The increasing integration of renewable energy continues to stress India’s electricity grid, causing repeated frequency fluctuations. The grid has seen persistent high frequency above the ceiling on 39 days in the third and fourth quarters of the financial year 2024-25, triggering concerns among grid operators and regulators.

The frequency was above the Indian Electricity Grid Code (IEGC) band of 49.90-50.05 Hz for over 20% of the time on these days during the two quarters.

The high-frequency periods were attributed to increased levels of solar power injection and the limited flexibility to reduce thermal generation to accommodate renewable energy production. On certain days, the down reserves during solar hours were completely depleted.

Adding to the challenge is the requirement that thermal power projects run during non-solar hours to ensure resource adequacy. These projects cannot be taken out of service during the high-frequency operation period.

According to a presentation made by Grid-India to the National Committee on Transmission in April this year, the current maximum instantaneous penetration of variable renewable energy has touched ~37%. It is expected to cross 40% in February-March 2026, likely exacerbating the situation.

Another challenge being faced is meeting the ramping requirement during evening hours. During this period, flexibility requirements increased significantly due to the increasing demand ramp and the simultaneous decline in solar generation.

The grid has recently experienced many high-frequency operations. For three days in August 2024, high frequency above the ceiling of 50.05 Hz was witnessed 26% to 38% of the time. All three days were Sundays, when power demand usually drops. The contributing factors were the over-injection of solar and wind energy, limited flexibility from hydropower stations, and pumped storage projects.

These high-frequency episodes prompted the Central Electricity Regulatory Commission (CERC) to issue directions to the national, regional, and state load despatch centers to ensure grid frequency remains close to 50 Hz. It said all users must adhere to their schedule of injection or drawal.

Power generator NTPC had told CERC that under IEGC-2023, generators have a supply obligation. However, beneficiaries have no corresponding obligation to give equal to or more than the minimum turndown level (MTL) schedules required for safe and reliable operations of the thermal power generating stations.

This has allowed beneficiaries to give schedules based on their consideration and ignore the technical requirement of the thermal units, resulting in stations continuing to receive infeasible schedules (full schedule during peak hours and negligible or less than MTL schedule during off-peak hours).

The central regulator noted that thermal station over-injection in a time block reached as high as 2,200 MW last August.

It suggested that a two-shift operation of some thermal plants be considered to address the challenges faced in meeting the demand during evening hours with thermal power and low demand for such power during solar hours.