Structural and operational factors of renewable energy curtailment in India in 2025

Demand forecasting errors, power system’s limited flexibility and constraints in transmission capacity came to the fore in India with renewable energy curtailment in 2025. 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.

With the rapid deployment of renewable energy, India’s non-fossil fuel-based capacity, dominated by solar, reached 266.7 gigawatts (GW) by December 2025. Of this, 135.8 GW is solar, representing 26% of India’s total installed power capacity, while non-fossil sources collectively account for 52%.

The Indian Electricity Grid Code (IEGC), 2010 was one of the key drivers of the growth. The IEGC assigns a statutory responsibility to load dispatch centres to ensure the evacuation of all available solar and wind generation. Essentially, renewable energy has a “must-run” status under the IEGC, subject only to grid security and the safety of personnel and equipment. Curtailment, therefore, is not intended as a routine operational tool.

Hence, the emergence of frequent renewable energy curtailment under emergency conditions as a notable feature of system operations in 2025 warrants closer examination of the underlying drivers and constraints.

In India, Inter-State Transmission System (ISTS)-connected solar projects are curtailed for two primary reasons: (1) system-wide emergency conditions (Tertiary Reserve Ancillary Services), and (2) constraints related to project-specific transmission infrastructure. These are explored further in the following sub-sections. Both types of curtailment are crucial to discuss, with transmission constraints generally accounting for a significantly higher volume of lost energy. In this report, however, we focus primarily on emergency TRAS, which we believe highlights problems that will emerge in future without appropriate action.

Tertiary Reserves Ancillary Services (TRAS) are a mechanism operated by the National Load Dispatch Centre (NLDC) to increase or decrease generation in order to maintain system security and grid stability when real-time conditions indicate potential risk to secure operation. Such conditions might occur during infrastructure outages or, more commonly in 2025, when demand is higher or lower than forecast. TRAS functions as the third line of defence in grid operation, after primary reserve (governor response) and secondary reserve (automatic generation control – AGC) ancillary services. The system operator, NLDC, procures TRAS to meet anticipated needs for up and down regulation.

When the tertiary reserves are unavailable or insufficient, the NLDC triggers emergency TRAS, requiring any eligible ISTS-connected generating station to adjust its output. Stations called upon are compensated financially for the loss of output. Emergency TRAS can be activated with minimal lead time, acting as an emergency operational response rather than a planned dispatch adjustment. The objective is not to optimise schedules but to arrest system instability and preserve grid security under fast-changing conditions.

Due to their operational flexibility, renewable generators are particularly able to provide down regulation, and are often called on for this purpose. For example, according to data reported for ISTS-connected solar projects in Grid-India’s daily VRE (Variable Renewable Energy) reports, on 25 May 2025, approximately 45 GWh of ISTS solar output, was curtailed. This increased to about 93.3 GWh on 12 October 2025.

Non-emergency operational curtailment is activated through the real-time system constraint, led by events like anticipated high frequency and heavy under drawl at the intra-state level. Unlike emergency TRAS-down, such curtailment is not guaranteed to be financially compensated. Volumes under this category of curtailment were relatively low.

The current largest structural driver of renewable energy curtailment in India is the mismatch between the deployment of renewable energy generation and associated transmission infrastructure. Deployment timelines for renewable projects are significantly shorter than those for transmission planning, approvals, and construction, creating a persistent mismatch.

The ISTS-connected renewable energy projects apply for connectivity under the Central Electricity Regulatory Commission (CERC)’s Connectivity and General Network Access (GNA) to the Inter-State Transmission System Regulations, 2022. Under this framework, renewable projects with long-term GNA hold firm and assured evacuation rights on the transmission system. In contrast, projects that are technically ready to generate but whose associated transmission systems are pending commissioning receive a temporary general network access (T-GNA). The temporary access limits scheduling to the residual transmission margin available on the network. When transmission capacity is constrained, allocating available margins to long-term GNA commitments exhausts the network’s residual capacity, leaving little or no margin for evacuation by T-GNA projects. As a result, the system operator lowers the schedules of T-GNA generators due to transmission constraints, leading to curtailment.

In December 2025, for instance, on some days, ~ 4 GW of solar capacity operating under the T-GNA framework faced complete curtailment especially between 11 a.m. to 2 p.m. Unlike emergency TRAS, transmission-constraint-led curtailment is not always guaranteed to be financially compensated and involves tedious process, making it a critical risk for new renewable projects

Transmission infrastructure inadequacy is widely recognised as a risk to renewable energy capacity addition. The central government is actively addressing the issue. Through its Green Energy Corridor initiative, the central government continues to focus on building transmission infrastructure in renewable-rich regions. Most recently, an amendment to the CERC’s General Network Access Regulations introduced time-segmented access during ‘solar-hours’ and ‘non-solar-hours’ to promote optimal utilisation of transmission corridors between solar, wind, and storage projects. In the near term, however, this issue will likely continue to be the largest source of curtailment nationally.