NHPC Subansiri: Unit 4 COD takes output to 1,000 MW

What NHPC announced on Unit 4

State-owned NHPC said it has started commercial supply of electricity from the fourth unit of its 2,000 MW Subansiri Lower Hydroelectric Project. In an exchange filing, the company declared the commercial operation date (CoD) of Unit 4 from 00:00 hours on 08.05.2026. NHPC also said that with this declaration, the CoD of four units of the project has now been announced. The remaining units will be informed “in due course,” as per the company’s filing. The Subansiri Lower project is one of the largest hydropower projects under execution in India. The latest unit-level milestone matters because commercial operation enables formal power supply and billing under applicable grid and offtake arrangements.

Project snapshot: capacity, location, and cost

NHPC is building the Subansiri Lower Hydroelectric Project with a planned capacity of 2,000 MW. The project comprises eight generating units of 250 MW each. It is located near North Lakhimpur along the Arunachal Pradesh and Assam border, and references to Gerukamukh and the Subansiri River place it along the inter-state boundary. NHPC has described it as a run-of-river hydroelectric scheme. The company has put the project cost at around ₹27,000 crore. As additional units achieve CoD, more capacity is expected to be available to the National Grid on a phased basis.

How the commissioning has progressed so far

NHPC’s updates over time show a step-by-step commissioning process across individual units. One milestone cited was the successful synchronisation of Unit 1 (250 MW) with the National Grid at 9:00 pm on January 31, 2026. Shortly after, Unit 3 (250 MW) commenced commercial operations at midnight on February 1, 2026. Separately, NHPC declared commercial operation of Unit 3 from 00:00 hours on 01.02.2026 in an exchange filing. For Unit 2, NHPC said commercial operations began on 23 December 2025, and the unit was virtually inaugurated by Union Power Minister Manohar Lal. With Unit 4 now declared under commercial operation effective May 8, 2026, NHPC has indicated that four units have achieved CoD.

Why “CoD” matters for a power project

The commercial operation date is a formal milestone for a generating unit. It marks when the unit is considered available for commercial supply under relevant rules and contracts. In practical terms, CoD is linked to when electricity can be scheduled and supplied on commercial terms, subject to applicable procedures. It also signals that a unit has completed key commissioning requirements needed for regular operations. NHPC’s filing-based disclosures typically use CoD to communicate these transitions to the market. Investors and power-sector stakeholders track CoD announcements because they indicate the pace at which planned capacity is moving from construction to operations.

Delays and the longer history of the Subansiri Lower project

The Subansiri Lower project has had a long development timeline. The original completion schedule was December 2012, according to the information provided. The commissioning was later delayed to May 2026 from an earlier announced end of the 2023-24 fiscal year. NHPC had commenced construction in January 2005 after obtaining forest clearance in October 2004, and the project received approval in January 2005. The project’s timeline is also described as “much-delayed,” with partial commercial production starting more than 13 years after the original schedule. Another update notes that after legal hurdles and clearance from the National Green Tribunal, NHPC resumed construction on October 15, 2019.

What partial operations mean for the grid

As units come online, they add incremental capacity to the National Grid. NHPC previously said that with the commissioning of Units 1 and 3, the project had contributed 500 MW of its planned 2,000 MW capacity to the National Grid at that stage. With the latest statement that CoD for four units has been declared, the implied commercial capacity under CoD is 1,000 MW (4 units x 250 MW). NHPC has also stated that, upon completion, the project is expected to generate about 7,421 million units (around 7.421 billion units) of renewable electricity annually. These additions are particularly relevant for supply stability in the northeastern region, as cited in the provided material.

What NHPC has said about the remaining units

NHPC has consistently communicated a phased commissioning plan for the remaining capacity. In earlier updates, the company said that with Unit 2 commissioned, the project was moving towards commissioning of three more units of 250 MW each shortly, followed by the remaining four units during 2026-27. In the latest Unit 4 filing, NHPC reiterated that CoD for remaining units will be intimated in due course. The sequence and timing of each unit’s commercial operation is therefore expected to be communicated through future exchange filings and company statements. The project’s completion will depend on how quickly remaining units move from installation and testing to synchronisation and CoD.

Key milestones so far (based on disclosed dates)

Market impact: what investors can infer from the update

The Unit 4 CoD announcement is a project execution update rather than a change in strategy, but it is still material because it confirms further progress on a marquee hydropower asset. The update also narrows the gap between planned capacity and operational capacity, at least at the unit level, since NHPC has explicitly said four units have achieved CoD. The cost marker of around ₹27,000 crore underscores the project’s scale and why execution milestones receive attention. The broader sector context remains that large hydro projects often face longer construction and clearance timelines, and unit-wise commissioning helps stagger operational ramp-up. Importantly, the company has not provided a date for the remaining units in the latest filing, only that the information will be shared later.

Conclusion

NHPC’s declaration of Unit 4 commercial operations from May 8, 2026 adds another 250 MW unit to the Subansiri Lower project’s operational stack. The company has now stated that CoD for four units has been declared in total, while the remaining units will be notified in due course. The next set of updates is expected through subsequent exchange filings as additional units clear testing, synchronisation, and commercial operation milestones.