An Introduction to CHP (Combined Heat and Power)

ABOVE: The Dachs CHP unit from Baxi (well, actually its subsidiary SenerTec) produces 5.5kW of electricity for up to 12kW heat output at an efficiency of up to 92 per cent. See baxi-senertec.co.uk for more information.

Combined heat and power, or CHP, is a bit of a good news/ bad news story. There are more players in the market and the technology is moving forward, but there are still very few machines actually available to buy.

CHP is the production of both heat and electricity from a single fuel source in a single machine. Machines fall into two broad groups: combustion engines and fuel cells. Typical operating efficiency is around 80 to 90 per cent, compared to the electricity coming out of the plug socket at about 27 per cent of the energy that went into the power station.

Internal Combustion Engine

The Baxi Dachs unit (ABOVE) and the Honda Ecowill are the main players; both are available in the UK and both are fairly expensive. The problem with this technology is the heat-to-power ratio. The Dachs, for instance, produces up to 12kW of heat and 5kW of electricity. To achieve a reasonable payback on the £15,000 capital cost means running the machine for something over 12 hours per day — 365 days per year. That will generate at least 144kWh of heat each day — a 200m2 well-insulated home can use less than half that.

The Honda Ecowill generates 1kW of electricity and 3kW of heat, which is too small for most UK houses so a top-up heating unit is needed. The machine still needs to run for perhaps 18 hours per day to meet the electricity demands, and the cost of around £5,600 makes it a difficult economic choice.

External Combustion Engine

Currently, leading contenders are E-ON, Baxi and Worcester Bosch. E-ON has taken on the WhisperGen unit and is anticipating sales of more than 80,000 units, although planned roll-out is “early 2010”. But that was the claim for early 2009 and early 2008. The WhisperGen can generate 8kW of heat and 1.3kW of electricity and costs about £3,000 installed. Again, it needs to run for more than 12 hours per day to keep up with electricity consumption, which would match the probable heat demand even of an older house.

Baxi has a larger machine in its EcoGen unit, generating 1.1kW of electricity and a massive 24kW of heat. The price is not available — nor is a roll-out date. The Worcester Bosch Greenstar unit generates 1kW of electricity and 7kW of heat. Again, the price is not available and roll-out is said to be early 2012.

All these machines seemed to be aimed at the retrofit market, as a replacement to gas boilers in older, less well insulated houses. In 2008 the WhisperGen was due to hit the market at below £2,000. The manufacturer said then that, “Any more than £2,000 will be commercially unacceptable” — meaning that homeowners would not switch from a condensing gas boiler at around £1,000 to a CHP unit costing three to five times as much if the fuel saving was only £150 per year.

Fuel Cell Technology

There are two big contenders in this market: Baxi with its Beta 1.5 unit and ITM-Power with its (as yet unnamed) machine. Neither machine is currently available but it seems likely that fuel cell technology will eventually rule the CHP world.

Fuel cell technology has some big advantages: it is very quiet, has on-demand production and it can use a variety of gases as the base fuel — natural gas, methane, propane or hydrogen. In ITM-Power’s case, it runs on hydrogen that the homeowner can produce on site. They provide all the kit necessary to use sunlight to split hydrogen from water, which is taken off under pressure so that it is immediately available for use. Again, price and roll-out information is not forthcoming, despite an official ‘launch’ in spring of 2009.

Getting good information from CHP manufacturers on their products is a job better suited to a dentist — which may say something about the state of the industry but probably more about the state of the products. Domestic CHP is potentially a very significant development. If units were available in a suitable range of sizes, at reasonable prices, with an easy means of being paid for the spare electricity generated, they could become the normal choice for boiler replacement. However, they still present no overall benefit. Since 2004 this has been ‘next year’s technology’, and it seems that it still is. The advances are undeniable, as is the fact that manufacturers are spending more on development. CHP will come, but when, in what form and at what price remains to be seen.

Further reading:

• The Death of Central Heating
• A Guide to Heating & Plumbing
• Saving Energy