Solar Photovoltaic System Design Info Sheet - Electrical Design
System voltage
Why? This affects the devices which can be used
and also the currents flowing in the cables.
High currents = thick and expensive cables fuses and switches.
Typical voltages:
12V < 500W max
24V < 1000W max
48V < 2000W max
But 12V devices are easier to find and cheaper.
Also can use an inverter to convert 12VDC to 240VAC.
Worksheet designed by:
renewable energy innovation www.re-innovation.co.uk
Wiring diagram
Why? This is to ensure it is wired correctly and for future reference
We need to produce a full wiring diagram including all the system
components. Check this with an electrician if unsure. Put as much detail
as possible on this design.
FUSE
FUSE
CHARGE
CONTROLLER
5A
2A
SOLAR BATT
SOLAR
PV
MODULE
12V 30Wp
12V
40Ah
BATTERY
LOAD
Cable sizing
Why? Must be correct or the resistance will cause a
voltage drop and incorrect operation.
You must use the correct thickness cable for the max current flowing
and the length of the cable run.
The resistance depends upon the size of cable, the cable material, the
length of the cable run, the maximum allowable voltage drop and the
operating temperature. Formulas are available.
Rule of thumb: Use 1mm2 cable thickness for every 5A
Or use the chart here:
100.00
90.00
80.00
70.00
60.00
Cable size for Cable Length and Current (12V 5%Volt drop)
1A
5A
1A
5A
10A
15A
20A 10A
50A
100A 15A
50.00
20A
40.00
30.00 50A
20.00
10.00 100A
0.00
0
20 40 60 80 100 120 140 160 180 200
Total Cable Length (m)
Charge controller
Why? This is needed to prevent over-charging and over-discharging of the battery
The charge controller (sometimes called a charge regulator) provides battery protection
and is very important.
Must be rated for correct current (generally the max current from the PV array) and voltage.
The charge controller acts like a big switch to either disconnect (series regulators) or dump
(shunt regulators) power from the PV array when the battery voltage is too high.
Lots of different types with different features including:
Voltage, current, power and energy display
State of charge measurement - like a fuel gauge for the battery
Low voltage disconnect - to stop the battery being too heavily discharged
The choice depends upon your budget and features required.
Fuses
Why? To protect wires and components from over-currents (such as a short circuit).
Battery is the main issue here as it can supply very high currents.
Ensure correct current and voltage rating. Fuse in both +ve and -ve is best.
Place fuses close to the battery side.
Many different types of fuses available. Some must be replaced (such as automotive fuses),
some can be reset (such as circuit breakers). This choice depends upon the cost and the
typical users.
BATTERY
FUSE
LOAD
Unprotected Cable Protected Cable