Enhancing the Utilisation of Non

Enhancing the Utilisation of Non
Department of Mechanical and Aerospace Engineering
Enhancing the utilisation of non-dispatchable
Renewable power
Author: Mark Dunn
Supervisor: Dr Paul Strachan
A thesis submitted in partial fulfilment for the requirement of the degree
Master of Science
Sustainable Engineering: Renewable Energy Systems and the Environment
2015
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Copyright Declaration
This thesis is the result of the author’s original research. It has been composed by the
author and has not been previously submitted for examination which has led to the
award of a degree.
The copyright of this thesis belongs to the author under the terms of the United
Kingdom Copyright Acts as qualified by University of Strathclyde Regulation 3.50.
Due acknowledgement must always be made of the use of any material contained in,
or derived from, this thesis.
Signed:
Date: 4th September 2015
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Abstract
The purpose of this thesis is to investigate opportunities of enhancing the utilisation
of non-dispatchable on-site Renewable power, when in excess to site demand. To
investigate this, an energy intensive factory that has deployed several on site renewable
energy technologies was studied. After analysis and modelling of the energy supply and
demand requirements of the factory, the project reviewed all possible electrical energy
storage technologies and progressed to differentiate the technologies that were most
applicable to the site under review.
One technology reviewed that does technically achieve the site requirements, is liquid
air energy storage, (LAES), which has the potential to deliver various benefits to the
factory, including almost 3,000 tonnes per year of CO2 reductions and £1m of energy
cost benefits, in addition to enhanced security of supply.
A detailed review of the background to LAES was completed before carrying out a cost
benefit analysis. This highlighted that the capital costs requirements of a LAES plant
currently prove prohibitively high, for this application, due to the development status
of the technology package. A sensitivity analysis indicates that individually, capital
costs or grid electricity price would need to move substantially to change the
commercial viability of the technology, but a more realistic combined impact is
possible.
The project concludes that there are selected emerging technologies, (LAES, Power to
gas, and batteries), that meet the site requirements, but future analysis is required to
assess the commercial viability of each, particularly with ongoing development,
improving efficiency and reducing equipment capital costs.
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Acknowledgements
This thesis concludes my studies with the University of Strathclyde as a part time
student. I would therefore like to thank all of the staff on the Renewable Energy
Systems and the Environment course for their help and in particular Dr. Paul Strachan,
from whom I have received valuable support throughout the last 2 years of study. My
family and work colleagues also need thanks for their patience and support in helping
me complete this thesis.
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Table of Contents
1.! Introduction .......................................................................................................... 11!
1.1.! Objectives ...................................................................................................... 11!
1.2.! Report Structure/ Project Methodology ........................................................ 15!
2.! Review of Energy Storage Technologies ............................................................. 16!
2.1.! Introduction: .................................................................................................. 16!
2.2.! Overview of Energy Storage Technology ..................................................... 17!
2.3.! Overview of Main Storage Technologies: .................................................... 19!
2.3.1.!
Pumped Hydro ........................................................................................... 19!
2.3.2.!
Compressed Air ......................................................................................... 20!
2.3.3.!
Thermal Energy Storage ............................................................................ 21!
2.3.4.!
Molten!salt (Sodium sulphur battery (NaS)) ............................................. 23!
2.3.5.!
Flow batteries ............................................................................................ 24!
2.3.6.!
Lead acid batteries ..................................................................................... 26!
2.3.7.!
Lithium-ion battery (Li-ion) (15) .............................................................. 27!
2.3.8.!
Flywheels ................................................................................................... 27!
2.3.9.!
Capacitors & Supercapacitors ................................................................... 28!
2.3.10.!
Electrolysis, Fuel Cell & Synthetic Natural Gas ................................... 29!
3.! Site Demand & On-site Generation ...................................................................... 33!
3.1.! Background ................................................................................................... 33!
3.2.! Data Analysis ................................................................................................ 34!
3.3.! Energy Management Opportunities with Storage ................................... 39!
3.3.1.!
The following section summarises the technical options available and
provides an approximate value that each revenue stream could bring. ........... 39!
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
3.3.2.!
The following section summarises the economic value of electrical
energy storage to the site. ...................................................................................... 40!
4.! Assessment of Applicable Storage Technologies ................................................. 43!
5.! Assessment of Liquid Air Energy Storage ........................................................... 45!
5.1.! Process Details .............................................................................................. 52!
5.2.! Key Benefits from analysis of the LAES ...................................................... 56!
5.3.! Assessment of the Site ................................................................................. 60!
6.! Conclusion ............................................................................................................ 66!
7.! Bibliography ......................................................................................................... 67!
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Table of Figures
FIGURE!1!:!PRIORITISING!OUR!MOST!MATERIAL!ISSUES,!SOURCED!FROM!GSK!WEBSITE.!(2)!.......................................!12!
FIGURE!2!:!TECHNOLOGY!OPTIONS!FOR!MITIGATING!SYSTEM!INTEGRATION!COST!IN!LOW!CARBON!SYSTEMS!(3)!!.............!17!
FIGURE!3!:!EXAMPLES!OF!ENERGY!STORAGE!TECHNOLOGIES!CLASSIFIED!BY!THE!FORM!OF!STORED!ENERGY!(3).!...............!17!
FIGURE!4!:!ENERGY!STORAGE!CLASSIFIED!BY!TYPICAL!POWER!RATINGS!AND!DISCHARGE!TIMES!(ADAPTED!FROM!EPRI).N.B.!
CAES:!COMPRESSED!AIR!ENERGY!STORAGE;!LAES:!LIQUID!AIR!ENERGY!STORAGE;!VRB:!VANADIUM!REDOX!
BATTERY;!PSB:!POLYSULFIDE!BROMIDE!BATTERY;!SMES:!SUPERCONDUCTING!(4)!.........................................!18!
FIGURE!5!:!SCHEMATIC!OF!THE!CRUCHAN!PUMPED!STORAGE!HYDRO!SCHEME.!(7)!....................................................!19!
FIGURE!6!:!RIDGE!ENERGY!STORAGE!&!GRID!SERVICES!L.P:!(6)!HTTP://WWW.RIDGEENERGYSTORAGE.COM,!ACCESSED!
14TH!AUGUST!2015!..........................................................................................................................!21!
FIGURE!7!:!VISUALISATION!OF!AN!LAES!PLANT.!SOURCE:!HIGHVIEW!POWER!BROCHURE.!..........................................!22!
FIGURE!8!:!NAS!BATTERY:!CELL!DESIGN!AND!50!KW !MODULE!(11)!......................................................................!23!
FIGURE!9!:!SCHEMATIC!DIAGRAM!OF!A!VANADIUM!REDOX!FLOW!BATTERY!SYSTEM!(8).!.............................................!24!
FIGURE!10!:!SCHEMATIC!DIAGRAM!OF!A!BATTERY!ENERGY!STORAGE!SYSTEM!OPERATION!(14)14!.................................!26!
FIGURE!11!:!SYSTEM!DESCRIPTION!OF!A!FLYWHEEL!ENERGY!STORAGE!FACILITY16.!......................................................!27!
FIGURE!12!:!SCHEMATIC!DIAGRAM!OF!A!SUPERCAPACITOR!SYSTEM.!......................................................................!28!
FIGURE13:!TOPOLOGY!OF!HYDROGEN!STORAGE!AND!FUEL!CELL!(8).!......................................................................!29!
FIGURE!14!:!SCHEMATIC!DESCRIPTION!OF!THE!POWERSTOSGAS!CONCEPT.!(8)!..........................................................!30!
FIGURE!15!:CONCEPT!OF!A!RENEWABLE!POWER!METHANE!PLANT!INTEGRATED!INTO!A!BIOGASSSNGSPLANT!AND!
ASSOCIATED!SANKEY!DIAGRAM!OF!THE!RENEWABLE!POWER!METHANE!CONCEPT!(9).!.......................................!30!
FIGURE!16:!GSK!SITE!SANKEY!DIAGRAM!AND!FORECAST!ELECTRICITY!DEMAND.!.....................................................!34!
FIGURE!17!:!KEY!STEPS!IN!LIQUID!AIR!ENERGY!STORAGE!(20)!..............................................................................!46!
FIGURE!18!:!VISUALISATION!OF!AN!LAES!PLANT.!SOURCE:!HIGHVIEW!POWER!BROCHURE.!........................................!47!
FIGURE!19!:!PROCESS!FLOW!FOR!THE!HIGHVIEW!LIQUID!AIR!ENERGY!STORAGE!SYSTEM!ADAPTED!FROM!SOURCE:!
HIGHVIEW!POWER!BROCHURE.!.............................................................................................................!48!
FIGURE!20!:!EXERGY!PERCENTAGE!AS!A!FUNCTION!OF!TEMPERATURE!DIFFERENCE!FOR!HEAT!AND!COLD!(20)21.!..............!49!
FIGURE!21:!LIQUID!AIR!ENERGY!STORAGE!FOR!POWER!GRIDS!LIQUID!AIR!CONFERENCE!ROYAL!ACADEMY!OF!ENGINEERS!
(20)!................................................................................................................................................!50!
7
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
FIGURE!22!:!SYSTEM!PFD!OF!HIGHVIEW’S!PILOT!PLANT!(13).!.............................................................................!55!
FIGURE!23:!PILOT!PLANT!HEAT!TO!POWER!RELATIONSHIP!(25)!:!...........................................................................!57!
FIGURE!24!:!ROUND!TRIP!EFFICIENCY!OF!LIQUID!AIR!ENERGY!STORAGE!SYSTEM!IN!COMPARISON!TO!WASTE!HEAT!
TEMPERATURE!(°C).!ANALYSIS!VIA!ASPEN!HYSYS!(23).!............................................................................!58!
FIGURE!25!:!RESULTS!(25)27!.........................................................................................................................!58!
FIGURE!26!M ODELLING!OVERVIEW!.................................................................................................................!60!
FIGURE!27!:!KEY!INPUTS!TO!THE!ENERGY!STORAGE!MODEL!..................................................................................!60!
FIGURE!28!:!KEY!INPUTS!TO!THE!ENERGY!STORAGE!MODEL!THE!ABOVE!PROCESS!WAS!USED!TO!DETERMINE!THE!MOST!
APPROPRIATE!USE!FOR!EXCESS!RENEWABLE!ENERGY!THAT!WOULD!HAVE!BEEN!CURTAILED!WITHOUT!ENERGY!
STORAGE.!.........................................................................................................................................!61!
FIGURE!29:!COST!PROFILE!FOR!LIQUEFACTION!AND!POWER!RECOVERY!UNIT!CONFIGURATIONS.!...................................!62!
FIGURE!30!:!EXPECTED!COSTS!FOR!A!2.5MW/5MW !PLANT!WITH!140MW H!OF!STORAGE.!.....................................!62!
8
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
List of Graphs
GRAPH!1!:!ROUTE!TO!CARBON!NEUTRAL!(FROM!GSK!BIOMASS!CONCEPT!REPORT!–!2014)!......................................!14!
GRAPH!2:!SITE!ELECTRICITY!GENERATION!AND!EXPORT!PROFILE.!...........................................................................!35!
GRAPH!3:!FORECAST!EXPORT!PROFILE!OVER!THE!9!MW !EXPORT!CAPACITY.!............................................................!36!
GRAPH!4:!CHART!OF!SITE!ELECTRICITY!EXPORT!LOAD!DURATION!CURVE!..................................................................!37!
GRAPH!5!:!INFLUENCE!OF!W IND!TURBINES!OF!EXPORT!CAPACITY.!..........................................................................!37!
GRAPH!6:!LOAD!DURATION!CURVES!FOR!EACH!ONSSITE!GENERATION!STRATEGY.!......................................................!38!
GRAPH!7!:!NPV!SENSITIVITY!ANALYSIS!OF!THE!SYSTEM!FOR!VARYING!CAPITAL!COST!AND!GRID!ELECTRICITY!PRICE.!...........!65!
!
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
List of Tables
TABLE!1!:!CHARACTERISTICS!OF!PUMPED!HYDRO!STORAGE!SYSTEMS!(7)!................................................................!20!
TABLE!2!:CHARACTERISTICS!OF!VARIOUS!ENERGY!STORAGE!TECHNOLOGIES.!NOTE:!TECHNOLOGY!STATUS!IS!ON!A!SCALE!OF!1!
–!5,!5!BEING!MOST!MATURE.!...............................................................................................................!32!
TABLE!3!:!SITE!RENEWABLE!TECHNOLOGY!INSTALLATIONS!GSK!............................................................................!33!
TABLE!4!:!!SITE!ELECTRICITY!DEMAND,!BREAKDOWN!...........................................................................................!35!
TABLE!5!:!OPTIONS!FOR!FUTURE!STRATEGY!OF!ONSSITE!GENERATION!(! !TECHNOLOGY!RUNNING,!! !TECHNOLOGY!OFFS
LINE).!..............................................................................................................................................!38!
TABLE!6:!GRID!SIDE!REVENUE!OPPORTUNITIES!FOR!AN!ENERGY!STORAGE!PLANT.!......................................................!42!
TABLE!7:!SUITABILITY!OF!VARIOUS!ENERGY!STORAGE!SOLUTIONS!TO!THE!IRVINE!SITE.!................................................!44!
TABLE!8!:!COST!BENEFITS!SUMMARY!OF!PROPOSED!SYSTEM .!................................................................................!63!
TABLE!9!:!ECONOMICAL!FEASIBILITY!OF!THE!SYSTEM!OVER!20!YEARS!......................................................................!64!
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
1. Introduction
1.1.
Objectives
The purpose of this thesis is to investigate opportunities of enhancing the utilisation
of non-dispatchable on-site Renewable power, when in excess to site demand. To
investigate this, an energy intensive factory that has deployed several on site renewable
energy technologies was studied, although the technologies and strategies investigated
are also applicable on a regional and national level.
Many organizations today have clear strategies on environmental sustainability,
GlaxoSmithKline (GSK) has corporate responsibility commitments that are aligned to
delivering our products, to our customers within a global market that are affordable and
have minimal impact on the environment.
GSK values use engagement with a range of external stakeholders as an effective tool
for gaining deeper insight into societal trends and expectations, as well as offering us
the opportunity to challenge our own assumptions about the way we work.
We are willing to fundamentally change the way we do things to better meet stakeholder
expectations. As well as ongoing stakeholder engagement, we carry out additional
research to determine current and emerging issues to help shape our approach to
responsible business.
For example, in 2013, GSK undertook a formal materiality analysis, gathering internal
and external perspectives on the key areas that have considerable financial, operational,
and/or reputational impacts on the company (see chart below). While this identified all
the issues relevant to our business, we focus our efforts on those of high or medium
importance to GSK and our stakeholders (1)1.
1
http://www.gsk.com/media/618264/gsk-responsible-business-supplement-2014.pdf
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Figure 1 : Prioritising our most material issues, Sourced from GSK website. (2)
From an environmental and product cost perspective “Energy and Climate change” and
“Security of supply” are relevant to this thesis.
“Energy & Climate Change” is one of the world’s most pressing issues and a major
threat to people’s health and global economic development. Impacts like extreme
weather and heat waves affect food production and availability of clean water and
sanitation, and threaten hard-won global health improvements.
By using resources more efficiently, and collaborating with others to tackle these
challenges, we can reduce costs and enhance competitiveness. GSK have set ambitious
goals to reduce carbon, water and waste across our value chain – from the sourcing of
raw materials and the impacts of our own labs and factories, to the use and disposal of
our products by patients and consumers.
GSK would like to be the most sustainable healthcare company and has set a target to
reduce its carbon footprint by 25% by 2020 and have a carbon-neutral value chain by
2050. The GSK Irvine Sustainability programme is a key element in achieving these
targets.
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Therefore, with the considerable investment that has been placed into the Irvine site
GSK continues to investigate the most cost efficient and environmentally favourable
technologies to maximize the benefits of this investment. There are several elements of
the site demand, related to the size/scale of the onsite generation that are key in
developing the need for this.
The GlaxoSmithKline (GSK) manufacturing facility, located in Irvine, Ayrshire, 30
miles South West of Glasgow, Scotland is the single largest energy consumer within
GSKs global network of 80 manufacturing facilities. The site is a key asset in the
manufacture of Antibiotics, converting primary raw materials, through fermentation,
enzymatic and extraction technologies, into Active Pharmaceutical Ingredients (APIs),
for GSKs global Augmentin franchise. Due to the large-scale fermentation, enzymatic
and extraction technologies required to manufacture these products, the quantity of
energy required is considerable. The facility runs 24/7 with infrequent downtime as
maintenance and cleaning activities are carried out within production cycles. On
average the facility has a 20 MWe power demand and an 18MWth heat demand that
results in a £15m annual energy cost. The subsequent Carbon footprint of the site is
considerable with a peak of 102,000 tonnes of CO2 from scope 1&2 emissions2 in 2014.
Despite increasing production volumes, over the last 6 years GSK Irvine has been
extremely successful in delivering year on year carbon footprint reductions, which have
been achieved through the installation of energy efficiency improvement projects
including, (electric motor upgrades, chiller, compressor, and motor control
improvements, transformer upgrades, lighting and HVAC control upgrades, 4MW
natural gas CHP with absorption chilling, and small scale solar PV for individual
buildings).
2
Scope 1 (Direct emissions): Emissions from activities owned or controlled by your organisation. Examples of Scope 1
emissions include emissions from combustion in owned or controlled boilers, furnaces, vehicles; emissions from chemical
production in owned or controlled process equipment.
Scope 2 (Energy indirect): Emissions released into the atmosphere associated with your consumption of purchased
electricity, heat, steam and cooling. These are indirect emissions that are a consequence of your organisation’s energy use
but which occur at sources you do not own or control.
13
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Alongside these efficiency improvements monitoring and targeting of key energy
users within the site, with real time performance management, that is aligned to GSKs
lean management system (GPS) was also developed.
Following the ongoing efficiency improvement activity, GSK has invested in largescale renewable technologies
•
Anaerobic digestion of site effluent to produce Biogas – 2x500 KW CHP.
•
Wind Turbine Generators – 2 x 2.5 MW installed, 2 x 2.5 MW planned.
•
Biomass –20 MWe / 18 MWth Recycled & Residue woodchip CHP.
Graph 1 : Route to Carbon Neutral (from GSK Biomass Concept Report – 2014)
14
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
1.2.
Report Structure/ Project Methodology
Section 2 - Error! Reference source not found., will establish an overview of
energy storage technologies and develop a selection process designed to identify the
most likely commercial or emerging technology that will enable the enhancement of
the use of excess non-dispatchable renewable power.
Section 3 - Error! Reference source not found., models the site power demands, their
variable profile in relation to the size of each on-site renewable technology. This also
needs to be considered in relation to the current 9MWe export capacity for spill of
surplus power into the distribution and transmission networks and a proposed
increased export capacity that is required for financial investment in a planned
20MWe Biomass CHP. Also within this section is a review of the financial impacts of
the import / export power prices and how this influences the need for onsite energy
storage.
Section 4 -Assessment of Applicable Storage Technologies, covers the comparison of
the reviewed energy storage technologies and investigates which technology or group
of technologies are most appropriate towards implementing electrical energy storage
within the Irvine site.
Section 5 - Assessment of Liquid Air Energy Storage (LAES), covers an assessment
of an emerging technology that has the potential to maximize the use of excess non
dispatchable renewable power and provides an overview of LAES. This includes a
detailed review of the technology constraints and details on its application within the
GSK Irvine site by modelling the site energy profile after implementation. Finally
completing a cost benefit analysis to identify if the technology is feasible for use
within the Irvine site and its sensitivity the capital cost and grid electricity price
movements.
Finally, section 6 - Conclusion completes the thesis by summarising the content and
identifying the recommendations required to facilitate the development and
implementation of this technology.
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
2. Review of Energy Storage Technologies
2.1.
Introduction:
Renewable energy sources, such as wind power and solar PV and Biomass/Biogas
CHP, as stated above have vast potential in minimising the reliance on fossil fuels and
subsequent unsustainable emissions of greenhouse gas. Within the GSK Irvine site the
size and scale of these technologies have been developed to provide the most
economical use of base load technologies, with Biomass CHP being scaled to the site
heat demand and Biogas CHP maximising the use of available waste streams. The
installation of wind energy achieves the sites energy demand requirements, enabling
the site to achieve full autonomy of net annual energy demand, although as seen in the
previous section the demand profile coupled with a variable and uncertain wind power
output results in the export “spill” of renewable power onto the grid and undesired
import of grid power at various times. This is also exacerbated by the reliance on
combined heat and power as the demand for heat sometimes occurs during, windy
periods, when electricity demand is low and wind generation is high. This combination
sometimes results in an oversupply of generation and has led to investigation of the
deployment of energy storage as a component of the site energy system.
Energy storage provides a solution to avoiding this situation by absorbing unusable
generation and moving it to times of high demand. To establish the feasibility of
integrating energy storage a technical and economic assessment of a variety of
competing technologies was required. This included demand response, capacity,
efficiency, cost, flexibility, impact on system stability and the maturity of each
technology. (2)3
Before assessing storage technologies it is important to note that there is a range of
alternative options available to mitigate this issue, for the Irvine site these include,
demand management and flexible generation, which have been described in section 1,
in addition to storage technologies.
3
The Role of Energy Storage with Renewable Electricity Generation, Paul Denholm, Erik Ela, Brendan Kirby, and Michael
Milligan Technical Report, NREL/TP-6A2-47187 January 2010
16
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Figure 2 : Technology options for mitigating system integration cost in low carbon
systems (3) 4
2.2.
Overview of Energy Storage Technology
Energy storage systems are normally classified by the form in which the energy is
stored (see Figure 3) and their key characteristics include the amount of power that
they can deliver, how much energy they can store, their round trip efficiency, and the
extent to which increasing numbers of charging / discharging cycles impacts their
performance.
Figure 3 : Examples of energy storage technologies classified by the form of stored
energy (3).
4
Strategic Assessment of the Role and Value of Energy Storage Systems in the UK Low Carbon Energy Future
Energy Futures Lab, Imperial College London, Report for The Carbon Trust, June 2012, Goran Strbac, Marko Aunedi, Danny
Pudjianto, Predrag Djapic, Fei Teng, Alexander Sturt, Dejvises Jackravut, Robert Sansom, Vladimir Yufit, Nigel Brandon
17
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Considering these various types of storage technology, the following diagram illustrates
typical system, power and storage sizes. An overview of typical characteristics of some
energy storage technologies is then provided in table 2.
Figure 4 : Energy storage classified by typical power ratings and discharge times
(adapted from EPRI).N.B. CAES: Compressed Air Energy Storage; LAES: Liquid Air
Energy Storage; VRB: Vanadium Redox Battery; PSB: Polysulfide bromide battery;
SMES: Superconducting (4)
18
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
2.3.
Overview of Main Storage Technologies:
2.3.1. Pumped Hydro
Pumped hydropower is at the present time the most widely utilised storage technology
in the world at around 99% of the current worldwide energy storage capacity,
representing around 127,000 MW (5)5. The technology developed can be scaled up to
several Giga watts (GW) and has a typical efficiency of 70% to 80%. Pumped storage
hydroelectric technology is well developed and well-suited for applications requiring
large power levels and long discharge times. The general configuration and
operational sequencing includes water being pumped into a storage reservoir during
times of low load when surplus electricity is available. This water is then released
through turbines to generate power supplying the peak demand.
Figure 5 : Schematic of the Cruchan pumped storage hydro scheme. (7)
5 "Energy storage - Packing some power". The Economist. 2011-03-03. Retrieved 17 July 2015.
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Pumped hydro schemes (PHS) are utilised in situations where an immediate supply of
power is needed, (spinning reserve) to cover demand peaks, frequency regulation and
voltage control.
By using variable speed turbines and pumps these facilities can either use available
electricity to transfer water between reservoirs to store potential energy, then during
peak-load periods, control the generation of electricity in response to the required
demand, (Power output can be changed in times of 10-30 ms). PHS has a low energy
density and therefore requires either very large reservoirs or a large height difference
between the upper and lower reservoirs which is a key aspect in limiting the
deployment of this technology. There are also concerns over the substantial
environmental impact and considerable initial capital cost although as an established
mature technology with high reliability and a lengthy lifecycle, PHS delivers a cost
effective means of large scale energy storage.
Table 1 : Characteristics of Pumped Hydro Storage systems (7)6
2.3.2. Compressed Air
Compressed air energy storage, (CAES) can be used to store excess renewable
electricity mechanically and is a commercialised technology at a scale that can
provide a power output in excess of 100MW from an individual installation.
The system utilised excess renewable power to compress air, this is done by injecting
it into large underground caverns or within surface tanks. During the compression
process the air heats up, this heat is utilised in the next stage when power is required.
6
Systems analyses Power to Gas: A technology review, Part of TKI project TKIG01038 – Systems analyses Powerto-Gas pathways Deliverable 1: Technology Review
20
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
During this second stage compressed air is released to drive turbines. This expansion
cools down the air cools down and must be re-heated to improve efficiency. The way
the cooling and reheating is utilised, characterises the CAES. If the heat produced on
compression is lost, the air needs to be reheated prior to expansion in the turbine, The
process is called diabatic CAES which has a low round-trip efficiencies typically
<50%. In an adiabatic CAES process, the generated heat is retained in thermal storage
prior to being used in the second stage during expansion in the turbine where typical
efficiencies of up to 70 % can be achieved. (8)7
Figure 6 : Ridge Energy Storage & Grid Services L.P: (6)
http://www.ridgeenergystorage.com, Accessed 14th August 2015
2.3.3. Thermal Energy Storage
Thermal energy storage covers a range of technologies that utilise heat energy which
can be stored in insulated environments. These technologies generally utilise a solid,
gas or liquid material and a package of equipment including the insulated thermal
store, chiller or refrigeration equipment, pumps and piping. One example of this!type!
7
Overview of current development in electrical energy storage technologies and the application potential in power system
operation, Xing Luo, Jihong Wang, Mark Dooner, Jonathan Clarke School of Engineering, The University of Warwick, Coventry
CV4 7AL, UK
21
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
of!technology is Cryogenic energy storage where liquid nitrogen or liquid air is used to
achieve the electrical and thermal energy conversion. For example, Liquid Air Energy
Storage (LAES) is an attractive option due to the high expansion ratio from the liquid
state to the gaseous state and the high power densities of liquid air compared to that of
gaseous state of air. !The technology as demonstrated by is modular, which means that
each of the charging, storage and discharging components of the system can be sized
independently. Charging the system works by using electricity to cool air down to 196° (Stage 1 in Figure 3-1 below) at which point it is in a liquid state, and every 700
litres of ambient air have been compressed to form 1 litre of liquid air. During Stage
2, liquid air is stored in an insulated tank at low pressure. This equipment is already
globally deployed for bulk storage of liquid nitrogen, oxygen and LNG. These storage
units also represent a small amount of the total capital cost of the system. Finally,
power is produced in Stage 3 by pumping the liquid air to a high pressure. On heating,
using stored heat from the air liquefier or waste heat from other processes, a high
pressure gas is produced which is then used to drive a turbine. During Stage 3, the
waste cold produced is stored and used at a later time to enhance the efficiency of
Stage 1. (10)8'
Figure 7 : Visualisation of an LAES plant. Source: Highview Power brochure.!
8
Liquid air energy storage – Analysis and first results from a pilot scale demonstration plant, Robert Morgan, Stuart Nelmes,
Emma Gibson, Gareth Brett, School of Computing, Engineering and Mathematics, University of Brighton, Brighton BN2 4GJ,
United Kingdom, Highview Power Storage, 1 Northumberland Avenue, London WC2N 5BW, United Kingdom
22
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
2.3.4. Molten!salt (Sodium sulphur battery (NaS))
The Sodium–sulfur battery (or NaS battery), along with the related lithium sulfur
battery, is one of the more advanced molten salt battery systems. The NaS battery is
attractive since it employs cheap and abundant electrode materials.
Sodium sulphur batteries as displayed in Figure 8, consist of liquid sulphur at the +ve
electrode and liquid sodium at the -ve electrode; both liquids are separated by a solid
ceramic electrolyte. The temperature is kept between 300 °C and 350 °C to ensure
that the electrodes remain molten. Sodium-sulfur batteries are a commercially
available with existing applications in distribution grid support, wind power
integration, and high-value service applications on islands. The round-trip ac-to-ac
efficiency of sodium-sulfur systems is approximately 80% with a life cycle of
approximately 15 years at 4500 cycles. The main disadvantage is the need to keep the
battery at a optimum temperature, therefore a separate or parasitic heat source is
required, which impacts its efficiency partially reducing the battery performance. The
technology is most suited to applications with daily cycling with a response time in
milliseconds making the application ideal for grid stabilisation9.
10
Figure 8 : NaS Battery: Cell design and 50 kW module (11)
9
International!Electrotechnical!Commission!(IEC)!S!Electrical!Energy!Storage!white!paper!2011.
23
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
2.3.5. Flow batteries
Flow batteries store energy in two external liquid electrolyte tanks. The operation of a
flow battery is based on the reduction-oxidation reactions of the electrolyte solutions
and occurs when electrolytes are pumped from the tanks to the cells which are
separated by ion selective membranes.
•
When charging, one electrolyte is oxidized at the anode and another
electrolyte is reduced at the cathode.
•
Electrical energy is converted to the electrolyte chemical energy.
•
On discharging the above process is reversed.
Flow batteries can be classified into the categories of redox flow batteries and hybrid
flow batteries, depending on whether all electroactive components can be dissolved in
the electrolyte. Figure 9 : Schematic diagram of a vanadium redox flow battery
system. shows a schematic diagram of a vanadium redox flow battery system.
Figure 9 : Schematic diagram of a vanadium redox flow battery system (8).10!
Redox flow batteries (RFB) have a catholyte (positive electrode) and anolyte
(negative electrode) which are stored in two different storage tanks and circulation
10
Overview of current development in electrical energy storage technologies and the application potential in power system
operation Xing Luo, Jihong Wang, Mark Dooner, Jonathan Clarke School of Engineering, The University of Warwick, Coventry
CV4 7AL, UK
24
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
loops, but are passed into a common electrochemical cell. The electrolytes react via a
redox reaction in the porous electrodes producing an exchange of charge. An ion
selective membrane which is permeable only to specific ions is in place to separate
each side of the electrode cell to equilibrate the redox reaction completing the circuit.
The Vanadium Redox Flow Battery VRB is one of the most mature flow battery
systems (12)11.
Hybrid flow batteries include the features of established secondary batteries and redox
flow batteries. Typical examples of a HFB are the ZnCe and the ZnBr systems. In a
ZnBr battery there are two aqueous electrolyte solutions which contain the reactive
components; these are based on zinc and bromine elements. These two electrolyte
solutions flow through the electrolytic cells during the charging/discharging phases,
where the reversible electrochemical reactions occur.
Electrical energy storage applications using ZnBr batteries are in their early stage of
development and not fully commercialised, but they have some clear benefits with
relatively high energy density and cell voltage with deep discharge capability and
good reversibility.
The disadvantages of flow batteries:
1. low performance resulting from:
a. non-uniform pressure drops and the reactant mass transfer limitation,
2. compared to traditional batteries flow batteries have high manufacturing costs
due to complicated system requirements
An advantage of flow batteries are:
1. Discharge duration can be increased by adding more electrolyte or regenerated by
replacing the depleted electrolyte.
2. They have a long life,
3. short response time,
4. low maintenance costs
11
Battery energy storage technology for power systems , An overview K.C. Divya, Jacob Østergaard Electr Power Syst Res 2009
25
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
5. Efficiency near 75%.
'
2.3.6. Lead acid batteries
Lead acid batteries (LAB) are the most widely used rechargeable battery and have
been commercially deployed for more than 100 years (13)12.
The cathode is made of Lead dioxide, PbO2 the anode is made Lead, Pb and the
electrolyte is sulphuric acid, H2SO4.
Pb + PbO2 + 2 HSO4− + 2 H+ → 2 PbSO4 + 2 H2O, E = +2.05 V
Figure 10 : Schematic diagram of a battery energy storage system operation (14)14
LABs have an efficiency of approximately 75 – 90%, their response times are
relatively fast, a low power leakage rate of <0.3% per day with relatively low capital
costs.!!One disadvantage is that they perform poorly at low temperatures and require a
temperature management system increasing the overall cost. This along with their
relatively low cycling times and energy density is limiting their application in
commercial Electrical Energy storage application s (14)14.
12
Handbook of batteries / David Linden, Thomas B. Reddy.—3d ed. 2002
26
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
2.3.7. Lithium-ion battery (Li-ion) (15)13
The main development of rechargeable Li-ion batteries is associated with its use in
small consumer electronic products. Li-ion is also now one of the leading
technologies for hybrid and full electric vehicles, with battery packs sized up to 50
KWh. The operation of this technology is achieved via the electrochemical reactions
between +ve and Li ions and anolytic and catholytic active materials. These
developments have been derived from research into the active materials used for
electrodes and the electrolyte,14 (4) and have provided systems with higher energy
density and specific energy, resulting in improvements in the speed of charging, with
relatively high round trip efficiencies (78%) and a lifecycle up to 4000 cycles.
On the downside the Li-ion battery technology may not be appropriate for long term
storage as they have a high leakage rate at between 1-5% per day. The life of the
materials is dependent on cycle depth of discharge and it is therefore unsuitable for
applications where they will become fully discharged.
2.3.8. Flywheels
These devices were developed and are in the main
now used for mitigation against power quality issues
and for bridging the switchover between different
power sources. (8)15 As this is not in line with the
project objectives, no further details are required.
Figure 11 : System description of a flywheel energy storage facility15.
13
!Electricity Energy Storage Technology Options, A White Paper Primer on Applications, Costs, and Benefits 1020676
Technical Update, December 2010!
14
!Review of energy storage technologies for wind power applications Francisco Díaz-Gonzáleza, Andreas Sumpera, Oriol
Gomis-Bellmunta, Roberto Villafáfila-Roblesb 2012.
15 X.!Luo!et!al.!/!Applied!Energy!137!(2015)!511–536
27
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
2.3.9. Capacitors & Supercapacitors
A capacitor is constructed from two electrical conductors, (metal foils) separated by
an insulating layer made from plastic or ceramic. When a capacitor is charged, energy
is stored in the dielectric material in an electrostatic field. Supercapacitors, contain
electrodes, an electrolyte and a porous membrane separator (Figure 12).
Figure 12 : Schematic diagram of a supercapacitor system.
The technology has a high power density and low charging times with a high round
trip efficiency of up to 97%, although energy density is low and power leakage rate is
extremely high at up to 40%. Capital cost is also relatively high. As such they are
more applicable to short term storage and power quality applications, including HV
power correction and UPS devices rather than large scale electrical energy storage.
Superconducting Magnetic Energy Storage (SMES)
An SMES can store electrical energy in a magnetic field created by the flow of
electric current in a superconducting inductor that is cooled to its superconducting
critical temperature. Electrical energy storage occurs when the current is increased
within the inductor, stored indefinitely as there is no degradation. Removal of this
energy is achieved by reducing the current within the inductor. At present the
technology delivers a high cycle life and a rapid response, but currently has a
relatively low energy density and high cost, and requires energy to constantly cool the
magnet (4)16.
16 Strategic Assessment of the Role and Value of Energy Storage Systems in the UK Low Carbon Energy Future
28
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
2.3.10.
Electrolysis, Fuel Cell & Synthetic Natural Gas
The use of electrolysis within electrical energy storage involves two technologies, the
production of Hydrogen by water electrolysis and the conversion of Hydrogen back to
electricity by reaction with Oxygen, (from air) within a fuel cell. This technology
system is shown below in Figure13.
Figure13: Topology of hydrogen storage and fuel cell (8).17
There are a number of major fuel cell groups which include (8):
• Alkaline Fuel Cell,
•
Phosphoric Acid Fuel Cell,
•
Solid Oxide Fuel Cell,
•
Molten Carbonate Fuel Cell,
•
Proton Exchange Membrane Fuel Cell,
•
Direct Methanol Fuel Cell,
This technology is in a development and demonstration phase and currently only has
an overall efficiency around 30% for the combined fuel cell and electrolyser system.
Energy Futures Lab, Imperial College London, Report for The Carbon Trust, June 2012, Goran Strbac, Marko Aunedi, Danny
Pudjianto, Predrag Djapic, Fei Teng, Alexander Sturt, Dejvises Jackravut, Robert Sansom, Vladimir Yufit, Nigel Brandon
17 X.!Luo!et!al.!/!Applied!Energy!137!(2015)!511–536
29
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Another related technology which is of interest is the development of a power to gas
system as shown in Figure 14 below.
Figure 14 : Schematic description of the power-to-gas concept. (8)
The initial step, as above is the conversion of electricity into hydrogen via water
electrolysis. This hydrogen produced can be utilised in several ways, either direct
power production through a fuel cell, in direct heating or via Methanation in the
production of renewable Methane for use /storage within the gas supply system.
A further adaptation is the concept of surplus renewable power to methane, which can
be stored in the natural gas grid and converted back to power through combined heat
and power when required (9).
Figure 15 :Concept of a renewable power methane plant integrated into a biogas-SNG-plant and
associated Sankey diagram of the renewable power methane concept (9).
This is an interesting concept particularly with the high heat demand within the Irvine
production facility, although the overall efficiency could be as low as 22% for a power-to30
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
methane-to-power plant (9). Therefore the Methane produced may be more valuable as a heat
source used on site rather converting back into electricity.
The following table (Table 2 :Characteristics of various energy storage technologies.
Note: technology status is on a scale of 1 – 5, 5 being most mature.)
provides an overview of all key
electrical energy storage technologies listed above. This is used in section 4 of the
report, after an assessment of the onsite generation and energy demand profile which
is covered in the next section of the report, (section 3). This is done to establish which
of the various technologies is most applicable to implementation within the Irvine
site.
31
Salt!is!heated!then!stored!in!an!insulated!container.!Heat!is!
extracted!to!boil!water!and!drive!a!steam!turbine!
S!
1000s!
0!
0.005!
S!
S!
1000s!
0!S!1!
10!S!
300!
5!S!500!
50!S!
2000!
5!S!10s!
0!S!0.01!
S!
1000s!
1!
S!
1000s!
1!
0.1!S!1!
1!
0!S!100!
0!S!100!
0.1!S!
500!
0!S!5!
15!S!
5,000!
50!S!
14,000!
Capacity!
(typical)!
MWh!
1!
0!S!25!
0!S!10!
0.01!S!
20!
0!S!10!
10!S!
2,500!
5!
2,000!
S!
Power!
(typical)!
MW!
hours!
hours!
seconds!
seconds!
5!S!1000!
5!S!1000!
0.1!S!6!
1!S!12!
1!S!6!
<!0.5!
1!S!20!
7!S!24!
60S80!
50S80!
75S80!
85S98!
30S38!
34S44!
85S98!
75S90!
60S75!
80S90!
40S75!
50S85!
minutes!
minutes!
seconds!
seconds!
minutes!
sec!S!min!
seconds!
seconds!
seconds!
seconds!
minutes!
seconds!
Discharge! Efficiency!Response!
time!
time!
hours!
%!
32
Table 2 :Characteristics of various energy storage technologies. Note: technology status is on a scale of 1 – 5, 5 being most mature.
Molten'salt!
delivers!power!
Air!is!cooled!to!~S196°C!and!stored!as!a!liquid.!Expansion!through!a!turbine!
Large!electrostatic!fields!between!two!conductive!plates!
separated!by!a!small!distance!
Capacitors!
Liquid'Air!
Energy'Storage!
Following!hydrolysis,!hydrogen!is!reacted!with!CO2!to!form!
methane!
Synthetic!
natural'gas!
Energy!stored!in!a!magnetic!field!created!by!the!flow!of!DC!
electricity!in!a!superScooled!coil!
Water!is!separated!into!hydrogen!and!oxygen.!Hydrogen!later!
used!to!generate!electricity!
Electrolysis!
Electromagnetic!
storage!
A!battery!in!which!lithium!ions!flow!from!negative!to!positive!
electrode!during!discharge.!
water!/!sulfuric!acid!electrolyte!
An!electrochemical!battery!with!lead!/!lead!sulfate!/!lead!oxide!plates!and!a!
Two!chemical!components!are!dissolved!and!separated!by!a!
membrane,!through!which!ion!exchange!occurs!
LiHion'batteries!
Lead'acid!
batteries!
Flow'batteries!
Store!electricity!as!rotational!energy!in!a!device!spinning!at!high!speed!!
Air!is!compressed!(store)!and!then!released!to!a!combustor!in!
a!gas!turbine!
Compressed'Air!
Flywheels!
Water!is!pumped!uphill!to!store!energy!and!released!downhill!
through!turbines!to!generate!electricity!
Description!
Pumped'Hydro!
Storage'type!
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
3!
3!
2!
2!
1!
1!
3!
4!
2!
3!
4!
5!
Technology!
status!
1!+!5!
25S30!
25!
>20!
4!S!12!
10!S!30!
10!S!30!
5!S!15!
3!S!15!
5!S!20!
15S20!
>25!
>50!
years!
>10,000!
>10,000!
104!
4!
10 S!
5
10 !
3!
10 S!
4
10 !
103!S!
104!
500!S!
104!
250!S!
1,500!
4!
10 S!
7
10 !
1,000!S!
>10,000!
>10,000!
>15,000!
cycles!
Lifetime! Lifetime!
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
3. Site Demand & On-site Generation
3.1.
Background
The GSK Irvine site has for several years implemented a programme of activity
focused at improving the energy efficiency of its processes and utilities. This activity
ranges from ways of working to improve demand management, replacement of
lighting with LEDs, motor replacement, monitoring and targeting and developing of
performance indicators to sustain improvements and promptly identify inefficiencies,
through to the installation of a 4MWe Natural gas Combined Heat and Power plant
(CHP) with absorption chilling and finally installation of on-site renewable energy
technologies such as the anaerobic digestion of waste effluent with 2x 500KW Biogas
CHP, 2x2.5MW wind turbine generators and a 20MW Biomass CHP. Management of
our manufacturing processes and utilities has also been reviewed over this time to
optimise resource requirements and minimise demand variability, through fixed
repeating schedules and management of batch operations.
Wind Turbines
Biogas CHP
Biomass CHP
Number of Units
4
2
1
Current Capacity
5 MW
1MW
N/A
(10 MW)
(N/A)
(20MW)
Heat Output
None
2 MW
18 MW
Incentive Scheme
ROC
FIT
ROC/RHI
Non dispatchable
Fixed
Variable
(Planned Capacity)
Ouput
(heat leading)
Table 3 : Site Renewable Technology Installations GSK
33
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
3.2.
Data Analysis
With committed capacity increases, the manufacturing site now has a total annual
electrical demand of 182GWh, with an average demand of 20MWe and peak demand
of up to 30MWe and a 162GWh heat demand with an average demand of 18MWth.
Figure 16: GSK Site Sankey diagram and Forecast Electricity Demand.
34
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
The strategy for utilisation of on-site generation is to maximise use of the waste to
energy and wind resources. This is followed by the Biomass CHP which is sized and
designed around delivering the heat demand from the site. As a result, in maximising
the Biomass CHP efficiency there remains an element of import and export.
Source'
'KWh/Yr''
TOTAL Site Demand
On Site Wind Turbine
Generation
On Site Biogas CHP
Power Generation
On Site Natural Gas
CHP
Power Generation
Site Import
Net Biomass
Generation
Total Generation
181,967,874
Available to Export
'%''
10%
n/a
23,404,608
10%
8,409,600
4%
28,776,600
12%
11,254,262
5%
160,965,523
69%
232,810,593
50,842,719
100%
22%
4%
12%
69%
5%
Table 4 : Site Electricity demand, breakdown of onsite generation and export
Graph 2: Site electricity generation and export profile.
A specific problem that the site will encounter after the installation of the biomass
CHP is the 9MWe export limit that is currently in place for the site. Whilst a revision
35
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
to this is underway requesting a larger export limit, this is not likely to be granted
until at least 2023. Analysis of the site electricity demand data and current/planned on
site generation data has determined the forecast export, shown in Graph 3: at half
hourly resolution.
Graph 3: Forecast export profile over the 9 MW export capacity.
Graph 3 Shows that, in the case where WTGs 3 and 4 are built, and all other
generators are present (natural gas CHP, biogas, WTGs 1&2 and the biomass CHP),
the export limit would be exceeded 24% of the time as seen in Graph 4.
36
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
A load duration curve for this export limit breaching is shown in Graph 4: .
Graph 4: chart of site electricity Export load duration curve
This export limit breach is primarily driven by the on-site wind generation. Graph 5 :
shows the correlation between the on-site wind generation and by how much the
export limit is breached.
Graph 5 : Influence of Wind turbines of export capacity.
This illustrates one of the drivers for an energy storage plant. With the natural gas and
Biogas CHP was running and all 4 wind turbines on line, the ramping down of on-site
37
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
generation to avoid breaching the 9MWe export limit would cost between £0.8 and
£1.5 million per annum, depending on the electrical strategy employed. The possible
scenarios that are required to curtail the on-site generation are shown in Table 5,
underutilisation of assets leading to an effective “loss” of renewable incentives (ROC
& RHI) and export income that could otherwise have been realised. The only option
that may be considered is case C, where the running strategy of the natural gas CHP is
changed to a back-up/ peak load and security of supply duty.
Cases
Base!Case
Case!A
Case!B
Case!C
Case!D
Case!E
Case!F
WTG!
1&2
WTG!
3&4
Nat'Gas'
CHP
Biogas'
CHP
Biomass'
CHP
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
Table 5 : Options for future strategy of on-site generation (! technology running, !
technology off-line).
Graph 6: Load duration curves for each on-site generation strategy.
However, another option could be utilising an energy storage solution, which would
store any electricity generated from the wind turbines that is in excess of 9MWe, in
order that it could be used on site at a later time, or exported when the total electricity
38
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
being exported is less than the limit. Results show that a considerable amount of
Electricity is available for storage and use at times when it can mitigate against import
and fill unused export capacity at other times.
3.3.
Energy Management Opportunities with Storage
There are a variety of different ways in which an energy storage plant could bring
value to the site.
3.3.1. The following section summarises the technical options available
and provides an approximate value that each revenue stream could
bring.
Black start for biomass CHP
This allows the biomass CHP to be restarted if grid power is lost and biomass plant
trips and would require approximately 2.5MWe of power to be discharged over 2
hours. There would be no response time requirements. It also provides a potential
capex avoidance of £2 million as there would be no need to install black start
capability for the biomass CHP. However, recent analysis for the biomass CHP
project has determined a limited economic case for black start capability for the
biomass CHP due to infrequent utilisation.
Off-grid power for critical users
If power supply from both the grid and the Biomass CHP are lost, an energy storage
plant could continue electricity supply to critical users to ensure that no batches of
product were lost. Approximately 5MWe of power required (to power air compressors
and critical control systems), with a potentially indefinite discharge time and a
response time requirement of less than 30 minutes (the length of time it takes for a
batch to be lost after a power interruption). A complete loss of connection to the grid
is anticipated approximately once per year and the Biomass CHP is expected to be
able to ride through approximately 75% of such events. The cost of a lost batch has
been estimated at approximately £1 – 1.5 million per batch.
39
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Continue full biomass generation in island mode
If the plant is operating in island mode, it is anticipated that the biomass CHP will
modulate its output in order to match the on-site power requirements. If an energy
storage plant was present, instead the biomass could continue to operate at as high a
load as possible, while the storage regulated the total supply to site by modulating the
power it is charging with. Due to the low frequency of occurrence, and low value of
this issue, this will not be explored further at this stage.
Wind Turbine Generation in island mode
If the plant is operating in island mode the wind turbines will have to stop generating.
An energy storage plant could in theory directly store any electricity being generated
by the wind turbines. Due to the low frequency of occurrence, and low value of this
issue, this will not be explored further at this stage.
Allow capacity for future Renewables
If any further on site generation is added, for example further wind turbines, they may
cause breaches even of an increased export limit. An energy storage plant could
mitigate this. This could contribute to GSK’s overall sustainability strategy as adding
renewable capacity at Irvine may be more straightforward than at other sites, and
could offset emissions at other sites. This “sleeving” of energy could also provide
cheaper electricity to other GSK sites.
3.3.2. The following section summarises the economic value of electrical
energy storage to the site.
Reduce need for imported electricity
During periods when the biomass plant is shutdown (e.g. annual shutdown and
unplanned outages), relatively expensive imported electricity is required. Instead, the
energy storage plant could be used to import low cost electricity and off peak times for
use at high cost times, reducing the site’s total energy bill.
40
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Improve EES performance
Waste heat from the biomass CHP, or steam extracted from the turbine, could be used
to increase the efficiency of the EES plant and therefore improve its overall
performance. For example in the Highview pilot plant trial results it is said that
approximately 47% of this waste heat used is converted back into electricity (13).
Internal arbitrage
This would involve storing energy when the export income is lower, and discharging
it selectively when the export income is higher (i.e. peak times, triad periods, red
DUoS periods etc). However, the price differential is currently not strong enough for
this to be economically viable. The price differential between the lower and higher
tariffs would have to be at least 1.43, while it is currently approximately 1.13.
Export limit breach avoidance
Avoid exceeding the 9MWe export limit (currently predicted to be exceeded 24% of
the year) by storing the energy instead. Previous recommendation was to turn off two
WTGs and the nat. gas CHP to avoid this.
Economic value to grid (i.e. revenue opportunities for the LAES plant)
The following table details the revenue opportunities available for the LAES plant
from grid services.
41
Discharge!the!storage!unit!to!increase!export!to!the!
grid!when!frequency!is!too!low!(too!much!demand!
compared!to!supply)!
As!above,!this!response!comes!online!after!the!
primary!response!but!can!be!required!for!longer!
Charge!the!storage!unit!to!increase!demand!on!the!
grid!when!frequency!is!too!high!(not!enough!demand!
compared!to!supply)!
The!grid!has!recently!started!providing!availability!
payments!for!providing!capacity!at!required!times.!
Frequency'response!
(primary)!
High'frequency!
response!
demand!when!generation!is!not!sufficient!
Table 6: Grid side revenue opportunities for an energy storage plant.
STOR!
Triad!charges!are!part!of!Transmission!Network!Use!of!
System!(TNUoS)!charges.Avoidance!of!import!during!
these!times!and!supplier!will!pay!extra!to!supply!more!
during!triad!periods!S!
Capacity!procured!by!national!grid!in!order!to!meet!
Supplier!will!pay!extra!to!supply!more!during!Red!
DUoS!periods!
Red'DUoS!
TRIAD!
Import!during!off!peak!times!(and!negative!energy!
prices),!export!during!peak!times.!
Grid'arbitrage!
Capacity'market!
Frequency'response!
(secondary)!
Instantaneous!frequency!response!(must!be!
generating!continuously!during!available!periods)!
Description!
Storage'technology'requirements:!
Frequency'control!
(instantaneous)!
Option!
42
<!4!hours!
3!hours!
(16:30!–!
19:30)!
30S90!mins!
2!hours!
Unlimited,!
usually!<30!
mins!
Unlimited!
30!mins!
30s!
Discharge!
time!
Unlimited?!
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
<20!mins!
4!–!6!
hours!
Months!
Months!
4!hours!
<30s!
<30s!
<10s!
£24!S!£27!
£19.4k!
Variable!
Variable!
£198K!
£54K!
"
"
"
"
"
£34!S!£37!
>40k!
X!
X!
X!
Response! LAES! Annual'value!
time!
?!
per'MW'per!
Instant!
X!
>£60k!
Option! to! gain! with! contract! for!
standby!capacity.!
Possibly!an!option!however!low!
value!due!to!relatively!small!
volumes!–!for!further!work.!
Option! to! gain! from! eliminating!
import!and!maximizing!export.!
Incompatible!with!9MW!limit!–!if!
9MW!is!already!being!exported!
the!capacity!cannot!be!offered.!
High!availability!also!required.!
Price!differential!currently!not!
strong!enough!–!see!section!5.2!
Incompatible!with!LAES!response!
time!
Incompatible!with!LAES!response!
time!
Incompatible!with!LAES!response!
time!
Incompatible!with!LAES!response!
time!
Notes'/'comments!
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
4. Assessment of Applicable Storage Technologies
The ideal characteristics of an energy storage plant that would suit the Irvine site vary
according to what the plant is trying to achieve. The main objective of the storage
facility is in support of minimise the amount of curtailed power generation from the
site wind turbines, to use this stored energy to avoid importing electricity from the
grid at peak demand times, including Triad periods and facilitate the potential for
standby generator payments such as the short term operating reserve (STOR).
The plant should therefore be able to store energy and supply power for significant
periods of time, ideally on a weeks/months timescale for the storage of energy, and in
hours for duration of supply. A quick response rate will also help support the site in
terms of ability to ride through power outages and other power quality impacts from
the grid connection. Capital costs are an important factor and along with operation
and maintenance costs, should all be minimised in order to keep the business case as
strong as possible. Assessment of the data in Table 6 comparing each technology
against the site objectives has enabled a clear focus on the most appropriate
technologies. This data highlights that there are only a couple of technologies
assessed to be applicable to the site’s electrical energy storage requirements. This is
Liquid Air Energy Storage (LAES) which will be investigated in more detail in the
following sections. The second technology electrolysis combined with production of
synthetic natural gas, will not be investigated in detail but due to the potential
synergies with the site power and heat requirements this will be proposed for further
assessment.
43
"
#
#
"
"
"
#
#
"
"
Very!short!discharge!time!
Very!short!discharge!time!
Assessed!in!rest!of!report!
Capacitors!
Electromagnetic!
storage!
Liquid'Air'Energy'
Storage!
Slow!response!time.!More!suited!to!solar!
installations!
44
Table 7: Suitability of various energy storage solutions to the Irvine site.
Molten'salt!
Very!low!efficiency.!Slow!response!time.!
However,!long!term!storage!possible!
Synthetic!natural'gas'Could!be!used!to!provide!gas!to!the!natural!
(Power'to'Gas)!
gas!CHP!
Electrolysis!
"
"
"
"
#
"
#
"
"
"
"
"
"
#
"
"
"
"
#
"
"
"
"
"
#
#
"
"
#
"
"
?
#
"
"
"
"
#
?
#
#
?
"
"
"
"
#
"
"
development'
Volume' duration'
Time'
Technology'
Storage' Discharge' Response' Lifecycle'
#
high!efficiency!but!low!charge/discharge!
cycle!lifetime!
Quick!response!time,!long!discharge!time,!
high!efficiency,!average!charge/discharge!
cycle!lifetime!
Suitable!for!grid!support.!Not!for!site!
support.!
Quick!response!time,!long!discharge!time,!
but!low!technology!readiness!and!
efficiency!
Quick!response!time,!long!discharge!time,!
Flywheels!
Flow'batteries!
Lead'acid!
batteries!
LiHion'batteries!
Requires!specific!geologic!features!
Response!time!of!minutes,!not!seconds!
Requires!specific!geologic!features!at!scale!
Comment!
Pumped'Hydro!
Compressed'Air!
Storage'type!
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
#
"
"
"
"
"
"
"
"
"
#
#
Location'
Site'
No
Yes
No
No
Yes
Yes
Maybe
No
No
Maybe
No
'
No
the'site'
Suitable'for'
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
5. Assessment of Liquid Air Energy Storage
Liquid Air Energy Storage, (LAES) (19)18
As discussed in the earlier sections of this project there are many different
technologies and forms of energy storage that were historically and are currently
deployed throughout the world. These range from large scale pumped-hydro storage
through mechanical devices to a variety of batteries technologies applied at various
scales and on many different applications. These are more commonly used
technologies but there are several emerging technologies that are not currently widely
utilised for electrical energy storage applications and may provide a better fit on
specific applications.
LAES is currently an emerging technology that indicates considerable potential in
either local or grid scale electricity storage when considering storage technologies
required for enhancing the use of non dispatchable renewable electrical energy.
This section covers a more detailed overview of the status of this technology in
general and its potential application to the Irvine site.
Electrical energy storage can deliver the benefit of improved energy management
through the removal of barriers to generation of renewable electricity, by acting as a
buffer between generation, demand and grid restrictions. This enhanced use of
renewable energy has the potential to deliver improved efficiency of renewable
installations without major behavioural changes from the customer. LAES storage has
the potential to achieve these benefits over a wide range of application scales from
localised industrial to grid scale applications. Figure 17 below outlines the key steps
within a LAES system from the use of non peak of excess renewable energy through
the required charging, storage and discharging steps required to supply electricity
back to the user when it is required. This includes the thermal recovery steps from
within the system and externally that are used to improve the overall round trip
efficiency.
18
Liquid Air in the energy and transport systems Opportunities for industry and innovation in the UK Summary Report and
Recommendations, David Strachan, The Centre for Low Carbon Futures 2013.
45
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Figure 17 : Key steps in Liquid Air Energy Storage (20)19
Technology background
Gaseous air is converted to a liquid by cooling it to a temperature of -196 °C and is an
established technology currently employed commercially with developed industrial
scale equipment as used within the industrial gases industry. The volume of gas to
liquid is 700:1, with the liquid being stored at atmospheric pressure in insulated
vessels. To convert this liquid back to a gas, heat is applied to change the phase, thus
increasing the volume by 700. This expansion can be used to power an engine or
turbine and if connected to a generator thus produce electricity. Ambient temperature
conditions can be used to achieve this but if a local source of low grade waste heat,
with a temperature up to 150°C is available, the efficiency of this step of the process
can be enhanced.
LAES system technology has been successfully tested and demonstrated via a fully
operational LAES pilot plant over the last two years, (350kW/2.5MWh) and current
developers are planning a 5MW/15MWh LAES system, funded by the Department of
19
Liquid Air Conference Royal Academy of Engineers 9th May 2013 Dr Robert Morgan Principle Research Fellow
46
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Energy and Climate Change with a grant worth over £8 million This system is due to
enter operation by the end of 2015.
The technology is modular, which means that each of the charging, storage and
discharging components of the system can be sized independently. Charging the
system works by using electricity to cool air down to -196°C (Stage 1 in Figure 18
below) at which point it is in a liquid state, with every 700 litres of ambient air being
compressed to form 1 litre of liquid air.
During Stage 2, liquid air is stored in an insulated tank at low pressure. This
equipment is already globally deployed for bulk storage of liquid nitrogen, oxygen
and liquid natural gas (LNG). These storage units also represent a small amount of the
total capital cost of the system.
Finally when required, power is produced in Stage 3 by pumping the liquid air to a
high pressure. On heating, using stored heat from the air liquefier or waste heat from
an adjacent process, a high pressure gas is produced which is then used to drive a
turbine. During Stage 3, the waste cold produced is stored and used at a later time to
enhance the efficiency of Stage 1 (20)19.
Figure 18 : Visualisation of an LAES plant. Source: Highview Power brochure.
47
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Stage 1
Stage 2
Stage 3
Figure 19 : Process flow for the Highview Liquid Air Energy Storage System adapted
from Source: Highview Power brochure.
Thermodynamics
Liquefied air is a cryogen and the high grade cold energy that it contains, is a better
thermal energy storage medium compared to heat (21)20. The figure below shows that
at a given temperature difference, the stored cold is more valuable than the stored heat
particularly at large temperature differences (20)21. They are able to store energy in
the form of sensible and latent heat and have a higher exergy density than many
thermal energy storage media. This enables them to be utilised as a more efficient
thermal energy storage medium.
20
YVONNE LIM1, MUSHTAK AL-ATABI1, RICHARD A. WILLIAMS LIQUID AIR AS AN ENERGY STORAGE: A
REVIEW Journal of Engineering Science & Technology.
48
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Figure 20 : Exergy percentage as a function of temperature difference for heat and
cold (20)21.
Cryogenic liquids, (liquids at temperatures below - 150°C or 123K) are used in many
engineering processes. They are produced by the Liquefaction of gases to increase
their density thus reducing the volume / mass for more efficient storage and transport.
Many liquefaction cycles have been developed for specific gasses and have been
modified to enable them to be applied to efficiently liquefy air. A thermodynamically
ideal liquefaction system can be represented by the Carnot cycle. This theoretical
system is represented by a reversible isothermal compression followed by a reversible
isentropic expansion.
49
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Figure 21: Liquid Air Energy Storage for Power Grids Liquid Air Conference Royal
Academy of Engineers (20)21
•
An isothermal process occurs when compression takes place at a constant
temperature (ΔT = 0). With the ideal gas law the isothermal process can be
expressed as: p / ρ = constant (where p= absolute pressure and ρ=density).
•
Isentropic (or adiabatic) expansion of a gas takes place with no flow of heat
energy either into or out of the gas. With the ideal gas law the isentropic
(adiabatic) process can be expressed as: pV = constant (where p= absolute
pressure V = gas volume).
21
Liquid Air Conference Royal Academy of Engineers 9th May 2013 Dr Robert Morgan Principle Research Fellow.
50
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Claude Cycle: Isentropic expansion (22)22
Isentropic expansion characterised by µs =dT/dP s (always >0) results in a larger
temperature drop for a given pressure drop than with isenthalpic expansion (22)22.
The performance of this system can be optimised by varying P2, T3 and x
When the process stream is at an appropriate high pressure and sufficiently low
temperature, the process stream is expanded via a Joule Thompson valve to produce
liquid.
The Joule-Thomson effect can be characterised by means of its coefficient, which at
constant enthalpy is the partial derivative of the pressure wrt temperature. The fluid
will cool on expansion if the coefficient is +ve and will increase in temperature if the
22
Cryogenic Systems Randall F. Barron Oxford University Press, 1985
51
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
coefficient is –ve and will vary for any given fluid and as a function of pressure and
temperature.
For a material, plotting a zero coefficient against pressure and temperature will give
the inversion curve. Below this curve on expansion the fluid is cooled. The maximum
inversion temperature can be derived showing that the fluid must be lower than this
temperature to cool on expansion. The process stream then passes through a separator
to isolate the liquid which is store in insulated low pressure vessels.
5.1.
Process Details
Highviews development of this system has used a hybrid approach that utilises
elements of the adiabatic and isothermal compressed air energy storage systems. This
improves the efficiency by removing the requirement of heat from a fuel source
(23)23.
The process flow for a liquid air energy storage system, as shown in Figure 22 : System
PFD of Highview’s Pilot!
Plant.
describes the stages and individual equipment
requirements of this thermodynamic system and is used as an input to modelling on
23
Thermodynamic modelling in MEI’s Liquid Air Energy Storage System Study: Emma Edwards1, Dr. Roger Dargaville,
Professor Paul Webley April 2014
52
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
process simulation systems such as Aspen HYSYS (21)2 0 . Such tools are used to
simulate a process under industrial conditions and in line with the systems
material properties and thermodynamic laws.
The flow sheet indicates the individual equipment, unit operations and process
streams used to complete liquefaction of the air. This involves the following items,
with each component being identified as a block within the modelling system (24)24.
1. Feed Compressor - With an acceptable isentropic efficiency
2. Mixers - The main purpose of the inline mixers is to ensure the input stream
and recirculation stream are processed into one homogenous output stream.
3. Recirculation compressors - With an acceptable isentropic efficiency
4. After Coolers –The pressurised process flow post compressors is cooled to an
acceptable temperature to enter the heat exchanger.
5. Splitter / Heat exchanger – Are used to separate fluid from the main process
stream and achieve an optimal temperature for the following stage.
6. Joule -Thompson Valve'– This is an isentropic JT valve that enables the
Claude cycle to work at a constant enthalpy. This results in a decrease in
pressure from which an appropriate drop in temperature is achieved, enabling
the phase change to liquid.
7. Expander – the second separated process stream is expanded through this
equipment before flowing into the separator.
8. Phase separator – this is used for separation/flashing the vapor liquid mixture
that is fed from the JT valve.
9. High Grade Cold Store – is charged from the waste heat from the next stage
during expansion and power generation and is used in the liquefaction s
24
STUDY OF CRYOGENIC CYCLES WITH ASPEN - HYSYS SIMULATIONS, SUNIL MANOHAR DASH, Department of
Mechanical Engineering National Institute of Technology, Rourkela 2009.
53
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
10. Liquid Storage - The liquid air is stored in an insulated tank at low
pressure. Most cryogenic tanks are typically held at <10 bar (100 MT scale)
or at atmospheric pressure at the >1,000 MT scale
11. Cryogenic Pump – used to pump the liquid to a high pressure.
12. Heat Exchangers – waste heat or ambient heat is applied to the liquid via
these heat exchangers. This changes the liquid into a gas.
13. Turbines – The gas is utilised to power a series of turbines and generators
when electricity is required.
To initiate the liquefaction process ambient air is taken through two compression
stages with air cooling after each stage. The heat produced during this compression
stage is stored within a thermal store, (hot water or oil) for use within the power
generation stage of the process.
Post compression refrigeration is carried out with the air being expanded in a
Claude cycle refrigerator. The efficiency of this operation is improved by utilising
cold recovered from evaporation that takes place during power generation stage.
Within the power generation step of the process, initially the pressure of the liquid air
is increased by pumping. An evaporation step then occurs to vapourise the air. The
gaseous air is then heated from the thermal store heat that was collected during the
liquefaction compression step. The gas is reheated during this multistage evaporation
and used to drive a series of turbine generators.
54
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Figure 22 : System!PFD!of!Highview’s!Pilot!Plant!(13).25
I addition to the basic scheme there are additional elements installed that are
designed to increase the systems round trip efficiency. These include two expansion
cycles during liquefaction to help run the compressors and waste heat recovery and
storage.
With the installation of heat and high grade cold storage, the integration of the
system with other processes that have waste heat or cold has been enabled. The
reheating stage includes the use of waste heat form out with the LAES plant. The
facility can also utilise cold from out with the plant, the main objective of this is to
optimise the system and further increase the round trip efficiency and maximise the
power output for any given amount of input power.
25
The application of liquid air energy storage for large scale long duration solutions to grid balancing Gareth Brett and Matthew
Barnett Highview Power Storage, London, UK. 2014. EPJ Web of Conferences 79, 03002 (2014)
55
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
5.2.
Key Benefits from analysis of the LAES
The main parameters associated with the performance of any electricity energy
storage system are indicated through the following:
1. Storage system energy density
Energy density is the volume of liquid air (kg) that are needed to deliver one MWh of
electricity back into the production site after the parasitic losses have been taken into
account. The developers of this technology (Highview) have noted that 10,000 kg per
MWh is normal although with the introduction of available waste heat recovery (up to
400 °C), from available external processes there is an expectation that 7,000kg/MWh
is achievable (18)26. (1 MWh = 3600MJ therefore liquid air at 7,000Kg/MWh = 0.514
MJ/Kg).
2. Electricity round trip efficiency
As with all electrical energy storage systems the round trip efficiency is one of the
most important factors. Optimising this along with minimising capital cost of plant
and equipment will have the greatest influence on whither the technology is
successful adopted.
The advantages stated about the round trip efficiency of Highviews LAES are based
on the utilisation of the use of waste cooling and waste heat from external sources to
the storage system. In the case of waste heat from an external source, the power
output of the generation step can be seen to improve from the use of low grade and
high grade waste heat. The following figure Figure 23: Pilot Plant heat to power
26
The application of liquid air energy storage for large scale long duration solutions to grid balancing Gareth Brett and Matthew
Barnett Highview Power Storage, London, UK. 2014. EPJ Web of Conferences 79, 03002 (2014)
56
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
relationship : highlights the impact of low grade waste heat temperature showing a
related increase in the on the Highview pilot plant power output.
Figure 23: Pilot Plant heat to power relationship (25)27 :
This indicates that a 1 °C increase in temperature of the waste heat gives a 1KW
increase in power output at this scale of plant. In addition to this additional analysis28
has indicated that modelling this further to evaluate a full range of waste heat
temperatures, enables a view of a general LAES system with a range of waste heat
27
Source - HIGHVIEW POWER STORAGE TECHNOLOGY AND PERFORMANCE
REVIEW MARCH 2012.
57
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
temperatures from 50 C to 300 C and demonstrated the round trip efficiency as a
function of the temperature (°C) of the waste heat stream:
Figure 24 : Round trip efficiency of liquid air energy storage system in comparison to
waste heat temperature (°C). Analysis via Aspen HYSYS (23)28.
Cold Recycle
In addition to the efficiency benefit experience with utilising waste heat a similar
efficiency benefit is noted when cold recycle is incorporated into the system. Figure
Figure 25 : Results27 below shows that pilot trials are in parallel with the profiled
guarantees for the liquefaction equipment and have also these and modelled efficiency
improvements. With lower temperature and losses within the cold recycle lower the
amount of work required by the liquefier per Kg of output.
Figure 25 : Results (25)27
28
Thermodynamic modelling in MEI’s Liquid Air Energy Storage System Study: Emma Edwards, Dr. Roger Dargaville,
Professor Paul Webley, 2 April 2014
58
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
3. Start-up response time
Response time – The system is said to have a response time of approximately 2.5
minutes when starting from standby to full power out. If starting from shutdown the
system is able to achieve full power output within < 20 minutes. Both scenarios
assume that there is a charged liquid energy store (18)25. The benefit of this fast
response time relate to the ability to claim STOR, where a 20 minute response time
to reach the set point output from an instruction is generally considered to be
acceptable for a STOR provider27.
4. Standing Losses
The liquid air energy storage system looses charge energy by heat loss to the
surrounding environment mainly from the bulk cryogenic store. To mitigate
against excessive losses the design of the insulation around these tanks is critical
to ensure overall efficiency of the system, (losses of less than 0.2% per day are
typical and compare favourably to energy losses from other technologies such as
batteries) (18)25.
5. Flexibility
The nature of the plant and equipment is such that it can be configures in a
modular approach and liquefaction units, storage vessels, cold store and cryogeneration equipment can all be sized independently. Although in general losses
are lower with the increase in size of turbo machinery and standing thermal losses
are lower in larger storage tanks. This inevitably improves the efficiency of large
installations (18)25.
59
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
5.3.
Assessment of the Site
From analysis of the GSK site supply and demand model, as discussed in section
0 the various sizing options for the energy storage plant were reviewed and the
most optimal units assessed via a savings model. The model was used to analyse
the business case for an energy storage plant.
Figure 26 Modelling overview
The basic architecture starts with a number of input streams, including the energy
demand and generation on an hourly basis, as developed with GSK for the
biomass CHP project.
Input
Units
Description
Baseline demand
On-site generation
Storage capacity
Storage minimum
Storage
capacitycharge power
kWh
kWh
kWh
kWh
kW
Total forecast demand on site (hourly data)
Total forecast generation by on-site generators (hourly data)
Volume of storage the plant is able to store
Desired minimum level of storage (e.g. if required for black start)
Maximum power storage can charge with
Storage discharge power
Export limit
Electricity to spill
kW
kW
-
Maximum power storage can provide while discharging
Any export limit that is in place on site
Select whether biomass / wind / nat. gas CHP are spilled if over
Prefer discharge to grid?
Y/N
Determine
a preference to export storage or use it to displace
limit
import
Figure 27 : Key inputs to the energy
storage model
Each of the 8760 hours in the year are then taken through a number of calculation
steps in the form of a decision tree, and the resulting profiles are then analysed
to provide a series of outputs.
60
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Figure 28 : Key inputs to the energy storage model The above process was used to
determine the most appropriate use for excess renewable energy that would have been
curtailed without energy storage.
The opportunities for maximising benefit from this energy were given a priority:
1. Charge the storage LAES tanks by using excess Renewable Energy.
2. Supplement site demand with stored energy, minimising electricity import.
3. Top-up existing export to 9MW
From this data the minimum recommended size for the liquefaction plant was
determined to be 300 tonnes of air per day, corresponding to a 2.5MW liquefaction
plant and a 5MW expansion turbine power recovery unit (PRU). This will enable an
appropriate volume of storage to be installed, which was estimated at 140 MWh.
Equipment Costs
The liquefaction equipment is found to be the most expensive item within the overall
system with the power recovery unit and storage equipment being relatively cheap in
61
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
comparison. The following data is derived from supplier information and factored for
scale the main items of equipment are commercially available and the costs below
include all balance of plant items and construction costs (25)29.
Figure 29: Cost profile for liquefaction and power recovery unit configurations.
The costs above reflect the early stage of this technology and reflect the “first of a
kind”. Hence there is an expectation that costs will reduce substantially on full
development of the energy storage system. For this assessment I have used the initial
costs for a current realistic appraisal of the technology.
The following table displays the required equipment to support a LAES system sized
around the base case (all planned onsite generation installed & 100% utilised), with
the likely unit costs as described above.
Equipment
Item'Cost'(£m)'
Liquefier (Charging Device)
9.6
PRU (Discharging Device)
4.4
Energy Store
0.2
0.3
Waste Heat Recovery
14.5
Total Basic unit
3.9
Additional Storage
18.4
Total Cost
Figure 30 : Expected costs for a 2.5MW/5MW plant with 140MWh of storage.
The above analysis indicated a total installed capital cost of £ 18.4 million.
29
Source - HIGHVIEW POWER STORAGE TECHNOLOGY AND PERFORMANCE REVIEW MARCH 2012.
62
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Benefit analysis
There are several key sources of income from the use of LAES in this configuration.
These include the (1) generation of renewable electricity from wind turbine
generators that would otherwise have been prevented due to the export cap. The value
of (2) Renewable Obligation certificates for this additional generation. The (3)
power recovered from this renewable electricity through the LAES system. The
value saved by using this power rather than (4) importing electricity from the grid.
There are further saving opportunities expected such as eliminating import of
electricity during (5) TRIAD periods and the income available for maintaining a
readiness for (6) STOR standby by generation for grid supply.
1.
2.
3.
4.
5.
6.
!
'
'
Cost/Benefit'
Unit!
Value'(p.a.)'
Curtailed Elec Gen (>9MW)
ROC Value for Additional
Generation Elec post LAES
Recovered
(65%)
Import Saving
TRIAD Saving
STOR Income
7. O&M Cost of LAES
8. Net Saving from LAES
KWh
£
KWh
£
£
£
£
£
£
10,273,386
397,580
6,677,701
641,059
198,000
54,269
£
£
-£
£
135,000
1,155,908
£
Table 8 : Cost benefits summary of proposed system.
These benefits are combined with expected annual (7) operational and maintenance
costs, associated with the running of the LAES plant and equipment to give an overall
annual saving of (8) £1.1m.
63
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
Following on from this analysis a Net Present Value (NPV) of the installation, during
the total lifetime of the project (20 years), assuming a discount rate of 7% was carried
out. The NPV obtained for this case study is negative, highlighting that the project is
not viable within the current economic model.
!
Discount!rate!
7.0%!
year!
Absolute!cost!
PV!
0!
1!
2!
3!
4!
5!
6!
7!
8!
9!
10!
11!
12!
13!
14!
15!
16!
17!
18!
19!
£''''''''18,400,000'
£'''''''''''1,155,908'
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!!1,155,908!
S£!!!18,400,000!
£!!!!!!1,080,288!
£!!!!!!1,009,615!
£!!!!!!!!!!943,565!
£!!!!!!!!!!881,837!
£!!!!!!!!!!824,147!
£!!!!!!!!!!770,230!
£!!!!!!!!!!719,842!
£!!!!!!!!!!672,749!
£!!!!!!!!!!628,738!
£!!!!!!!!!!587,605!
£!!!!!!!!!!549,164!
£!!!!!!!!!!513,237!
£!!!!!!!!!!479,661!
£!!!!!!!!!!448,281!
£!!!!!!!!!!418,954!
£!!!!!!!!!!391,546!
£!!!!!!!!!!365,931!
£!!!!!!!!!!341,992!
£!!!!!!!!!!319,618!
20!
£!!!!!!!!!!!1,155,908!
£!!!!!!!!!!298,709!
!
NPV!
H£''''''6,154,291'
!
Simple!Payback!
15.9'
Table 9 : Economical feasibility of the system over 20 years
From this data a sensitivity analysis was carried out to investigate the impact of the
following 2 factors:
1. Reduction in capital cost of the plant and equipment.
2. Increase in the import electricity value.
64
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
From this analysis it is seen that either an independent reduction in the capital cost of
the plant of £18.4m to £12 m or and separate increase in cost of grid electricity to
£0.19 /KWh, provides a positive NPV.
A more likely scenario is a combined an optimisation of the capital cost with a
smaller increase in grid electricity cost to make the project commercially viable.
Graph 7 : NPV sensitivity analysis of the system for varying capital cost and grid Electricity
price.
Environmental Saving
The environmental saving is also noted in that the quantity of electricity off-set by the
additional renewable energy generated by the wind turbine generator is approximately
3,000 tonnes. This is based on a power recovery unit output of 6,700 MWh and a CO2
grid electricity conversion factor of 0.4585 (26)30.
30
Government conversion factors for company reporting, DEFRA / DECC, http://www.ukconversionfactorscarbonsmart.co.uk/
65
Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
6. Conclusion
The Irvine site can benefit from the implementation of an electrical energy storage
technology, designed to enable greater utilisation of all implemented and planned
renewable energy technologies. Form the data above it can be seen that the site could
offset imported electricity by storing excess or curtailed renewable electricity.
Assessment of a range of electrical energy storage technologies has identified that there
are limited applicable technologies available. This is due to the location, scale and
response time of the technology, in relation to the modelled site demands and volume
of generated electricity.
One technology that does technically achieve the delivery requirements is liquid air
energy storage, (LAES) and has the potential to deliver various benefits to the Irvine
site, including almost 3,000 tonnes per year of CO2 reductions and £1m of energy cost
benefits in addition to enhanced security of supply.However, the capital cost
requirements of a LAES plant currently prove prohibitively high for this application,
due to the development status of the technology package.
Due to the various and significant benefits available to the site with an energy storage
facility, it is recommended that further work is carried out to investigate the alternative
emerging storage technology of power to gas. This looks to be a viable alternative for
the use of unused renewable energy and as the site has a considerable heat demand it
may well be a suitable alternative.
Both technologies are at key development stages and the adoption of either will be
dependent on the future commercial equipment costs. Future feasibility activity should
keep an overview of these technologies along with the third option of battery
technology that is likely to develop more quickly and will reduced in prices
significantly (currently reducing at 15-20% per annum (14)) over the next few years to
become a very competitive option.
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Enhancing the utilisation of non-dispatchable Renewable power - Mark Dunn
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