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.