The Nam Theun 1 is a 650MW run-of-the-river hydroelectric power plant under construction in the Bolikhamxay province of Laos.

The £925m ($1.3bn) project is being developed by Nam Theun 1 Power Company, a joint venture of Phonesack Group (PSG, 32%), Chaleun Sekong Energy Company (CSE, 28%), Electricity Generating Public Company of Thailand (EGCO, 25%), and Electricite Du Laos (EDL, 15%).

While construction works on the project were started in 2017, the reservoir impounding began in June 2021. Commissioning is scheduled for May 2022.

The Nam Theun 1 hydroelectric power facility is expected to produce up to 2,638 gigawatt-hours (GWh) of electricity a year.

The Nam Theun 1 is the last project to be developed in the Nam Theun-Nam Kading hydropower cascade scheme in Laos. The 1GW Nam Theun 2 power plant on the Nam Theun River has been operational since March 2010.

Location and site details

The Nam Theun 1 hydroelectric power project is being developed on the Nam Kading River, 33km upstream of its inter-junction with the Mekong River.

The project site lies in the Pakkading district of the Bolikhamxay province of Laos, approximately 220km away from Vientiane.

Nam Theun 1 dam details

The Nam Theun 1 hydroelectric power project features a 177m-high roller compacted concrete (RCC) dam with a crest length of 771.5m. It is designed to create a reservoir of up to 2.02 billion cubic metres (Bcm) of water storage capacity.

The project also involved the construction of two cofferdams.

Nam Theun 1 hydroelectric power project make-up

The Nam Theun 1 hydroelectric power plant will be equipped with two 260MW turbines and one 130MW turbine operating at a water head of 140m.

The project also involves a diversion channel, a headrace tunnel connected to 10m-diameter steel penstocks, as well as a spillway and a tailrace channel.

The electrical transmission infrastructure at the project site will include transformers, low and medium-voltage switchgears, and a 500kV gas-insulated substation (GIS).

Power evacuation from Nam Theun 1

The electricity generated by the Nam Theun 1 hydroelectric power plant will be evacuated into the grid through a 500kV transmission line connecting the Nabong substation located in the Nabong village, Pakngum, Vientiane, near the Laos-Thailand border.

Construction equipment and infrastructure

The Nam Theun 1 dam construction was facilitated by a conveyor belt system to deliver concrete from a batching plant.

The construction site also features a sand and gravel processing facility along with workshops for coarse crushing and soil screening.

Power offtake

Thailand's state-owned power utility Electricity Generating Authority of Thailand (EGAT) signed a long-term power purchase agreement (PPA) to offtake 514.3MW of electricity from with Nam Theun 1 power plant in September 2017.

Electricite Du Laos also entered another agreement to purchase 130MW of electricity from the Nam Theun 1 facility.


A group of Thai banks including the Bangkok Bank, the Export Import Bank of Thailand, the Siam Commercial Bank, and the TISCO Bank are providing financial support for the Nam Theun 1 power project.

Contractors involved in the Nam Theun 1 hydropower project

Cooperativa Muratori e Cementisti (CMC) (40%), a construction company based in Ravenna, Italy, in consortium with Italian-Thai Development Public Company (ITD) and Vietnamese state-owned Song Da Corporation, was contracted for civil and hydro-mechanical works of the project in December 2016.

Song Da Corporation’s scope of work included blasting, excavation, and transportation of soil and rock. The company was also engaged in constructing the crushing and batching plant as well as the cofferdams for the project in April 2018.

ATB Riva Calzoni, a company based in Italy, was subcontracted by CMC to supply penstocks and other hydro-mechanical equipment, while China’s state-owned Sinohydro Bureau 3 was engaged in civil works of the project in November 2019.

Andritz was contracted to supply electro-mechanical equipment including turbines, generators for the plant in August 2016.

Pöyry (now Afry) was engaged by PSG as the owner’s engineer, while Simem, a construction company based in Italy, was contracted to supply concrete batching plant and NMS Industries provided the sand and gravel processing system.

Right Tunnelling, a company based in Thailand, was subcontracted by PSG for underground excavation along with concrete lining works for the project.