NHPC's Subansiri hydropower project starts partial commercial operations

New Delhi: NHPC Limited's much-delayed 2,000 MW Subansiri hydropower project along the Assam-Arunachal Pradesh inter-state boundary on Tuesday started commercial production partially, 13 years after the original completion schedule.

The state-run energy major, in a statement, said that unit-2 was inaugurated virtually by Union Power Minister Manohar Lal from New Delhi, marking a significant step in commissioning India's largest hydropower project.

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The Subansiri Lower Hydroelectric Project has eight units of 250 MW each and other units of the facility will start commercial production in the coming period.

Lal lauded the achievement as a proud milestone in NHPC's journey, saying, "The commissioning of this unit is not just a technical achievement, but a testament to years of hard work, dedication and teamwork."

The Subansiri project stands as a symbol of India's commitment to clean and sustainable energy, supporting Northeast India's growth, strengthening the national grid and advancing the country's ambitious Net Zero goals.

"With the commissioning of unit-2, the project is moving swiftly towards commissioning of three more units of 250 MW each shortly, followed by phased commissioning of the remaining four units during 2026-27," NHPC said.

Upon full commissioning, the power plant will make a significant contribution to India's renewable energy capacity, enhance national grid resilience and usher in a new era in massive clean energy contribution, it added.

As India's largest hydropower project, the Subansiri project is designed as a run-of-the-river scheme with small pondage, diverting water through eight head race tunnels (HRTs) to generate 7,422 million units (MU) of renewable electricity annually.

"Apart from supplying electricity to 16 beneficiary states across India, the Subansiri project will provide free power allocations to Arunachal Pradesh and Assam, while the northeastern region will receive 1,000 MW from the project, significantly strengthening regional energy availability," the statement said.

Earlier, the commissioning of the Subansiri Lower Hydroelectric Project was delayed till May 2026 from the earlier announced 2023-24 fiscal end. The original completion schedule was December 2012.

The project cost was anticipated to escalate more than four times to around Rs 26,075 crore at the time of completion from the initial estimate of Rs 6,285 crore in December 2002.

During the construction phase, the project engaged around 7,000 local people daily, and created numerous direct and indirect jobs through contractors, service providers and local markets.

"The project features the largest dam in Northeast India, a 116-metre high concrete gravity dam, which not only strengthens regional infrastructure and grid resilience but also enhances flood moderation and water management in the Subansiri river basin," the Navaratna entity said.

The Subansiri project is a showcase of engineering excellence and determination, housing India's heaviest hydropower generator rotors, largest stators and biggest main inlet valves, it added.

"The project is the first of the cascaded dams on the Subansiri River and plays a critical role in flood moderation. The project provides a dedicated 442 million cubic metre flood cushion for safer management during the monsoon season," the company stated.

With a gross reservoir storage of 1,365 million cubic metres at full reservoir level (FRL), the project ensures that approximately one-third of the reservoir remains empty during flood periods, enabling it to absorb excess floodwaters and protect downstream communities, it added.

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

The Subansiri Lower Hydroelectric Project, which faced multiple bottlenecks since its inception stage, has been delayed several times and its deadline for commissioning has been revised on many occasions.

NHPC had commenced the construction work of the Subansiri project in January 2005 after obtaining forest clearance in October 2004.

Construction work of the ambitious project on Subansiri River was stalled from December 2011 to October 14, 2019 due to protests by locals and many groups fearing safety and downstream impact.

To address the concerns of the agitators, multiple committees were formed by the Assam government and the Centre. The outcomes of their reports varied from one to another.

After clearing all the legal issues by the National Green Tribunal (NGT), the NHPC re-started construction of the project from October 15, 2019.

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