1. Identify what are the power of the equipment that you want to run on solar energy and the hours to run it them everyday. Take an example a 14" DC fan 20W to run 12 hours at night and a 16W dc light to run 5 hours at night.
2. The formula of the power of the solar panels needed is
power of equipment X running hours X lost factor / 4 hours of sunshine. Lost factor for DC equipment is 1.1 and for AC equipment is 1.5. Lost factor include the humidity and high temperature in the equator zone, battery charging and discharging lost, inverter conversion lost and power factor of ac equipment..
3. From the example, the solar panel needed for the dc fan is 66W and the solar panel needed for the dclight is 22W. So the total solar panel needed will be 88W. In this case, you can buy 1 pieces of 75W solar panels or 1 piece of 100W solar panel. If the fan and light is ac, then the solar panel needed will be 120W.
4. This calculation will work fine if the solar panel is not place under shade.
See the next page on how to calculate the size of the battery needed.
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