New Delhi: Amid concerns over the impact of intermittent renewable energy generation on grid stability, state-run NTPC has decided to install flexible coal-based thermal power units to provide balancing support and ensure reliable power supply.The power giant said the rapid expansion of renewable energy capacity is transforming the power sector and driving the country’s clean energy ambitions, but its growing share is also driving the need for flexible power sources that can respond quickly to changing grid conditions.NTPC has invited expressions of interest for sub-critical thermal power units of 150-250 megawatt (MW) capacity that can operate in two shifts and run at a minimum technical load of 25% of their installed capacity. These units are intended to balance fluctuations in electricity demand and renewable energy production rather than operating continuously at full load.“Through this initiative, NTPC aims to identify technology providers and EPC (engineering, procurement and construction) partners to develop highly flexible thermal generation solutions that strengthen their commitment to grid reliability, sustainability and India’s growing energy transition needs,” the company said.NTPC said its entire thermal fleet was currently operating at a technical minimum load of 55% during low demand periods and providing various grid-support services that help maintain frequency, keep reserve power available and adjust generation in response to fluctuations in renewable energy generation, thereby improving grid resilience and reliability.With limited hydropower capacity, gas-fired generation and large-scale energy storage systems to balance the grid, thermal power plants continue to play an important role in supporting the electricity supply.While solar energy contributes about 25% of the daytime electricity demand, its intermittent nature due to weather conditions, seasonal variations and geographical factors requires continuous support from thermal plants to maintain stable power supply and grid frequency. The role of thermal plants increases at night when solar energy is not available.Stating its preference for the technology, NTPC said its operational experience shows that sub-critical thermal units can provide greater flexibility than supercritical and ultra-supercritical technologies for certain grid-balancing requirements due to lower operational stress due to smaller parameter variations. The company said their ability to operate efficiently at low loads and adapt to frequent start-stop cycles could make them an important enabler for higher renewable energy integration in the future.