India’s rapid solar capacity expansion is running ahead of its power system’s ability to absorb clean energy, leading to the curtailment of 2.3 terawatt-hours (TWh) of solar generation in 2025 — enough electricity to power hundreds of thousands of homes, according to a new report by energy think tank Ember.
The curtailed solar output resulted in 2.11 million tonnes of unrealised carbon dioxide abatement, highlighting how grid inflexibility, rather than lack of demand, is emerging as a critical bottleneck in India’s clean energy transition, the report said
India added a record 38 GW of solar capacity in 2025, but the power system struggled to absorb this surge, especially during midday hours when demand was weak and coal plants could not ramp down fast enough. “Curtailment in 2025 was not caused by excess solar capacity, but by insufficient flexibility across the power system,” the report noted.
Widening Midday Gaps
In October 2025, average midday demand fell by 14GW year-on-year to 185GW, twice the decline seen during evening hours, widening the gap between daytime solar output and evening peak requirements. To ensure grid stability and meet later demand, system operators were forced to keep coal plants running, even as solar output peaked.
As a result, renewable power was curtailed through Tertiary Reserve Ancillary Services (TRAS), an emergency grid-balancing mechanism.
“Due to their operational flexibility, renewable generators are particularly able to provide down regulation, and are often called on for this purpose. For example, according to data reported for ISTS-connected solar projects in Grid-India’s daily VRE (Variable Renewable Energy) reports, on 25 May 2025, approximately 45 GWh of ISTS solar output, was curtailed.
This increased to about 93.3 GWh on 12 October 2025,” the report said. Between May and December 2025, emergency curtailment accounted for nearly 18% of average monthly solar generation, it added.
While renewable generators were compensated between ₹5,750 crore and ₹6,900 crore — Ember cautioned that curtailment represents a broader economic and environmental loss. “Every unit of curtailed solar is a missed opportunity to displace fossil fuel generation,” the report said.
Coal Operational Constraints
A key constraint remains coal’s inflexibility. Coal-fired plants still supply nearly 75% of India’s electricity, but most operate with a minimum technical load of 55%, limiting their ability to ramp down during high solar periods. More than 40% of coal capacity is also not available for ancillary services, reducing real-time dispatch flexibility.
Transmission bottlenecks compounded the problem. In December 2025, around 4 GW of solar capacity operating under temporary grid access faced full curtailment during midday hours in some regions due to inadequate transmission readiness.
The report warned that curtailment risks will grow as solar capacity continues to expand faster than electricity demand. To address this, Ember outlined three urgent priorities: retrofitting coal plants for deeper flexibility, scaling up energy storage, and expanding demand-side response.
India currently has 7.2 GW of pumped hydro storage and just 0.5 GWh of battery storage, far below what is needed for a high-renewables system. Without rapid progress on flexibility, the report cautioned, India risks diluting both the climate and economic gains of its clean energy transition.