Using solar energy to enhance biogas production from livestock residue – A case study of the Tongren biogas engineering pig farm in South China

• A large-scale solar-powered water-heating system was integrated with a biogas plant.
• Yields of biogas generated by the integrated system were 11.2% higher than from the system used river water.
• The biomass energy transformation ratio of solar-powered water-heating system was increased by 14.3%.
• Methane content of the two fermentation systems was identical.
• Economic analysis revealed the cost effectiveness of adding a solar energy collector device to this biogas generation system.

Due to the rapid growth in the global energy demand and to the growing concerns regarding energy supply, more attention has been paid to the development of bioenergy, especially the one derived from anaerobic digestion. In our study we used solar energy to improve the efficiency of anaerobic fermentation at the Tongren Pig Farm in Haining city, Zhejiang province, China. Haining, located at 30°15′–30°35′N and 120°18′–120°52′E, has the average winter temperature of about 5 °C. At the farm, solar energy collectors, with a total area of 100.8 m2 and a volume of 6 t water were installed to heat the water in fermentation digesters. Comparison shows that biogas production was 2540 m3 more or 11.2% higher than that of the CK with no differences in the methane content, which can also be translated into a 14.3% increase of pig manure energy transformation efficiency.