Micro CHP - bringing power to the masses?

Those in favour of Micro CHP argue that it has the power to be a disruptive heating technology, because of its revolutionary impact in getting so much more for less. But how effective is it?

Micro CHP is considered to be anything up to about 10kW, although the larger models are generally sold to small businesses such as restaurants. At the lower end, a 1kW model called Ecowill has sold very well in Japan -- in the last financial year 10,000 units were shipped. Manufacturer Delta estimates that 16,000 units were sold in 2005, representing about 31MW of generating capacity. Although only five companies offer products on a commercial basis, several others express confidence that they will have a product ready for the market by next year or the following year. Micro CHP markets may see an exponential growth over the next three to five years, enthusiasts say.

But critics argue that the technology is still untested. Units, typically the size of a fridge, can sit in the kitchen and run continuously in order to provide heat and electricity. Running on gas, they share the same advantages as large scale CHP -- in other words more benefit for the same amount of gas. Nevertheless, the units are expensive with a long payback time, although recent legislation in the UK may help to reduce this is especially if surplus electricity can be exported back to the grid.

Does it really save carbon?

A study at Heriot-Watt University in Edinburgh of residential micro CHP (Stirling engine) in four different climate conditions concluded that there was a slight benefit - 0.4 to 0.8 tonnes per year of carbon per kilowatt, depending on the technology. This depended to some extent on the coincidence of the demand for heat and the demand for electricity; and whether it was possible to store excess electricity or export it to the grid and gain carbon credits for doing so. This was highlighted as being particularly desirable for future policy change. The tick-over gas usage and power management regime would also need to be tightly controlled in order to ensure the carbon benefits required.
Jon Slowe of Delta argues that a Stirling engine product costs around £600 more than a conventional boiler but will save between £100 and £200 a year.

Looking slightly further into the future, fuel cell driven micro CHP will be a more efficient option, and is being introduced in Japan now. This is likely to have a much better carbon impact. Government support is required to encourage mass production of units and therefore bring the price down.

Mark Hinnells, at the Environmental Change Institute, University of Oxford, has modelled a whole series of policy initiatives leading to a 60% reduction in the carbon impact of our homes by 2050 which include the promotion of fuel cell powered CHP.

Additionally, if you think about it, running one of these units is like leaving the motor of car running continuously -- therefore in an expected lifetime of say 13 years, if it were a car, it would be travelling many hundreds of thousands of miles – like going to the moon and back several times. Moving parts wear out, and therefore maintenance might be expected to be expensive (accelerated testing is being conducted). Service agreements will therefore need to be entered into by consumers with a cost impact similar to those currently used for gas combi boilers.

Micro CHP in the short term is therefore expected to establish itself only in niche markets. More aggressive growth is possible towards the end of the decade if HVAC manufacturers engage more firmly with the technology. Hinnells argues that the only way this is like this to happen on a large scale is if energy service companies (ESCOs) take up the management of energy in the home and implement Micro CHP on a wide scale. They should see the technology as a good investment.

Virtual power plants

However, an experiment in the Netherlands shows a slightly different model. Drawing on a real-life research that used 15 Stirling engine power micro CHPs in the same housing estate, Renee Kamphuis of the Netherlands’ Energy Research Centre argues that in the future such clusters can be aggregated to create what they call 'virtual power plants'. These intelligent clusters can draw power on demand as the grid requires it.

Householders would receive the benefit of selling their surplus electricity drawn in this way, but would have to accept that for some of the time their units might be remotely controlled. Naturally such a system implies the introduction of an IT network into every home.

However such networks are likely to be introduced into homes anyway in order to roll out so-called smart meters, which can be read remotely by the electricity or gas utility company. It is a small leap from this to imagine that they could actually draw power from your unit and pay you for it when they needed it. This would create a truly distributed decentralised grid.

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