The Subansiri Lower Hydroelectric Power Project has begun generating electricity after a two-decade journey, with its first unit synchronised to the national power grid at 6.12 pm on Wednesday. The 2,000 MW project, implemented by NHPC, comprises eight units of 250 MW each. A second unit has also begun generation, while three more units are expected to be commissioned this month. Full commissioning is targeted for March 2027.

Project consultant A.N. Mohammad told The Assam Tribune that synchronisation marked a defining moment in India’s hydropower progress. He said Unit 1 and Unit 2 completed mechanical runs on 26 October and 6 November, respectively. Units 1, 3 and 4 will be synchronised after wet commissioning tests, adding 1,000 MW by December 2025. The commercial operation date will be confirmed shortly. The final four units are scheduled for phased commissioning between 2026 and 2027. When fully operational, the plant is expected to supply 7.421 billion units of renewable energy annually, bolstering India’s clean-energy ambitions.

Mohammad highlighted the project’s turbulent history. Conceived in January 2005 at Gerukamukh on the Assam–Arunachal border, construction stalled for eight years—from 2011 to 2019—due to protests, litigation and concerns over dam safety and downstream ecological impact. Work resumed in October 2019 after the government introduced enhanced safeguards.

Several expert panels reviewed the project. The Technical Expert Committee (TEC) addressed hydrological concerns, while the Dam Design Review Panel (DDRP) mandated key safety upgrades, including widening the dam from 171 metres to 271 metres, adding upstream and downstream cut-off walls, improving foundation grouting and installing rock anchors. The National Committee for Seismic Design Parameters (NCSDP) approved seismic safety measures.

A major cumulative impact study by the Central Water Commission in December 2014 required an environmental flow of 240 cubic metres per second to protect aquatic ecosystems. The Subansiri River’s volatile history—including massive floods triggered by the 1950 earthquake—also shaped design decisions. The project’s 1,365 MCM reservoir incorporates a 15-metre flood cushion of 442 MCM and 60 km of downstream embankment fortifications, increasing river-carrying capacity by 15–20 per cent.

Downstream development works worth over Rs 4.7 billion have been undertaken, covering health, education, livelihoods and infrastructure for affected communities. Once operational, Assam will receive 208 MW as per hydropower norms, an additional preferential allocation of 300 MW, and 25 MW of free power. Arunachal Pradesh will receive 12 per cent free power as the host state, with the remaining electricity distributed to other regions, including the Northeast.

The project cost has risen from Rs 62.85 billion at 2002 prices to about Rs 260 billion today, primarily due to prolonged construction, cost escalation and interest during construction, Mohammad said.