NHPC’s Subansiri Hydropower Project begins partial commercial operations after 13-year delay

After years of delays and prolonged uncertainty, NHPC’s 2,000 MW Subansiri Lower Hydroelectric Project, located on the Assam–Arunachal Pradesh inter-state boundary, has finally begun partial commercial power generation. The project started operations on Tuesday with the commissioning of Unit-2, marking a major milestone more than 13 years after its originally scheduled completion in December 2012.

In a statement, the state-run power major said Unit-2, with a capacity of 250 MW, was virtually inaugurated by Union Power Minister Manohar Lal from New Delhi. The commissioning represents a significant step towards the full operationalisation of India’s largest hydropower project.

The Subansiri Lower Hydroelectric Project comprises eight generating units of 250 MW each. NHPC said additional units will be commissioned in a phased manner in the coming period. With the latest development, the project is now moving towards the commissioning of three more units of 250 MW each shortly, followed by the remaining four units during 2026–27.

Congratulating NHPC, the Union Power Minister described the commissioning as a proud milestone, stating that it reflects years of perseverance, dedication and teamwork. He said the project symbolises India’s commitment to clean and sustainable energy, while supporting the growth of the Northeast, strengthening the national power grid and advancing the country’s Net Zero ambitions.

Once fully commissioned, the Subansiri project is expected to significantly boost India’s renewable energy capacity, improve grid resilience and mark a new chapter in large-scale clean energy generation. Designed as a run-of-the-river scheme with small pondage, the project diverts water through eight head race tunnels to generate an estimated 7,422 million units of renewable electricity annually.

NHPC said the project will supply power to 16 beneficiary states across the country. In addition, Arunachal Pradesh and Assam will receive free power allocations, while the northeastern region as a whole will benefit from an allocation of 1,000 MW, substantially strengthening regional energy availability.

The project, however, has had a long and troubled journey. Its commissioning had earlier been pushed to May 2026 from the initially announced 2023–24 fiscal timeline. The original completion target was December 2012. The estimated cost of the project has escalated sharply, rising from an initial Rs 6,285 crore in 2002 to around Rs 26,075 crore at the time of completion.

During the peak construction phase, the project provided daily employment to nearly 7,000 local people and generated numerous direct and indirect jobs through contractors, service providers and local businesses.

NHPC highlighted that the project features the largest dam in Northeast India—a 116-metre-high concrete gravity dam—which enhances regional infrastructure, strengthens grid stability and contributes to flood moderation and water management in the Subansiri river basin. The project also showcases advanced engineering, housing India’s heaviest hydropower generator rotors, largest stators and biggest main inlet valves.

As the first in a series of cascaded dams on the Subansiri River, the project plays a crucial role in flood control. It provides a dedicated flood cushion of 442 million cubic metres, ensuring safer water management during the monsoon season. With a gross reservoir storage of 1,365 million cubic metres at full reservoir level, nearly one-third of the reservoir remains vacant during flood periods to absorb excess water and protect downstream areas.

NHPC has also implemented extensive riverbank protection and erosion control measures along the Subansiri River, completing works up to 30 km downstream and extending them to 60 km at an investment of Rs 522 crore.

Construction of the Subansiri project began in January 2005 after forest clearance was granted in October 2004. However, work was suspended between December 2011 and October 2019 following protests by local communities and civil society groups over safety concerns and potential downstream impacts. Several committees were formed by the Assam government and the Centre to address these issues, with varying conclusions.

After resolving legal hurdles and obtaining clearance from the National Green Tribunal, NHPC resumed construction on October 15, 2019, paving the way for the project’s long-awaited operational debut.