Feasibility of hydropower generation on existing Legedadi water supply scheme, Addis Ababa-Ethiopia

Abstract

Hydropower can be harnessed by installing in-pipe turbines with the reduced cost compared with hydropower dam construction. Legedadi Water Supply Scheme is found in Addis Ababa and is fed by gravity. This research assesses the hydropower potential of the existing large water transmission pipelines in line with their financial viability. The research required the collection of data from pipe flow (for 29 years from the system record) and pipe layout drawings believed to be useful for estimating the power. The available pipe layout drawing was processed to prepare a profile view with the help of AutoCAD CIVIL 3D. From the profile view, the gross heads and length of the pipelines were obtained. The exploitable power and financial viability of the projects were estimated by RET Screen software. The raw water main (DN1200) was discovered to have a head of 12.46 m and to convey up to 1.47 m3/s at 90% exceedance over a length of 550 m. The two treated water mains have a head of 19.15 m with a flow of 1.14 m3/s at 90 % exceedance via DN1200 and 0.29 m3/s at 90% exceedance via DN900 over a length of 18.4 km. The most suitable sites for the installation of turbines were at the inlet of the treatment plant and the Kotebe Terminal Reservoir. The Toshiba Hydro-eKIDS turbine was selected since it might work efficiently with large flow variation.The annual energy output from the raw water main to be obtained was 1,208 Mwh,
with an estimated cost of $461,000 and an annual savings or revenue of $75,946. For the treated water mains, 1,193 Mwh (DN1200) and 344 Mwh (DN900) could be extracted with an estimated cost of 414,500$ (DN1200) and 135,900$ (DN900). The annual revenue for treated water mains is 75,068$ (DN1200) and that for DN900 is 18,842$.