Renew On Line (UK) 61

Extracts from NATTA's journal
Renew, Issue 161 May-June2006
   Welcome   Archives   Bulletin         


The Energy Review

Climate Policy arrives

Tidal and wave power

Micro CHP Results

Policy developments

Where the money goes.

UK round up

Climate Threats

Global News

EU News

News around the world

Nuclear News

4. Micro CHP doubts

The Carbon Trust has been carrying out assessment trials of micro and small Combined Heat and Power units, and its preliminary results, especially for domestic scale micro CHP, do not look very good. Whereas some developers have talked in terms of a 25% reduction is emissions compared with that produced using conventional energy systems, and some models had predicted up to 40% savings, the trials have found that at most, in practice, over the full year, some of the units have only averaged only 18% reductions and in some case much less. Indeed some units yielded 18% lower reductions than achieved by conventional systems. The Trust warns that these are only preliminary results from a small number of units (since the deployment of units has in the event been delayed), and larger trials are underway. But it says ‘If this trend continues for the full trial, there will be a material risk of an increase in emissions if Micro-CHP is deployed at scale without regard to the different performance characteristics of specific technologies and the circumstances of their installation, maintenance and use’.

The Trust says that in the original project plan, the technology suppliers had committed to have in place over a hundred units at this stage of the trial, but ‘unfortunately all suppliers have experienced significant delays, some of over two years’. It adds ‘This was in the main due to a lack of experience with the technology as it emerged into the market place. In total there are now 40 units within the Carbon Trust’s field trial being monitored and delivering data.’

They go on ‘In view of the complexity of operation, and taking account of the wide range of applications and technologies within the trial, several tens of installations operating over at least a full year are needed before statistically valid results can be obtained and this is not now expected to be possible until 2007 given ongoing delays in supplying units into the trial’.

Nevertheless they were able to provide some early indications of carbon saving performance- which they say indicate that ‘performance is not as encouraging as had been hoped at the outset of the trial. About a third of the Micro-CHP installations in the trial would appear to reduce emissions and about a third increase them with the remainder showing no discernable difference.’ However ‘the performance of Small-CHP in businesses seems to be much stronger, where a number of installations appear to offer cost-effective carbon savings’.

The problem with the domestic micro-CHP units seems to be that the overall annual energy efficiency is lower than expected (electricity conversion efficiencies are put at 5-15%), since not much heat is needed is summer, which means that not much electricity is generated then. In addition the units take time to warm up to operational temperature and this energy is not available for heating the home; if switched on and off regularly to meet varying domestic heat requirements, this warm up time/heat loss can be significant.

We’ll review this report in detail in Renew 162. Meanwhile, it is at:

* The Energy Saving Trust has produced a report for the DTI which is more optimistic about the potential of micropower in general i.e. including micro wind, PV, micro-biomass & heat pumps as well as micro-CHP. It says that by 2050 these technologies could be supplying 40% of UK electricity and reducing emissions by 15% from what they would otherwise be. However, micro-CHP stirling engine systems only seem to contribute around a 1.9% reduction: see our Reviews section, which also reports on the delays facing micro-CHP. The EST report is at:

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