India curtailed 2.3 terawatt-hours (TWh) of solar power in 2025, despite rapidly expanding renewable capacity, as the country’s power system struggled to adapt to rising daytime solar generation and weak demand growth, according to a new report by global energy think tank Ember.
The curtailment — equivalent to the annual electricity use of nearly 400,000 households — highlights a growing mismatch between India’s clean energy ambitions and the flexibility of its power system, the report titled Beyond Capacity: Why India’s Power System Must Get Flexible said.
Solar surplus, system stress
India added a record 38 GW of solar capacity in 2025, pushing non-fossil fuel capacity to 50 per cent of total installed power capacity. But instead of displacing fossil fuel generation, a portion of this clean energy was switched off to maintain grid stability.
Between May and December 2025, the national grid operator curtailed 2.3 TWh of solar power through emergency measures, with nearly 40 per cent of the curtailment occurring in October alone. The main reason: the system could not ramp down coal plants fast enough during periods of low daytime demand.
“Solar curtailment in 2025 was not driven by excess solar capacity, but by insufficient system flexibility,” the report said.
Coal flexibility: Major bottleneck
At the heart of the issue lies India’s coal fleet. Coal plants are required to operate above a minimum technical load (MTL) of 55 per cent, limiting how much they can reduce output during sunny hours.
In October, when solar output peaked but electricity demand dipped due to milder weather, coal plants remained online to meet evening demand. This forced grid operators to curtail solar generation instead.
On some days:
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Midday solar availability reached 50-65 GW
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Coal output stayed above 100 GW
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Solar generation was cut despite demand existing later in the day
Carbon and cost impact
The curtailment had tangible climate and economic consequences:
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2.11 million tonnes of CO2 emissions were not avoided
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Equivalent to emissions from 400,000 households annually
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Solar generators received Rs 5,750-Rs 6,900 crore ($63-76 million) in compensation
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Clean power was paid for, but not used
“This represents a notional loss to the system,” the report noted, as fossil fuel generation was not displaced despite available clean power.
Transmission bottlenecks add to problem
Apart from operational issues, transmission constraints worsened curtailment. In December 2025, nearly 4 GW of solar capacity faced complete evacuation restrictions during peak solar hours due to delays in transmission infrastructure.
Projects operating under temporary grid access were especially vulnerable, often receiving no compensation for lost generation.
A warning for India’s energy transition
The report warns that what happened in 2025 is an early signal of future risks. While solar capacity is growing rapidly, demand growth is slower, and flexibility measures — storage, flexible coal operations, and demand-side management — are not scaling at the same pace.
Without urgent action:
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Solar curtailment could become routine
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Clean energy investments may lose value
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Emissions reductions could stall despite rising renewable capacity
What needs to change
Ember identifies three urgent priorities:
1. Make coal more flexible: Enforce lower minimum operating levels and enable two-shift operations.
2. Scale up energy storage: India currently has just 0.5 GWh of battery storage; this must rise sharply to absorb excess solar power.
3. Unlock demand-side flexibility: Faster rollout of smart meters and stronger time-of-day tariffs are needed to shift consumption to solar hours.
India’s clean energy transition is no longer constrained by generation capacity, it is constrained by flexibility. As the report concludes, “Curtailment in 2025 was not a failure of renewable energy, but a warning that the power system must evolve faster to keep up with it.”