Example a 14" stand fan 75W to run 3 hours at night and a 15W light to run 4 hours at night. Solar panel needed is 90W.

1. The formula of the battery needed is
power of solar panel X 5 hours sun X 2 (50% discharge) / 12V

2. From the example, the battery needed is 75AH 12V.

3. The 50% discahrge factor is set at 2 in order to maintain the normal battery life span. The deep cycle battery is recommended to discahrge only 50% of the power stored. Over discahrge fo the battery will shorten the life time. Normal car battery is not recommended to use in solar system because they are designed for only 5 to 10% discharge.

See the next page on how to select the charge controller.