PVWatts Calculator
National Renewable Energy Laboratory (NREL)
PVWatts estimates the electricity production of a grid-connected photovoltaic system. You pick a location, enter the nameplate capacity, module type, array type (fixed roof mount, fixed open rack, one-axis or two-axis tracking), system losses, tilt and azimuth, and get annual and monthly output, plane-of-array irradiance and capacity factor, plus hourly data. There are options for bifacial modules, albedo and monthly soiling losses, and an API with a free key. It suits first estimates and checking contractor proposals. Limitation: it is a simplified model with no string, inverter or detailed shading design.
Ratings & Reviews
| Licence type | Completely Free |
|---|---|
| Licence terms | A free web tool from a US national laboratory, with no registration needed for the interface. The API needs a free developer key and is limited to 1,000 requests per hour. |
| Platforms | Runs in the Browser |
| Engineering field | Architecture, Electrical & Electronics |
| Tool type | Engineering Calculators |
| Vendor site | pvwatts.nrel.gov |
This link goes to the vendor site. EngiFree hosts no installers and distributes no cracked versions.
Last verified: 2026-10-17
