Biopower is created by the conversion of fuels derived from recently living organisms and/or municipal solid waste into energy in the form of electricity. The organic matter used as the initial fuel source or feedstock is called biomass. For biopower to be considered renewable, the feedstock must be available on a recurring basis.
When considered as a renewable resource for reducing greenhouse gas emissions, biomass is generally considered carbon-neutral even though it does release carbon into the atmosphere when converted to electricity. Because the carbon in the feedstock was recently removed from the atmosphere by the plants and trees from which it is derived, the use of this matter as fuel does not release a new source of carbon into the atmosphere.
Types of biopower
There are many different types of biopower. These can be differentiated by the biomass source and by the methods used to convert the biomass into electricity. Sources of biomass with potential for use in biopower include:
- Solid wood, wood chips, pellets, sawdust, and shavings
- Agricultural residues such as stalks, leaves, husks, and shells
- Energy crops such as fast-growing trees and grasses grown specifically as biomass
- Algae grown as biomass
- Animal manure
- Byproducts of municipal sewage treatment
- Municipal waste buried in landfills
- Solid municipal waste diverted prior to the landfill
- Organic residues from food processing and breweries.
Biomass contains chemical energy. The chemical energy is most commonly converted to thermal energy via combustion. The thermal energy is then converted to kinetic energy, which is then converted to electricity by a generator. Various methods are used to make these multiple conversions.
An alternative use for biomass is to convert the chemical energy directly to electricity using a fuel cell.
Chemical energy is converted to thermal energy through either direct or indirect methods of combustion. Direct methods simply combust the solid biomass without converting its form.
Indirect methods convert the biomass to an intermediate fuel, either gas or liquid, which is then combusted. Indirect methods include gasification, digestion, and liquid fuel conversion.
Biopower generation units may be either centralized or decentralized. Many smaller systems are located at or near the source of biomass and the power produced may be consumed internally by the host facility or connected to the distribution system. This is called distributed generation. In some cases, biopower is used at larger centralized power plants.
Biopower is created using various technologies. For a description of each, see the following: