Air Pollution
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Acid Rain
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Climate Change
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Ozone Depletion

Combined Heat & Power

During electricity generation, a large amount of low-grade heat is produced as a by-product. In conventional power stations this heat is lost. In combined heat and power (CHP) systems the heat produced during electricity generation is recycled rather than wasted, thereby increasing the efficiency of the system. CHP is usually only used as a supplement to grid mains electricity supply.

High capital and maintenance costs deter individual users from investing in CHP, and therefore CHP schemes are more likely to be used by the public, industrial and commercial sector. The main markets tend to be those requiring a great deal of heat, for example leisure centres, hospitals and industrial sites with process heating requirements, especially the chemical, brewing and paper industries. Sewage treatment works sometimes use CHP fuelled by biogas, emissions released during the decomposition of sewage.

The increased fuel efficiency of CHPs gives them a potentially useful role in helping to combat global warming, by decreasing carbon dioxide emissions. The reduction in carbon dioxide emissions can be as much as 50%, depending on the fuel being replaced by CHP. Acid rain can also be reduced by the use of CHP, by cutting emissions of sulphur dioxide and nitrogen oxides. However, one disadvantage of a CHP plant that is close to the point of use is the increased noise level.

The UK Government is promoting CHP through the Energy Efficiency Office's Best Practice Programme, and through the Energy Saving Trust. CHP currently provides about 4% of the UK's electricity.