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: www.thecarbontrust.co.uk/carbontrust/about/publications/181105_01.pdf
* 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: www.dti.gov.uk/energy/consultations/pdfs/microgeneration-est-summary.pdf
