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Biogas A gaseous fuel composed of methane and carbon dioxide, produced from the decomposition of organic material in landfill sites. Biogas is a form of biomass (see below) and as such regarded as renewable and relatively clean, because it returns to the atmosphere the carbon dioxide which it absorbed in its lifetime, which would in any case, over time, be released into the atmosphere.

Biomass A collective term for all organic subtonics of relatively recent origin (non-fossil fuels) that can be used for energy production. Biomass may be solid (e.g. wood), liquid (e.g. vegetable oil used for motor fuel), or gaseous (biogas).

Carbon capture
The technique of collecting carbon dioxide from fossil fuel burning before it is released into the atmosphere and storing it where it cannot easily escape - e.g. unmineable coal seams, the deep ocean.

Carbon footprint
A representation of the total effect human activities have on the climate in terms of the total amount of greenhouse gases produced (measured in units of carbon dioxide).

Carbon trading
A system whereby countries or individual companies are set emission targets. Those that cannot meet theirs can buy 'credit' from the countries/companies which exceed their targets - e.g. if an overall target of 10% reduction in emissions is set, a country/company which achieves 15% could 'give' its surplus 5% to a country/company which achieves only 5% - thus the overall target is still met.

Climate change Statistically significant changes in climate persisting for an extended period (decades or more). Climate changes have occurred naturally in the past - for instance the ice ages which covered northern Europe and America in ice sheets, and occur periodically because of natural phenomena such as changes in ocean current, volcanic eruptions and so on.

However, when the term 'climate change' is used in the debate on energy it refers to changes in climate believed to be the result of global warming, for instance more frequent and intense storms, more frequent prolonged droughts, extremes of weather, such as the unusually hot summer in Europe in 2003.

Cogeneration The simultaneous production by means of a single fuel source of useful energy (usually electricity) and heat that can then be recovered for use as additional energy.

Decentralised energy Energy facilities that operate at a local level on a small scale, as opposed to large centralized facilities such as the national grid (see below).

Decommissioning The process of removing a nuclear reactor from service and dismantling it so as to make the site available for unrestricted use (i.e. with no need for safety precautions). The process of decommissioning can take many years. For instance, the Hunterston nuclear reactor is not scheduled to be fully decommissioned until 2090.

Enriched uranium Uranium whose uranium-235 content has been increased to make it more suitable for fission.

Fossil fuels A fuel such as coal, oil and natural gas produced by the decomposition of ancient (fossilized) plants and animals. Fossil fuels store carbon (one of the key elements in the chemistry of living things) which is released as carbon dioxide when it is burned.

Gasification A thermochemical process that converts a solid or liquid fuel source (e.g. coal, organic waste) to a gaseous fuel

Global warming The temperature of the earth is controlled by the balance between the input from energy of the sun and the loss of this back into space. About one third of heat from the sun is reflected back into space. The rest is absorbed by the atmosphere and, mainly, by the land and oceans. The earth's surface becomes warm and emits heat which is trapped by naturally occurring greenhouse gases and warms the atmosphere. If this did not happen, the Earth's average temperature would be roughly -200C.

However, greenhouse gases are being increased by the burning of fossil fuels and it is accepted by most scientists that the result of this is to increase the amount of heat trapped in the atmosphere (or, to put it another way, to reduce the amount lost into space) and so to raise the temperature of the Earth, resulting in melting of the icecaps, shrinking of glaciers and consequent changes in climate.

Greenhouse gases The main naturally occurring greenhouse gases are water vapour and carbon dioxide. The main manmade greenhouse gas which affects global warming is carbon dioxide.

Insulation Covering or lining a space or substance with a material that prevents the passage of heat energy, for instance lining a loft space with rockwool, covering a hot water cylinder with an insulating jacket.

Isotope A member of a chemical element family which has two or more nuclides with the same number of protons but a different number of neutrons so that while their chemical attributes are the same their physical attributes may be different - for instance carbon-12, which is stable, and carbon-14, which is radioactive. There are three naturally occurring radioactive isotopes in uranium, uranium-234, uranium-235 (see enriched uranium) and uranium-238.

Microgeneration Generating energy on a domestic scale- e.g. by having a wind turbine or photovoltaic cells on the roof of a house.

National grid The transmission network of pylons and cables through which electricity moves from suppliers to customers in the UK.

Nuclear fission The process by which a nucleus splits into two or more large fragments of comparable mass, simultaneously producing vast amounts of energy. As well as being used to generate electricity this process can be used to produce atomic explosions.

Nuclear fusion The process by which two light nuclei combine at extremely high temperatures to form a heavier nucleus and release vast amounts of energy.
This is believed to be the process from which the sun and other stars derive their energy. As well as being used to generate electricity this process can be used to produce hydrogen bomb explosions.

Photovoltaic cells Cells which convert light (usually sunlight) into electricity

Plutonium The fissionable isotope of plutonium is plutonium-239. It is produced artificially in fast breeder reactors by neutron irradiation of uranium-238 and is highly toxic. Its half-life is 24, 360 years. It is a preferred fuel for nuclear weapons. Over one third of the energy produced in most nuclear plants comes from plutonium-239.

Solar thermal energy The conversion of the radiant energy from the sun into heat by using solar thermal collectors, which absorb the heat from the sun and retain it.

Trigeneration The simultaneous production of electricity, heating, and cooling.

Wind turbine A wind-driven machine containing curved rotors or blades inside a wheel on a revolving shaft; wind or air pressure against the blades turns the wheel, and the rotating shaft may then drive a dynamo to produce electric power.





created 5 May 2005

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