Biogas can be produced in large-scale plants connected to animal farms or in smaller-scale domestic units. Large-scale plants (more than 2,500 tpa of bio-waste and/or biogenic industrial waste) run on a well-established technology. In OECD countries, about 200 plants are in operation. In China, there are over one thousand bigger plants, many of which use industrial waste from paper, sugar and the pharmaceutical industry as feedstock. Domestic biogas units also run on a well-established technology. In 2010, China installed 4.9 million units for a total of 40 million operational plants. India constructed almost 120,000 units in the fscal year 2009-2010 within the National Biogas and Manure Management Programme (NBMMP). In March 2010, it had a total of 4.25 million biogas plants. SNV installed 4,750 domestic biogas plants in nine African countries between 2007 and 2010 (SNV, 2011). In Kenya, Tanzania and neighbouring countries, biogas is traditionally used in small and very small installations for household energy and for social institutions. With GTZ support, over 1,000 small and medium-size plants and one bigger digester of over 100m³ capacity were installed in Tanzania from 1983 on. In Niger, a system for a household with seven members needs dung from five head of cattle yielding around 11.3 m3 of biogas per day. Estimates suggest a significant potential in rural areas, from 9% of rural households in Mali to 8-15% in Burkina Faso, 23-28% in Uganda, 29% in Senegal and 35% in Rwanda (GTZ, 2010).
A study for Niger estimates an installation cost of USD 875 per household and annual operating and maintenance costs of 4% of the investment. Biogas use reduces wood fuel and kerosene use and residues can be used as a substitute for commercial fertiliser. The return on investment is 22-28% (EPM Consulting, 2008).
A recent study examined the theoretical potential of power generation from 13 types of biomass from agro-industrial businesses in Kenya to municipal waste in Nairobi (GTZ, 2010). The report concludes that the potential electric capacity of generated biogas is high. Biogas from all examined sub-sectors could cover up to 16% of total Kenyan electricity production. Municipal solid waste, sisal and coffee production are the most promising sectors with the greatest potential. However, specific electricity production costs for small plants (50 kWel) range from 0.11 to 0.29 USD/kWh. In comparison with the cost estimates in Table 2, this is in line with other new renewables options.