Solar radiation is inherently variable. It is not a steady fuel source like coal or gas. For a solar plant owner or engineer, anticipating these variations is critical for grid integration and financial planning.
The variation happens on two main timescales. Daily variation is driven by the Earth’s rotation. Irradiance rises from zero at sunrise, peaks at solar noon, and falls to zero at sunset. This bell-curve shape defines the solar generation profile.
Seasonal variation is driven by the Earth’s tilt (23.5°) as it orbits the sun. In India, for example, Global Horizontal Irradiance (GHI) typically ranges between 4.0 and 6.0 kWh/m²/day depending on the season and location:
- Summer: High irradiation due to longer days and higher solar elevation angles.
- Monsoon: A significant drop in irradiation due to cloud cover. The “quality” of light changes too, with a much higher fraction of diffuse radiation.
- Winter: Lower sun angles reduce intensity. In northern India, fog and haze can further severely reduce GHI.
Understanding these patterns prevents “sticker shock” when generation drops in winter or monsoon. It also informs the electrical design, ensuring inverters are sized to handle peak summer output without clipping, while staying efficient during lower winter production.
