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India’s experience in 2025 signalled that limited system flexibility will present a growing barrier to solar integration without prudent planning
Solar is meeting a growing share of daytime electricity demand and altering net load patterns. In 2025, this coincided with weaker-than-forecast daytime demand and limited operational flexibility. The coal fleet, which must remain available for the evening peak, could only ramp down so far during the day without breaching technical and reliability limits. As a result, system operators relied on real-time schedule revisions and emergency interventions to maintain grid security, leading to solar curtailment on certain days.
Although these generators get compensated for curtailed solar energy – based on emergency Tertiary Reserve Ancillary Service (TRAS) provisions – this phenomenon represents a notional loss to the system. Clean electricity is not delivered, fossil generation is not displaced and emissions reductions are foregone.
In 2025, emergency curtailment was primarily a result of muted demand and operational issues like forecasting error. However, as renewable penetration increases, such curtailment could become routine without an appropriate response. To avoid this, flexibility must keep pace with solar capacity. The coal fleet must flex further, energy storage must be deployed and demand-side response must be accessed. Curtailment this year did not reflect a lack of demand for clean power, but highlighted the flexibility required from the rest of the system to integrate it.
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. 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.
Solar curtailment between May and December 2025 for emergency reasons was driven primarily by the system’s inability to sufficiently flex conventional generation and create headroom for solar during periods of lower-than-forecast daytime demand.
On several occasions, the coal fleet’s load factor at midday was close to the mandated minimum thermal load (MTL) of 55%, and the fleet was not able to flex down further than this.
Even though renewable energy generators would receive approximately between INR 5,750 million – INR 6,900 million (~USD 63 million – USD 76 million) in compensation payments for the curtailment, the power system lost an estimated 2.11 million tonnes of unrealised CO2 abatement. This highlights that solar curtailment results in both economic and environmental losses, despite generators being compensated.
The experience of 2025 signals how the power system must evolve as solar capacity expands rapidly. Flexibility buildout across the three levers (supply, store and shift) now needs to keep pace with solar capacity additions.
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