For three days in August 2024, India’s electricity grid witnessed persistent high frequency above the ceiling of 50.05 Hz for 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 plants due to high inflows and high reservoir levels. Inadequate flexibility of intra-state thermal generating stations and under-drawal, insufficient liquidity in the day-ahead and real-time markets (DAM/RTM) in the power exchanges, resulting in states committing more units, also added to the challenges.

A report by the Grid Controller of India said grid frequency remained above the 50.05 Hz limit for 226, 120, and 258 minutes on August 4, 11, and 25, respectively, during solar hours. The maximum instantaneous frequency on these days was 50.39 Hz, 50.33 Hz, and 50.38 Hz, respectively.

On these days, solar penetration as a percentage of the demand at the time of the highest frequency was 19.39%, 21.3%, and 18.45%, respectively.

Similar grid frequency fluctuations were witnessed in December 2022 when the frequency deviated dangerously from the acceptable range of 49.90 -50.05 Hz, oscillating from 50.5 Hz to 49.41 Hz.

In August this year, the Central Electricity Regulatory Commission issued regulations related to the deviation settlement mechanism. These regulations seek to ensure that grid users do not deviate from their schedule of drawal and injection of electricity in the interest of the grid’s security and stability.

The Grid India report said such sustained high-frequency operations threaten grid security. While short-term (real-time, day-ahead, and week-ahead) operational planning can offer only temporary relief, sustainable interventions are needed to manage high frequency in the long term.

Grid India asked all user entities to analyze the events and take measures to ensure the security and reliability of the country’s power systems.

It reiterated its earlier suggestions to enhance flexibility in grid operations. They include:

• Reduction in minimum turn-down level of intrastate thermal stations as per CEA regulations
• Reduction in minimum turn-down level to 40 % of Maximum Continuous Rating (MCR)
• Two-shift operation of selected thermal units with a high energy charge rate
• Incentivize flexible operation by notification of compensation for part load operation and start/stops
• Implementing a resource adequacy framework
• Increase the capacity of long-duration storage
• Power market reforms to reduce fragmentation of the market, raise market cap, and introduce negative pricing
• Frequency response from renewable energy sources
• Curtailment of renewable energy generation as a last resort during sustained high-frequency

As per the Indian Electricity Grid Code (IEGC) 2023, the National Reference Frequency is 50.000 Hz, and the allowable frequency band is 49.900 Hz -50.050 Hz. IEGC mandates that the National Load Despatch Center, Regional Load Despatch Center, and State Level Loan Despatch Center endeavor to keep the grid frequency close to 50.000 Hz. If the frequency goes outside the allowable band, they must restore it within the permissible band of 49.900 Hz – 50.050 Hz as soon as possible.

All grid users must maintain their drawal per schedule to ensure frequency remains within the specified band. On regular days, the frequency remains within the IEGC-specified band for around 75 to 80% of the time.

Drop in Electricity Demand

The Grid India report said a more pronounced reduction in electricity demand was observed after July 31, coinciding with the intensified monsoon activity in the northern states. As a result, electricity demand in August saw a notable decline, fluctuating between 175 GW and 209 GW.

Solar generation remained consistent and stable throughout this period, with daily peaks around 40 GW. Despite the reduction in overall demand, solar generation continued at its typical levels, creating an oversupply situation during peak solar hours.

Wind generation also remained between 20 GW and 25 GW in the first week of August, tapering to between 10 GW and 18 GW later in the month. The high initial wind output and the gradual decline introduced additional variability into the grid, challenging operators to manage the fluctuating wind supply while balancing it with the steady solar output and increasing hydropower generation.

With a record amount of solar installations projected over the next five years, the frequency of grid-related issues will continue to rise unless battery energy storage is urgently integrated into the system.