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Glossary terms used on this page

CO₂

CO₂, or carbon dioxide, is made up of the elements carbon and oxygen. It exists quite naturally in our atmosphere, as part of the carbon cycle. Everyday processes in the plant and animal world both add CO₂ to the atmosphere and take it out. However, because it is a greenhouse gas - meaning it affects the temperature of the earth - the exact level of CO₂ is important. Burning fossil fuels releases CO₂ into the atmosphere, hence the anxiety that extensive use of these fuels is causing climate change.

Eco-friendly

Eco-friendly, or environmentally friendly, is a term applied to goods, services, processes or people deemed to do minimal harm to the environment. The term is shorthand for 'ecologically friendly', ecology being the study of the relationships between living organisms and their environment.

Embodied energy

Embodied energy - sometimes referred to as 'embedded energy' - is the energy used (and therefore the CO₂ emissions) in manufacturing, packaging and transporting a product, material or service. So when calculating the CO₂ savings from a new energy-efficient product such as a boiler or washing machine, its embodied energy needs to be taken into account. Usually the energy saved in use will quickly compensate for the embodied energy, but in some cases - such as small urban wind turbines - it may be that a product will use more energy in its manufacture than it will save across its lifetime.

Emissions

Emissions are the CO₂ (and other greenhouse gases) produced by energy use, usually calculated and stated as an annual tally: also referred to as your carbon footprint. Your personal emissions can be direct - such as the gas you personally use to heat your home or the petrol you burn to power your car - or indirect - meaning the energy use that has gone into the products or services you buy. The latter, such as the emissions caused by the manufacture of your new TV, or the packaging your food comes in, are also referred to as embodied emissions.

Kilowatt-hours (kWh)

A kilowatt-hour is an amount of energy equivalent to a power of one kilowatt (a thousand watts) running for one hour. The unit is commonly used on electricity meters. If you know how many kilowatt-hours of energy your household uses, you can translate this into kilograms of CO₂ emitted by multiplying it by 0.527. A megawatt hour (MWh) is an amount of energy equivalent to the power of one megawatt (a million watts) running for one hour. Similarly, a gigawatt hour (GWh) is a billion watts for one hour, and a terawatt hour (TWh) is a trillion. While your domestic gas bill will be set out in kWh, the output for a power station, for example, will obviously be expressed in one of these much larger units.

National Grid

The grid, or National Grid, is a privately owned network of electricity supply lines that stretch from the power stations where the electricity is generated to the homes and businesses where it is used. In some parts of the UK, local or domestic microgeneration may make it feasible to live "off grid", while some homes in remote parts of the country have no choice because it does not reach them. In some cases, microgeneration means there is potential for people to sell surplus electricity back to the grid.

Solar energy

Energy derived from the sun's rays.

Solar panels

Solar panels, usually roof-mounted, use the energy of the sun to generate electricity for home use, with the potential to sell surplus back to the grid. Light shining on a panel of photovoltaic cells creates an electric field across layers of semiconductive material, causing electricity to flow.