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. There is no formula needed but to get a charge controller more than the maximum power of the solar panel produced.

2. The normal charge controller in the market has a maximum currrent of 40A. Anything beyond that will be in the high price range. It is not advice to configure a high power system on 12Vdc because of the high current. It is adviced to convert the system with a inverter to AC with the input of 24Vdc or 48Vdc.

3. The output power of the charge controller is also a point that most of the people neglected. From the example the 90W solar panel selected will need a charge controller of more than 5.15A (maximum currrent that a 90W panel produced) input. The Phocos charge controller selected wil be the 12V 8A. The output power from the charge controller will be limited (12Vx8A) 96W. The charge controller will alarm and cut off the output if the currrent drawn is more than 8A. If your equipment has a high startup current or power, you will need to select a higher range charge controller to suit your equipment.

4. MPPT (Maximum Power Point Tracking) charge controller is designed to maintain the solar panel voltage at the optimum voltage to charge the battery, even when the sun ligth is low. Thus stored more power to the battery compared to normal charge controller. Not popular to use in the lower power system because of high in price.

See the next page on how to select the inverter.