Biomass
Biomass is one of the oldest sources of energy used by humans – ever since we started using fire, we have been using bioenergy in some way. Biomass materials are currently used to provide heat and electricity as well as for fuels to run transport vehicles. In this way, biomass already makes an important contribution to the UK’s renewable energy supply. Considerable untapped resource potential also exists, so in future bioenergy could play a significant role in helping the UK to meet a range of carbon reduction targets and renewable energy targets.
In energy terms, biomass can be viewed as a form of stored solar energy. The sun's energy is captured and stored (via photosynthesis) in the biomass material. The carbon dioxide emitted when the biomass is burnt is largely balanced by the carbon dioxide that was captured during its growth. Sustainably managed fresh growth of more biomass material can recapture the emitted carbon dioxide resulting in very low overall (net) emissions to the atmosphere.
One of the ways in which the energy captured in biomass can be directly released is via simple combustion of the material which can then be used to provide heat (e.g. via steam or hot water) and or electricity.
Alternatively biomass can be converted into an intermediate product such as liquid fuel (often referred to as a biofuel). Liquid transport fuel is produced using a range of different conversion processes to refine the biomass. Bioethanol has been used for many years as a gasoline substitute. It is traditionally produced by the fermentation of sugars, with sugar beet and wheat being the most likely sources in Europe. Biodiesel can be produced from vegetable oil.
Advanced biofuels
Advanced biofuels are currently the subject of worldwide research and development. There is considerable research taking place on alternatives to biofuels derived from food crops. The possibility of using feedstocks containing lignin and cellulose, such as wood and straw rather than sugars and starches is attractive as it these would not be competing with the use of crops for food, and this also avoids concerns about the sustainability of crop-based biofuels. Other abundant biomass sources such as algae offer possibilities for sustainable, low cost biofuels.
Biodegradable wastes from sources like dairy, vegetable peelings or manure also provide a substantial biomass resource. Energy generation from the methane produced from landfill sites is a well-established energy source. Another way to convert oraganic waste to energy is anaerobic digestion, which produces a methane-containing biogas, which can be used for heat and electricity generation and as a transport fuel.