A massive 38GW of solar capacity was added in India in 2025, yet curtailment emerged as a key theme of the year. Image: SECI.

India’s power system faced growing integration challenges in 2025 as solar curtailment emerged as an early signal of insufficient grid flexibility, according to a new report from energy think-tank Ember.

According to the report, India reached a milestone last year with non-fossil fuel sources accounting for around 50% of installed power generation capacity. However, Ember said grid security concerns led to the curtailment of renewable energy, highlighting the need for faster deployment of flexibility solutions as solar capacity continues to scale.

Solar met an increasing share of daytime electricity demand in 2025, altering net load patterns. This coincided with weaker-than-forecast daytime demand and limited operational flexibility, particularly from the coal fleet, which must remain online to meet evening peak demand. As coal plants were unable to ramp down further without breaching technical limits, system operators relied on emergency interventions, resulting in solar curtailment on several days.

Ember estimates that 2.3TWh of solar generation was curtailed between May and December 2025 through emergency Tertiary Reserve Ancillary Services (TRAS), with nearly 0.9TWh occurring in October alone. The curtailment was primarily driven by muted demand and forecasting errors, rather than excess solar capacity.

While renewable generators were compensated for curtailed output under TRAS provisions, Ember said the curtailment represented a notional loss to the system. Clean electricity was not delivered, fossil fuel generation was not displaced and emissions reductions were foregone. The report estimates that curtailment led to 2.11 million tonnes of unrealised CO2 abatement, despite compensation payments between INR5.75 billion (US$61.8 million) and INR6.9 billion (US$74.9 million).

“A massive 38GW of solar capacity was added in 2025, yet curtailment emerged as a key theme of the year,” said Ruchita Shah, energy analyst at Ember. “While grid security-related curtailment may not be a major concern in isolation, it served as a real-world stress test for a high-solar future.”

India’s installed solar capacity reached around 135.8GW by December 2025, representing 26% of total installed power capacity, while non-fossil sources accounted for approximately 52%. Under India’s Electricity Grid Code, renewable energy has “must-run” status, with curtailment permitted only under grid security or safety concerns.

Beyond operational issues, Ember said transmission constraints remained the largest structural driver of renewable curtailment, particularly for projects operating under temporary grid access arrangements. On some days in December 2025, around 4GW of solar capacity faced complete curtailment during midday hours due to inadequate transmission availability.

The report concluded that as solar capacity continues to grow faster than electricity demand, curtailment could become routine unless system flexibility improves. Ember said flexibility must keep pace with renewable additions through greater coal fleet flexibility, accelerated deployment of energy storage and expanded demand-side response, warning that reliance on curtailment would undermine India’s decarbonisation goals.

You can read Ember’s full report, Beyond capacity: why India’s power system must get flexible to harness its solar potential report, here.

By Shreeyashi Ojha