Increasing the potential of Biogas in Sub-Saharan Africa: Development of the optimal biogas system design model

This research presents the development of an optimal biogas system design model (OBSDM), which determines the most suitable biogas system design based on the context and priorities of the intended user(s) in the region of Sub-Saharan Africa (SSA). The model can be used as a decision-making tool, assisting biogas installers, program implementers, and other stakeholders in the biogas industry to carry out initial assessments on the type of biogas systems that are optimal for specific applications, particularly at the household-scale. To determine the optimal biogas system design, the model assesses the feasibility of different types of biogas system designs and sizes based on user-defined inputs, including energy and fertiliser requirements, feedstock (type, amount, and rate of supply), water supply, land use (area, soil type, groundwater level), and climate (ambient temperatures). The feasible biogas system designs and sizes are then compared and ranked based on the priorities of the intended user(s). These priorities are defined in the input through rating eight sustainability criteria related to biogas technology – reliability, robustness, simple operation & construction, lowcost, technical efficiency, environmentally benign, local materials and labour, and save time – according to their importance to the intended user. The output of the model provides a recommended biogas system design and size with estimates of expected costs, energy and fertiliser production, and links to contact the supplier. To develop the OBSDM, literature reviews were carried out on the types of biogas system designs applicable to SSA, specifically at the household-scale; the types of feedstocks available in the region; and, the tools and models that currently exist for biogas technology. Part of this literature review was used to help assess the energy production potential of different types of feedstocks that could be used in biogas systems in SSA. Databases on available digester types, sizes, and feedstocks were also developed for the model. The OBSDM was created in Microsoft Excel using Visual Basic for Applications (VBA) programming, and is recommended to be made freely accessible. It has been tested by applying household survey data from Kenya and Cameroon, as well as a detailed study of household biogas systems in the central and eastern districts of Rwanda. The outcomes from this analysis indicated that the model is able to recommend biogas system designs that are appropriate to the context and priorities of the intended user. However, the accuracy of the model outputs is highly dependent on the accuracy of the inputs. Through the Kenyan, Cameroonian, and Rwandan case studies, it is apparent that future development of biogas technologies in the region should focus on systems that require minimal water, and can be constructed from less expensive and energy intensive, local materials. Overall, this research aims to help increase biogas dissemination in the region through raising awareness about its potential, as well as encouraging industry stakeholders to make appropriate design choices that will ensure long-term sustainability of the biogas system and maximum benefits to the intended user(s)