# Dimensioning of a solar/battery backup system

```Dimensioning of a solar/battery backup system
IT+46
May 2008
Agenda
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What is dimensioning?
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User requirements and input data
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Solar dimensioning
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Battery dimensioning
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What is dimensioning?
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How much energy is available?
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What voltage/current do I want to obtain?
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How long do I need autonomy?
What equipment do I need to cover my needs in terms of electricity?
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How many solar panels and batteries?
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How much energy is available?
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Measured in W/m2
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Statistical data from weather stations
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Solar history
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The amount of solar energy available
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Always plan for the worst!
Sun peak hours/day
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Normalized value of solar radiation of 1000 W/m² at 25 C
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5 peak sun hours corresponds to a daily solar radiation of 5000 W/m².
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Nigeria: 4 peak sun hours
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User requirements
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Power consumption
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Total consumption of all electrical devices
Anatomy
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How many days should the system work without power input?
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Equipment specification
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Battery
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Capacity (Ah)
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Max discharge (%)
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Voltage (V)
Solar Panels
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Nominal power (W)
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Practical example
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Autonomy: 5 days
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Battery –
Voltage: 12V
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Capacity: 100 Ah
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Max discharge: 50%
How many batteries do we need?
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How much current do we need?
Power = Voltage * Current = V * I
I = P/V = 120 / 12 = 10 A
We need an output of 10A from the batteries
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How much energy do we need?
In 1 day:
10 A * 24h = 240 Ah
12 V * 240 Ah = 2880 Wh
In 5 days:
5 * 240 Ah = 1200 Ah
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How much energy do we need?
Assuming:
Max discharge level: 50%
Battery capacity: 100 Ah
Energy storage required: 1200 Ah / 0,5 = 2400 Ah
No of batteries: 2400Ah / 100Ah = 24
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How many solar panels are needed?
Assuming:
4 sun peak hours 4000 W/m2
Panel peak current: 5 A
Energy needed/day: 240 Ah
Energy provided: 5 A * 4h = 20 Ah
No panels: 240/20 = 12
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Conclusion
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Use radiation data for the worst month
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Are they any possible energy savings?
Be careful with the units! –
W vs Wh = V. Ah –
A vs Ah
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Project Assignment
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Measure power consumption in your apartment
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Design a solar power backup system
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Provide a budget for the installation
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Assumptions:
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12 V installation
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Batteries of 100 Ah, 50% discharge
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2 sun­peak hour worse month
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60 Wp, 5 A panel at sun­peak
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