Technology Directory

Directory of low carbon technologies

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Combined Heat and Power

Combined Heat and Power (CHP) plants are power plants that make use of both electrical and heat outputs, resulting in a more efficient use of fuel overall. When electricity is generated from fossil fuels in a standard power plant, a significant proportion of the energy in the fuel is converted to heat rather than electricity and lost. In contrast a CHP system captures the heat and supplies it to users close to the plant or as hot water or steam to be piped further afield. CHP is also referred to as cogeneration as the plant is simultaneously generating heat and power. CHP fuelled with natural gas is a low carbon rather than a zero carbon option, but using biomass as a fuel allows the possibility of renewable CHP.

The heat from a CHP unit can be used to drive a cooling system such as an absorption refrigerator. Plants producing electricity, heat and cooling are often referred to as CCHP (Combined Cooling Heat and Power), tri-generation or poly-generation plants.

CHP can be used at a range of scales, from multi megawatt industrial installations (large scale CHP) to 1kW domestic units (micro CHP). Large scale plants generally use gas and steam turbines for electricity generation. Smaller plants are most often based on engines (internal combustion engines and stirling engines being the two main types) but can also use turbines. Alternative options for CHP generation include fuel cells which are currently at the early demonstration stage.

Large scale CHP installations, when correctly sized, designed, installed and managed, can reduce the overall carbon dioxide emissions associated with the production of equivalent quantities of heat and power. The economic viability of CHP is sensitive to the relative prices of gas and electricity (known as the spark spread).

Similarly, the benefits of Micro CHP are maximised when it is deployed in the most appropriate way. The carbon saving potential of Micro-CHP has been found to be best in buildings which require long and consistent heating periods, such as leisure centres or care homes because it ensures the plant operates for many hours at a time, rather than intermittently. The Carbon Trust recently reported CO₂ savings of 15-20% for small commercial applications in its major field trial.