Solar TOOL
Solar System Size Calculator
Estimate capacity from annual use. Use the calculator below with your own numbers.
Solar System Size Calculator
Estimate capacity from annual use.
Change the example inputs to your own values. Check the method and limitations below.
How to use this calculator
Enter Annual use (kWh), Peak sun hours/day, Performance (%). The result updates in your browser as you edit an input. The prefilled values are examples only.
How the estimate works
Divide annual kWh by 365, peak sun hours, and the performance factor. A site-specific model is needed for a reliable design.
What can change the answer?
Peak sun hours is not the same as daylight hours. Shade, orientation, snow, temperature, and inverter losses require a location-specific production model.
Before relying on the result
Check that the figures use the same units and period. Compare the result against a current label, quote, contract, employer policy, or official dataset when appropriate. This estimate does not include factors you have not entered.
Further reference
For source data or a more detailed method, see National Laboratory of the Rockies: PVWatts production model. The calculator does not automatically import data from this source.
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