The calculator below, developed by the National Renewable Energy Laboratory as the PVWatts solar calculator, is intended to help anyone interested in going solar to estimate the kWh performance of a potential PV installation as well as the potential one-year savings.

To use the calculator, enter:

1) The address for the solar array

2) System size (Number of Modules x Module Size (watts) / 1,000 W/kW)

a. Sample: 20 modules x 340 watt module /1,000 = 6.8 kW

3) Module type – in most instances the default should be “standard”

4) Array Type – in most instances this should be “Fixed (roof rack)”

5) System Losses (%) – leave as is

6) Tilt – degree angle of the solar

7) Azimuth – compass heading for the solar (note: 180 is due south)

8) Rate ($/kWh) – utility rate for energy. Chicago area average is approximately $0.104/kWh

Note: click on the question mark icons to learn more about each variable.

Please also note that while the calculator is an excellent tool to get an idea of what solar can do for you, it is not a replacement for obtaining quotes from installers. It also does not factor in shade from obstacles such as trees or tall buildings. ISEA recommends getting three quotes before moving forward on installation. You can find installers near you on the Find a Professional page.

For best results, please make sure your browser is updated. Safari or Chrome are recommended.

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