Solar Panel Calculator

This solar panel calculator sizes an array from three numbers you supply: your monthly kilowatt hours, the peak sun hours a day for your location, and the system loss percentage that covers inverter, wiring, soiling and heat. It returns the panel count, the system size in kW, the roof area needed and the share of your usage the array would cover, and a second action works the output of a system you already have. A third action gives simple payback from the installed cost, any credits and your electricity rate. The estimate does not model shading, roof tilt, azimuth, snow or local weather beyond what is already built into the sun hours and losses you enter, so treat it as sizing rather than a production guarantee.

Calculator Type
Panel Area and Roof Area In
Reads the panel footprint below in this unit and answers the roof area in it too. Everything else on this form -- kilowatt hours, watts, peak sun hours and percentages -- is the same in either system.
Take the average of twelve bills, not one summer month.
A yearly daily average for your location. Roughly 4 in the northern states, 5 to 6 in the southwest.
The rating on the module, at standard test conditions.
Inverter, wiring, soiling, heat and mismatch together. 14% is the common default.
Off the module datasheet, in the unit you picked above. About 18 sq ft for a 60 cell module and 21 for a 72 cell one, which is 1.67 m2 and 1.95 m2. Leave it blank for the 60 cell figure.
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The rating on the module, at standard test conditions.
A yearly daily average for your location. Roughly 4 in the northern states, 5 to 6 in the southwest.
Inverter, wiring, soiling, heat and mismatch together. 14% is the common default.
Leave at 0 to skip the money lines.
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The price before any credit or rebate.
Take this from the output action, or from your installer.
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