Small-scale biogas : A techno-economic comparison of Internal Combustion Engines, Micro Gas Turbines and Stirling Engines

Gas driven power generation is expected to increase in the near future due to significantly lesser environmental impact than oppose to conventional fuels like coal and oil. Today, Natural Gas (NG) is the dominant product on the market and biogas, which originates from degradable organic waste, has not reached its full market potential due to bottlenecks in utilization. Biogas often contain less methane and more trace elements than NG and is therefore seldom feasible to use in power generation. Especially at small biogas flows, the equipment needed for cleaning of the gas is often too expensive to consider. The biogas used in this study was assumed to contain 55 % methane with trace elements of hydrogen sulfide (H2S), moisture and Siloxanes. One way to surpass this cleaning step is to use externally fired machines, like Azelio’s 10 kWel GasBox which is a Stirling engine coupled with a gas preheater and combustion chamber. A model was developed which analyzed both costs and operation parallel with the two most market mature options, Internal Combustion Engines (ICE) and Micro Gas Turbines (MGT), which indicated that the GasBox is competitive at small biogas flows translating to less than 100 kWel output due to this. A market analysis and screening with a Multi-Criteria Analysis (MCA) was performed to locate markets for which the demand for a product like the GasBox existed. The study showed that there is an estimated demand for around 53 000 units in the German agriculture, which is one of the worlds most innovative markets when it comes to both biogas and renewable energy in general. Further on, it was discussed what is needed from both understanding the market but also the technologies involved for succeeding on the market