Flexible Power Generation


Managing large-scale renewable energy integration through flexibility

India has adopted a low-carbon path to meet its growing power demand. The Government of India is actively promoting renewable energy (RE) to bolster energy efficiency and security for the country, reduce oil imports, and improve air quality. The focus on expanding India’s RE capacity — targeted to reach 175 GW by 2022 — represents an immense economic and environmental opportunity but also a huge challenge to grid stability.

Transitioning to a flexible power system

Generation of energy from sources like wind and solar is variable and unpredictable due to changing weather conditions. Large-scale integration of this variable RE into the electricity grid necessitates changes in the functioning of existing power generating capacity, which in India is largely coal-based, so that grid reliability and stability are not compromised. India’s RE integration plans, thus, critically hinge on its coal-based power plants having the flexibility to tune their generation responsively to variable RE generation. An evidence-based approach to this critical imperative has been demonstrated by the Greening the Grid-Renewable Integration and Sustainable Energy (GTG-RISE) program, a partnership between the United States Agency for International Development (USAID) and the Ministry of Power (MoP), Government of India. GTG-RISE conducted a series of prioritized innovation pilots and demonstrations to validate technologies and solutions to support large-scale RE integration into the Indian power grid.

The GTG-RISE pilot on coal-based flexible generation supports the Ministry of Power’s efforts to build a resilient and self-reliant power sector and meet India’s ambitious RE goals.

Evidence-based approach to mitigating operational challenges

GTG-RISE conducted a four-year (2017–2020) pilot to identify the technical interventions and operational changes needed to implement flexibility in coal-based pants. The pilot was undertaken at a total of four coal-fired units in partnership with power utilities at national and state levels: at the national level with National Thermal Power Corporation Limited (NTPC), which produces almost 74% of India’s coal-based power generation, and at the state level with Gujarat State Electricity Corporation Limited (GSECL).

The pilot leveraged best practices and international experience as it studied flexibility needs of coal-fired plants and the techno-economic impact on plant equipment’s life. GTG-RISE carried out detailed technical feasibility studies at the four pilot sites/units (a total of 1,400 MW) to assess the units’ preparedness, including the technical interventions needed for flexibility and their cost implications. The studies were followed by low-load test runs, conducted based on the procedure developed by GTG-RISE in collaboration with Bharat Heavy Electricals Limited (BHEL). Low-load test runs were conducted at NTPC’s Mouda unit in Maharashtra and GSECL’s Ukai unit, with gradual reduction of technical minimum up to 40% while maintaining all other operating parameters under stable conditions and without any supplementary oil firing support. The test runs gauged the responsiveness of plant equipment when subjected to low loads on a sustained basis. Data from test runs was analyzed to arrive at comprehensive recommendations about the specific changes needed in operational practices and procedures and the retrofits/upgrades required. The pilot also built the capacity of key plant personnel for flexibility operations; more than 500 plant engineers and officials were trained through trainings, knowledge dissemination workshops, and executive exchanges.

Over its past four years, the coal flexibility pilot made a notable impact, providing a comprehensive set of recommendations that can prove the building blocks for nationwide rollout of flexible operations at coal power plants. In addition to NPTC and GSECL, the pilot’s results also lent inputs and support to the Central Electricity Authority (CEA), Central Electricity Regulatory Commission (CERC), and Power System Operation Corporation Limited (POSOCO). It provided robust data and evidence on flexible operations to these lead power sector entities in India, supporting them to identify, address, and bring out changes to existing policies, guidelines, and regulations in the near future. The key recommendations emanating from the pilot have been captured in a summary report, titled ‘Transition towards flexible operations in India’ (available at https://www.gtg-india.com/). Some key outcomes of the regulatory consultation paper, including increased operations and maintenance (O&M) cost due to life consumption on account of cyclic operation and higher cost from increased oil consumption due to frequent start/stops, etc., got featured in the CEA report on coal flexibility, tilted ‘Flexible operations of thermal plants for integration of renewable generation’ (2019).

Paving the way for successful RE integration

The pilot’s studies and test runs have generated evidence to inform the development and implementation of a long-term flexibilization roadmap for the county and boost integration of renewables. Importantly, the pilot has built a business case for policy and regulatory changes to implement coal flexing on a larger scale in India.

Some of the pilot’s recommendations are already being adopted: NTPC is retrofitting Nitrogen sparging and blanketing system across its country-wide thermal power plants to prevent long-term corrosion damage during flexible operations. Further, based on the experience and learning from the flexibility study of Ukai TPS Unit # 6 (500 MW), GSECL has finalized the scope for major renovation and modernization (R&M) at Ukai TPS Unit # 3 and # 5, covering the majority of requirements for flexible operation. The scope covers the minimum technical load of 40% without oil support as well as control and instrumentation (C&I) upgrade to facilitate flexible operation.

In what is a crucial testimony to the pilot’s success and part of its scalability efforts, GTG-RISE has also supported Karnataka Power Corporation Limited (KPCL) to scale up its interventions and make its coal plants more flexible. Based on the project’s inputs, KPCL is conducting similar studies at two of its units (BTPS Unit #2 500 MW and RTPS Unit #5 200 MW).

The flexibility pilots with NTPC and GSECL have also contributed to the broader objective of reducing greenhouse gas emissions, with an estimated 24.25 MMtCO2e reduction at the pilot level and potential 714.83 MMtCO2e reduction by 2030. The pilot has set standards for flexing coal-based plants in the country to balance the grid in the face of increasing variable RE penetration. Its results have served to improve the capacity of participating Indian states to finance and manage growing levels of grid-tied RE and establish new mechanisms to balance variable RE in the country.

Insights from the pilot will go a long way to support the country in addressing variability in RE generation effectively, a critical achievement that will spur progress on India’s decarbonization journey.

Success at a glance


  • To download the pilot success story, please click here.

Events & Activities

To share knowledge with and train stakeholders, various workshops, bootcamps and executive exchange programs have been organized, under the USAID’s GTG program, on Coal Generation Flexibility so far.


India is witnessing unprecedented expansion of its renewable energy (RE) capacity, driven by the Government of India’s strong commitment to decarbonization. The country has set ambitious clean energy goals, with a target of reaching RE capacity of 175 gigawatt (GW) by 2022 and 450 GW by 2030. As renewable sources like wind and solar are variable and have unpredictable generation, their increased deployment demands a fundamental change in how power systems operate. Studies suggest that integration of 175 GW of RE into the power grid will lead to daily net load swings of more than 80 GW and pose techno-commercial challenges, necessitating the overall power generation to be more responsive and flexible.

In India, given the country’s limited gas and hydropower resources, coal-based thermal power plants is the preferred choice for flexibility to accommodate RE. Thermal power plants must adjust their output based on power generation from RE to ensure there is no ‘over-generation’ in the power system, which can lead to frequency-based grid instability, and subsequently even grid collapse. When there is more RE power in the system during daytime, coal plants must reduce their generation to the technical minimum but increase their output in the evening when RE generation starts declining. In some instances, coal plants may have to start and stop frequently to ensure grid stability. Ignoring such flexibility requirements can lead to severe grid imbalance. Proactive attention and effort toward securing flexibility in operations of coal-based power plants is thus an imperative.

USAID’s GTG-RISE pilot was conceived to mitigate the operational challenges that large-scale RE integration would pose for grid performance. The overarching aim was to ascertain coal-based generation units’ technical and commercial feasibility for faster ramp up/ramp down of operations in response to variable RE and the technical minimums needed vis-a-vis the existing operational procedures, equipment, processes, and practices. The pilot also sought to identify the measures and interventions (including retrofits and operational changes) needed and the cost of such interventions. It also aimed to examine the compensation requirements due to cycling, conduct low-load test runs at select units, and strategize on fleet-wide operations of utilities with coal-based units.

The pilot’s specific objectives were to:

  • Study and recommend the changes required in coal-based power plants
  • Estimate the cost of achieving flexibility, including initial capital investment and operational and maintenance expenses
  • Support in building a business case with associated commercial compensation mechanisms for flexibility to inform discussions with MoP, CEA, and Central Electricity Regulatory Commission (CERC)
  • Provide insights to CERC on compensation for generation units to act as flexible units
  • Train and enhance capacity of stakeholders through knowledge dissemination workshops and other events
  • Ensure scale-up and replicability of the pilot for larger adoption of flexible operations

Stage 1: Techno Economic Assessment & Roadmap

  • Technical due diligence and detailed feasibility assessment
  • Establishing reliable costs of flexibilisation – capex as well as opex

Stage 2: Regulatory Pathway and Fleet Level Strategies

  • Assistance in framing Regulatory Mechanisms for Flexibility.
  • Assistance in building fleet level strategies for NTPC / GSECL

Stage 3: Pilot Implementation

  • Technical Assistance in pilot / fleet level implementation to NTPC
  • Leverage private partnerships and contribution in investments

Stage 4: Scale up

  • Assist in fleet-wide implementation and national scale up
  • Capacity building of operators – Procedures and Operational Toolkits

Large-scale integration of RE introduces additional variability and uncertainty into the power system, making conventional power stations’ responsiveness and operational flexibility critical to sustain grid reliability and stability. The Government of India’s Ministry of Power (MoP) and the Central Electricity Authority (CEA) have taken cognizance of this imperative and set an agenda for thermal units to operate in tandem with RE generation. In support of this new operating regime for greater integration of RE, the GTG-RISE initiative conducted a pilot on flexible generation of coal-based power plants. The case study provides more in depth details of the GTG-RISE Pilot overview, interventions, impacts, successes and scalability roadmap for the flexible generation in India. For more information please download the case study here.

The central component of GTG, RISE initiative, aims to design, implement and scale-up series of prioritized innovation pilots that support the integration of RE into the grid. Each pilot has its own implementation roadmap, stakeholder commitments, coordination and collaborations and periodic reviews by appropriate Government and regulatory counterparts. Towards this, a ‘Pilot Review Board’ (PRB) has been established for each pilot with an aim to promote transparency, ownership and accountability with the key GOI counterpart and other key stakeholders. PRB envisages to guide to address challenges, support stakeholder participation, help promote pilot awareness and lessons learned, and contribute to the sustainability of the individual pilots. PRBs is also there to review the ongoing performance of pilot activities and to recommend corrective action to maximize sustainability and minimize risk if any. Likewise PRBs will also review the challenges met or overcome in the scaling of pilot activities and make recommendations to support scaling.

Each innovative pilot requires different skill sets of technical expertise and respectively necessitates separate PRB for the pilot. The nominated PRB members represent policy makers, state and central regulatory bodies, grid operators, relevant utilities and even representatives from Original Equipment Manufacturers (OEMs)/Associations. Supported by GTG-RISE team, USAID’s Contracting Officer Representative (COR) for GTG-RISE initiative is the convener of the PRB. The PRB Members details for pilot on flexible operation of coal power plants are provided below:

Member Name Member Designation Member Organization
B C Mallick Chief Engineer Central Electricity Authority (CEA)
Rajeev Kumar Director CEA
Alok Kumar Sr. Dy. General Manager POSOCO
Saif Rehman Dy. Manager POSOCO
Somesh Bandyopadhyay General Manager NTPC
Arun Kumar Roy Deputy General Manager NTPC
B A Gandhi Executive Engineer GSECL
Monali Zeya Hazra Contracting Officer Representation (COR) USAID/India GTG-RISE
Shubhranshu Patnaik Chief of Party (COP) USAID GTG-RISE Initiative