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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 //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, and is intended to provide an indication of the possible interannual variability in generation for a Fixed (open rack) PV system at this location.

Version 8.0

Current Version: 8.4.0
Release Date: September 5, 2024
PVWatts® API Version: 8.0

Information for Developers: The current version of PVWatts® is based on the PVWatts® V8 API, which runs Version 275 of the SAM Simulation Core (SSC) pvwattsv8 compute module with weather data from the PSM V3 TMY tmy-2020 and PSM V3 Himawari TMY tmy-2020 datasets from the National Solar Radiation Database (NSRDB).

Version 8 is a major update with improved models and several new features.

  1. Support for bifacial modules.
  2. New monthly irradiance loss inputs for for soiling and or snow.
  3. Optional input for albedo (ground reflectance).
  4. New solar resource data from National Solar Radiation Database (NSRDB) PSM V3 TMY tmy-2020 and PSM V3 Himawari TMY tmy-2020, updated from older NSRDB datasets from 2015.
  5. Improved internal models of the photovoltaic module, module thermal effects and inverter. These models are consistent with implementations in the NREL System Advisor Model (SAM) Detailed PV model.
  6. Update module type parameters to better reflect current market conditions.

This version updates the SAM Simulation Core (SSC) compute module from pvwattsv5 to pvwattsv8, and the PVWatts® API on the NREL Developer Network from PVWatts® API V6 to PVWatts® API V8.