Combined heat and power (CHP) is a technology which can provide a building with both heating and electricity, generated in a single process, with a typical ratio of about 2:1. Domestic installations are usually powered by mains gas or LPG, although larger commercial units can run on a variety of fuels.

Unlike conventional electrical generation – where coal and gas-fired power stations have to vent huge amounts of unused heat into the atmosphere – CHP captures a much higher proportion of the heat produced, which ensures much greater efficiency. In addition, the relative efficiency of the process is higher as the electricity is generated on-site, which means that losses incurred through the transmission and distribution network can be avoided.

As with other various other renewable electricity-generation technologies, micro-CHP is eligible for Feed-in Tariff payments. The Government has limited this to the first 30,000 units, although take up has been extremely low with only 1% of this number registered by February 2012. This is for very small installations of less than 2 kW.

Firstly, we’ll look at the benefits of CHP:

• Produces electricity for use within the building
• Can produce significant reductions in running costs and carbon dioxide emissions if sized correctly

There is however one limitation that should be taken into account:

• CHP units operate most efficiently when running for long periods, generally for more than 18 hours a day. Large hot water demand, and large enough thermal stores to store the generated hot water, are required

In addition, there are some other considerations that should be borne in mind:

• Only the first 30,000 micro CHP installations are eligible for Feed In Tariffs, and therefore this needs to be considered when reviewing running costs and payback periods
• An incorrectly sized CHP unit will cost more money to operate, and emit more carbon dioxide, than conventional solutions
• There is a significant step in capital cost once CHP units with a larger thermal output than 17 kW are considered, so correct sizing is essential
• Micro CHP boilers are not suitable for small well-insulated dwellings, as there isn’t sufficient heat demand to operate efficiently

If you’d like to find out more about combined heat and power units, and their suitability for a particular project, please contact us.