State-owned NHPC has commenced commercial operations of the second unit of the 2,000 MW Subansiri Lower Hydroelectric Project, with Unit-2 (250 MW) declared operational from 00:00 hours on December 23, 2025, according to a stock exchange filing. The 8×250 MW run-of-the-river project is located at Gerukamukh near North Lakhimpur, along the border of Arunachal Pradesh and Assam, and involves regulated water storage on the Subansiri river. Developed under the Ministry of Power at an estimated cost of about Rs 270 billion, the project will house eight Francis-type turbines and, once fully commissioned, will be India’s largest hydroelectric power station with an installed capacity of 2,000 MW. NHPC Director (Projects) Sanjay Kumar Singh visited the site to oversee the start of commercial operations, inspecting key infrastructure including the main dam, diversion tunnel and spillway structures, and reviewing pending works with contractors and stakeholders. Unit-1 (250 MW) was successfully test-synchronised with the national grid on December 3, signalling operational readiness. NHPC said the project is expected to generate around 7,421.59 million units of electricity in a 90 per cent dependable year. The remaining four units are scheduled for sequential commissioning during 2026–27, further strengthening national power supply. Construction of the concrete gravity dam—116 metres high from the riverbed and 284 metres long—began over two decades ago. The project faced prolonged delays due to technical, environmental and social challenges, including an eight-year halt between 2011 and 2019 amid protests and legal proceedings over dam safety and downstream ecological concerns. Work resumed in October 2019 following strengthened mitigation measures. NHPC officials said the Subansiri project is designed as a run-of-the-river scheme, leveraging natural river flows while limiting construction scale and environmental impact compared with large reservoir projects, aligning with India’s push for scalable and ecologically sensitive hydropower development.