What is Bioenergy?
Bioenergy is energy derived from biomass which includes biological material such as plants and animals, wood, waste, (hydrogen) gas, and alcohol fuels. In essence bioenergy is the utilisation of solar energy that has been bound up in biomass during the process of photosynthesis. The photosynthesis process uses solar energy to combine carbon dioxide from the atmosphere with water and various nutrients from the soil to produce plant matter - biomass. It is a renewable energy source.
Biomass is all organic material, an example being plant matter. It is either:
- the direct product of photosynthesis (for example plant matter – leaves, stems, etc.) or
- the indirect product of photosynthesis (for example animal mass resulting from the consumption of plant matter).
EU Directive 2001/77/EC (RES-E) - promotion of electricity produced from renewable energy sources
'Biomass' shall mean the biodegradable fraction of products, waste and residues from agriculture (including vegetal and animal substances), forestry and related industries, as well as the biodegradable fraction of industrial and municipal waste.
Types of biomass that are used to provide bioenergy include:
- wastes streams, including residues from forestry and related industries
- recycled wood
- agricultural residues and agrifood effluents
- manures
- the organic fraction of municipal solid waste
- separated household waste and sewage sludge
- purpose grown energy crops including short rotation forestry, miscanthus grass, etc.
For more information download the SEAI Briefing Document on Biomass (.pdf, 150kb) or Biomass Factsheet (.pdf, 2082kb)
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Biofuel is a term used for biomass which has been prepared/upgraded to provide bioenergy. Biofuel can be either:
- solid biofuel, e.g. wood pellets (see Wood energy) straw (www.videncenter.dk/uk/index.htm) publications - Straw for Energy Production - Technology - Environment - Economy
- liquid biofuel e.g. biodiesel, which can be used as a vehicle fuel (see Liquid biofuels ).
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Bioenergy, or energy from biomass, supports a wide range of national policy goals:
- Key energy goals including security and diversity of supply and the development of indigenous renewable energy sources
- Key environmental goals such as greenhouse gas emissions reduction * and waste management
- Key agricultural goals offering new opportunities for farmers in the context of CAP reform
- Key social goals such as employment generation in rural areas and enhancement of local economies
*Note 1: The carbon dioxide (CO2) emitted on combustion of biomass is taken up by new plant growth, resulting in zero net emissions of CO2 –bioenergy is considered to be carbon neutral. However, it should be remembered that there are some net CO2 emissions associated with bioenergywhen looked at on a life cycle basis – emissions from fossil fuels used in cultivation / harvesting / transport of the biomass. These are generallysmall compared to the CO2 avoided by displacing fossil fuels with energy from biomass.
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Bioenergy can be exploited primarily through:
- Combustion: Biomass (e.g. wood chips) can be burned to provide process and/or space heating. The combustion of biomass can also be used to raise steam to drive engines / turbines which are coupled to generators producing electricity.
- Anaerobic digestion: Biomass (e.g. animal manure) can be transformed to biogas by anaerobic digestion and the biogas can be used to fuel a gas engine or gas turbine, or burned in a boiler to provide heat or to raise steam.
Other technologies for the exploitation of bioenergy include gasification and pyrolysis but these are not as commercially developed as combustion and anaerobic digestion.
The principal pathways for the exploitation of bioenergy are shown in the following diagram.
Heat Production
The majority of current biomass-derived energy comes from wood combustion to produce heat. Direct combustion processes for heat production and driving a steam cycle are already commercial, with a constant drive for the improvement of their efficiency and reduction of their pollutant emissions. There are two different systems of creating heat: small scale heating and district heating systems. The first ones uses logwood, pellets, woodchips, etc., the other, typically based on either fluidised bed boilers, can burn wood chips, peat, refuse-derived fuel, waste wood, sawdust and straw.
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Co-generation of heat and power
Combined heat and power (CHP), the simultaneous production of heat and power, is suitable for small scale applications. It can be used to provide space heating and domestic hot water to individual houses or a group of buildings. Excess electricity generated may often be exported to the grid. This relatively new technology has reached the commercialisation stage also for small scale applications (50-500 kW).
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Contact:
Tom Knitter
Sustainable Energy Authority of Ireland
Renewable Energy Information Office
Unit A, West Cork Technology Park
Clonakilty
Co. Cork
Tel: 023 8842193
Email: tom.knitter@reio.ie
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