3450
Crystalline
(€ 240)
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
Tenesol
250 W
1.64
19
9.03
1.63
19
8.8
Table 14 illustrates the total cost and space required for the total number of modules
needed in a solar array calculated in table 11. During the table compilation, different
modules were evaluated for comparison purposes to illustrate the solar array investment
difference. These values were as follow:

A 300 W poly-crystalline solar module – R 3 299/module and 1.94 m²/module
(ReneSola).

A 300 W mono-crystalline solar module – R 4 140/module and 1.96 m²/module
(Tenesol).

A 250 W poly-crystalline solar module – R 2 990/module and 1.64 m²/module
(Solaire).
Table 14: Solar array investment difference
System with batteries
Scenario 1
Scenario 2
Scenario 3
System without batteries
Scenario 1
Scenario 2
Scenario 3
300W Polycrystalline
Number of Modules
58
48
34
51
41
30
Total space required
113 m²
93 m²
66 m²
99 m²
80 m²
58 m²
Total Cost
R 191 340 R 158 350 R 112 170 R 168 250 R 135 260 R 98 970
€ 13 340
€ 11 030 € 7 820 € 11 730 € 9 430
€ 6 900
Total weight
1 680 kg
1 390 kg
990 kg
1 480 kg 1 190 kg
870 kg
300W Monocrystalline
Number of Modules
58
48
34
51
41
30
Total space required
113 m²
94 m²
66 m²
100 m²
80 m²
59 m²
Total Cost
R 240 120 R 198 720 R 140 760 R 211 140 R 169 740 R 124 200
€ 16 750
€ 13 860 € 9 820 € 14 730 € 11 840 € 8 660
Total weight
1 310 kg
1 080 kg
770 kg
1 150 kg
920 kg
680 kg
250W Polycrystalline
Number of Modules
68
56
40
60
49
35
Total space required
112 m²
92 m²
66 m²
98 m²
80 m²
57 m²
Total Cost
R 203 490 R 167 580 R119 700 R179 550 R146 630 R 104 740
€ 14 190
€ 11 690 € 8 350 € 12 520 € 10 230 € 7 300
Total weight
1 290 kg
1 060 kg
760 kg
1 140 kg
930 kg
670 kg
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
84
Table 14 specifically illustrates the difference between the total cost and space needed
for different power rated modules and different type of modules. The solar array size for
a mono-crystalline and poly-crystalline with a 300 W power rating was the same, but a
factor that was not taken into account is that a mono-crystalline module has a higher
efficiency value than poly-crystalline modules. This in turn can decrease the number of
modules needed in an array and since the efficiency values of these modules were not
supplied, the solar array size for the respective module types could not be calculated.
Assuming the array size is the same, the cost for a mono-crystalline module or array is
more expensive and more space is needed compared to poly-crystalline modules.
The difference between the power ratings of the same type of module was also analyzed. As seen in table 14, a higher number of modules are needed for a smaller power
rating module (250 W). And as expected, even though the smaller power rating module
cost less per module, the total cost for the array size needed is more expensive than using the higher power rated modules. The space needed for these different modules does
not have a big difference, thus the deciding factor would be the total cost for an array.
Therefore, the 300W ReneSola poly-crystalline solar module was used for the rest of the
evaluation and calculations.
The roof area of the container was calculated as follow:
A = L x B = 6 m x 2.33 m
= 13.98 m²
The number of 300W ReneSola solar modules that will fit on the roof of the container
was calculated as follow:
13.98 m² ÷ 1.96 m² = 7.13
Thus only seven 300W solar modules would be able to fit on the roof of the container.
The rest of the panels or all of the panels can either be ground – or pole-mounted.
5.2.3
Wind turbine sizing
There is no universal formula to size a wind turbine, thus the choice of turbine depends
on the energy a wind turbine needs to produce for energy consumed by the appliances
or at one time. The power consumption at one time was already calculated and supplied
in table 10. These values gave an indication of the size wind turbine that was needed to
85
produce the power requirement. A bit bigger turbine was considered to take into account
efficiency losses.
Table 15: Wind turbine specifications
Manufacturer
Earth Power
10KW
Rated
Power
Output
(W)
Price
Cut -in
Speed
(m/s)
Rated
Speed
(m/s)
15 000
(Max)
10 000
(Rated)
R138 150
(€ 9 630)
3 – 25
11
8 000
(Max)
R72 840
12
5 000
(€ 5 080) 3 - 35
(Rated)
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
Earth Power
5KW
Tower
Rotor
Weight
Height Diameter
(kg)
(m)
(m)
15
7
1 250
12
5
357
The wind resource available and the recommended tower height entry level were evaluated as follow:

Wind resource
The figure below illustrates the wind resource available in Johannesburg, SA. The average daily minimum is marked by the red band, the maximum wind speed by the green
band, and the average wind speed with the black band. The figure also illustrates the
value and date of the highest and lowest wind speed according to the maximum and
average colored bands. Thus over the course of the year, the typical wind speeds vary
from 3 m/s to 7 m/s. The highest average wind speed of 5 m/s occurs around 16 October. At this time the average daily maximum wind speed is 7 m/s. The lowest average
wind speed of 3 m/s occurs around 17 May. At this time the average daily maximum
wind speed is 5 m/s.
Figure 48: Wind Speed in Johannesburg, SA (WeatherSpark, 2014).
86

Tower height
It is recommended to site a wind turbine at least 6 m above any surrounding obstacles in
a 76 m radius (Energy Matters, 2012). Assuming the container would be the only obstacle in a 76 m radius from the wind turbine, the turbine recommended entry level tower
height should be around 10 m.
Recommended entry level = Container height + 6 m
= 2.896 m + 6 m
= 8.896 m ≈ 9 m
Since the recommended entry level was assumed to be 9 m and it is generally accepted
that wind speed measurements are based on readings at 10 m above ground, both wind
turbine sizes (10 kW and 5 kW) would not be able to produce the power requirements
needed. Mentioned above, the typical wind speeds vary from 3 m/s to 7 m/s over the
course of the year, but these turbines need wind speeds of 11 to 12 m/s to generate their
rated power. Johannesburg receives on average wind speeds of 3 to 5 m/s, and thus it
can be assumed that these turbines will generate the minimum usable power as these
wind speeds only reach the cut-in wind speed. Even though the highest maximum wind
speed during the year is 7 m/s, not enough power is extracted by the 10 kW wind turbine to supply the energy demand the whole year through (in all three scenarios).
A wind energy system might not be a suitable option in Johannesburg, S.A. as the wind
turbines are unlikely to provide a cost-effective way of producing electricity. It has to be
kept in mind that the evaluation was made for the resource available at a height of 10 m.
Increasing the tower height exposes a wind turbine to higher and cleaner wind speeds.
Therefore it is crucial to measure the power a wind turbine can provide at different
heights with different wind speeds before installing a wind turbine system.
In theory the maximum power that a wind turbine can extract from a free steam can be
calculated by using the equation below:
Maximum power in a free stream = (16/27) (v³Aρ ÷ 2)
Thus the estimated maximum power that can be extracted by the Earth Power 10 kW
wind turbine (information available in table 15) was calculated as follow:
87
Maximum power in a free stream = (0.59) ((5 m/s)³(38.485 m²)(1.225 kg/m³) ÷ 2)
= 1 738.544 kgm²/s³
= 1 738.44 W
Where:

16/27 is a constant known as the Bertz limit,

v is the wind speed which was used at 5 m/s,

A is the swept area which was calculated to be 38.485 m² (calculated: A = π(3.5
m)²), and

ρ is the air density which equals 1.225 kg/m³ according to the International
Standard Atmosphere (ISA).
Table 16 was compiled to illustrate the theoretical maximum power that can be extracted by the Earth Power 10 kW and 5 kW wind turbines according to different wind
speeds. The table was compiled to illustrate the increased power that can be extracted
with higher wind speeds and different size rotor swept area.
Table 16: The estimated maximum power extraction by the respective wind turbines.
Earth Power 10kW
Earth Power 5kW
(Rotor diameter = 7 m)
(Rotor diameter = 5 m)
Rotor Swept Area = 38.485 m²
Rotor Swept Area = 19.635 m²
3 m/s
380 W
190 W
5 m/s
1 740 W
890 W
7 m/s
4 770 W
2 430 W
9 m/s
10 140 W
5 170 W
11 m/s
18 510 W
9 440 W
Wind speed
As seen from table 16 above, in theory the power these wind turbines can extract form
the wind increases dramatically when the wind speed increase and also when the rotor
diameter increases. But it has to be kept in mind that these power outputs are only estimated values for illustration purposes and that the actual amount of electricity produced
may be drastically lower than calculated. The lower than calculated values are due to
the fact that the Bertz limit of only 59% was taken into account, where according to the
Carbon Trust, anecdotal evidence suggests that the capacity factor for a small-scale
88
wind turbine generally ranges between 12 – 20% or less than 25% (Carbon Trust,
2008). Thus to make sure a wind energy system will be financially worthwhile, it is
advisable to contact a professional before installing a wind energy system.
As mentioned before, a wind energy system might not be a suitable option in Johannesburg, S.A. as the wind turbines are unlikely to provide a cost-effective way of producing
electricity. This does not mean that a wind turbine system cannot be utilized in other
cities and countries where a service facility can be located. The Earth Power 10 kW
wind turbine was chosen to complete further evaluation of a wind turbine system, assuming that this type of wind turbine is able to generate enough power for the power
consumption demand in all three scenarios if given optimal wind resources.
5.2.4
Battery sizing
The formulas to calculate the battery size were as follow:

The watt-hours of storage needed:
Watt-Hours of Storage Needed = Total Watt-hours per day
x Autonomy Multiplier
x Battery Temperature Correction Factor (table 6)
÷ 0.5 (correction for 50% depth of discharge)

The battery watt-hours:
Battery Watt-Hours = Battery Ampere-Hours x Battery Voltage

The number of batteries needed:
Number of Batteries Needed = Watt-hours of storage needed ÷ Battery Watt-hours
Thus the watt-hours of storage needed were calculated as follow for scenario 1 (table
10):
Watt-Hours of Storage Needed = 44 664 Wh/day x 3 days x 1.190 ÷ 0.5
= 318 900 Wh
Where:

the total watt-hours per day used was 44 664 Wh/day,

the autonomy multiplier value used was 3 days,
89

battery temperature correction factor used was 1.190 as the average low temperature reaches 10ºC (table 6), and

the correction for a 50% depth of discharge.
Table 17 was compiled to illustrate the watt-hours of storage needed according to the
different total watt-hours per day (supplied in table 5).
Table 17: Watt-hours of storage needed
System with batteries
Total Watt-hours (Wh) per day
Scenario 1
Scenario 2
Scenario 3
44 664
36 664
26 122
Autonomy Number
x 3 days
Battery Correction factor
x 1.190
Depth of discharge
÷ 0.5
Watt-Hours of Storage
Needed
318 900
~ 319 000
261 780
~ 262 000
186 511
~ 187 000
The battery watt-hours were calculated as follow for the Trojan J185H-AC lead acid
battery:
Battery Watt-Hours = 225 Ah x 12V
= 2 700 Wh
where:

the battery ampere-hour was 225 Ah,

and the battery voltage was 12 V (as supplied in table 18)
Thus the battery watt-hours were calculated and included in the battery specification
table below.
Table 18: Battery specifications
Ampere- Volts
hour (Ah) (V)
Battery
Watthours
(Wh)
Dimension
Weight
LxWxH
(kg)
(mm)
Manufacturer
Type
Price
(R)
Trojan
J185H-AC
Lead
Acid
4 210
(€ 290)
225
12
2 700
58
381 x 178 x
371
M-Solar
C100
Lead
Acid
11 750
(€ 820)
900
6
5 400
133
585 x 262 x
460
90
U.S. Solar
Lead
Acid
2 800
(€ 200)
130
12
1 560
Trojan
T145
Lead
Acid
2 890
(€ 200)
260
6
1560
33
264 x 181 x
295
2 640
65
522 x 238 x
240
Victorian Ener5 920
AGM
220
12
gy
(€ 410)
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
330 x 171 x
248
As seen from the battery specification, the higher the watt-hours of a battery, the more
expensive, heavier and bigger the dimension of the battery. The AGM battery is an exception which will be discussed below.
The number of batteries needed was calculated as follow for scenario 1:
Number of Batteries Needed = 318 900 Wh ÷ 2 700 Wh
= 119 Batteries
where:
the battery storage needed were calculated supplied in table 17, and
the battery watt-hours were calculated and supplied in table 18.
Table 19 below was compiled for comparison purpose taking into account the different
battery watt-hours and the different battery storage needed. The table results illustrates
the number of batteries needed, including the total cost, the space required, and the total
weight for the battery bank. The different batteries compared and their respective watthours were:

Trojan J185H-AC lead acid battery (2 700 Wh),

M-Solar C100 lead acid battery (5 400 Wh),

US Solar lead acid battery (1 560 Wh),

Trojan T145 lead acid battery (1 560 Wh), and

Victorian AGM battery (2 640 Wh)
Table 19: Comparison table according to different batteries
System with batteries
Watt-Hours of Storage
Needed
Trojan J185H-AC (12V)
Number of batteries
Scenario 1
Scenario 2
Scenario 3
318 900
261 780
186 510
119
97
70
91
Total Cost
R 500 990
€ 34 930
2.99 m³
6 902 kg
R 408 370
€ 28480
2.44 m³
5 630 kg
R 294 700
€ 20 550
1.76 m³
4 060 kg
60
R 705 240
€ 49 180
4.23 m³
6 780 kg
49
R 575 950
€ 40 170
3.45 m³
5 540 kg
35
R 411 390
€ 28 690
2.47 m³
3 960 kg
205
R 574 000
€ 40 030
2.87 m³
167
R 467 600
€ 32 610
2.34 m³
120
R 336 000
€ 23 430
1.68 m³
205
R 592 450
€ 41320
2.89 m³
6 770 kg
167
R 482 630
€ 33 660
2.35 m³
5 510 kg
120
R 346 800
€ 24 190
1.69 m³
3 960 kg
121
99
R 716 320
R 586 080
€ 49 960
€ 40 870
Space Needed
3.61 m³
2.95 m³
Total Weight
7 870 kg
6 440 kg
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
71
R 420 320
€ 29 310
2.12 m³
4 620 kg
Space Needed
Total Weight
M-Solar C100 (6V)
Number of batteries
Total Cost
Space Needed
Total Weight
US Solar (12V)
Number of batteries
Total Cost
Space Needed
Trojan (6V)
Number of batteries
Total Cost
Space Needed
Total Weight
Victorian AGM (12V)
Number of batteries
Total Cost
The number of batteries needed in a battery bank to supply the battery storage needed
depends mainly on the watt-hours a battery can provide. The higher the watt-hour (size)
per battery, fewer batteries is needed in the battery bank. The less batteries needed in a
battery bank does not necessarily mean the battery bank would be less expensive.
Comparing the two highest watt-hour batteries, the Trojan 12V and M-Solar 6V batteries. The M-Solar 6 V battery produces the highest watt-hour per battery of all the batteries, thus fewer batteries are needed in the battery bank. The number of M-Solar 6V batteries needed is almost half compared to Trojan 12V batteries needed in the battery
bank. But taking into account the total cost for the M-Solar 6V battery bank, it is more
expensive to invest in this kind of battery and more space is needed to mount the battery
bank.
92
Comparing the two batteries which has the same watt-hour (1 560) per battery, the U.S
Solar 12V and Trojan 6V batteries. The number of batteries needed in the battery bank
would be the same for both types of batteries. The total cost and space needed for these
batteries would be different as the cost and dimension for these individual batteries differ. This might be because a 6 volt battery is more expensive than a 12 volt battery or
due to the fact that these batteries are produced by different manufacturers. But a general conclusion that can be made is that batteries should not be chosen for a battery bank
for its high rated ampere-hour or watt-hour, but should be looked at as a whole. Thus,
the total cost, the total space needed, its total weight, and other specific criteria.
Take for example the AGM battery which costs more, needs more space, and weighs a
lot more compared to all the other batteries (even batteries with higher watt-hours). But
AGM lead acid batteries are non-hazardous, resistant to cold temperature, not inclined
to heat up, able to hold a static charge for a long time, and has a higher discharge rate
than the others batteries (Roos, C., 2009). Therefore the choice of battery will depend
on the investor. For further evaluation and calculation purpose, the Trojan J185H-AC
(12V) battery was used as it produced the lowest total cost, space needed, and weight
for a battery bank according to the battery bank sizing.
Table 20 shows the difference in battery bank size when a different autonomy number is
utilized to size the battery bank. The same battery (Trojan J185H-AC (12V)) was used
in all the calculations for the evaluation for the number of batteries needed. The table
results also illustrates the number of batteries needed, including the total cost, the space
required, and the total weight for the battery bank.
Table 20: Comparison of a battery bank according to lower autonomy number
System with batteries
Autonomy Number 3
Watt-hours of Storage needed
Number of batteries needed
Total Cost
Space Needed
Total Weight
Autonomy Number 1
Watt-hours of Storage needed
Number of batteries needed
Scenario 1
Scenario 2
Scenario 3
318 900
119
R 500 990
€ 34 940
2.99 m³
6 900 kg
261 780
97
R 408 370
€ 28 480
2.44 m³
5 630 kg
186 510
70
R 294 700
€ 20 550
1.76 m³
4 060 kg
106 250
40
86 740
33
62 170
24
93
Total Cost
R 168 400
R 138 930
€ 11 740
€ 9 690
Space Needed
1.01 m³
0.83 m³
Total Weight
2 320 kg
1910 kg
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
R 101 040
€ 7 050
0.60 m³
1 390 kg
The autonomy number used depends on the facility need and the system connection. An
autonomy number of 3 were used for a stand-alone system with a battery bank, and the
autonomy number of 1 was used for a grid-connected system with a battery bank. As
seen from above, the autonomy number used to size a battery bank has a dynamic effect
on the batteries needed, the total cost, space needed, and weight of a battery bank.
The autonomy number is the number of days estimated for which the battery bank is
sized to produce power when the energy generating component, the solar array or wind
turbine, cannot produce the power needed. Usually a battery bank is sized for 1 to 3 day
in a stand-alone system, but when the system is grid-connected less backup time is necessary. Grid-connected system only uses a battery bank to anticipate for power outages
or according to investors' choice. Therefore a grid-connected system with a battery bank
is usually sized for 8 hours, but this value depends on the particular needs or the length
of the expected power outages.
5.2.5
Charge controller sizing
The formula used to size the charge controller was:
Charge controller rating (A) = (Input Wattage ÷ Battery Voltage) x 1.3
Thus the charge controller rating was calculated for the total solar array wattage output
according to scenario 1 (table 11) for a system with batteries:
Charge controller rating (A) = (17 400 W ÷ 48 V) x 1.3
= 471.25 A
where:

the input wattage was the total watts produced by the solar array as this value
would be the input wattage for the charge controller – 300 W x 58 solar modules
= 17 400 W, and
94

the battery voltage was assumed to be 48 V. (Most systems today are 24 or 48
VDC and most grid-connected systems operate at 48 volts or higher (Wholesale
Solar, 2014).), and

1.3 was an additional 30% factored in due to factors that can cause a sporadic
increase in current levels.
Table 21 illustrates the charge controller size that would be needed according to the
solar array size that was calculated in table 6 for a system with batteries.
Table 21: Charge controller for a 300 W poly-crystalline solar array
Solar System with batteries
Scenario 1
Scenario 2
Scenario 3
58
48
34
17 400 W
14 400
10 200
472 A
390 A
277 A
Number of modules
Input Wattage
Charge controller rating
A charge controller rating was calculated for a wind turbine according to a specific wind
turbine chosen. Charge controller for the Earth Power 10 kW rated wind turbine:
Charge controller rating (A) = (10 000 W ÷ 48 V) x 1.3
= 271 A
where:

the input wattage was the total watts produced by the wind turbine as this value
would be the input wattage for the charge controller – even though the wind turbine can produce 15 000 W, it was assumed that the wind turbine would not be
able to produce the maximum power rating as the wind resource does not exceed
the rated power and can only produce the rated power which is 10 000 W, and

the battery voltage was assumed to be 48 V, and

1.3 was an additional 30% factored in due to factors that can cause a sporadic
increase in current levels.
Table 22: Charge controller specifications
Manufacturer
Current Rating
Price
Voltage
Type
Steca Tarom - 440
40 A
R 4 730
€ 330
48 V
Hybrid
Microcare : 100 Amp
100 A
R 11 020
12 – 48 V
Solar MPPT
95
€ 770
Limit – 150 V
60 A
R 3 160
Max Current
€ 220
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
*Kestrel: 300I
Wind Turbine
The choice of the charge controller will depend on the charge controller rating, energy
generating system, and the system connection. Therefore the highest charge controller
rating was chosen for each energy generating equipment found on the online eco stores
illustrated in table 22 above. It has to be kept in mind that there would be a lot more
choices available in the market from different manufacturers at different ratings and
prices. These charge controllers were chosen as their price and specifications were
freely available. The total costs of the charge controller for each system were calculated
using the charge controller specifications above and the results compiled below (table
23).
Table 23: Charge controller cost by type of system
Solar System with batteries
Charge controller rating
Microcare : 100 Amp
(Charge controllers needed)
Total cost
Scenario 1
Scenario 2
Scenario 3
472 A
390 A
277 A
(4.72 ≈ 5)
R 55 120
€ 3 840
(3.9 ≈ 4)
R 44 090
€ 3 080
(2.7 ≈ 3)
R 33 070
€ 2 310
Worksheet 1
Worksheet 2
Worksheet 3
271 A
271 A
271 A
Wind turbine System with batteries
Charge controller rating
Krestel : 60 Amp
(Charge controllers needed)
Total cost
(4.52 ≈ 5)
(4.52 ≈ 5)
R 15 790
R 15 790
€ 1 100
€ 1 100
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
(4.52 ≈ 5)
R 15 790
€ 1 100
The charge controller for a solar system depends on the solar array size and the total
watts the array produce. Therefore the results in table 21 were used to calculate the total
cost for the charge controller according to the charge controller rating. The total cost of
the charge controller for a wind turbine system was calculated to be the same value.
This is due to the fact that the charge controller is sized according to the wattage rating
96
for the specific turbine chosen. The wind turbine charge controller were sized according
to its rated power as explained (10 000 W), when wind resources are available higher
than the rated wind speed, the maximum power output (15 000 W) should be used to
size the charge controller.
5.2.6
Inverter sizing
The formula used to size the inverter was:
Inverter rated power (W) = Total watts of the appliances or devices x 1.3
Thus the inverter rating was calculated for the total watts consumed at one time according to scenario 1 (table 10):
Inverter rated power (W) = 5 502 W x 1.3
= 7 150 W
where:

the total watt consumption of all the appliances at once were calculated in table
10, and

1.3 was an additional 30% factored in due to factors that can cause a sporadic
increase in current levels.
Table 24 shows the results of the inverter rated power calculated for the total watts the
appliances can consume at one time.
Table 24: Inverter rated power
Scenario 1
Scenario 2
Scenario 3
Total Watts at one time
5 502 W
4 502 W
5 502 W
Inverter Rated Power
7 150 W
5 850 W
7150 W
Table 25: Inverter specifications
Rated
Power
Price
Type
Microcare
10 000 W
R 43 878
(€ 3 060)
Bi-Directional
(Grid-connected incl. Battery bank)
*SMA : Sunny Tripower
10000TL
10 000 W
R 68 257
Grid Tie
(€ 4 760) (Grid-connected excl. Battery bank)
Manufacturer
97
MLT Drives : Oasis 6048
R 33 781
Off Grid
6 000 W
Pure Sine Wave
(€ 2 360)
(Stand-alone incl. Battery Bank)
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
The choice of the inverter will depend on the inverter rated power, and the system connection. Therefore the highest inverter rating was chosen for each system connection
found on the online eco stores illustrated in table 25 above. It has to be kept in mind that
there would be a lot more choices available in the market from different manufacturers
at different ratings and prices. These inverters were chosen as their price and specifications were freely available. A bi-directional inverter is used when a system is gridconnected with a battery bank. This type of inverter converts not only DC to AC, but
can also convert AC to DC. The total cost of the inverter for each system connection
were used directly from the table above, as the inverter choice are not defined by the
type of system used but the system connection type.
5.2.7
System connection types
The system connection types that were taken into account to produce a energy generating system for a service facility were as follow:


Solar system
◦
Stand-alone system with a battery bank
◦
Grid-connected system with a battery bank
◦
Grid-connected system without a battery bank
Wind turbine system
◦
Stand-alone system with a battery bank
◦
Grid-connected system with a battery bank
◦
Grid-connected system without a battery bank
Different components were needed to complete a specific system connection. The different system connection types and their components needed were as follow:

Stand-alone system with a battery bank - energy generating equipment + battery
bank + charge controller + inverter

Grid-connected system with a battery bank - energy generating equipment + battery
bank + charge controller + inverter
98

Grid-connected system without a battery bank – energy generating equipment +
inverter
Table 26 below was compiled to illustrate the difference in the estimated cost for complete systems. The total cost of the systems calculated below does not include mounting
structures, wiring, installation (labor) cost, and safety and metering equipment. The
costs were calculated to supply a general estimate on how much a system's major components would cost and for comparison purposes. Comparisons such as the cost difference between the system connection types, the cost difference between the system sizes
according to the power consumption demand, and the cost difference between the system types. The following major components sized above were specifically used in the
table compilation which also indicates where the values were derived from:

Solar array - 300W Poly-crystalline solar panel (calculated in table 14)

Wind turbine – 10 kW Earth Power wind turbine (supplied in table 15)

Battery bank – 12V Trojan J185H-AC battery (calculated in table 20)

Autonomy number 3 for a stand-alone system, and

Autonomy number 1 for a grid-connected system

Charge controller – (calculated in table 23)

Inverter – (calculated in table 25)
99
Table 26: Total estimated system cost
Solar System
System connection type
Stand-alone incl. Battery bank
 Solar Array
 Battery Bank (Autonomy 3)
 Charge Controller
 Inverter
Grid-connected incl. Battery bank
 Solar Array
 Battery Bank (Autonomy 1)
 Charge Controller
 Inverter
Grid-connected excl. Battery bank
 Solar Array
 Inverter
Scenario 1
Scenario 2
Scenario 3
R 781 140
R 644 600
R 473 720
€ 54 480
€ 44 950
€ 33 040
R 458 740
R 358 250
R 290 150
€ 31 990
€ 24 980
€20 240
R 236 510
R 203 520
R 167 230
€ 16 490
€ 14 190
€ 11 670
Scenario 1
Scenario 2
Scenario 3
R 688 620
R 596 090
R 482 420
€ 48 020
€ 41 570
€ 33 640
R 366 220
R 336 750
R 298 860
€ 25 540
€ 23 480
€ 20 840
R 206 410
R 206 410
R 206 410
€ 14 400
€ 14 400
Wind turbine System
System connection type
Stand-alone incl. Battery bank
 Wind Turbine
 Battery Bank (Autonomy 3)
 Charge Controller
 Inverter
Grid-connected incl. Battery bank
 Wind Turbine
 Battery Bank (Autonomy 1)
 Charge Controller
 Inverter
Grid-connected excl. Battery bank
 Wind Turbine
 Inverter
€ 14 400
(€ 1 = R 14.36 @ 25 September 2014) (xe.com, 2014)
The table above shows that a stand-alone system is the most expensive compared to a
grid-connected system with and without a battery bank. This is due to the big battery
bank that is needed. A grid-connected system with a battery bank is not as expensive as
a stand-alone system. A grid-connected system does not need to produce 100% of the
power demand and are only sized to anticipate for power outages, where stand-alone
system needs to produce 100% of the power demand and a larger battery bank is needed
to anticipate for cloudy or non-windy days. Thus the initial investment for system con-
100
nection types including a battery bank increases the initial investment in general, but the
investment will depend on the autonomy number used.
The total cost from worksheet 1 to 3 can vary dramatically, take for example a standalone (solar and wind turbine) system, the difference in the initial investment is about R
100 000. The reason for these differences is due to the fact that the system components
are sized according to the power it needs to provide, the estimated power consumption
demand. Therefore the table shows the importance of using approximate values to estimate the power consumption demand as it has an effect on the initial cost for the system.
The cost difference between a solar and wind turbines system also relies on the estimated power consumption demand. When sizing a solar system, the solar array is dependent on power demand, thus the higher the power demand, the bigger the solar array, the
more expensive the system. Where on the other hand, a wind turbine does take the power consumption demand into account, but it is sized according to its rated power it can
generate according to the wind resource available. Therefore one big enough wind turbine was used compared to a solar array that needs a number of solar panels to produce
a specific amount of power. This is clearly indicated in the grid-connected systems excluding a battery bank. The type of system does not affect the battery bank size since a
battery bank is sized according to the power consumption demand and the autonomy
number.
The table below is an illustrative example of the total space and weight that would be
needed in a solar system according to the system size and system connection types. The
example only takes into account the estimated solar array and battery bank. The space is
a very important factor to consider; especially where space is limited and a personal
micro solar plant might not be allowed on a location. Weight is important as it can increase the total cost due to transportation cost. Therefore it will have an effect on a decision to purchase these components locally or from abroad.
101
Table 22: Space and Weight
Solar System
System connection type
Scenario 1
Scenario 2
Scenario 3
Solar array space needed
112.52 m²
93.12 m²
65.96 m²
Battery bank space needed
2.99 m³
2.44 m³
1.76 m³
Solar array and battery weight
8 584 kg
7 018 kg
5 055 kg
Solar array space needed
112.52 m²
93.12 m²
65.96 m²
Battery bank space needed
1.01 m³
0.83 m³
0.60 m³
Solar array and battery weight
4 002 kg
3 306 kg
2 378 kg
Solar array space needed
98.94 m²
79.54 m²
58.20 m²
Solar array weight
1 479 kg
1 189 kg
870 kg
Stand-alone incl. Battery bank
Grid-connected incl. Battery bank
Grid-connected excl. Battery bank
Wind turbine System
1 250 kg
102
5.3. Rainwater harvesting system
Johannesburg receives on average 543 mm of rainfall per year, or average 45.3 mm per
month. July is perceived as the driest month of the year when an average of 4 mm of
rainfall occurs, and January is perceived as the wettest month with an average of 125
mm. (Climatemps, 2014) According to weather underground, high volume thunderstorms has a precipitation value between 14 – 18.03 mm per storm event. There were 2
higher values but they were treated as outliers since those values were extraordinarily
high. (Weather Underground, 2014) By taking into account these average values, the
water resource available and storage capacity needed were calculated.
Water resource available
The rainwater resource that can be harvested was estimated by the following formula:
Net Runoff = Catchment area x Rainfall x 0.95
Thus the annual net runoff that can be harvested by a rainwater harvesting system was
calculated as follow:
Annual Net Runoff = Catchment area x Average Rainfall per year x 0.95
= 13.98 m² x 543 L/m² x 0.95
= 7 211.58 L
where:

the catchment area was the roof area of container measured to be 13.98 m²,

the rainfall measured was an average of 543 mm per year (or 543 L/m²), and

0.95 is the runoff coefficient for a pitched metal roof.
The average net rainfall was calculated for the following events by utilizing the same
equation as above:

Monthly (45.3 mm) = 602 L

Wettest month (125 mm) = 1 660 L

Driest month (4 mm) = 53 L
Collection capacity needed
The collection capacity for a high volume storm was estimated by utilizing the same
formula as above. The measure indicates the size of the storage tank that can be ac-
103
quired to reduce water loss due to overflow in a storm. The capacity was calculated as
follow:
Capacity needed = Catchment area x Rainfall expected in a local high volume storm x
0.95
= 13.98 m² x 18.03 L/m² x 0.95
= 239.46 L
The estimated water need was calculated per month. Since the re-grinding machine's
water tank (20 L) will be changed at least once a week, the estimated minimum water
need was calculated to be:
20 L x 4 times a month = 80 L/month
Estimated pipe size
The pipe size was estimated by utilizing the rule of thumb - 1 cm² of gutter cross section
per 1 m² of roof area, thus the estimated minimum pipe size = 14 cm² cross section. The
pipe diameter was calculated by using the equation to calculating the area circle and
converting it to diameter.
Area = 2 x (Diameter ÷ 2)²
= 5.3 cm
Sizing a rainwater harvesting system involves estimating the resources available, the
storage capacity needed, and the pipe size. The estimated resource availability values
calculated above were (on average) 7 212 liters collected yearly, 602 liters collected
monthly, 1 660 liters collected on the wettest month, and 53 liters collected on the driest
month. The estimated storage capacity needed can either be 80 liters which is the minimum amount needed to replace the regrinding water once a week, or 240 liters which is
the amount of water that can be collected in a high volume storm event. The pipe size
was estimated to be a minimum of 5.3 cm in diameter. The minimum pipe size is to
allow water flowing fast and freely through the system.
A volume of 80 liters water is needed per month to replace the water in the grinding
machine storage tank once a week, thus the minimum volume for rainwater storage capacity needed is 80 liters. By taking into account the minimum storage capacity needed
and the estimated resource available during the driest month (53 liters), July would not
104
be able to produce the required minimum water needed for the month. Therefore it
might be advisable to invest in a bigger storage capacity to plan for dry months such as
in July. Since Johannesburg receives an average monthly net rainfall of 602 liters that
can be collected, a bigger storage capacity of 80 liters can definitely be invested in.
105
6
CONCLUSION
A rainwater harvesting system can be applied anywhere in the world if needed. Therefore a rainwater harvesting systems would especially be beneficial in locations where
water is scarce and/or not connected to a municipal water supply. The system require
few skills, little supervision to operate, with minimal maintenance such as keeping the
roof, gutters, and filters clean. The system can also be connected to the grinding machine's filtration system to filter out unwanted impurities collected in the water through
its course to the storage tank before the water is replaced. With a bit of initiative and
UV protected supplies the system can easily be installed DIY. A rainwater harvesting
system takes up minimum space, depending on the storage capacity needed.
The storage capacity needed depends on how many times the water in the grinding machine is going to be replaced. Taking into account the estimated resource available during the driest month(s) of the year, the storage capacity can be estimated to collect the
required minimum water needed per month. The storage capacity does not necessarily
have to be for the required monthly volume needed, but can be according to any desired
volume. Individual storage tanks can always be added later if more storage capacity
would be needed or desired.
A passive solar design is the easiest method to start transforming the service facility into
a sustainable service facility. This method does not need to be implemented just to decrease energy use, but can be implemented to increase the thermal comfort in the service station. The design elements, principles, and considerations that need to be taken
into account can easily be applied and implemented to the service facility as the container is limited in size.
Basically the orientation depends if the location is in the northern or southern hemisphere and weather the side of the doors should face east or west. The heating and cooling depends on the climate and controlling the heat gain and natural ventilation in the
service facility. There are various different techniques discussed which can easily be
applied and modified in controlling heat gain and natural ventilation to suit a specific
climate/location. The most important principle that needs to be considered in the service
facility is insulation. As mentioned above, the container is constructed out of corrugat-
106
ed iron (a low thermal mass material) which reacts quickly to external conditions. For
this reason it is of utmost importance that the container is insulated and insulating the
container would cater for seasonal as well as daily variations in temperature.
Thermal mass should be taken into account in each step of the designing process. This
principle can sometimes not be considered on its own. Take for example a design principle that needs consideration, it does not matter on the location, the choice in window
and shading the window. According to the container specified layout, metal equipment
will be stacked by the window. This means that sunlight that strikes on these equipment
will heat the metal and in turn radiate the heat into the container space. This can be very
beneficial during cold temperatures, but will cause uncomfortable temperatures during
warm temperatures. Due to this phenomenon, extra care should be taken when considering a passive design.
Well coupled insulated and thermal mass with innovative shaded or unshaded ways can
achieve efficient thermal comfort. A passive solar design can be utilized anywhere
across the world and can also be implemented to a certain degree according to comfort
and investment.
Renewable energy is also available everywhere throughout the world, but these technologies are expensive, need a lot of space and it has to be remembered that they are not
maintenance free. These technologies also rely and are affected by the weather which
reduces their reliability. It is inconclusive whether a renewable energy system would be
a suitable choice for the service facility as it is not black and white. There are too many
depending factors that need consideration at a location due to the fact that these systems
are site specific. Wind turbine system would only be a viable option if the wind resources are optimal for a wind turbine at the location. Solar systems can be erected
throughout the world but the size of the solar array dependent on the solar irradiance
(peak sun hours) at that location. For some places it would just be too expensive to install a solar system. Other depending factors would be space, devices that needs power,
the weight of transport, permits and regulations, and funds available.
Globally, each country differs, not just in their regulations but also in resources available. Therefore another depending factor that needs consideration is whether the location
already has usable power available or not on the site. In my opinion if power is not
107
available a system can be sized and the cost compared to the cost of laying power lines.
Also when power is provided but not freely available, a system can be sized accordingly
and invested in to reduce the power cost or other renewable technologies can be researched.
During the course of sizing these systems different sources supplied different methods
to size a system's major components. The manner in sizing these components were basically the same as explained above but other values such as, the derating factors or using
ampere instead of watts, were used to size these components. These methods were utilized for interest sake and it was found that the results were different from the results
explained above. Therefore it is crucial to utilize approximate values from the start, values pertaining specifically to the location and situation, and the method above should
only be used as an estimate. The estimated size can also be compared with other methods before deciding to invest in an energy generating system. When a decision is made
and before installing a system, a professional should be contacted to get a complete project quote.
108
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APPENDICES
Appendix 1. Service facility specifications (CONFIDENTIAL)
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Appendix 2. Grinding machine specifications (CONFICENTIAL)
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Appendix 3. Online Links
Climate:
Weather Underground: http://www.wunderground.com/
World Climate and Temperatures: http://www.climatemps.com/
World Weather and Climate Information: http://www.weather-and-climate.com/
WeatherSpark : http://weatherspark.com/
Latitude:
World Climate and Temperatures: http://www.climatemps.com/
Maps of the World: http://www.mapsofworld.com/lat_long/
Solar Elevation Calculator:
Keisan Online Calculator: http://keisan.casio.com/exec/system/1224682277
Overhang Calculator:
EcoWho: http://www.ecowho.com/tools/passive_solar_eaves_calculator.php
Solar Irradiance Calculator:
Solar electricity handbook: http://solarelectricityhandbook.com/solar-irradiance.html
Tilt Angle Calculator:
Solar electricity handbook: http://solarelectricityhandbook.com/solar-anglecalculator.html
Wind speed at a different height:
Wind Profile Calculator: http://wind-data.ch/tools/profile.php?lng=en
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