What it does
PVWatts estimates photovoltaic production from location, system size, array characteristics, orientation and loss assumptions.
PVWatts estimates grid-connected PV output from location/weather, DC system size, module/array type, orientation and loss assumptions. Monthly or hourly results can be downloaded, with the station and system specification retained alongside the estimate. The version 8 developer guide distinguishes monthly AC energy in kWh from hourly AC power in W; its JSON/XML endpoint needs a developer key and has a documented 1,000-request hourly limit. That API scope is separate from the website's file downloads. PVWatts deliberately simplifies technology and site details, so its module categories do not resolve every product-specific performance difference. The website's weather-based output range describes interannual variability for fixed open-rack systems at that location, rather than a warranty or a site-specific design validation.
Strengths
- Location-based photovoltaic estimates
- Monthly and hourly result downloads
Watch out for
- Model simplifies technology and site-specific behavior
Best for
- Exploring a preliminary photovoltaic scenario
Sources
- PVWatts Calculator (Oct 26, 2026)
- PVWatts8 Developer I/O Units and Access Limits (Oct 26, 2026)