Micro combined heat and power (Also known as Micro CHP)

What do Micro CHP systems do?

Micro combined heat and power is a heating technology producing heat and electricity simultaneously in an individual building from the same energy source.

Micro-CHP systems main output is heat with some electricity generation. A typical ratio might be 6:1 for domestic appliances.

Once warmed up the potential generation capacity of a system for domestic use is up to 1kW of electricity per hour or just about enough to power the lights and appliances.

As with other systems, e.g. Hydro, surplus electricity can be exported back to the National Grid. The amount of electricity generated will depend on how long the system is running.

Currently the majority of domestic micro-CHP systems require mains gas or LPG as a heating fuel. However there are some that can also run on bio fuels or oil. Gas and oil are fossil fuels and not renewable energy sources, but the Micro CHP technology is still considered to be a low carbon technology because it supplements and reduces the use of fossil fuels and the taking of energy from the National Grid. It is more efficient.

Comparable in size and shape to an ordinary modern domestic boiler micro CHP systems can be wall hung, or floor standing. Servicing & maintenance costs are estimated to be similar to a standard boiler, although a specialist will be required.

The single crucial difference to a standard boiler is their ability to generate electricity whilst heating water.

How do micro CHP Systems work?

There are 3 main micro-CHP technologies.

They generate electricity in differing ways:

Stirling Engine micro-CHP
Stirling engine micro CHP generally requires a short warm-up period before starting to produce electrical power. It is best suited for buildings with lower heat demands, such as homes.

Fuel cell CHP technology 
This is relatively new both to the UK and globally. it is still at a developmental stage and therefore not currently available to consumers. The fuel cells work by removing energy from fuel at a chemical level rather than burning it.

Internal combustion engine CHP
The most proven technology. They are essentially truck diesel engines modified to run on natural gas or heating oil. They are usually connected directly to an electrical generator, with the heat from the engine’s cooling water and exhaust manifold being utilised. These systems produce twice as much heat as electrical power.

What are the benefits of Micro CHP?

  • Reduced fuel bills, especially when compared to conventional electric heating
  • Electricity generation as a by-product of heat. When the micro CHP is generating heat, it will also generate electricity to be used in the property or exported.
  • Reduced carbon footprint. Generating electricity on site means saving significant amounts of carbon as there are minimal losses compared to the National Grid.
  • Requirement for fuel deliveries is reduced
  • Can provide both electricity and hot water
  • Simple Installation. The Micro CHP one should fit in the same location as any existing traditional boiler. It will require an electrician to work with the heating engineers, but competent companies should be able to arrange this.
  • Additional income . Micro CHP is eligible for Feed-In Tariff income. For more details on this go to the Energy Saving Trust Web site at http://www.energysavingtrust.org.uk/Generate-your-own-energy/Sell-your-own-energy/Feed-in-Tariff-scheme You will earn for each kWh generated by your system and also for each kWh you export.

Is a Micro CHP system suitable?

Here are a few key questions to consider:

What other options are there?
Other low carbon technologies such as wood-burning stoves may offer greater savings both financially and in and carbon use.

Is the property well insulated? 
Since they only generate electricity when there is a demand for heat, micro CHP systems are most cost effective in houses with large heating needs that cannot be reduced by other means such as upgrading insulation, draught- proofing and other low carbon heat technologies such as wood-burning stoves.

For properties that are more challenging to improve in terms of insulation and draught-proofing, such as older buildings which have a higher than normal heat load, a micro-CHP unit may be an option.

Is the system intended for a new development?
The installation costs can be reduced by combining with other building works.

What are the costs and savings?

Typical system cost will start from around £5,500

These will depend on several factors; some of them are set out below.

It is important that the system is appropriately controlled for the demands being placed upon it. Actual savings figures will always depend on relevant exact fuel prices

Fuel costs
Using a Micro CHP system does not mean an end to fuel bills, but does offer the opportunity to reduce them.

Old and new system efficiency 
The efficiency of the old heating system is/was will have dictated how much it cost to run and the size of heating bills. If the original system was operating inefficiently these could have been high, so the difference between the new and old running costs will be greater, with significantly more saving.

Temperature setting: 
If you use the heat pumps to increase the ambient temperature of your building from previous levels with your old heating system then you can expect your heating bills to be higher and no savings to be made. 18 to 21 degrees Celsius is the optimum setting for your thermostat.

Using the controls 
Efficient and effective control of the system is the only way to get the most out of it. Ask your chosen installer to explain in detail how to control the system for maximum efficiency.

The majority of domestic micro CHP systems have two burners, one small (engine burner) and one large (supplementary burner). Electricity will be produced when the small burner is being used. Managing the use of the heating and hot water will make sure you get the best ratio of heat to electricity as possible.

If heat for hot water and water for space heating is required at the same time the boiler may use the larger burner, thus using more gas and not producing electricity.

Micro CHP systems should be designed, installed and run to meet the heating needs of the building. Electrical generation is secondary, a by-product rather than a core aim. Electricity will only be generated when there is a demand for heat.

Want to know more?

To find renewable technologies to suit your property, try the Energy Saving Trust energy selector tool at. http://www.energysavingtrust.org.uk/renewableselector/start/

Curious about the Technologies?

For more information on home energy generation technologies, contact your local Energy Saving Trust Advice Centre on 0800 512 012.

For specific technology questions, visit the Heat Pump Association at http://www.feta.co.uk/hpa/