Guwahati: NHPC Limited has commissioned the fourth unit of the 2,000 MW Subansiri Lower Hydroelectric Project (SLHEP), taking the project’s operational capacity to 1,000 MW.
The 250 MW Unit 4 of the project, located along the Assam-Arunachal Pradesh border, commenced commercial operations from midnight of May 8, NHPC said in a statement.
With the latest commissioning, four of the project’s eight generating units are now operational. Unit 2 was commissioned in December 2025, followed by Unit 3 in February 2026 and Unit 1 in March this year.
NHPC said the remaining four units are scheduled to be commissioned in phases by the end of 2026.
The Subansiri Lower Hydroelectric Project, being developed on the Subansiri river, is expected to generate around 7,421 million units of electricity annually after full commissioning. The state-owned power producer said the project would help meet peak electricity demand, strengthen grid stability and support integration of renewable energy into the national grid.
The project, however, has had a prolonged and contentious history since construction began in 2005 after forest clearance was granted in 2004.
Work remained suspended between December 2011 and October 2019 following widespread protests in Assam over safety concerns, seismic vulnerability and downstream ecological impact. Construction resumed after legal challenges before the National Green Tribunal (NGT) were resolved and certain design modifications were introduced.
Originally scheduled for completion in 2012, the project has witnessed a steep escalation in cost. NHPC said the project cost has risen from an initial estimate of Rs 6,285 crore in 2002 to around Rs 27,000 crore at completion.
The company said the project incorporates multiple environmental and safety measures, including sediment management systems, flood moderation provisions and year-round environmental flow releases to maintain downstream ecology.
NHPC also stated that no habitation would be submerged by the project and that compensation and rehabilitation measures are being implemented in accordance with the Arunachal Pradesh Rehabilitation and Resettlement Policy.
The company said compensatory afforestation activities are being carried out in Assam and Arunachal Pradesh through CAMPA funds. It added that riverbank protection works, flood forecasting systems and early warning mechanisms have also been put in place downstream.
Apart from power generation, NHPC said investments have been made in healthcare, education, drinking water, livelihood support and skill development in project-affected areas.