Solar Shading: The Silent Killer of System Performance
Shading is the most underestimated factor in rooftop solar. Even 10% shading on a string-connected system can reduce output by 30–50% because of the "weakest link" effect — one shaded cell limits the entire string.
Common Shading Sources in Indian Homes
- Water tanks (overhead): Most common in Indian rooftops. Shadow moves throughout the day.
- Staircase covers/structures: Fixed shadow, usually morning or evening.
- Adjacent building walls: Affects east/west facing panels more in morning/evening.
- TV antennas and pipes: Create long thin shadows that still affect full cell rows.
- Trees: Partial, moving shadow. Worst type for string inverters.
String Inverter vs Optimizers for Shaded Roofs
String inverters: All panels in a string perform at the level of the weakest (shaded) panel. Even 5% shading → 15–30% loss. Power optimizers or microinverters: Each panel operates independently. 5% shading → only 5% loss. The extra cost (₹8,000–₹15,000) is worthwhile if shading affects more than 15% of the array.