FLOW
Movement of water from a river into an intake pipe and then downhill into a TURBINE. 'Flow' refers to movement of a quantity of water (such as m3 /sec).

HEAD
The difference in height over the course of the FLOW that creates an increase in water pressure to drive the TURBINE. ' Head' can be described in feet or meters, or by pressure such as p.s.i. Nam Theun 2 has a head of approximately 350 meters.

PENSTOCK
The pipe through which water is discharged at high pressure and velocity into the TURBINE

POWERHOUSE
The building that houses the TURBINE and other generating machinery.

TURBINE
There are many different types of turbines, all of which are turned by moving water to generate power. The two main types are reaction turbines (such as the Francis model), which are completely submerged in water, and impulse turbines (such as the Pelton model), which rotate in air and are spun by high-speed jets of water. Exactly what turbines are used will be determined by the FLOW, HEAD and other factors, such as the electricity end user's power supply requirements.

Nam Theun 2 will have four 250 MW Francis turbines (for supply of intermediate and peak power to EGAT) and two 43 MW Pelton turbines (for supply of power to EDL).

RUN OF RIVER
A hydropower project where the river flow on its own provides the pressure to spin the TURBINE This type of project has no reservoir to store water inflow from the catchment area.

STORAGE
A hydropower project where water is stored in a reservoir and then channeled into the TURBINE in line with the demand for electricity. Nam Theun 2 is a storage project.

TRANS-BASIN
A hydropower project where water is diverted from one river system into another separate system. Nam Theun 2 will take water from the Nam Theun system and discharge it into the Xe Bang Fai system.

REGULATING POND
A reservoir for storing water that has passed through the TURBINE before its release into a river. The regulating pond allows better control of downstream flows as water is discharged.

POWER DEMAND
National demand for energy can be split into three basic categories: Baseload, Intermediate and Peaking. Baseload power plants run all of the time to meet minimum power needs; peaking power plants are only run to meet power needs at times of highest demand; intermediate power plants fall between the two - Nam Theun 2 is primarily designed to supply intermediate power to Thailand . Because electricity cannot be 'stored', intermediate power plants are well suited to meeting changing energy demand, since they tailor their output as appropriate. Nam Theun 2 will operate at a contracted minimum 16 hours a day, with the potential for a further 8 hours generation instantly available if needed.