A Performance Calculator
for
 Grid-Connected PV Systems		                                    

PVWATTS calculates electrical energy produced by a grid-connected photovoltaic (PV) system. Researchers at the National Renewable Energy Laboratory developed PVWATTS to permit non-experts to quickly obtain performance estimates for grid-connected PV systems within the United States and its territories.

In a grid-connected PV system, PV modules, wired together to form a PV array, pass DC electricity through an inverter to convert it into AC power. If the PV system AC power is greater than the owner's needs, the inverter sends the surplus to the utility grid for use by others. The utility provides AC power to the owner at night and during times when the owner's requirements exceed the capability of the PV system.

 
Two Calculators:
Choose a calculator by clicking on "Version 1" or "Version 2".
Version 1
Version 1 allows the user to select a location from a map (United States and Territories) or from a text list (U.S. and outside the U.S.) The calculations may be done using the default system parameters, or the user may specify the PV system size, local electric costs, whether a fixed or tracking PV array, and the PV array tilt and azimuth angles. PVWATTS calculates monthly and annual energy production in kWh and savings in dollars. The user may also choose to output hourly AC power data which can be saved to a text file.

Version 2
Version 2 allows the user to select a U.S. location (based on a 40 km grid cell) by using NREL's Internet Map Server (IMS) at http://www.nrel.gov/gis. Because PVWATTS Version 2 uses additional input data, the results may differ slightly from those for PVWATTS Version 1. Version 2 can be run only for the 48 contiguous states, Alaska and Hawaii. The use of the Internet Map Server increases the complexity of PVWATTS, but provides additional information for locations.

Note: The IMS site works best in Internet Explorer on both PC and Macintosh platforms. To see other browser/platform pairs that support the IMS click here.

For more information about how photovoltaic (PV) systems work, please see the following sites:

For manufacturers and suppliers of PV modules, systems, etc.,.. please see

Consumer Guides

Financial Incentives and Programs

Net Metering Information


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