Biogas resources are organic crops and wastes, such as wood and paper residues, landfill gas, biogas from sewage wastes, and other agricultural wastes, converted to usable energy. Globally, the most common use of biogas is heating and cooking. However, there is a noticeable amount of biogas converted to electricity. One of the governing economic factors of biogas is the cost associated with shipping the fuels. These shipments can quickly move the cost per kWh to a noncompetitive level. Because of these costs, most of the biogas generation is in dispersed and customer-sited operations smaller than 100 MW.
In the U.S., there is approximately 10.5 gigawatts of biogas generating capacity. This capacity has remained constant for the past five years. The majority of this capacity is generation within the industries that produce their own fuel resources, such as the paper and lumber industries. These sectors have experience little growth in the recent past, and in turn, biogas has not seen any growth. Despite this relative stagnation, there is a shift occurring in the industry. Most new biogas capacity additions are using landfill gas and digester gas as fuel which frees them from an industry specific presence.
A further shift is expected to occur as technologies develop that allow smaller facilities to economically use available fuels. These operations could include farmers and other smaller industries in remote settings where this generation is most likely to be economically viable. One of the technologies expected to contribute to this shift is the Stirling engine, which is uniquely capable of handling diverse non-liquid biogas fuels because of its external combustion design.