Preliminary technical and economic feasibility study of binary power plant for Chiweta geothermal field, Malawi

Insufficient electricity generation capacity that is failing to meet the ever increasing electricity demand coupled with low electrification rate and low per capita consumption of electricity in Malawi are some of the reasons causing Malawi to search for alternative sources of energy to complement the current predominantly hydro generation capacity. Having manifestation of geothermal in some parts of the country, geothermal energy is being considered for development in line with having a diverse national energy mix. By virtue of its location in the western branch of the East African Rift System, which is relatively cooler than the eastern branch due to its lower geothermal temperature gradient, developing geothermal in Malawi for electricity generation can focus on utilizing binary technology until such a time when subsurface studies proves otherwise. The field of focus that has high promising geothermal potential in Malawi with the highest geothermal water surface temperature measured so far, is Chiweta geothermal field measuring 79°C. Technical and economic analysis of four binary power plant models has been done using Engineering Equations Solver software as a technical analysis tool and NPV, IRR and Discounted Payback Period as economic analysis tools. Technical and economic performance of all the four models is satisfactory with wet cooled recuperative binary model emerging the best performer in both analyses. However, due to issues of pressure drop in heat exchangers and the fact that the model’s performance is similar to a wet cooled basic binary, it is recommended for Malawi to develop a wet cooled basic binary for its promising Chiweta field which would generate a net power of 10 MW at a total development capital cost of approximately US $49.5 million. The capital cost can be recovered in 17 years at a discount rate of 12 % while selling electricity at the prescribed tariff of US $0.105/kWh as informed by Malawi’s Feed-in Tariff policy.United Nations University, Geothermal Training Programm