Definition
Global Horizontal Irradiance (GHI) is the total solar radiation received on a horizontal surface per unit area, in W/m². It is the sum of direct beam (DNI projected) and diffuse horizontal irradiance (DHI). GHI is the foundation metric for solar resource assessment.
Annual GHI Benchmarks (kWh/m²/yr)
| Region | GHI |
|---|---|
| Atacama (Chile) | 2,400–2,600 |
| Saudi Arabia | 2,200–2,400 |
| Rajasthan India | 2,000–2,200 |
| US Southwest | 1,900–2,150 |
| Spain (south) | 1,800–2,000 |
| India (national avg) | 1,800–1,900 |
| Texas | 1,650–1,850 |
| Karnataka India | 1,750–1,900 |
| US Midwest | 1,400–1,600 |
| Germany | 1,000–1,150 |
| UK | 850–1,100 |
Data Sources
- NREL NSRDB: US gold standard, 30-year TMY.
- Meteonorm 8: Global, 20-year averages, default in PVsyst.
- Solargis: Premium global, hourly satellite-derived.
- PVGIS: European Commission, free.
- NASA POWER: Global, free.
- On-site pyranometer: Site-specific measurement.
Key Takeaways
- GHI = total solar radiation on a horizontal surface, in W/m² or kWh/m²/yr.
- Foundation for POA irradiance and specific yield calculation.
- Sources: NSRDB (US), Meteonorm 8, Solargis, PVGIS, on-site measurement.
- Annual GHI ranges from ~900 kWh/m²/yr (Northern Europe) to 2,600 (Atacama Desert).
- Use 20+ year TMY data for bankable energy yield assessments.
Frequently Asked Questions
5 commonly searched questions about GHI (Global Horizontal Irradiance).
What is GHI?
Global Horizontal Irradiance — the total solar radiation per square meter on a horizontal surface. Sum of direct beam (DNI × cos(zenith)) and diffuse horizontal.
What's typical annual GHI?
Desert: 2,000–2,500 kWh/m²/yr. Tropical India: 1,800–2,000. US Sunbelt: 1,800–2,100. US Midwest: 1,400–1,600. Northern Europe: 950–1,150.
Where do I get GHI data?
NREL NSRDB (US), Meteonorm 8 (global), Solargis (global premium), PVGIS (Europe), NASA POWER (free), site measurement from on-site pyranometers.
Is GHI the same as POA?
No. GHI is on horizontal surface. POA (Plane of Array) is on tilted module surface. POA = GHI × transposition factor (typically 1.05–1.20 depending on tilt/latitude).
Why does GHI matter for solar?
It's the upstream input to POA, which directly drives PV energy yield. PR × POA × kWp = annual energy.
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