India’s energy transition is at a crossroads. Driven by a changing climate, a growing population and rapid urbanisation, electricity demand has risen sharply over the past decade. Peak demand has climbed from about 135 gigawatts (GW) in 2013 to over 270 GW in 2026. India’s renewable capacity is expanding at an unprecedented pace, too. By November 2025, half of the country’s installed power capacity was based on non-fossil fuels, five years ahead of its original 2030 target. Solar has been the star performer: its installed capacity has more than tripled in six years, surpassing 160 GW in 2026. Its share of electricity generation rose from 3.6 per cent in 2019-20 to 8.9 per cent in 2025-26, according to the Central Electricity Authority (CEA).
This rapid growth could help close the demand-supply gap while decarbonising a power sector that still relies on fossil fuel coal for roughly two-thirds of its electricity generation. Instead, it has exposed a weakness in the system: parts of the grid cannot absorb all the clean electricity India produces. Renewable generation has, in other words, outpaced the infrastructure needed to integrate it. Why? To understand the challenge, and what can be done about it, one must first know how the power system works.
Power systems are typically built around conventional generators, most of them fossil fuel-based. In India, the power grid relies heavily on coal-fired plants. These are designed to run for long periods at relatively high-capacity utilisation, or plant load factors (PLFs), and provide a steady, reliable output (base-load power) to meet constant electricity demand and economic efficiency. Continuous generation from these synchronous or base-load power plants ensures grid stability by maintaining frequency and voltage levels.
The National Load Despatch Centre (NLDC), under the national grid operator Grid-India, is at the top of the dispatch hierarchy. Supported by five regional load despatch centres, NLDC ensures integrated working of the power system, which operates in 15-minute blocks, with 96 blocks making up a day. Generators receive day-ahead schedules based on forecasts of demand, available generation and network constraints, and adjust output as actual conditions diverge from those forecasts.
This system worked reasonably well when most electricity came from coal-fired plants that could generate continuously and adjust output when instructed. Renewables are different. Solar generates most of its electricity during the day and none after sunset. Wind output varies with the weather. Demand, mean- while, follows its own rhythm, shaped by temperature, economic activity, industrial schedules, festivals and even the time of day. Electricity demand typically rises in the early morning from 6 am, as households and businesses begin their day and peaks around 3 pm-4 pm. A second sharper rise is recorded between 6 pm and 10 pm. Solar generation does almost the opposite: it rises through the morning, peaks around midday and falls rapidly towards sunset, just as demand is approaching its evening peak. The resulting gap, at times, is so steep that coal-fired plants fail to ramp up their production to cater to the demand.
Around midday, as solar output rises, the opposite happens: net demand—the amount of electricity that must be supplied by conventional generators after accounting for renewable generation, which enjoys “must-run” status under the central and state grid codes—falls sharply. Plot the two movements together and the curve resembles a duck: a deep trough during solar-rich hours followed by a steep evening climb. Hence the term “duck curve”.
Analysis of Grid-India’s daily power supply data by the Centre for Science and Environment (CSE), a research and advocacy organisation in Delhi, shows that India’s “duck curve” is beginning to deepen …
This article is part of the cover story "Coal's new flex", originally published in the August 16-31, 2026 print edition of Down To Earth