Caution: Photovoltaic system performance predictions calculated by PVWatts® include many inherent assumptions and uncertainties and do not reflect variations between PV technologies nor site-specific characteristics except as represented by PVWatts® inputs. For example, PV modules with better performance are not differentiated within PVWatts® from lesser performing modules. Both NREL and private companies provide more sophisticated PV modeling tools (such as the System Advisor Model at http://sam.nrel.gov) that allow for more precise and complex modeling of PV systems.
The expected range is based on 30 years of actual weather data at the given location and is intended to provide an indication of the variation you might see. For more information, please refer to this NREL report: The Error Report.
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The energy output range is based on analysis of 30 years of historical weather data for nearby , and is intended to provide an indication of the possible interannual variability in generation for a Fixed (open rack) PV system at this location.
Welcome to the new PVWatts. What's new?
PVWatts® was updated on December 11th, 2015 to provide additional information to users on the potential interannual variability in energy predictions in US locations. When calculating results, PVWatts® makes several assumptions, include uncertainties in weather and cannot reflect all the variations between PV technologies and site-specific characteristics. PVWatts® predictions are intended to represent typical behavior of a similar real-life PV system.
We are often asked about the annual variation in what the system will produce and how different the actual results will be.
We analyzed 30 years of historical solar irradiance and weather patterns for 239 locations in the US. The historical data was used to estimate PV system production ranges for two prototypical system configurations and create charts to show how your annual results may vary in a nearby location.
The calculated results from PVWatts® are an estimate of what you might actually experience, and are based on assumptions, uncertainties, and incomplete information about your particular PV system and location. The new internanual variability information provides ranges for possible energy generation in different years, and be useful in deciding whether to install a PV system.
We hope you enjoy using this latest version of PVWatts!
The NREL PVWatts Team.