India needs around 10 gigawatt-hours (GWh) of battery storage immediately to stop renewable energy curtailment, according to a report by energy think tank Ember.
Coal Plants Force Curtailment
The report found that keeping coal-fired power plants above their minimum technical loads (MTL) forced the curtailment of around 2.1 terawatt-hours (TWh) of renewable generation in FY2025-26, equivalent to 1.3 percent of total renewable generation.
With solar power flooding the grid at midday, several coal-fired power plants are required to operate at or below their MTL — the minimum level at which they can safely operate, the report said.
As a result, grid operators are curtailing clean electricity to keep coal-fired power plants online for the nighttime surge in demand and to provide necessary reserves.
Storage as a Solution
In 2026, around 10 GWh of storage, charging during the midday solar window, would have been enough to absorb that surplus, keep coal above its safe operating floor 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,” said 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,” he added.
Coal's Structural Limitations
The report highlighted that the core issue is that coal still provides almost all of the grid’s flexibility, including ancillary reserves. As solar capacity has grown, coal is being cycled from near-full output at night to its lowest point at midday every day.
For example, on March 6, 2026, solar and wind reached 41 percent of the generation mix at midday, pushing coal down by around 49 gigawatts (GW) in six hours before it had to climb back up by 51 GW in the evening as solar generation fell. “Coal was built for sustained high output, not this daily deep cycling,” Rodrigues said.
Once coal reaches its MTL, around 55 percent of rated capacity, it can no longer provide downward reserves, and renewable generation must 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 percent 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.”
