The most efficient, cleanest way to convert biomass to power is via gasification. This can be accomplished in such a way as to produce a fuel gas rich in CO and methane or a synthesis gas rich in hydrogen and CO which can also be used as an intermediate in production of liquid fuels and organic chemicals. Both types of gases have been shown to power both spark and compression combustion engines and have been extensively used for this purpose, paricularly in Northern Europe during WW II. Gasification is thus different from combustion, where adequate air (oxygen) is employed to exothermically convert the majority of the biomass to water and carbon dioxide and simultaneously produce large quantities of particulates and noxious emissions. The goal with endothermic controlled gasification is to produce an energy rich gas in an oxygen deficient environment so that the energy is retained in the gaseous products. This requires proper design and operation of the gasifier.
In some cases, it may be advantageous to reform the hydrogen and carbon monoxide gases catalytically to produce methane, thereby increasing the calorific value of the gas.