production rate of these biogas specific engines. At the time of this analysis, biogas specific gen-sets are not available for smaller-scale biogas systems.
There is the potential that carbon dioxide in the biogas could appreciably lower the efficiency of a biogas engine generator [18], although there are other claims that the presence of CO2 has a small effect on the efficiency [1,23]. To account for the possibility that CO2 could lower the efficiency of biogas engine generators, a lower engine efficiency bound of 25% was chosen.