# Solar Energy – How to Select the size of a Solar Panel and Battery

7 Apr

Go Solar, Go Green

• Make sure that you have enough battery power as well as solar power; you may need multiple batteriesenough to cover the Amps per hour draw (AH) and multiple panels.

• Battery capacity is measured in Amp Hours (AH). You need to convert this to Watt Hours by multiplying the AH figure by the battery voltage (12V). For a 20AH, 12V battery the Watt Hours figure is 20 x 12 = 240 WH. This means the battery could supply 240 Watts for 1 hour, or 102W for 2 hours i.e. the more energy you take, the faster the battery discharges.
• The power generation rating of a Solar panel is also given in Watts. 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 (this factor allows for natural system losses).

For the 100W Solar Panel in 8 hours* of sunshine, 100 x 8 x 0.85 = 680 WH. This is the amount of energy the Solar panel can supply to the battery.

• The power consumption of appliances is given in Watts (Energy Saver, 10W). To calculate the energy you will use over time, just multiply the power consumption by the hours of use. The 10W light fitting, on for 2 hours, will take 10 x 2 = 20WH from the battery. Repeat this for all the appliances you wish to use, then add the results to establish total consumption