Pre-feasibility studies of Hemang hydropower site

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Ghana, though has a good number of small to medium hydro power potential sites, has still not exploited all of them. The focus of this thesis is a pre-feasibility study of the technical and financial viability of power generation from a medium hydropower potential site, the Hemang site, on the Pra River in the Western region of Ghana. This study is carried out using recent flow data (1980 -2011) from the gauge station on the Pra River. The results are compared with previous studies carried out on the Hemang site by ACRES International in 1985. The power capacity, yearly energy output, greenhouse gas reduction and financial feasibility of the potential hydro site are studied in this work. The study also covers a preliminary sizing of some mechanical components (water passages) including turbine, draft tubes and penstocks for the Hemang site. RETScreen® project analysis software package was used in both the technical and financial analysis of the project. The sizing of water passages, however, was done using codes written in MATLAB®. Technical analyses of the power output capacity and yearly energy output of three (3) hydro-turbine types (Kaplan, Propeller, and Francis) operable at the same given head and design flow and also the possible reduction in greenhouse gas (CO2) by the prospective project were performed. The highest power capacity and annual energy output of the site is determined to be 70.524 MW and 225,346 MWh respectively with a Kaplan type turbine. The power capacities and annual energy output results of the Hemang site using the recent flow data on the Pra River is seen to have reduced as compared to the values stated by the Acres International’s 1985 study with flow data from 1944-1984. The financial analysis (using RETScreen® cost and financial analysis modules) was carried out on a range of electricity export rate (US$ 50/MWh - US$ 150/MWh). With a project life of 40 years and an electricity export rate of US$ 64.90/MWh, the project’s net present value (positive) is found to be about 5 times the project’s initial cost, which indicates the project is financially viable to only an extent. At the same electricity export rates, the project has an equity payback time of 13.4 years and an after-tax internal rate of return of 13.7%. This value of IRR, however, makes the project financially uncompetitive with similar project elsewhere in Africa. A greenhouse gas (GHG) analysis on the project reveals that the project will annually cut GHG emission (CO2) by 109,739 tonnes.
A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Ghana, in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE IN Mechanical Engineering Department of Mechanical Engineering College of Engineering