The Project in brief
The Nam Theun 2 Power Company (NTPC) is an industrial and development investment owned by two private shareholders and the Lao Government, backed by commercial lenders and international financial institutions including the World Bank and the Asian Development Bank. It is described by the Lao Government as "an essential part of the country's development framework" that "is likely to provide the first real possibility for Laos to gradually reduce its dependence on Official Development Assistance".
The Nam Theun 2 Hydroelectric Plant began producing electricity commercially in 2010 after almost two decades of planning and construction activities. The Power station has an installed capacity of 1,070 MW that can generate 6000 Gwh of electricity per year. About 95% of the power is exported to Thailand.
Nam Theun 2 has been designed to incorporate a complete set of economic, environmental and social programmes to mitigate its effects on local people and ecosystems, and to improve living standards in the areas over entire Project area. These programmes cover catchment, reservoir and downstream areas, and have been designed in consultation with local villagers, under international guidelines and recommendations from various international financial institutions.
NTPC is a key company for Lao PDR development and is expected to generate 2 billion US$ in government revenue over the 25-year concession period.
The flows of the Nam Theun River have been measured, either directly or indirectly, since 1950 and records show an average flow of 7.5 billion cubic metres of water each year.
The reservoir capacity is 3.9 billion m3 and, based on the long-term average, could be filled easily in the wet season. Indeed, based on the statistics available, the water flows of the Nam Theun were greater than the reservoir’s total capacity in 49 out of the 50 years since records began, meaning that the water flows of the Nam Theun would have filled the reservoir’s “live capacity” (i.e. the water volume that can be used for generating purposes) in just one year.
Such statistics allowed the project partners to design and develop the NT2 scheme, and to confidently negotiate a long-term Power Purchase Agreement (PPA). Nevertheless, as the ability of NTPC to supply energy to EGAT depends on, inter alia, hydrological conditions, the PPA incorporates a mechanism that stabilises the Company’s cash flow by dampening the effects of hydrological variation from one year to the other.
Dam and Reservoir
The Project reservoir has inundated 40% of the Nakai Plateau by creating a shallow reservoir (on average 7 m deep) with a surface area of 450 km2 at full supply level. This will reduce in size to a surface area of a little as 70 km2 at the end of the dry season.
The reservoir has been formed by construction of a 39-m high gravity dam with a crest length of 325 m across the Nam Theun, plus 13 small earthwork saddle dams along the west bank of the reservoir. A spillway and stilling basin have been specially designed for the purpose of reservoir level control.
A 5-km long headrace channel has been excavated in the reservoir floor to direct the stored water to the intake structure. Three kilometres of headrace tunnel, pressure shaft and pressure tunnel transport water from the intake structure to the power station. After passing through the turbines the water enters the Regulating Pond, which has a live storage capacity of 8 million m3, allowing the Project to control releases of water back into the natural river system. The Regulating Dam releases water into a 27-km man-made Downstream Channel, which carries its flow to the Xe Bang Fai River.
The Power Station is located at the foot of the escarpment of the Nakai Plateau in the Nam Kathang Valley. To fit with the EGAT requirement for intermediate peaking power, the Power Station is equipped with four 250 MW Francis Unit turbines that can provide EGAT with 995 MW or 5,636 GWh of electricity per year. In addition, two 43 MW (nominal rating) Pelton Units can provide EDL with 75 MW or 300 GWh of electricity per year, and cover internal power station needs.
Both the seller (NTPC) and the main buyer (EGAT) have built transmission lines on their own sides of the Lao-Thai border for delivery at the border. Accordingly, electricity generated at the power station for EGAT is delivered to the border near Savannakhet via a 138-km double-circuit 500 kV transmission line constructed by the Project. EGAT has constructed a 160-km 500 kV line from the border to its substation at Roi Et in north-east Thailand. The electricity delivered at the power station for EDL is transmitted to Thakhek via a 70-km long 115 kV transmission line. EDL will also take up to 15 MW of energy from the power station switchyard via 22 kV lines to the resettlement villages.
A Dam Safety Review Panel, composed of eminent, independent, technical experts was formed and given the authority to scrutinise the design, construction, commissioning, operation and maintenance of the Project. The Panel's role is to ensure that the Project conforms with all requirements of the World Bank’s Dam Safety Policy, including design, hydrology, engineering and downstream impacts. Members if the Panel have regularly inspected project sites and facilities since the beginning of construction.
In addition, all stages of construction are being strictly monitored to meet stringent health and safety demands. A full-time monitoring and survey team is permanently on site to monitor construction areas and worker camps to ensure that safety and environmental requirements are met and that all thresholds specified in the Emergency Contingency Plan are observed. There are 21 sample points around the site to monitor leakage, water quality, movements and displacements. Both NTPC and the Head Contractor operate safety teams for the benefit of local residents, workers and visitors, and community education is given to educate local people about the changes in their physical environment and the potential dangers of waterways and transmission lines.