Biomass is available in a variety of forms and is generally classified according to its source (animal or plant) or according to its phase (solid, liquid or gaseous). Generally, bioenergy can be derived from sources such as forests and energy crop plantations, residues from primary biomass production, and by-products and wastes from various industrial processes.

Forests, woodlands, short rotation forestry and other arboricultural activities (for example, park maintenance) are a source of wood fuel. Fuel can also be obtained from energy crop plantations using species such as willow, eucalyptus, sugarcane, miscanthus, energy grain, hemp, oilseed rape, sunflower and sugar beet. Residues represent another possible source of fuel. This includes residues from food and industrial crop production (for example, cereals, sugarcane, tea, coffee, rubber trees,
oil and coconut palms) and residues from forestry activities (for example, from stem wood production). By-products and wastes may also originate from sawmill waste, manure, sewage sludge, abattoir waste and municipal solid waste. Generally, these are sources of low-cost fuel.

Biomass and waste needing disposal can be burned directly or converted to intermediate solid, liquid or gaseous fuels to produce heat, electricity and transport fuels. A number of biomass conversion technologies are currently commercially available. In addition, there is a potential for technological advances and commer­cialization of more efficient technologies for production of electricity and transport fuels in a rather near future. Table 2.1 shows a range of biomass technology options and corresponding end-uses, indicating also the status of these technologies.

There are significant differences among European countries when it comes to the exploitation of biomass resources. The bulk of biomass being used consists of fuelwood for domestic heating. The use of biomass for district heating is substantial in a few countries such as Austria, Finland and Sweden, mainly fed by fuelwood and wood residues from the forestry and wood-processing industry. In Denmark, straw is used to some extent. In comparison, the use of biomass in industry and for power generation is modest. In some countries, such as Sweden, electricity is generated in combined heat and power plants connected to district heating. In addition, biofuels in transport applications represent a small fraction of the bioenergy use in countries such as Austria, France, Germany, Italy and Sweden.

A large biomass potential remains unexploited in Europe, for example in the form of residues from woodland management measures, agricultural residues, organic waste from industry and households and energy crops (see also Table 11.1). The total biomass potential is estimated at 6759.2 PJ (161.4 Mtoe), with the largest contribu­tions coming from woody residues (i. e. wood residues from stem wood production, thinning from managed forests, and wood waste from the wood products industry and arboricultural activities) and from a variety of annual and perennial energy crops (Bauen and Kaltschmitt, 2001).