India’s rapid solar energy expansion faced an unexpected challenge in 2025. Despite adding record levels of new capacity, a significant amount of clean electricity never reached homes or businesses. Between late May and December 2025, India lost 2.3 terawatt hours (TWh) of solar generation because the power system could not safely absorb it. Energy think tank Ember reports that operators carried out this curtailment as an emergency measure to protect grid security.
The lost solar power is not a small number. It equals around 18% of India’s average monthly solar generation, which stands at about 13 TWh. In simple terms, operators switched off nearly one-fifth of a typical month’s solar electricity during this period. October alone accounted for 0.9 TWh of curtailed solar energy, making it the single biggest month for such losses.
Why solar power had to be switched off
Solar curtailment occurs when operators ask power plants to reduce or stop generation, even though sunlight is available and panels are ready to produce electricity. In 2025, grid security concerns drove this decision. The system operator had to curtail solar generation because other power sources were already running at their maximum capacity.
Several factors came together at the same time. First, daytime electricity demand turned out to be lower than expected. Exceptionally mild temperatures reduced the need for cooling, which usually drives high power use during the day. As a result, demand forecasts proved to be weaker than actual conditions.
At the same time, solar generation continued to rise sharply. India added a massive 38 gigawatts (GW) of new solar capacity during the year. This meant that during sunny daytime hours, total electricity supply often exceeded demand. Normally, excess supply could be managed by reducing output from other power plants. However, coal-fired power stations, which still form the backbone of India’s electricity system, could not reduce their output beyond certain technical limits.
Coal plants had to remain online to ensure enough electricity would be available in the evening, when solar generation drops sharply and demand typically rises. This created a mismatch during the day. Too much electricity was being produced, but not enough demand existed to consume it. With limited options to store the excess energy or shift demand, solar curtailment became necessary to avoid grid instability.
In many cases, this curtailment was implemented as an emergency measure. The power system simply did not have enough “headroom” to handle the surplus solar generation safely. As a result, clean energy that could have replaced coal was instead left unused.
Transmission bottlenecks and financial impact
Grid security issues played a major role in 2025, but the report also highlights that transmission constraints cause most of the solar curtailment across India. Electricity must travel from solar-rich regions to areas where people use power. When transmission lines become congested or incomplete, operators may have to reduce solar output even if demand exists elsewhere.
This creates a major risk for new solar projects. In many cases, curtailment caused by transmission issues does not come with guaranteed financial compensation. Developers may lose revenue even though their plants are fully capable of generating power. This uncertainty can affect investor confidence and slow down future renewable energy deployment.
For emergency curtailment linked to grid security, affected solar generators did receive compensation through emergency Tertiary Reserve Ancillary Service mechanisms. The total estimated compensation ranged between INR 5,750 million and INR 6,900 million. In dollar terms, this amounts to roughly $63 million to $76 million. While this helped reduce financial losses, it did not address the broader system inefficiencies that led to the curtailment in the first place.
Beyond economics, there was also an environmental cost. The curtailed solar energy could have avoided around 2.1 million tonnes of carbon dioxide emissions if it had displaced coal-based generation. This is roughly equal to the annual emissions of about 0.4 million households in India. In other words, the power system’s inability to absorb clean energy led to higher pollution levels than necessary.
What 2025 reveals about India’s power system
Experts do not describe the 2025 solar curtailment as a crisis on its own. Lower-than-expected demand, rather than structural failures, triggered most of it. However, the events served as a real-world stress test for a future where solar power plays a much larger role in India’s electricity mix.
The findings show a clear reality. Building solar capacity alone is not enough. Clean energy can only scale efficiently if the power system becomes more flexible at the same pace. Flexibility means the ability to quickly adjust supply and demand in response to changing conditions.
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The analysis identifies three key areas where flexibility must improve. First, other generation assets need to be able to ramp their output up or down more easily during periods of high renewable generation. This would reduce the need to keep coal plants running at fixed levels during the day.
Second, energy storage must expand rapidly. Storage systems can capture excess solar power during the day and release it during the evening or night, when demand is higher. Without sufficient storage, surplus solar energy has nowhere to go.
Third, demand-side measures are essential. Shifting non-critical electricity use to times when solar generation is high can help balance the system. For example, operators can schedule industrial processes or water pumping during sunny hours instead of peak evening periods.
The experience of 2025 shows that India is entering a new phase of its energy transition. Solar capacity is growing fast, but the supporting systems must evolve just as quickly. The lost 2.3 TWh of solar generation stands as clear evidence that flexibility, transmission, and grid management are now as important as building new power plants.
These facts show a simple truth: the growth of clean energy brings new challenges, and we must manage them effectively to ensure that the system can fully use every unit of renewable power generated.
