What it is
PVWatts is a free online tool from the National Renewable Energy Laboratory (NREL) that estimates the energy production and cost savings of grid-connected solar PV systems. Enter your location (any address in the US), system size, array type (fixed, 1-axis tracking, 2-axis tracking), tilt angle, azimuth, and electricity rate. PVWatts calculates monthly and annual energy production using the National Solar Radiation Database, accounting for weather, panel degradation, and system losses.
Why we picked this
PVWatts is the gold standard for residential solar estimation because it uses the same radiation database and performance models that solar installers use for professional system design. When a solar company quotes you a system, they likely ran PVWatts (or its professional API equivalent) to generate the estimate. Running it yourself gives you an independent check on vendor quotes. The tool is deliberately simple: 5 inputs, immediate results. No account required, no data harvested, no sales funnel.
Key takeaways
- PVWatts uses the National Solar Radiation Database (NSRDB) with 30+ years of satellite-derived solar data for location-specific production estimates.
- A typical 6kW residential system in a sunny US location (Phoenix, LA) produces 9,000 to 10,000 kWh annually; in a cloudy location (Seattle, Pittsburgh) 6,000 to 7,500 kWh.
- The tool accounts for real-world system losses (inverter efficiency, wiring, soiling, shading, panel degradation) providing conservative estimates closer to actual production than marketing materials.