NREL released a new version of PVWatts® in September 2014 which changes the results
significantly to more accurately reflect PV performance outputs from current systems. Note that the results will typically increase 7 to 10 percent.
This version updates the default derate/loss values, uses a modern inverter curve and adds several options.
You can read more about this update here. The old versions PVWatts V1 and PVWatts V2 have been retired.
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Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations.
PVWatts® is a registered trademark by Alliance for Sustainable Energy, LLC in Golden, CO, 80401.