NSRDB / TMY3

Key Takeaways

• NSRDB = NREL’s free US solar weather database.
• Hourly + half-hourly + sub-hourly data, 1998+ coverage.
• TMY3 is the canonical Typical Meteorological Year format.
• Used widely in PVsyst, SAM, Helioscope.
• Preferred over Meteonorm for US bankable projects.

How NSRDB and TMY3 Fit Into a Yield Simulation

NSRDB is the archive; TMY3 is what actually gets loaded into a simulation. NREL builds the underlying database from a satellite-derived model covering roughly 2 million grid points across the US, with hourly GHI, DNI, DHI, temperature, and wind speed reaching back to 1998. Because no lender wants a P50/P90 estimate built on a single arbitrary year, NREL distills that multi-year record into a TMY3 file — one synthetic 8,760-hour year assembled by selecting the most statistically representative month for each calendar month across the full historical span. That single file is what a designer actually imports into PVsyst, SAM, or Helioscope’s Site definition step, where it drives the transposition, temperature, and loss models behind the final yield number.

Worked Example

Consider a ground-mount project in Arizona. Instead of pulling one year of on-site pyranometer data (which the project doesn’t have), the engineer downloads the NSRDB TMY3 file for the nearest grid point from NREL’s data viewer. That file already encodes the site’s long-term solar resource — including its seasonal cloud patterns and dust-driven soiling risk — as a single representative year, so it drops straight into the simulation without any manual weighting or averaging. For a US-based project like this, NSRDB TMY3 is generally preferred over Meteonorm precisely because it’s satellite-derived, free, and tuned specifically to US conditions rather than interpolated from a sparser global station network.

Related Reading

Weather data is only useful once it’s run through a simulation engine and turned into a number a lender will sign off on. Our guide to advanced PVsyst analysis and how accurate yield predictions save millions covers how the choice of weather source, including NSRDB, shapes P50/P90 outcomes, and the bankable PVsyst reports guide walks through what US lenders expect to see documented alongside an NSRDB-sourced TMY3 file. If you’re comparing simulation platforms before locking in a weather-data workflow, our roundup of the best solar design software for 2026 is a useful starting point.