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PVWatts Calculator National Renewable Energy Laboratory


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 https://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.

 

Disclaimer: The PVWatts® Model ("Model") is provided by the National Renewable Energy Laboratory ("NREL"), which is operated by the Alliance for Sustainable Energy, LLC ("Alliance") for the U.S. Department Of Energy ("DOE") and may be used for any purpose whatsoever.

The names DOE/NREL/ALLIANCE shall not be used in any representation, advertising, publicity or other manner whatsoever to endorse or promote any entity that adopts or uses the Model. DOE/NREL/ALLIANCE shall not provide

any support, consulting, training or assistance of any kind with regard to the use of the Model or any updates, revisions or new versions of the Model.

YOU AGREE TO INDEMNIFY DOE/NREL/ALLIANCE, AND ITS AFFILIATES, OFFICERS, AGENTS, AND EMPLOYEES AGAINST ANY CLAIM OR DEMAND, INCLUDING REASONABLE ATTORNEYS' FEES, RELATED TO YOUR USE, RELIANCE, OR ADOPTION OF THE MODEL FOR ANY PURPOSE WHATSOEVER. THE MODEL IS PROVIDED BY DOE/NREL/ALLIANCE "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY DISCLAIMED. IN NO EVENT SHALL DOE/NREL/ALLIANCE BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER, INCLUDING BUT NOT LIMITED TO CLAIMS ASSOCIATED WITH THE LOSS OF DATA OR PROFITS, WHICH MAY RESULT FROM ANY ACTION IN CONTRACT, NEGLIGENCE OR OTHER TORTIOUS CLAIM THAT ARISES OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THE MODEL.

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!

This is Version 6 of NREL's popular online photovoltaic system calculator.


New Solar Resource Data

PVWatts Version 6 uses the newest data from the NREL National Solar Radiation Database (NSRDB). The new NSRDB data covers the Americas including Hawaii between about 21 degrees South latitude (about 300 km North of Sao Paolo, Brazil) to about 60 degrees North (about 200 km south of Anchorage, Alaska), and the Indian subcontinent and parts of Central Asia as shown in this map:

Image of map showing coverage area for NSRDB data. If you are visually impaired and cannot read this graph, select the Need Help link at the bottom of the page for assistance.

You can still use solar resource data available in the older version of PVWatts by choosing a legacy data option, but we recommend using the new data because of its higher quality, better spatial resolution so you can use data for the exact location of your project, and because it covers a larger part of the world. See Help for more about the solar resource data.

Performance Improvements

Behind the scenes, we have migrated PVWatts to the cloud. While you will not see the effect of this change, it will minimize website down times and give us more flexibility to add computing resources as more people use the site.

Other Enhancements

  1. Change the distance in miles shown on the Resource Data and Results pages to be the distance between the system location and the center of the NSRDB grid cell. In older versions, the distance was between the location and legacy weather station.
  2. Update the solar resource map to better reflect the latest solar resource data sources.
  3. Change default location to the NREL campus in Colorado from Latitude 0° and Longitude 0° in the Atlantic Ocean.
  4. Update Tilt to automatically change when you choose an array type. For fixed arrays, the default tilt angle is 0° and for tracking arrays, it is 20°. As always, you can type a value for Tilt to override the default value.
  5. Change the default value of DC to AC Size Ratio (On the System Info page under "Advanced Parameters") from 1.1 to 1.2 to reflect current trends in the photovoltaic market.
  6. Update the labels for economics inputs on the System Info page and results on the Results page to better reflect how the model works: The value of electricity generated by the system is based on a simple, flat electricity rate, not a cash flow model.
  7. Remove India-specific features and documentation. Now that weather data for India and many other countries is available from the NREL NSRDB, we can use the same version of PVWatts for any location in the world.
  8. Review and revise Help documentation to reflect the latest updates and enhancements.
  9. Update supporting supporting libraries (e.g. Google maps).
  10. Refactor data management system to correct minor bugs and make maintenance easier in the future.
  11. Add aSSL to comply with federal regulations.

We hope you enjoy using this latest version of PVWatts!

The NREL PVWatts Team.