Nirav Dhanani 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.
GHI in Yield Modeling and Bankability
GHI by itself doesn’t tell you what a plant will generate — it has to be split into DNI and DHI, then transposed onto the array’s plane using tilt, azimuth, and ground reflectance before it becomes an energy number. This is the same sequence a tool like PVsyst runs internally, which is why lenders and EPCs scrutinize the source GHI dataset as closely as the shading and system-loss assumptions in a PVsyst tracker yield study. Thin GHI data — a short historical record, coarse satellite resolution, no ground-truth correction — shows up downstream as a wider, less trustworthy spread in the P50/P90/P99 yield report that debt providers sign off on.
For hybrid or BESS-integrated plants, day-to-day GHI variability (cloud transients, seasonal swings) also feeds directly into dispatch and storage-sizing logic, which is one reason irradiance quality gets compared closely in write-ups like HOMER Pro vs PVsyst for hybrid solar simulation.
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.
Related Reading
Because GHI is the raw irradiance input every yield simulation starts from, it’s worth seeing how the leading tools actually consume it — Solar Simulation Software 2026: Lender-Grade Yield Picks compares the options project teams use to turn a GHI dataset into a bankable energy number. Since satellite-derived GHI can vary meaningfully within a country, it’s also worth sanity-checking a chosen dataset against ground-level context — state-wise solar irradiance data for India is a useful reference for Indian sites. Once GHI has been converted into an energy yield, that figure drives project economics directly — tools such as SurgePV’s generation-financial modeling platform take the resulting yield curve and use it to underwrite IRR and debt-sizing assumptions.
Frequently Asked Questions
6 commonly searched questions about GHI (Global Horizontal Irradiance).
What is GHI?
What's typical annual GHI?
Where do I get GHI data?
Is GHI the same as POA?
Why does GHI matter for solar?
Does cloud cover affect GHI?
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