India curtailed 2.3 TWh of solar generation between May and Dec. 2025: Ember

The system operator regularly had to curtail solar generation as an emergency measure to maintain grid security, as other resources were already flexing to their maximum capabilities. Lost solar generation highlights the need for flexibility to grow at pace with solar capacity.

January 27, 2026 Uma Gupta

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A new report by energy think tank Ember finds that India had to curtail 2.3 terawatt hours (TWh) of solar generation between late May and December 2025, with 0.9 TWh in October alone. The total recorded curtailment is equivalent to 18% of the average monthly solar generation of 13 TWh.

The report stated that a combination of forecast error, low daytime demand due to unusually mild temperatures and rising solar generation led to periods of daytime oversupply in 2025. The inability to flex the coal fleet beyond technical limits restricted the system’s ability to provide sufficient headroom, making solar curtailment necessary to maintain grid security.

“Weaker-than-forecast daytime demand coincided with continued solar expansion, resulting in periods where cumulative supply was higher than demand. This was because enough coal capacity had to remain online to meet the evening demand, with the mismatch leading to grid security concerns,” said the report.

It added that the extent of avoided curtailment in the future will depend on how accurately demand is forecasted, how decisively India resolves transmission bottlenecks and how rapidly it scales flexibility resources.

“A massive 38 GW of solar capacity was added in 2025. Yet, curtailment of renewable energy emerged as a key theme of the year, driven by transmission constraints and grid security concerns through emergency measures. In many ways, such curtailment defeats the very purpose of building this capacity,” says the report’s author Ruchita Shah, Energy Analyst at Ember.

“While grid security-related curtailment in 2025 may not be a major concern in isolation, as it was largely triggered by lower-than-expected demand, it served as a real-world stress test for a high-solar future. It highlighted a fundamental reality: clean energy cannot scale efficiently without flexibility,” she added.

While the report focuses on the reasons behind the emergency curtailment of solar, it notes that transmission constraints are the largest cause of solar curtailment nationally, and represent the largest risk to new projects as they are not guaranteed to be compensated financially.

With regard to emergency curtailment, Ember estimates that affected solar generators received an estimated INR 5,750 million – INR 6,900 million ($63 million – $76 million) in compensation through emergency Tertiary Reserve Ancillary Service (TRAS) mechanisms. The report highlights that in addition to the economic cost, there is also an environmental price to pay. The curtailed solar could have avoided around 2.1 million tonnes of CO2 emissions had it displaced coal generation—roughly equivalent to annual emissions by 0.4 million households in India.

The report argues that 2025 serves as an indicator of the power system’s requirements in a high-renewables future, showing that improvements in India’s system flexibility must keep pace with solar capacity growth. It notes that India is already taking steps in this direction and recommends a three-level strategy, to be implemented in the near to mid term, to increase flexibility. First, ensuring that other generation assets are capable of ramping up or down during periods of high renewable output. Second, expanding storage capacity to store excess renewable energy for times of higher demand. Finally, shifting non-critical demand to periods of high renewable availability as another key step in preparing for the future.

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