Financial and economic feasibility of bio-digesters for rural residential demand-side management and sustainable development

This paper addresses the financial and economic feasibility of biogas production to meet energy demands at a household or village scale. To this effect, the potential cost and benefit of biogas digesters were explored. The biogas digesters were characterised under controlled conditions before being deployed to the KrwaKrwa and Upper Ncera villages in the Eastern Cape, South Africa. At the control site, meteorological weather parameters that influence biogas production were monitored continuously. Based on typical rural household electrical usage profile from 2-years of data observed at the sub-station level, assumptions about the cooking times and electrical demands were made. It was found that the bio-digesters are capable of supplying the energy required for cooking, provided the digesters are continuously fed at least every 5th day. Also, 1.0 m3 of CH4 is equivalent to 4.70 kWh of electricity. With reloading after every 5th day, the total biogas produced per day over 31 days is 2.93 m3. This is equivalent to demand-side avoidance of 13.77 kWh/day and monetary savings of R26,88/day or R833,43/month. A financial cost of approximately R 17 000,00 per digester, Net Present Value of R22 000,00 and a payback period of 22 months was obtained for the feasibility of the project. Based on the findings of the study, it can be said that biogas digesters are financially sound investments and economically feasible at both household and societal levels. These digesters can also ensure that the household remains above the poverty threshold.