New Delhi: State-run NHPC Limited informed the stock exchanges on Wednesday that the test synchronisation of the 250 MW Unit-2 of the 2,000 MW Subansiri Lower HE Project with the national grid “has been successfully achieved on 02.12.2025 (evening).” The company added that “the Commercial Operation (CoD) of Unit#2 is expected in the month of December, 2025.”
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The Subansiri Lower Hydroelectric Project is a run-of-river scheme with water storage on the Subansiri river at Gerukamukh on the Assam–Arunachal Pradesh border, designed with eight units of 250 MW each to deliver 2,000 MW, making it India’s largest hydroelectric project by installed capacity once fully commissioned. NHPC has said the project is expected to generate around 7,400–7,500 million units of electricity annually in a high-dependability year, strengthening grid stability and supporting power demand in the North East as well as the wider national grid.
Construction at Subansiri has faced prolonged delays due to environmental concerns, local protests and repeated monsoon-related damages, pushing the expected completion date far beyond the original December 2012 schedule and inflating the cost from an initial estimate of about Rs 6,285 crore to roughly Rs 26,075 crore. NHPC has reiterated that despite recent monsoon incidents described as causing “minor damages”, there is “no risk at all to the dam structure,” while acknowledging that such events have contributed to the slippage in commissioning timelines.
Unit-1 of Subansiri Lower entered wet commissioning in October 2025, with NHPC confirming that a 250 MW unit had been test-run and that four units in total were ready for test runs at that stage. Following wet commissioning, the company outlined that the next step would be to synchronise at least two units with the national grid, paving the way for initial power generation; with Unit-2 now test-synchronised, a combined 500 MW can be progressively brought into operation as procedures are completed.
Earlier guidance from NHPC and project-related disclosures indicated a plan to commission three units of 250 MW each starting from June 2025, subject to National Dam Safety Authority clearance, with the remaining five units to follow in phases by May 2026. More recent updates, however, have pointed to commissioning of the full 2,000 MW being pushed out to around May 2026, reflecting the impact of fresh site challenges and reworked schedules. In its latest investor commentary, NHPC has projected that regulated equity for Subansiri Lower will be fully factored in from financial year 2026–27, implying a material step-up in earnings contribution once all units are commercially operational.
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With the test synchronisation of Unit-2, NHPC moves closer to unlocking a large chunk of new regulated hydro capacity, reinforcing its position as a leading central public sector hydropower utility. Company executives have previously highlighted that full commissioning of Subansiri Lower could add several thousand crore rupees to annual revenue and support the government’s broader clean-energy and grid-balancing objectives by providing flexible peaking power from the North Eastern region.