NREL's PVWatts® API estimates the energy production of grid-connected photovoltaic (PV) energy systems based on a few simple inputs.
Version 6 is the current version of the PVWatts API, and is the version used by NREL's online version of PVWatts. Updates from Version 5 include using the latest NREL National Solar Radiation Database (NSRDB) and minor changes to default values.
Version 4 has been replaced by version 6, and is scheduled to be shut down at the end of July 2018.
Version 5 has been replaced by version 6, and is scheduled to be shut down at the end of December 2018.