India's rapid expansion of renewable energy capacity is running into an increasingly familiar constraint: coal plants that cannot be switched off fast enough to accommodate surplus clean power. A new analysis from energy think tank Ember quantifies the scale of the problem and points to battery storage as a straightforward remedy.

Curtailment at Scale

In fiscal year 2025–26, approximately 2.1 terawatt-hours of renewable electricity generation was curtailed across India — power that was produced but deliberately suppressed rather than fed into the grid. Ember's researchers calculated that figure represents roughly 1.3 percent of total renewable generation for the period, a seemingly modest share that nonetheless points to a structural friction building within the country's power system.

The root cause, according to the analysis, is not a lack of transmission capacity or insufficient demand, but rather the operational characteristics of coal-fired power plants. Those facilities cannot simply be throttled down to zero output; each plant has a minimum technical load — a floor below which it cannot safely operate — and grid operators must respect that floor. When solar generation surges during midday hours, the combination of renewables and coal running at their minimum technical limits can exceed what the grid can absorb, forcing curtailment of the cleaner source.

The Storage Solution

Ember's report argues that the problem is solvable with a comparatively modest deployment of battery energy storage. The analysis estimates that roughly 10 gigawatt-hours of storage capacity, strategically charged during periods of peak midday solar output, would have been sufficient to absorb the surplus renewable generation recorded in 2025–26. By shifting that excess electricity into storage rather than curtailing it, grid operators could simultaneously keep coal plants at or above their minimum technical load and deliver the stored energy during subsequent high-demand periods.

The 10 GWh figure is notable in the context of India's broader energy ambitions. The country has set aggressive targets for both renewable capacity additions and energy storage deployment, and Ember's finding suggests that even a targeted, relatively contained storage rollout could eliminate the curtailment losses recorded in the most recent fiscal year.

Coal's Lingering Grip

The dynamic described in Ember's analysis illustrates the tension at the heart of India's energy transition. Coal continues to supply the majority of the country's electricity and, critically, provides grid stability services that cannot yet be fully replaced. Minimum technical load requirements mean that coal plants act as a kind of floor on thermal generation, one that periodically conflicts with the output profiles of solar and wind resources.

Curtailment driven by this constraint is distinct from curtailment caused by grid congestion or weak transmission links, though both erode the economics of renewable investment. When developers and financiers calculate returns on solar or wind projects, curtailment directly reduces revenue and can complicate the bankability of new capacity. At 1.3 percent of total renewable generation, the current curtailment rate may appear manageable, but Ember's analysis implicitly warns that the figure is likely to grow as India continues adding renewable capacity without a commensurate expansion of flexible storage or demand response.

Implications for Grid Planning

The Ember findings arrive as Indian grid planners and policymakers are already grappling with how to integrate hundreds of gigawatts of new solar and wind capacity over the coming decade. Battery storage procurement has been gaining momentum, with central and state-level tenders for grid-scale systems increasing in frequency. Ember's 10 GWh benchmark offers a concrete data point: the storage volume needed not to achieve some future ambition, but simply to recover the renewable energy that was already being generated and wasted in a single fiscal year.

Whether that storage is procured as standalone systems, co-located with renewable projects, or embedded in hybrid tenders remains an open question of policy design. What Ember's analysis makes clear is that the technical solution exists, the scale is well-defined, and the cost of inaction is measurable in terawatt-hours of clean electricity that the grid could have used but did not.