India needs around 10 GWh of battery storage immediately to stop renewable energy curtailment when the coal fleet cannot ramp down below its technical minimum, according to a new analysis by energy think tank Ember.

With solar power flooding the grid at midday, several coal-based power plants are required to operate at or even below their minimum technical loads (MTL) — the lowest levels at which they can safely operate. As a result, grid operators are curtailing clean electricity to keep coal-based power plants online for the nighttime surge in demand and to provide necessary reserves.

Ember’s analysis found that about 2.1 TWh of renewable electricity generation was curtailed in fiscal year 2025–26, running from April 1, 2025, to March 31, 2026, equivalent to 1.3% of total renewable generation, to keep coal-fired power plants operating at their minimum technical load. The report estimates that around 10 GWh of energy storage, charged during peak midday solar generation hours, would have been sufficient to absorb this surplus renewable output, maintain coal plants above their minimum technical load, and avoid the curtailment altogether.

“Solar and wind curtailment is becoming a visible part of India’s real-time grid balancing, and the volumes are already noticeable and rising,” says the report’s author, Neshwin Rodrigues, Senior Energy Analyst at Ember. “Without sufficient flexibility, including storage, this could become a constraint on the next phase of renewable energy growth.”

The report highlights that the core issue is that coal still provides almost all of the grid’s flexibility, including its ancillary reserves. As solar capacity has grown, coal is being cycled from near-full output at night to its lowest point at midday every single day.

For example, on March 6, 2026, solar and wind reached 41% of the generation mix at midday, pushing coal generation down by around 49 GW in six hours before it had to climb back up by 51 GW in the evening as solar collapsed. “Coal was built for sustained high output, not this daily deep cycling,” says Rodrigues.

Once coal plants reach their minimum technical load — around 55% of rated capacity — they can no longer provide downward reserves, and renewable generation would need to be curtailed to keep the fleet at this technical minimum. By April 2026, coal was breaching that floor in more than half of all midday dispatch intervals. Renewable curtailment met 37% of down-regulation that month, up from near zero a year earlier.

“This is curtailment required purely to keep coal plants at their MTL,” Rodrigues said. “Before the system even considers reserve requirements or grid constraints, renewable generation is being cut simply to make space for coal to remain operable. The constraint is structural.”

With solar capacity on the rise, the report highlights that curtailment of clean electricity is increasing in the absence of the country deploying alternatives like battery storage for grid flexibility. India added around 24 GW of solar capacity between October 2025 and April 2026, reaching approximately 154 GW. Peak-hour curtailment had returned to 4% of solar and wind generation by April 2026, comparable to the most constrained months of late 2025, despite April falling outside the worst seasonal window.