Bioenergy comprises all energy produced from biomass (which represents more than 80% of energy production in this sector) or from biofuels. Regarding Portugal, the highlighted biofuel is biogas, a mixture of gases produced by the biological decomposition of organic matter, in the absence of oxygen.
Biomass is all organic matter of plant or animal origin capable of regenerating itself in a short time and in a sustainable way. Biomass comprises the by-products of the forest, agriculture, livestock and urban solid organic waste.
In forest biomass plants, electricity is produced through the direct burning of biomass. This burning makes it possible to obtain heat energy that transforms liquid water into steam which, in turn, is used to drive turbines and drive electric generators. Although this process releases CO₂ into the atmosphere, the balance of CO₂ emissions is null, since the plants that gave rise to the fuel during their life cycle absorb amounts of CO₂ that offset the emissions.