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This
section is intended for those who are considering the purchase of a micro CHP
system, either for their own home or for clients. Although technical
details are generally available from the links to suppliers' web sites,
specifiers and other professionals may wish to consult the Papers
section to gain a better understanding of the wider issues surrounding micro
CHP. Products which are available on a commercial basis are clearly identified as
such in their descriptions and contain a link to the supplier. Before
considering the purchase of a micro CHP system, however, you should consult the Calculator
section, or undertake some other economic viability assessment, to see
whether your investment is reasonable.
For details of product types, click on
the links at the bottom of each column. Please note that
currently, only Stirling engines and Internal Combustion Engine based
products are commercially available.
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The majority
of true micro CHP systems are currently based on external combustion
technology as their characteristics are best suited to this stationary,
constant running application.
External
combustion engines separate the combustion process (which is the energy
input to the engine) from the working gas, which undergoes pressure
fluctuations and hence does useful work.
As the combustion process is used to
provide a continuous heat input to the working gas, it is more
controllable and generally more
efficient, cleaner and quieter than internal combustion engines.
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Internal
combustion engines inject fuel and air into the cylinders where
combustion occurs. The resulting temperature and pressure changes
of the fuel/air mixture (which is also the working gas) act on the
piston to produce useful work.
As the combustion process is cyclical,
rather than continuous, it is more difficult to ensure complete combustion of the
fuel, and noise and pollutant emissions tend to be higher.
Early mini CHP products were derived from
automotive engines converted to run on Natural Gas and suffered from
very high service costs and unreliable operation. Current models,
however, have been specifically developed for extended operation between
services.
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In
a fuel cell, the chemical energy within the fuel is converted directly
into electricity (with by-products of heat and water) without any
mechanical drive or generator.
In theory this can result in high
electrical conversion efficiencies and low emissions. However,
numerous additional components are required to condition the fuel and
to convert the DC electrical output into AC suitable for domestic
installations; their theoretical potential has yet to be realised in any
practical domestic product.
It is only recently that fuel cells have
been begun to be developed specifically for micro CHP applications and it is
unlikely that commercially viable products will be available before
2010.
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There
are numerous experimental technologies which may at some future date
result in useable products. These include thermo-ionic
technologies which utilise temperature difference acting on metals to
produce electricity and thermo-photovoltaic units which convert the
radiant energy emitted by the burner to produce electricity from
infra-red PV cells. Although these are relatively inefficient and
produce little power, there may be applications, for example, in "self-powered
boilers" for which such concepts are of value.
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