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| A micro-CHP unit installed in a kitchen: it generates electricity from gas and heats your water and building. |
The Phase 2B Government Response to the consultation outlines the degression rate of different technologies, and the good news is that most technologies do not lose much support. One even gets enhanced support.
This technology is micro-CHP, which represents an opportunity for some householders and businesses to purchase a new boiler that not only heats the building but also generates electricity.
These gadgets run on gas and are fridge-sized. However, like their big brother, conventional CHP plants, they have high upfront costs which has deterred people from buying them. A unit can set you back anything from £6,500-£10,000.
It's in Japan that this technology began and has become relatively big-time, because many manufacturers are Japanese. The global micro-CHP market expanded by more than a third last year and was worth €466 million in 2011, but is set to expand to €1 billion this year, though mostly in Germany and Japan.
Baxi Ecogen's model (pictured above), for example, has a heat output of 24 kW (enough for three average homes) and a maximum electrical output of 1 kW, enough to maintain back-up power in the event of a power cut, or boil a kettle.
The rate of FIT payback is 12.5p for 1kWh. Suppose you had it going all year without stopping you would earn almost £1100. Simple arithmetic shows it would then take at least six years to pay off (though you would make further savings on electricity). But you probably wouldn’t have it on all the time.
Hang on a minute, you say, if it runs on gas, it's not renewable. So why is it being supported by the FIT? And if it is being supported, then when the Renewable Heat Incentive kicks in, surely owners will also get reimbursed for the heat they generate, too?
Besides the FITs announcement, the Energy and Climate Change Department has also just published for consultation its proposals on the non-domestic side of this scheme, which show what renewable heat technologies are supported and how much support they will get, so we can answer this question.
Up for support are biomass boilers and stoves, ground source heat pumps, and solar collectors for hot water and space heating.
But not micro-CHP.
So, the reason why it's being supported is purely because it makes more efficient use of the gas, making the boiler 90% efficient instead of, say, 55%. Not because it is truly sustainable.
This is interesting, because further down the line are different types of micro-CHP boilers which run on fuel cells, which can therefore, at least in theory, run on renewable energy.
As a result of this support, micro-CHP will see some increase in installations in the UK, but to really achieve this it will need far more public education.
In practice, the technology is very specific in application. The current crop of models are based on the Stirling engine, Organic Rankine Cycle (ORC) or internal combustion engine. The first two have high thermal efficiency and output but low electrical efficiency (10%), and this is a sticking point.
A 2007 trial by the UK’s Carbon Trust concluded that micro-CHP can cut electricity bills and overall CO2 emissions by 15–20% when they’re the lead boiler in larger contexts like care homes, district schemes, apartment blocks and leisure centres.
The best individual building for them therefore is a medium-to-large, moderately well-insulated one, maybe with solid walls, solid floors and no loft space, that is hard to insulate well and has a relatively large heat demand. Or they could be used in a cluster of buildings.
This is why there is, sensibly, no condition attached in the feed-in tariffs scheme for micro-CHP, announced last Friday, to having a certain level of energy efficiency in the building, as there is with the other technologies.
In the above context, micro-CHP units can potentially deliver carbon savings of 5–10%; fewer than a condensing boiler, since capacity is likely to be best matched to demand, for both heat and power.
This morning I was in a 200-year-old energy-inefficient house heated by a gas-fired Aga. Although it is the middle of summer (if you can call it that) the Aga had to be on in order to boil a kettle. Consequently, the doors were open to prevent the kitchen from overheating.
Micro-CHP is the only reasonable, more efficient upgrade option possible for such a house that gives them the same level of comfort and ease of use. Biomass wouldn't do that because of the space and labour requirement for pellets or timber. Modern pellet-fired boilers can also consume a fair amount of electricity in their motors. The roof of this particular house faces east-west, so no form of solar power is appropriate.
Micro-CHP offers limited benefits for smaller and newer dwellings, however, because they are more energy-efficient or have too little requirement for heat. The key to success in micro-CHP is matching the thermal output to the building’s pattern of use, so that they operate not intermittently but for many hours at a time, making the value of electricity generated, which will be helped by the feed-in tariff, pay for the marginal investment in as little as three years in a typical family home. It therefore works best with a buffer storage tank to save the surplus heat for later.
Grid connection for electricity export is crucial to micro-CHP’s widespread acceptance. On average, half of all electricity generated by a typical 1kWe micro-CHP device is exported to the grid, as it’s not needed at the time.
Reliability is also a key issue; service agreements will be essential.
So you shouldn’t yet trade in your condensing boiler, which has about the same overall heating efficiency without also producing electricity, but you might keep an eye on developments.
Superinsulated homes will have to wait until the next generation of machines, based on fuel cells. These generally come in two types – proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs). They have a heat to power ratio that is approximately equal, so for example they could produce 5kW of heat and 5kW of electricity.
It's an interesting technology. As the Government is fond of saying: “we need a mix of different generation technologies in this country". The same is true at the micro level. There is no one size fits all. Micro-CHP has a valuable part to play, as long as it is installed in the appropriate spaces.
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