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.

Micro-CHP works in a similar way to a standard gas boiler. Floor standing versions are available now, and wall-mounted varieties are due to be launched early in 2009. 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.

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. The Carbon Trust suggests that if the technology is going to be widely taken up, customers will need to be paid for electricity that they export to the grid. The trial found half of all domestic electricity generated by a 1kWh micro-CHP system is exported.

Much development and cost reduction is required if micro-CHP is to reach the mass market, according to technology specialist, Cambridge Consultants. They predict that it offers the opportunity to develop a new kind of business model where the power company owns the CHP device, and sells the customer heat and power, rather than gas and electricity (sounds great for the power company, but how good is it for the customer to be tied in to one supplier?).

It’s too early to say.

From the blog:

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