Concept 1 / 3
Solar Radiation Fundamentals
Solar constant: E₀ = 1368 W/m² (outside atmosphere)
Beer-Lambert law — atmospheric attenuation:
I = I₀ · e^(−τ · AM)
- AM = 1/cos(θ_z), θ_z = zenith angle
Air Mass values:
- AM 0: above atmosphere (space)
- AM 1: sun directly overhead
- AM 1.5: θ_z ≈ 48.2° — standard test condition (STC) for solar cells
At STC: I = 1000 W/m², T_cell = 25°C, AM = 1.5
Germany annual irradiance: ~1,000–1,100 kWh/m²/year
- Summer: ~5–6 kWh/m²/day
- Winter: ~0.5–2 kWh/m²/day