A Combined Heat and Power (CHP) system is a small power plant that captures the waste heat produced whilst it’s generating electricity and makes it available as useful heat: hence the name – it gives you usable heat and power; and it does come more or less ‘in a box’, funnily enough. The supermarket equivalent would be ‘buy one get one at half price’. We call it ‘the box that saves money’.

The reason for the financial benefit is that grid electricity is so much more expensive per unit than mains gas (known in the trade as the spark spread).

Put in £2 worth of gas in a CHP and get out a £1 worth of heat and £3 worth of electricity, and reduce your emissions by up to 30%. Isn’t this the best-kept secret in the energy industry?


Diagram showing how a gas CHP works

How Does a CHP Work?

A CHP system uses gas to power a boiler. The resultant high heat drives a generator to produce electricity. The remaining heat, which would otherwise be wasted, is used for local heating. This makes it much more energy-efficient than conventional heat or electricity production.

How Big Is a CHP System?

Like conventional heating plant, it comes in a range of sizes to serve a wide variety of heat and power requirements. A CHP suitable for a typical school requirement is only about a meter cubed in volume and would normally be installed in an existing plant room. Key point – it would augment rather than replace existing boilers (which would therefore work less hard and could be resized appropriately on replacement).

What Is the Ideal Source of Energy for a CHP System?

The ideal source of energy is mains gas. To gain the full benefit, all the heat and power generated needs to be used on site, so correct sizing is essential. Generally, there should be plenty of conventional uses for the electricity already (e.g. lighting and IT), but the CHP could also be used in conjunction with electric vehicle (EV) charging or battery storage; or even in combination with a heat pump.

How Much Does a CHP System Cost?

Cost-effectiveness is always site and usage dependent, but a typical school application – e.g. serving a sports hall with a swimming pool – would be less than £100,000. This would pay for itself in 3 to 5 years, depending on heat usage and the school’s gas and electricity rates. The life of the system could then be up to 15 years, making the net benefit (benefit minus costs) between 2 and 3 times the original capital outlay. Note that at this sort of scale it counts in VAT terms as an energy-saving material and therefore can be eligible for the reduced rate of VAT.

It seems curious that more schools have not taken advantage of this option. If you would like to know more, get in touch.