There are three things to consider when choosing a solar panel & battery combination
How much energy can a battery store?
Battery capacity is measured in Amp Hours (eg 20AH)
Convert this to Watt Hours by multiplying the AH figure by the battery voltage
For a 20AH, 12V battery the Watt Hours figure is 20 x 12 = 240WH
This means the battery could supply 204W for 1 hour, or 102W for 2 hours
The more energy you take, the faster the battery discharges.
How much energy will your appliances use over a period of time?
The power consumption of appliances is given in Watts (eg 21" fluorescent light, 13W)
Calculate the energy you will use over time by multiplying the power consumption by the hours of use.
A 15W light fitting, on for 2 hours, will take 15 x 2 = 30 Watt Hours from the battery.
Repeat this for all the appliances you wish to use, then add the results to establish total consumption.
How much energy can a Solar panel generate over a period of time?
The power generation rating of a Solar panel is also given in Watts (eg KE-ET20 = 20W) To calculate the energy it can supply to the battery, multiply Watts by the hours exposed to sunshine then multiply the result by 0.85 (factor to allow for normal system losses).
A 20W Solar panel in 4 hours of sunshine is 20 x 4 x 0.85 = 68WH
68WH (watt hours) is the amount of energy the Solar panel can supply to the battery. |
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