Arunachal: Subansiri Lower HE project synchronizes 250 MW unit 2 with National Grid
Guwahati: The NHPC successful synchronized the 250 MW Unit (Unit#2) of the 2000 MW Subansiri Lower HE Project (out of 8 Units of 250 MW each) located at Gerukamukh along Assam-Arunachal Pradesh border with the National Grid on Tuesday (December 2, 2025.)
NHPC Ltd said this synchronization marks a renewed surge in India’s clean energy capabilities and solidifies the SLHEP’s status as the nation's most anticipated hydropower project.
NHPC Chairman and Managing Director Bhupender Gupta, virtually presided over the moment, while Rajendra Prasad, Executive Director & Head of SLHEP, and I.P. Ranjan, Executive Director (O&M), were present at the site to witness the achievement.
The commissioning process began with Unit#1 and Unit#2, which completed their mechanical runs on October 24 and November 6, 2025, respectively, NHPC Ltd said in a statement.
According to NHPC Ltd, the Immediate Goal is to proceed rapidly with the synchronization of the remaining three units—Unit#1, Unit#3, and Unit#4—with comprehensive wet commissioning tests underway. These three units are expected to deliver an additional 1000 MW of output within December 2025.
The Future Expansion will see the final four units scheduled for sequential connection during 2026–27. Upon full completion, the SLHEP is expected to contribute 7.421 billion units of pristine, renewable energy annually, playing a critical role in strengthening the country’s energy security and achieving India’s carbon neutrality targets.
The SLHEP faced an eight-year hiatus from 2011 to 2019 due to protests and court battles in Assam over concerns about dam safety and downstream ecological fallout.
The project roared back to life in October 2019 following robust intervention and the implementation of fortified mitigation plans based on expert recommendations.
The Design Enhancements prescribed by the Dam Design Review Panel (DDRP) included widening the dam from 171 meters to 271 meters, extending upstream cutoff walls, and adding downstream barriers against seepage.
Intensive foundation grouting and the use of rock anchors with cable tendons were mandated to anchor the abutments. Furthermore, the National Committee for Seismic Design Parameters (NCSDP) scrutinized and approved the project's seismic safeguards.
To address environmental concerns, a landmark study led by the Central Water Commission (CWC) mandated a steady 240 cubic meters per second environmental flow to nurture the river's aquatic life, MHPC Ltd added.
Furthermore, the project is designed as a vigilant guardian against the Subansiri River's notorious floods. The reservoir incorporates a 15-meter flood cushion capable of holding 442 million cubic meters, acting as a vital buffer against extreme weather.
For Downstream Protection, comprehensive riverbank fortifications spanning 60 kilometers downstream have boosted the channel's capacity by 15–20%, alongside upliftment initiatives worth over Rs. 470 crores for affected communities.
The power allocation from the national endeavour adheres to Central Hydropower norms: Arunachal Pradesh (Host State) reaps 12% free power as per national policy. Assam secures a preferential 300 MW allotment plus 25 MW of free electricity, in addition to its standard 208 MW slice. The remaining power is allotted to other states, including those in the Northeast.
The project cost has increased from Rs. 6,285 crores (2002 price level) to approximately Rs. 26,000 crores at the current price level, primarily due to the extended construction period, escalation charges, and interest during construction (IDC).