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 3 hours at night and a 15W 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) / 5 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 67.5W and the solar panel needed for the light is 18W. So the total solar panel needed will be 85.5W. In this case, you can buy 1 piece of 90W solar panel or 2 pieces of 50W solar panels.

4. The calculation will work fine if there is 5 hours strong sun a day. What is it is a raining day? If your equipment is important and must work on raining day, you have to double or triple the amount of solar panels to cater for 1 or 2 raining days.

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