The Indian power grid is navigating a complex transition, driven by the increasing integration of renewable energy sources. This shift towards sustainability introduces operational intricacies, particularly in maintaining the delicate balance of grid frequency. Recognising the challenge of high-frequency grid operations, the Central Electricity Regulatory Commission (CERC) has issued a suo motu order outlining a comprehensive strategy to mitigate associated risks and enhance grid stability. This approach addresses the root cause of high frequency, encompassing thermal power plant flexibility, state-level demand management and the operational dynamics of renewable energy generation.
Background
The impetus for the CERC’s intervention stemmed from Grid Controller of India Limited’s (GRID-INDIA) report highlighting recurring instances of grid frequency exceeding the permissible Indian Electricity Grid Code band 49.900-50.050 Hz during August 2024. Prolonged periods above 50.05 Hz on August 4, 11 and 25, 2024, with peak frequencies reaching alarming levels, underscored the urgent need for corrective measures. GRID-INDIA attributed these high-frequency episodes to a confluence of factors including suppressed demand due to weather and weekend effects, over-injection by intermittent variable renewable energy sources, limited flexibility of hydro and pumped storage, inadequate responsiveness from intra-state thermal plants, coupled with under drawal by some states, a scarcity of interstate down reserves and market dynamics encouraging inflexible operational practices.
As per the CERC’s analysis, the issue of high frequency arose due to the thermal generators’ obligation to maintain their minimum technical loading, leading to over-injection during periods of low demand. Simultaneously, the merit order despatch principle, prioritising renewable energy, could result in thermal plants being scheduled below minimum technical loading during solar hours, yet required to remain online for the evening peak. The economic incentives for discoms to procure cheaper power from the market during off-peak hours further exacerbated this issue, leading to erratic scheduling that disregards the technical constraints of thermal units.
CERC’s response
The regulator’s response is multifaceted, targeting key contributors to high-frequency events. A cornerstone of this strategy is the introduction of a pilot project for the “two-shift operation” of selected regional thermal generating stations. Recognising the inherent design capabilities of modern thermal plants for flexible operation, the initiative aims to optimise power plant utilisation by allowing them to ramp down or shut down during periods of low demand (typically during peak solar generation hours) and ramp up to meet the evening peak demand. To incentivise participation in the mechanism, the CERC has proposed a compensation of 20 paise per kWh for the down reserve created by these units during their off-bar periods. The National Load Despatch Centre (NLDC) has been entrusted with the task of identifying suitable units, preferably rail-fed 500 MW plants, and formulating a detailed operational procedure within two months. A comprehensive feedback report on the pilot’s impact, both operational and financial, is mandated after six months.
Addressing the issue of underdrawal by states, the CERC reiterated the importance of intra-state generating stations operating at flexible minimum turndown levels (MTLs), aligning with the provisions for interstate plants. The regulator noted the concerning instances where states with available generation reserves were simultaneously overdrawing power during high-frequency events, highlighting a need for better coordination and utilisation of state-level resources. The ongoing efforts of a subgroup, under the aegis of the Forum of Regulators, to assist state thermal plants in lowering their MTL up to 55 per cent underscore this focus on enhancing flexibility at the state level.
The CERC also observed the events of over-injection by renewable energy generating stations (REGS) contributing to high-frequency episodes. Data for August 25, 2024 revealed substantial over-injection by REGS, even when the grid frequency was already elevated. The regulator noted the existing deviation settlement mechanism regulations, which, until recent amendments, allowed over-injection by renewable energy within a certain band without penalty, even during high-frequency conditions. While acknowledging the recent amendment that reduces charges for over-injection of scheduled infirm power during high frequency (above 50.05 Hz) to zero, the CERC emphasises the need for active participation of REGS in maintaining grid stability.
In this context, the CERC has directed the NLDC to furnish data on the primary response ancillary services (PRAS) provided by REGS during the high-frequency events. Despite the Grid Code mandating PRAS capability for specified wind and solar sellers, there is no clear record of their actual response. Furthermore, recognising the increasing controllability of REGS equipped with power plant controllers, the CERC has tasked the NLDC with identifying additional REGS, including wind sources, for a pilot study on operationalising automatic generation control (AGC). The NLDC is required to submit implementation modalities and suitable commercial mechanisms to incentivise AGC participation from REGS within three months.
Looking forward to long-term solutions, the CERC has also directed its staff to explore the modalities for implementing energy storage systems at thermal generating stations. This forward-thinking approach aims to capture excess renewable energy during periods of high generation and low demand, effectively preventing over injection and providing a valuable resource for grid balancing during peak demand or periods of low renewable output.
In essence, the CERC’s suo motu order represents a comprehensive and proactive strategy to address the growing challenges of maintaining grid stability in an era of increasing renewable energy penetration. By focusing on enhancing the flexibility of thermal power plants through two-shift operations, promoting better demand-side management at the state level, and actively engaging renewable energy generators in grid balancing mechanisms, the regulator is laying the foundation for a more resilient, reliable and sustainable Indian power system. The emphasis on pilot projects, data-driven analysis and stakeholder consultation underscores a pragmatic and adaptive approach to navigating the complexities of the energy transition. The successful implementation of these measures will be critical in ensuring a secure and affordable power supply for India’s future.
Aastha Sharma