Combined Heat and Power (CHP)

If you’re looking to make some energy savings and reduce your carbon footprint, combined heat and power (CHP) is one approach you might want to consider – especially if it’s time to replace an ageing boiler. With the promise of generating your own electricity alongside keeping your house warm and your water hot, this sort of power supply has a clear appeal right from the off.

However, although CHP has been around for a long time on a large scale, it has only very recently become available for domestic use – and it may not be suitable for every home. Understanding a little of the way the whole thing works can obviously be a big help towards deciding if it is right for you.

How It Works

CHP’s alternative name of “co-generation” really gives the game away – it’s all about producing heat and electricity from the same process and at the same time. There’s nothing particularly new about the idea – after all, power stations do this all the time, burning coal or gas to make steam and generate electricity.

Although some of them are themselves CHP plants, often supplying district heating schemes, in many the heat is not used and is simply lost to the surroundings.

At the domestic scale, CHP involves a boiler, usually powered by natural gas, which behaves just like a conventional unit to provide hot water, but with the additional bonus of generating electricity. Since they use virtually the same amount of gas as a conventional boiler, the upshot for your home is that you effectively get some of your power for free.

In addition to what is known as “micro” CHP suitable for individual homes, there are also “mini” versions suitable for swimming pools or large buildings in the community such as hotels or residential homes. As well as being powered by mains gas, there are types of CHP available which use diesel, paraffin, LPG and even wood chips.

Heat and Power

CHP boilers are rated by how much power and heat they generate, which is given in kilowatts (kW) – kWe for electrical production and kWt showing the heat output. A typical home system would be rated at around 1kWe, which obviously means you’re hardly going to be self-sufficient when it comes to your household power requirements, but it will be a useful supplement to reduce what you need to draw – and pay for – from the grid.

When it comes to making the switch to a combined heat and power system, it is usually a fairly easy thing to do. CHP units are designed to be installed in place of existing gas boilers, which means that they can normally fit exactly where the old one was – avoiding the need for planning permission, since no changes are being made to the external vents or flues.

Never the less, it is worth checking with the local authority just to make sure of the position – and talking to their Building Control Officer to ensure that you comply with the Building Regulations.

The actual installation will need to be done by a properly qualified fitter – essential if your grant application under the Low Carbon Buildings Programme has been successful – and do remember that your new unit will need more frequent servicing that a conventional boiler.

Is CHP For You?

On the face of it, a combined heat and power supply has a lot going for it, but it is not necessarily the answer to everyone’s prayers. For one thing, although it tends to get wrapped up in the whole renewables/micro-generation/low carbon blanket, most of the available CHP units still rely on a fossil fuel to work.

Although offsetting your electricity demand while you warm your house this way qualifies as carbon-saving, it certainly can’t be counted as a form renewable energy.

CHP is also unlikely to make you a huge saving in energy costs; it has been estimated that an average home installing micro-CHP would save around £150 – and this includes selling some of the surplus electricity generated back to the energy supply company.

According to heating specialists, the installation needs to run for at least 12 hours a day to be economical, but the longer the unit runs, the greater the savings, so if you’re likely to want a continuous power supply for most of the day, CHP might well be the perfect solution. Whatever your needs, it’s certainly worth considering combined heat and power.