In-pipe hydropower potential: case of Nairobi city water and sewerage Company

Abstract

There exists hydropower potential in gravity-fedwater supply systems. This power can be harnessed by installing in-pipe turbines without the costs and environmental impacts associated with hydropower dam construction. The existing Gigiri water supply system forNairobi Cityis a gravity-fedsystemwithhigh hydropower potential. This project investigates viability of integrating in-pipe turbinesin the system for the purpose of generating electricity.The project involved survey of the existing system in order to establish the available head and flow useful for estimating the power. It was found that the raw water mains had a head of 23.27 m and conveyed up to 5.2 cubic metres per second through 1200 mmand 1400 mm pipes over a pipe length of 6.1 kilometres. The treated water mains were found to have a head of 112.07 m with a total flow of 2.96 cubic metres per second in four phases. The most suitable sites for installation of the in-pipe turbines were at the treatments works (Ng’ethu water works) and at the Gigiri reservoirs. The Toshiba hydro eKIDS turbine when installed at the sites potentially could extract the highest power compared to Lucid spherical turbines and the Reverse Pump turbines. The extractable power at Ng’ethu water works was estimated as 450 kW while at Gigiri reservoirs the extractable power was 900 kW.The power from the raw water mains could be able to run the treatment works while the power at Gigiri reservoirs could be sold to the national grid.The extraction of this power would however result into flow reduction of up to 11.48 percent and 21 percent for the raw water mains and treated water mains respectively. The reduction for the treated water mains comestoapproximately 2,592m3/hrwell within volume fluctuations of 4,500m3/hrat the Gigiri reservoirs. The findings of this project show that whenin-pipe turbines areinstalled in the Gigiri water supply system, up toa potential of1.35 MW couldbe generated. The resulting flow reduction would be within the current fluctuations at the Gigiri reservoirs