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Micro Combined Heat and Power

What is Micro Combined Heat and Power?

This refers to a heating technology which generates heat and electricity simultaneously, from the same energy source, in individual homes or buildings. This contrasts with conventional ways of generating electricity where vast amounts of heat is simply wasted.

Whilst strictly not renewable, as currently CHP installations burn gas or oil as a heating fuel, it is considered a ‘low carbon technology’ because of it’s efficiency in providing both heat and electricity.

How does it work?

There are 3 main micro-CHP technologies. The difference is the way in which they generate electricity, which can be done in the following ways:

  • Stirling engine
  • Fuel cell
  • Internal combustion engine

Stirling Engine micro-CHP

Stirling engines are typically for buildings with smaller heat demands and would be appropriate for domestic applications in the UK. The latest Stirling engine based micro CHP units allow electricity to be generated sooner after being turned on, and are more efficient at producing heat.

Fuel cell

CHP technology is new to the market in the UK and globally. Fuel cells work by taking energy from fuel at a chemical level rather than burning it.

Internal combustion engine

CHP is the most proven technology. These are essentially, and sometimes literally, truck diesel engines modified to run on natural gas or heating oil, which are connected directly to an electrical generator. Heat is then taken from the engine’s cooling water and exhaust manifold. Generally they produce twice as much heat as electrical power and have, to date, been primarily used in larger commercial-scale applications in the UK.

Systems consist of one of the above, a generator to produce electricity, a heat recovery system to obtain the useable heat from the engine, a cooling system to dissipate heat, combustion and ventilation air systems to provide fresh air and remove exhaust air, a control system to maintain safe and efficient operation and lastly an enclosure to provide a physical barrier and form of protection.

Most domestic micro CHP systems will have two burners, one small (engine burner) and one large (supplementary burner). If you want hot water only then the boiler will use the small burner, and generate electricity at the same time. However, if you want to heat hot water and water for space heating at the same time the boiler may have to use the larger burner, which uses more gas, but will not produce any additional electricity.

Electricity generation comes second to the production of heat (typical ratio of about 6:1 for domestic appliances) – electricity is only generated when heat is produced.

Is it suitable?

  • A micro-CHP unit resembles a gas condensing boiler and can be wall hung, or floor standing.
  • Installation is easy, however an electrician will also be required. Existing radiators do not need to be replaced.
  • Servicing costs and maintenance are estimated to be similar to a standard boiler – although a specialist will be required.
  • Electricity is only generated when heat is produced, therefore in the warmer months when you do not heat your home you will have to draw more electricity from the grid.
  • The carbon saving potential of Micro-CHP has been found to be best in buildings which require long and consistent heating periods, such as care homes, hotels etc.
  • CHP may be an option for hard to treat properties (such as solid wall, older buildings) which have a higher than normal heat load and cannot easily/ cost effectively be insulated.

What are the benefits?

A typical micro CHP until will deliver the same comfort levels as a conventional boiler.

A reduction in electricity bills, as you only need to draw on electricity from the National Grid when heating is not required. A typical domestic system is expected to have the potential to generate up to 1kW of electricity per hour once warmed up. This would be enough to power the lighting and appliances in a typical home. The amount of electricity generated ultimately depends on how long the system is running.

Noise levels are comparable with conventional central heating systems.

Receive payment for energy exported to the grid: Small scale generators of electricity (up to 5MW) can apply to a Smart Export Guarantee (SEG) Licensee to receive payment for the electricity exported back to the National Grid.  SEG Licensees offer different rates, therefore generators should shop around to find the best SEG rate. To see the current list of SEG Licensees click here.



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