Solar Irradiation in India: Complete Guide (2026)
India receives some of the world's highest solar irradiation — the annual GHI (Global Horizontal Irradiance) ranges from 1,500 kWh/m²/year in Northeast India to 2,200+ kWh/m²/year in Rajasthan. This data is critical for accurate solar project sizing.
Key Terms
- GHI (Global Horizontal Irradiance): Total solar energy received on a horizontal surface per unit area. Measured in kWh/m²/year.
- PSH (Peak Sun Hours): Equivalent hours of 1000 W/m² irradiance. Equal to daily GHI ÷ 1000. Used to calculate daily panel output.
- DNI (Direct Normal Irradiance): Direct beam radiation perpendicular to the sun. Used for concentrated solar power (CSP) projects.
- Tilt Factor: Tilting panels toward the equator increases captured irradiation by 5–15% depending on latitude.
India's Solar Resource Map
The highest GHI zones in India are the Thar Desert (Rajasthan) and Rann of Kutch (Gujarat). South India has moderate but consistent irradiation year-round with less seasonal variation than the north.
Seasonal Variation
June–August monsoon months see 30–40% reduction in generation across most of India. Rajasthan and Gujarat are less affected. System sizing should account for this seasonal dip when calculating battery storage or grid dependence.