Estimating hydropower generation potential of the Metolong dam

Abstract

Metolong dam is located 30 km east of Maseru town, with the dam retaining wall built inside the Phuthiatsana River. The purpose of the dam is to supply portable water to Maseru, Roma Mazenod, Morija and Teyateyaneng. The Instream Flow Requirement (IFR) given post Metolong dam construction and meant to sustain life downstream of the dam was used to estimate how much hydropower can be generated from IFR. Even though the study is aimed at assessing the hydropower generation potential of the dam, it did not address the sedimentation rate occurring inside the dam per year and how much storage capacity is lost due to sedimentation. Microsoft excel spreadsheet is used to estimate how much electricity can be generated from IFR and to examine how the water temperature affects the electricity projections. The results show that the dam has the capacity to produce 65kW from In-stream flow requirement (IFR) in April, as a month with the highest IFR and 7 kW in September, as a month with the lowest IFR. These power production figures are studied together with the water temperature in three scenarios to observe the effects of water temperature on power production. The outcome is that they seem to have no significant effect. The power production is based on when a Radial flow PAT (Pump As Turbine) of 0.6 efficiency and generator of 0.955 efficiency are attached at IFR release point. The dam head ranges between 23 m – 44 m for IFR, with water releases of 0.01 m3/s – 0.3 m3/s. This power can be used for distributed generation or net metering by the Water and Sewage Company (WASCO). The financing of the project is not expected to exceed $50 000 given the condition of the already installed penstock at the recovery period of less than 4 years factoring in fluctuations of power brought by those of IFR for environmental purposes downstream of Metolong dam.