There are four basic calculations that you need to do before you can get on with buying a system that would fulfill all your requirements. These are:
• Electrical load or power requirement
• Sunshine availability
• Size of the Photovoltaic array and
• Size and number of batteries
Calculate total electrical load or power requirement
Before you think of setting up a solar PV system you need to calculate the electrical load that you want it to handle.
Typical household electrical appliances and their run times.
Hours used per day
Four CFL lamps (each 15W)
(For uncertainty to anticipate daily electrical load of appliances, it is recommended to multiply daily estimated load by a factor of 1.5. This factor accounts all the system efficiencies, including wiring and interconnection losses, as well as the efficiency of the battery charging and discharging cycles)
Total power requirement (T.P.) =1.5 × Electrical load Wh/day
Calculate sunlight availability
Also known as insolation value, it is the amount of solar energy in hours, received each day on an optimally tilted surface during the worst month of the year. For India the insulation value range is between 4 – 5.5 hours.
Total number of sunshine hours (S.H.) = _____h/day.
Calculate array size
The size of the PV array is calculated by dividing Total Power Requirement by the number of Sunshine Hours.
Total array size required = T.P. ÷ S.H. = _____W.
Size and number of batteries
It is determined by multiplying Total Power Requirement with five which results in Wh and this value is divided by battery voltage (e.g., 12V) to get the value in Ah.