How to Calculate Photovoltaic Energy Load and Array Size for Solar Panel Installation

The calculator below will help you determine the correct solar panel array size for your home, given your typical energy usage and the insolation value of your geographic area. To use the calculator, input the energy consumption of an item in your home in the form (w,h) where w is the wattage and h is the average daily hours of use. Each parenthetical pair should be separated by a comma. The methodology for computing your solar energy installation needs is explained below the calculator.

Average number of hours of sunlight per day during the worst month of the year: hours.

Photovolatic Load = watt hours
Array Size Needed = watts


The photovoltaic load on your solar energy system is the total watt hours of energy your home uses, the electrical demand. To figure that quantity, first find the average daily watt hours of each item in your home. (Multiply each device's wattage by its average daily hours of use. If you don't know the wattage, you can calculate it by multiplying the voltage by the number of amps.) Add up the watt hours of every energy consuming device in your home and multiply the sum by 1.4 to account for miscellaneous usage and phantom loads.

Next, determine the average number of hours of sunlight your home receives during the darkest month of the year. In the Northern Hemisphere, this month is December. This number of hours represents the worst case scenario for the amount of sunshine your solar panels can absorb.

Divide your home's photovoltaic load by the daily sunlight hours to compute the necessary wattage of a solar panel system. The watts you need will determine the array size of your solar panel installation.

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