Combined heat and power (CHP) is a way of generating heat and electricity simultaneously. It has been in use in the industrial sector since the energy crisis of the 1970s and has become more popular recently due to the threat of climate change.

While not actually a form of renewable energy, CHP is included here because it is a way of generating some of your own electricity, and can result in a significant fall in your carbon footprint. It has been flagged up by some commentators as the best way to lower domestic carbon emissions.

Micro-CHP (domestic-sized) is different from many of its industrial forebears, as they tend primarily to generate electricity, with heat as a useful bi-product. Micro-CHP is being developed to produce heat (replacing a domestic boiler) and generate electricity as a bi-product.

Research by the Carbon Trust published at the end of 2007 found that micro-CHP is most suited to larger homes with three or more bedrooms, or older houses where it is not currently cost effective to improve insulation (such as those with solid brick walls). This type of home could see carbon emissions reductions of between 5 and 10 per cent.

The micro-CHP systems work best in buildings where they operate for many hours at a time, rather than intermittently. These tend to be ones that need long and consistent heating periods.

Micro-CHP works in a similar way to a standard gas boiler. Both floor standing and a wall-mounted varieties are available. There is also potential for biomass fuelled CHP, but domestic versions are not likely to reach the market in the near future.

• A condensing boiler heats your hot water and – through your central heating system – your house.
• The steam produced is captured and used to produce electricity (using a Stirling engine or, potentially in the future, a fuel cell).
• This electricity can be used in the house, or exported to the grid.

Relatively small amounts of electricity are generated – and only when the central heating is on. The aim is to reduce the amount of electricity you draw from the grid (most of which comes from sources high in carbon emissions), not to replace your electricity supply.

Find a CHP installer.

The only wall-hung micro-CHP unit available so far is the Baxi Ecogen, which is only available through the British Gas installer network. Feedback on YouGen indicates that they are doing their best to deter potential customers from buying. Pre-launch, prices were expected to be around £3,000, but we're had reports of quotes in the £6 - 8,000 range.

The only wall-hung micro-CHP unit currently available is the mains gas version of the Baxi Ecogen. Although it looks like a traditional boiler, it is double the weight, which means it must be hung on a double brick or concrete wall on the ground floor, with space to site three meters nearby. There isn't a combi version, so you will also need space for an insulated cylinder. An LPG version for houses off the gas grid is expected any time from Calor.

In the pipeline:

The WhisperGen is expected to be sold by E.on in early in 2011. It is free standing, and roughly the same size as a dishwasher.

Ceres Power aims to launch a fuel cell-based product onto the mass market in 2011. Also expected in 2011 is the wall-mounted Genlec - which claims to be a "low cost" micro-CHP technology comprising an Organic Rankine Cycle module.

Worcester-Bosch is trialling the Greenstar CDi Dual Gen, which uses a sterling engine with condensing boiler technology. It is expected on the market in 2012.

From the blog:

Is domestic CHP dead and buried?

Long awaited Baxi Ecogen Micro-CHP unit launched

First wall-hung micro-CHP unit due this year (2009)

Good Energy rewards renewable heat generators

Selling the electricity you generate

Support for microgenerators increased this month (April 09)

Sources:

Micro CHP

Carbon Trust

Cambridge Consultants