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" stand fan 75W to run 4 hours at night and a 16W light to run 4 hours at night.

2. The formula of the power of the solar panels needed is
power of equipment X running hours X 1.5 (lost factor) / 4 hours of sunshine
lost factor include the humidity and high temperature in the equator zone, battery charging and discharging lost and inverter conversion lost.

3. From the example, the solar panel needed for the fan is 112.5W and the solar panel needed for the light is 24W. So the total solar panel needed will be 136.5W. In this case, you can buy 1 piece of 140W solar panel or 2 pieces of 60W solar panels.

4. This calculation will work fine if there is 4 hours strong sun a day.

See the next page on how to calculate the size of the battery needed.