Small scale combined heat and power

Small scale combined heat and power (CHP)

Combined heat and power (CHP) is a process by which both electricity and heat are generated in a single process. The CHP unit provides a continuous source of electricity and produces heat in the form of hot water or steam that can be used for space heating or running hot water.

There are three sizes of CHP, large scale, mini and micro. The large scale tends to be for major industrial or commercial applications and the mini for swimming pools, hospitals or housing estates. The micro is for single domestic households.

Combined heat and power systems use conventional generators such as internal combustion engines, Sterling engines and  fuels cells. Micro CHP tends to use four-cylinder Sterling engines and can be powered by diesel, paraffin, natural gas or LPG.

Q. Are all homes suitable for CHP?

A. CHP units generate electricity and in doing so produce heat.. To make the unit cost-effective it is necessary to find a use for the heat. Homeowners also need to consider whether they required a continuous supply of electricity because heating specialists consider that CHPs  need to run for at least 12 hours a day to make them economical. The longer the unit is allowed to operate the greater are the savings. 

Q. Can I export the energy generated to the national grid?

A. Where a house is linked to the national grid a CHP system can be used to supplement the mains electricity. When the CHP is not generating enough power, mains electricity can be used. If the CHP generates more electricity than is needed, the excess can be exported to the national grid by agreement with the regional electricity company. The price paid for exported electricity is far less than that paid for importing.

Q. How much do CHP units cost?

A. Gas consumption is virtually the same for a conventional gas boiler and a micro CHP unit. Savings are made through the electricity generated. Analysts predict that the average home with micro CHP could save £150 per year on energy costs. This saving includes the sale of electricity back to the energy supplier. As the micro CHP market grows and becomes more competitive this figure should rise. Most households are only likely to invest in CHP when their existing boiler breaks down or reaches the end of its useful life.

Q. What grants are available for microgeneration technologies for householders?

A. The Department of Energy and Climate Change (DECC) run a Low Carbon Buildings Programme that provides micro -generation grants for householders www.lowcarbonbuildings.org.uk .

Q. How can I find an installer?

A. Recipients of Low Carbon Buildings Programme grants must use accredited installers and materials. The list of accredited installers is a useful resource even if you are not applying for a grant for all types of renewable technologies.

Q. Is planning permission needed to install CHP in a house?

A. Domestic CHP systems can be installed in place of standard domestic boilers so planning permission may not be required if there are no changes to location and openings for flues. However, it is worth contacting the local council Building Control Officer to ensure compliance with Building Regulations.

Q. Do CHP units require more maintenance than a conventional boiler?

A. Yes. A conventional boiler should be serviced annually by a CORGI registered plumber but a CHP unit would require more frequent servicing. 

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