India needs to integrate its rapidly expanding renewable energy sector with its coal-based power fleet to ensure a smooth and cost-effective energy transition, according to a new study by the Centre for Science and Environment (CSE).
The study, Flex to Fix: Deciphering India’s Coal Flexibilisation Challenge for RE Integration, estimates that coal power flexibilisation could create an additional 18-34 GW of space for renewable energy and potentially reduce power-sector emissions by 7.66-8.37 per cent, equivalent to 92-101 million tonnes of CO₂ annually.
CSE released the study along with another report, Beyond Baseload: Reforming Thermal PPAs for India’s Energy Transition, at a national dialogue in New Delhi on Friday. The event brought together representatives and experts from the Central Electricity Authority (CEA), Central Electricity Regulatory Commission (CERC), GRID-India, Bharat Heavy Electricals Limited (BHEL), National Thermal Power Corporation (NTPC), Torrent Power, think tanks, civil society and academia.
The discussions focused on how coal power flexibilisation and reforms in thermal power purchase agreements (PPAs) could facilitate greater renewable energy integration, improve grid stability and keep electricity costs affordable for consumers.
“That is our central challenge,” says Sunita Narain, Director General of Centre for Science and Environment (CSE). “The growth and transformation that India’s power sector is witnessing has meant that we must work towards greater flexibility in the grid. Enhancing the flexibility of the existing coal fleet can play a role in balancing the system and enabling greater integration of renewable energy.”
“We are not talking about renewable vs coal here. We are talking about renewable and coal, and about how to integrate the two. The task is not to replace coal, but to displace it,” adds Narain.
Renewable growth puts pressure on conventional generation:
India reached 50 per cent non-fossil-based installed power capacity in November 2025, five years ahead of its original 2030 target. However, the rapid expansion of renewable energy, particularly solar power, has changed the demand-supply dynamics of the electricity grid.
According to Parth Kumar, Programme Manager, Sustainable Industrialisation unit, CSE and one of the lead authors of the reports, solar capacity has increased 3.5-fold in the past six years and now exceeds 160 GW.
“The problem, however, is the rapid growth in RE (renewable energy), particularly solar energy — which has seen a 3.5-fold capacity increase in the last six years and now exceeds 160 GW — has fundamentally altered the demand-supply balance in the grid. This has resulted in creation of deep variability and operational stress across the day in conventional generation, leading to instability in the national power grid. The consequences have been significant economic and environmental losses.”
The study notes that GRID-India recorded multiple instances in 2024 when grid frequency breached the 49.9-50.05 Hz threshold, increasing the risk of grid disturbances and blackouts due to over-injection by thermal generating units. According to the report, the risk has increased with the continued rise in solar penetration.
What is coal flexibilisation?
Coal flexibilisation involves modifying and operating coal-fired power plants so they can vary their generation more quickly in response to changes in electricity demand and renewable generation.
“When solar and wind are producing plenty of electricity, the coal plant can reduce its output. When renewable generation falls — such as during night-time — or demand rises, it can quickly increase generation again,” Kumar explains.
Such flexibility requires changes to plant equipment and control systems, as well as operational modifications. Plants need to operate safely at lower loads, ramp generation up and down more quickly and withstand more frequent start-ups and shutdowns. The process can also require improved maintenance and fuel management, operator training and upgrades to plant controls and other equipment.
Flexibilisation could reduce the need for additional storage:
The CSE study argues that coal flexibilisation can provide a cost-effective source of flexibility while India expands battery storage, hydro and other balancing resources.
Kushagra Goyal, Senior Research Associate, Sustainable Industrialisation unit, CSE, said the role of coal cannot be overlooked as it remains the country’s largest source of electricity generation.
“Our research shows coal flexibilisation remains a cost-effective option. In fact, the systemic benefits of flexibilisation extend beyond cost-effectiveness and can provide much greater flexibility to the power grid. Gas, hydro and battery storage are significant and critically important solutions, but with coal still continuing to be the largest source of power, we cannot overlook its role in meeting the system-wide flexibility needs of an evolving power system.”
According to the study, India currently has only around 3 GWh of battery storage capacity in operation against a target of 34.72 GWh. Without coal flexibilisation, the country could require an additional 184.4 GWh of battery storage, potentially increasing system costs.
The report estimates that coal flexibilisation could add between Rs 0.272 and Rs 0.457 per kWh to tariffs, depending on the technology, age and condition of individual plants.
The study also draws on experiences from China, Chile and Germany, concluding that coal flexibilisation can serve as a transitional measure for increasing renewable energy penetration while delivering additional CO₂ reduction benefits.
B C Mallick, Principal Chief Engineer II, CEA, also backed the approach at the report release.“Flexibilisation offers a low-cost, technically feasible solution that can be deployed immediately.”
CSE recommendations:
CSE has called for a series of measures to accelerate coal power flexibilisation in India. These include conducting baseline studies of individual generating units to assess their technical condition and readiness, as well as determining compensation requirements for equipment damage and life consumption.
The organisation has also recommended comprehensive and aligned tariff coverage by the Centre and states to account for life consumption, testing periods and operator training. It has called for wider adoption of regulatory frameworks supporting thermal flexibility.
CSE further recommends replacing an approach based largely on penalties with stronger incentives, including preferential treatment in Merit Order Dispatch or lump-sum payments for plants that meet specified flexibility targets.
It has also called for a review of the phasing plan for coal power flexibilisation, with priority given to efficient, lower-emission plants based on heat-rate and emissions performance.
Nivit K Yadav, Programme Director, Sustainable Industrialisation unit, CSE, said greater policy certainty would be necessary for thermal power companies to invest in retrofits and adjust their operating schedules.
“Thermal power plants need policy certainty to plan the retrofits and align their schedule to incorporate these recommendations. Flexibilisation is the bridge between today’s coal-dependent system and a future renewable-dominant grid. Without redressal and correction in implementation and regulatory alignment, India risks undermining the hard-won gains of its renewable energy transition.”
(A CSE media briefing)
