The 456 MW Upper Tamakoshi hydropower plant in the upper Himalayas entered into full commercial production in September, enabling Nepal to generate an energy surplus during the wet season.
Tracetebel, which was responsible for implementation planning and construction management called the Upper Tamakoshi hydroelectric project “a prestigious milestone in the energy transition in Nepal”.
The plant was developed by Upper Tamakoshi Hydro Power Limited, a subsidiary of the Nepal Electricity Authority (NEA), the state electricity utility, in partnership with Nepal Telecom (NTC), Citizen Investment Trust (CIT) and Rastriya Beema Sansthan (RBS). The four public entities hold a combined majority share (51 per cent). The general public holds a 49 per cent share, having contributed to the project’s financing through the project company’s initial public offering (IPO).
The peaking run-of-river plant, with an 822 m gross head, a design discharge of 66 m3/s and an installed capacity of 456 MW, is designed to generate up to 2281 GWh annually, which is equivalent to the country’s total annual consumption at present. The project will benefit the whole country from the surplus of electricity, according to Tractebel. Electricity costs will decrease while Nepal could export electricity to India, generating an important source of revenue.
The major components of the project are the intake, a 22 m-high concrete dam, twin de-sanding basins, a 7.86 km-long headrace tunnel, a 360 m-high surge shaft, a 495 m-long penstock pipe, an underground powerhouse with six Pelton turbines, a 2.9 km-long tailrace tunnel, and a 47 km long 220 kV transmission line to Khimti substation. Construction of the project began in 2012 but its development has overrun its budget and timetable primarily as a result of major damage to the site caused by the severe earthquake of 2015, multiple setbacks owing to equipment breakdown and technical mishaps as well as issues relating to transportation of equipment to the site as a result of weak infrastructure such as poor roads and bridges. The project cost has increased to Rs 73 billion, including interest on loans, from an initial cost estimate of Rs 49 billion. Interest payments on long-term loans alone jumped from Rs 6.7 billion in 2016 to Rs 14.42 billion by 2020.
Dry commissioning of all six units was completed in July 2019. Filling of the reservoir and simultaneous wet test of the dam and intake were accomplished in March 2020. The lower and upper vertical shafts, considered the most challenging works of the project, were completed in July 2020. Andritz Hydro supplied and installed the complete electro-mechanical equipment, under a contract signed with the developer in February 2012, including a 220 kV GIS and the mechanical balance of plant, as well as a 2.5 m, 85.6 bar pressure rating, and a 170 ton spherical valve as the main shut-off valve. The Austrian group also carried out the hydro-mechanical works, including penstock installation, which it took over in 2018 from Texmaco, after the Indian contractor withdrew from the project, admitting that installing the massive penstock pipes was beyond its scope.
In a second stage, the project company plans to divert the water of Rolwaling Khola to the head works of Upper Tamakoshi so as to increase its dry season energy by 221 GWh, and to build the Rolwaling Khola plant with capacity of 20.2 MW, generating another 105 GWh per annum.