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The PVWatts® Calculator is a web application developed by the National Renewable Energy Laboratory (NREL) to estimate the electricity production of a grid-connected roof- or ground-mounted photovoltaic (PV) system based on a few simple inputs that allow homeowners, installers, manufacturers, and researchers to easily gauge the performance of hypothetical PV systems that use crystalline modules.

Getting Started

To begin using the calculator, you simply type in the address or geographic coordinates for a potential PV system. Based on the location, PVWatts® automatically identifies applicable solar resource data for your system. To represent the system's physical characteristics, PVWatts® requires a value for five inputs:

  • The system's DC size,
  • array type,
  • a DC-to-AC derate factor,
  • tilt angle, and
  • azimuth angle.

Using an hour-by-hour simulation over a period of one year, PVWatts® estimates the annual and monthly electricity production of a PV system, as well as, the cost and value of the electricity produced by the system. The cost of electricity estimates are based on whether the PV system is on residential or commercial property, its installation cost, and the retail cost of electricity.

Important Note

The PVWatts® Calculator is suitable for very preliminary studies of potential locations for PV systems using crystalline silicon modules. However, your production estimates do not account for many factors that are important in the design of a highly efficient system. If you are using PVWatts® to assist in designing a PV system, consult with a qualified professional to verify the final system design is based on a complete assessment of the location using more detailed analysis and design tools.

If you would like to offer suggestions or feedback, please email us at

PVWatts® supports the U.S. Department of Energy's Solar Energy Technologies Program.

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