How does a CHP work?

Nigel A-F

How does a CHP work?

Is this the best kept secret in the energy industry? Put in £2’s worth of gas and get out a £1’s worth of heat and £3’s worth of electricity; and reduce your emissions by up to 30%.

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

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 back 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 less costs) between 2 and 3 times the original capital outlay.

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. It would augment rather than replace existing boilers, (which would therefore work less hard and could be resized appropriately on replacement).

The ideal source of energy is mains gas, but CHPs will work off LPG or biomass (which also attracts RHI). To gain the full benefit the heat and power generated all 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.

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




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