India must rapidly improve power system flexibility to prevent rising solar curtailment from undermining its clean energy expansion, according to a report released today by energy think-tank Ember.
India achieved 50pc non-fossil fuel-based power generation in 2025, but curtailed about 2.3TWh of solar power over May-December for grid-security reasons, largely because the power system lacked sufficient flexibility to absorb rising midday solar generation, the report said. The country also had to keep enough coal capacity on line to meet evening demand.
Solar curtailment in 2025 was driven mainly by operational constraints, including limited flexibility in the coal fleet and weaker-than-expected daytime demand, rather than excess renewable supply. India added a record 38GW of solar capacity in 2025, sending total installed solar capacity to around 136GW, but flexibility additions did not keep pace, Ember said.
India's coal fleet could only ramp down to the mandated minimum thermal load of 55pc, limiting the system's ability to accommodate solar output at midday. As a result, the national grid operator had to repeatedly rely on emergency interventions, including tertiary reserve ancillary services (TRAS), to maintain grid stability, leading to solar curtailment. Coal still supplies the bulk of India's electricity, accounting for about 75pc of power generation in 2024, according to the report.
Curtailing solar generation results in a notional loss of clean power despite renewable generators being financially compensated for curtailed output, and "is a missed opportunity to displace fossil fuel generation", the report said. Compensation payments for security-led curtailment were around 5.75bn–6.9bn rupees ($63mn–76mn), according to Ember, and these costs are ultimately socialised across the power system, and indirectly passed on to consumers through electricity tariffs.
Additionally, the curtailment resulted in around 2.11mn t of CO2 abatement foregone in 2025, according to Ember.
Unexpectedly weak daytime demand in 2025 — partly due to milder temperatures and growing behind-the-meter solar generation — exacerbated grid balancing challenges. 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.
Solar curtailment linked to grid security is currently smaller than curtailment caused by transmission constraints, but could become routine as solar capacity continues to grow faster than demand, without parallel investments in flexibility, Ember warned.
To integrate higher shares of solar power efficiently, India must expand flexibility across three areas — more flexible coal operations, energy storage deployment, and demand-side response, the report said. Measures include deeper coal ramping capability, faster rollout of battery storage, and accelerating smart metering to enable time-of-day tariffs to incentivise consumers to shift demand in line with system needs.
"Clean energy cannot scale efficiently without flexibility," Ember said, adding that India's experience in 2025 serves as an early stress test for a high-solar future rather than evidence of excess renewable capacity.
