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There are three main things to consider when choosing a solar panel & battery combination:-
1) How much energy is it possible to store in a solar battery?
Battery capacity or power is measured in Amp Hours (eg 20AH)
Convert Amp hours to Watt Hours by multiplying the Amp hour figure by the battery voltage
For a 20AH, 12V battery the Watt Hours figure is 20 x 12 = 240WH
In other words the solar battery could supply 240Watts for 1 hour, or 120Watts for 2 hours
It's not a good idea to totaly drain a battery so leave between 40-50% for a longer life.
For the same 20AH, 12V battery the better Watt Hour figure is 20 x 12 x 1/2 = 120WH
2) How much energy will your appliances consume over a given period of time?
Power consumption of household appliances is given in Watts (eg 21" fluorescent light, 13W)
Calculate the energy used over time by multiplying the power consumption by the hours it's switched on.
A 15W light fitting, on for 2 hours, will take 15 x 2 = 30 Watt Hours from the battery.
Do this for all the appliances you want to use and add the results to calculate total consumption.
3) How much energy/power can a solar panel produce over a period of time?
The power rating of a solar panel is also given in Watts (eg 20W) To calculate the energy it can produce and store in the battery, multiply the Watts by the hours exposed to sunshine then multiply the result by 0.80 (factor to allow for normal system losses).
A 20W Solar panel in 4 hours of sunshine is 20 x 4 x 0.80 = 64Watt Hours
64Wh (Watt hours) is the energy this solar panel can supply the battery or inverter (if it's a grid tie system)
For some more help and advice please just contact us
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