Abstract: Biogas production is a clean renewable energy source that can improve lives in
developing countries. However, winter temperatures in some areas are too low to enable
enough biogas production in small unheated digesters to meet the energy requirements of
households. Low-cost, high yield reactors adapted to the local climate are needed in those
situations. A decision-support model was developed to assist in the design of biogas reactors
capable of meeting households’ year-round energy needs. Monthly biogas production
relative to household energy needs was calculated for the scenario of suburban Hanoi,
Vietnam. Calculations included pig number, slurry (manure water mixture) dilution,
retention time and biogas/solar heating. Although using biogas to heat the digester increased
biogas production, it did not lead to an energy surplus, particularly with the 1:9 slurry
dilution rate commonly used on pig farms. However, at a 1:3 slurry dilution, the use of solar
heating to provide 90% and biogas 10% of the heat required to heat the digester to 35 °C
improved the biogas production by 50% compared to psychrophilic production. The energy
needs of an average five-person family throughout the year required 17 fattening pigs. This
model can establish the best solution for producing sufficient energy throughout the year.