PVGIS vs NASA POWER: Which Solar Irradiance Data Should You Trust?
Both are free, both are authoritative — but they serve different purposes. Here's when to use each and what the numbers actually mean.
Two Free Solar Databases
When calculating how much energy your solar panels will produce, the most important input is peak sun hours per day — the daily equivalent of full-sun radiation at your location. Two trusted free sources:
PVGIS (Photovoltaic Geographical Information System) is published by the EU Joint Research Centre. It covers Europe, Africa, and parts of Asia with very high spatial resolution (3 arc-seconds ≈ 90 m grid). Data is based on satellite imagery from 2005–2020.
NASA POWER (Prediction of Worldwide Energy Resources) is a global dataset at ~50 km resolution. It covers every coordinate on Earth, making it the best fallback for locations outside PVGIS coverage.
Key Differences
| PVGIS | NASA POWER | |
|---|---|---|
| Coverage | EU + Africa + Asia | Global |
| Resolution | ~90 m | ~50 km |
| Data source | Satellite (SARAH-3) | Reanalysis model |
| Best for | European addresses | Americas, Oceania |
Which Is More Accurate for Residential Use?
For European locations, PVGIS is more accurate — its higher resolution captures local terrain effects like valley shading that NASA POWER's coarse grid misses. Studies comparing measured PV output to predictions show PVGIS has a mean bias error of under 3% for most EU locations.
VoltSun uses PVGIS as the primary source and falls back to NASA POWER for locations outside its coverage. Both APIs are free with no registration required.