In HOMER, the term biogas refers to gasified biomass. Biomass feedstock (such as wood waste, agricultural residue, or energy crops) can be gasified by thermo-chemical or biological processes, and the product may be called one of several different names, including synthesis gas, syngas, producer gas, and wood gas.
Whatever the feedstock and the means of gasification, the major constituent gases of biogas are typically carbon monoxide, hydrogen, and carbon dioxide, plus a significant amount of nitrogen (about 50% by weight) if thermal gasification is performed in the presence of air. Minor constituent gases include methane and water vapor.
Biogas typically has a low heating value compared with fossil fuels, particularly if it contains a large amount of nitrogen, which is noncombustible. But it has several advantages over solid biomass, including cleaner combustion, higher efficiency, and better control.