India's installed solar capacity crossed 100 gigawatts in April 2025 — a milestone that arrived faster than nearly every official projection from just five years ago. But the number itself understates the structural change now underway in how the grid dispatches power.
The merit order is moving
In India's electricity dispatch system, power plants are scheduled in order of their variable cost — cheapest first. Solar, with near-zero variable cost, always dispatches when available. As solar capacity has grown, it has progressively displaced the thermal plants that used to fill the noon demand window.
"The afternoon coal backing-down we see today was structurally impossible in 2020. There simply wasn't enough solar on the grid to cause it."
Solar generation during the midday window has grown 4.4× since 2020. Coal's share of the same window fell from 68% to 49%.
State-level variation
The displacement effect is not uniform across India's five regional grids. Southern and Western regions, which have the highest solar penetration, are already experiencing what analysts call midday demand inversion — where net load actually falls during peak sunlight hours.
| Region | Solar capacity | Coal midday share | vs. 2022 |
|---|---|---|---|
| Southern | 38.4 GW | 41.2% | −24.9pp |
| Western | 29.7 GW | 47.8% | −21.5pp |
| Northern | 18.6 GW | 56.4% | −14.8pp |
| Eastern | 8.1 GW | 68.9% | −5.7pp |
The stranded asset question
The regions that added solar fastest are seeing the sharpest erosion of coal's midday role. This has profound implications for how thermal plants recover fixed costs — plants that were built on assumptions of 80%+ plant load factors are now regularly dispatched at 60–65% during summer afternoons.
What comes next
Battery storage is the obvious answer, and India's BESS tenders are accelerating. But at current addition rates, meaningful grid-scale storage is still 3–4 years away. In the interim, the grid will rely on hydro flexibility, demand response, and inter-regional transmission to absorb the midday solar surplus.