What is GHI?

Global Horizontal Irradiance (GHI) is the total solar energy received on a horizontal surface per unit area. It is the most commonly used solar resource metric for comparing sites and sizing systems.

GHI components

GHI = DNI × cos(solar zenith angle) + DHI

• DNI (Direct Normal Irradiance): Radiation from the solar disc on a perpendicular surface. Critical for CSP and concentrating PV.
• DHI (Diffuse Horizontal Irradiance): Radiation scattered by the atmosphere from all sky directions. Important in cloudy/monsoon climates.

India's GHI map

• Rajasthan / Gujarat (highest): 5.5–6.5 kWh/m²/day
• Andhra Pradesh / Karnataka / Telangana: 5.0–5.8 kWh/m²/day
• Maharashtra / MP: 4.8–5.6 kWh/m²/day
• Tamil Nadu / Kerala: 4.5–5.3 kWh/m²/day
• Northeast India (lowest): 3.5–4.5 kWh/m²/day

Using GHI for system sizing

E (kWh/year) ≈ P_installed (kWp) × GHI_annual (kWh/m²/yr) × PR

Delhi example (GHI ≈ 1,862 kWh/m²/yr, PR = 0.78): 10 kWp system → ~14,500 kWh/year.

Data sources

MNRE's Solar Radiation Resource Assessment (SRRA) network and NASA POWER provide validated India-specific GHI data.