CHP FAQ

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Q. What is Combined Heat & Power?

A. Combined Heat and Power (CHP) is the simultaneous generation of usable heat and power (usually electricity) in a single process. Through the use of an absorption cooling cycle, trigeneration or Combined Cooling Heat and Power (CCHP) schemes can also be developed. CHP is a highly efficient way to use both fossil and renewable fuels and can therefore make a significant contribution to the UK’s sustainable energy goals, bringing environmental, economic, social and energy security benefits.

CHP systems can be employed over a wide range of sizes, applications, fuels and technologies. In its simplest form, it employs a gas turbine, an engine or a steam turbine to drive an alternator, and the resulting electricity can be used either wholly or partially on-site. The heat produced during power generation is recovered, usually in a heat recovery boiler and can be used to raise steam for a number of industrial processes, to provide hot water for space heating, or, as mentioned above with appropriate equipment installed, cooling.

Because CHP systems make extensive use of the heat produced during the electricity generation process, they can achieve overall efficiencies in excess of 70% at the point of use. In contrast, the efficiency of conventional coal-fired and gas-fired power stations, which discard this heat, is typically around 38% and 48% respectively, at the power station. Efficiency at the point of use is lower still because of the losses that occur during transmission and distribution. (see DUKES electricity chapter for more details)

In contrast, CHP is a form of a decentralised energy technology. CHP systems are typically installed onsite, supplying customers with heat and power directly at the point of use, therefore helping avoid the significant losses (which occur in transmitting electricity from large centralised plant to customer.

Further reading:
CHP section of Carbon Trust Knowledge Centre
Where the following can be downloaded:
CHPClub Manager’s Guide on Packaged CHP
CHP Club Manager’s Guide on custom-built CHP
Good Practice Guide 388 - Combined heat and power for buildings

Digest of UK Energy Statistics CHP Chapter

CHPQA

Also check our Members’ profiles which have some excellent material posted there

Some other online technical guides which free to download include:
ASEAN COGEN 3 project report: Available Cogeneration Technologies in Europe (Part I & II)

Guide to Combined Heat and Power Systems for Boiler Owners and Operators

Q. What are the benefits of CHP?

A. CHP delivers a range of economic, environmental and benefits - some of these accrue to its users, some to operators of the electricity grid and yet others to the wider community:

Cost savings - CHP’s high efficiency leads to a reduction in the use of primary energy. Precious fuels are used much more efficiently, so less is used. And less fuel used means significantly lower energy costs to the end user. Savings vary, but can be between 15% and 40% compared to imported electricity and on-site boilers.

Lower emissions - less fuel burnt means reduced emissions of carbon dioxide (the main greenhouse gas) and other products of combustion. Indeed CHP could provide the largest single contribution to reducing carbon dioxide emissions. Host organisations that wish to reduce their environmental footprint benefit - as does the environment.

Increased security and power quality - CHP systems can be designed to continue to operate and serve essential loads during an interruption to mains power supplies, increasing security of energy supplies. CHP can also supply higher-quality power than that from the grid - this can be important for computer data centres etc.

Grid reinforcement - siting an on-site CHP unit within the electricity grid can strengthen the network and remove the need for network operators to upgrade the system there

Q. Where can CHP be used?

A. CHP is a family of energy conversion processes, rather than a single technology, so it can be used to provide energy to anything from a single home to a large industrial plant, or even a whole city. Unlike conventional power plants, CHP units are sited close to where their energy output is to be used.

The main design criterion is that, to make the investment worthwhile, there must be a need for both the heat and electricity produced by the CHP unit.

In the home, a microCHP unit resembling a gas-fired boiler will provide both heat for space and water heating, as does a boiler, but also electricity to power domestic lights and appliances. MicroCHP units are a very new technology only recently appearing in the UK market, but the potential for them is as large as the number of homes in the country.

For commercial buildings and small industrial spaces, a factory-assembled, ‘packaged’ CHP system is appropriate. Here, an electricity generator, heat exchanger, controls and either an engine or a turbine is packaged together into a CHP unit that can be connected to the heating and electricity systems of the building.

Some building types, particularly those that need a lot of energy, or operate around the clock, are particularly suitable for CHP - leisure centres, hotels, hospitals and many others. CHP systems can, with the addition of a chiller, supply cooling for air conditioning systems as well as heating - such an arrangement is often called a ‘trigeneration’ system.

Homes and buildings fitted with CHP are usually also connected to the mains electricity grid, and may also retain back-up boilers, so that they are never short of an energy supply, during maintenance of the CHP plant, for example, or during periods of unusually-high energy loads.

Industrial CHP plants tend to be designed and built individually to fit the industrial process they serve. These CHP plants are based on gas turbines, steam turbines or engines, together with electricity generators and control systems. The very largest CHP plants rival traditional power-only plants in size and deliver huge quantities of energy - but at a much higher efficiency

Some industrial processes are particularly well-suited to CHP, those that use lots of heat and operate around the clock - the manufacture of paper, chemicals, food and drink products, as well as refineries, are among those that can benefit most from CHP.

Community heating systems serve whole towns, areas of cities or, in a few cases, whole cities. Here, one or more CHP plants supply heating to a grid of insulated hot water pipes that carry heat to a range of buildings, including public and private sector flats. As well as CHP plants, boilers and other sources of heat may feed heat into the grid. Buildings that take heat from the community heating system do not need their own boilers. Meanwhile, the electricity generated is used to help run the community heating plant, and within the customer buildings, or is exported to the electricity grid.

Community energy systems supply cooling, as well as heating and electricity, to buildings.

Q. What is the Government’s CHP target?

A. In recognition of the significant carbon saving potential of CHP, following the first Earth Summit negotiations in 1992, the then Conservative Government, established in 1993, the first target for CHP of 4 GW (4,000MW) by 2000. With the rapid development of schemes at this time, this target was raised the following year to 5 GW as part of the Government’s Climate Change Programme.

The present Government increased this once again in 2000, establishing the current target of 10,000 MW by 2010, which remains a key element of the Government’s revised Climate Change Programme, issued in March 2006.

The latest Government statistics (up to 31 December 2005) show that 5,792MW of CHP capacity is operating in the UK. (Further information detailed in CHP Statistics).

Q. What is The Government’s CHP Strategy?

A. Defra published the Government's Strategy for Combined Heat and Power to 2010 in April 2004. This, along with a number of other Government reports on CHP can be downloaded from Defra’s CHP webpage.

More recent policy statements on CHP have been made in the March 2006 Climate Change Review and the July 2006 Energy Review .