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SOFC technology was largely discounted as
unsuitable for micro CHP due to its relative inflexibility to modulate
power output and limitations in thermal cycling. However, the very high
potential efficiency, the ability to internally reform fuel and other
technical features may eventually make this the leading technology for
micro CHP.
A number of potential configurations are
possible including continuous baseload operation, which may mean that
these units will operate to meet thermal demand
of water heating throughout the year with a supplementary burner to meet variable
space heat requirements. In this
configuration, high electrical efficiency units such as the CFCL
Bluegen, avoid the need for flexible output to prevent heat dumping.
Products with lower electrical efficiencies (and consequent higher heat
to power ratios) do, however, need to modulate to maintain the heat
output below the daily hot water demand of the home. Japanese SOFC
products in particular, tend to be offered with a lower electrical
output and efficiency, and are configured to limit output in line with
the requirements of the Japanese market to minimise export of generated
power from the home. |
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The Hexis Galileo unit is a SOFC in which
excess gas (that is gas which is not consumed within the fuel cell to
generate electricity) is burned within the fuel cell stack to allow a high degree of
flexibility in the thermal output.
However, this results in not only a relatively
low electrical efficiency (30%), but a high thermal output such that its
performance is similar to PEM fuel cell technology.
The extremely high capital cost of these units means that the product
faces significant challenges before approaching economic viability.
In 2012, the German boiler manufacturer
Viessmann, which also has a partnership with Panasonic for their
PEM technology, acquired a 50% share in Hexis.
Field trials are ongoing with a number of German utilities within the
Callux programme. |
CFCL have established a marketing base and
powder plant in the UK as well as
a manufacturing facility in Germany. In 2008 they supplied demonstration versions of
their Netgen micro CHP package to energy utilities in Australia, New
Zealand. and Germany.
CFCL now have collaboration agreements with Gaz de France
(France), EWE (Germany), and EON (UK) as well as boiler manufacturers Brunns (DE),
Ideal (UK) de Dietrich (France), and Paloma (Japan).
In 2010, CFCL launched the
Bluegen 1.5kWe as
a stand-alone unit providing continuous baseload electricity as well as
600Wt for domestic hot water use. This product is now available
through distributors in Germany, Netherlands and the UK.
Electrical efficiencies greater than 60%
have been demonstrated. |
A UK based developer with an
intermediate (5-600ºC)
temperature SOFC using a metal supported cell which claims to overcome
the challenges of thermal cycling. However, this also means that it
requires external reformation implying additional cost, complexity and
loss of efficiency.
In 2010, a laboratory version was demonstrated to investors and field trials were planned for 2011.
The fuel cell itself was wall-mounted, with
the balance of plant housed in an adjacent fridge-freezer sized cabinet. However, in 2012, Ceres announced a revised
strategy in which they would focus on fuel cell development only,
working with partners to package the fuel cell into a micro CHP product.
Ceres have partnership agreements with
Centrica (British Gas), Bord Gais and Calor Gas. In July 2013,
they announced an OEM partnership with Korean boiler manufacturer KD
Navien to
develop a micro CHP product for the Korean market. |
Following initial attempts to develop both
low and high temperature PEM
fuel cell technology, Vaillant have now partnered with SOFC stack
developer Staxera, using planar cell technology.
In customary fashion, Vaillant have chosen
to focus on reliability (ahead of electrical efficiency), with a unit
producing 1kWe at an efficiency of only 30%, comparable with other
European PEM and SOFC products (Baxi Innotech and Hexis respectively),
but only half that of the CFCL product. However, Vaillant claim
not only service intervals of 10,000 hours, but the ability to cycle
frequently without any noticeable degradation in performance.
The prototype
"wall-mounted" SOFC shown below, is considerably larger than a wall-mounted
gas boiler and contains only the fuel cell components, the remainder
being contained in a number of additional boxes. |
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Availability
Field trials in DE, CH
2005
Laboratory re-design 2006
Callux field trial 2012 |
Availability
Bluegen 1.5kWe available now
in UK, NL, DE (€25,000)
Packaged micro CHP version field trial 2012 |
Availability
2016 |
Availability
2013 Participation in German Callux field trial |
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Kyocera have developed a "flat tubular" SOFC comprising a series of
parallel tubes within one ceramic tablet. This robust
configuration is used as the core fuel cell technology for a number of
Japanese micro CHP products.
Osaka Gas are collaborating with Kyocera on this 0.7 kW SOFC micro-CHP system,
but have yet to announce a launch date for their PEM fuel cell
systems despite demonstrating several. This could be an indication
that they recognise the inherent advantages of SOFC and, like others are
moving towards that technology.
The lower electrical output than European
micro CHP units is a consequence of the Japanese market requirement to
avoid export of generated electricity. |
Aisin launched their SOFC product in 2012
through Osaka Gas, and announced their collaboration with
Bosch for the European market in early 2013.
With slightly better performance to other
Japanese SOFC (46.5% v 45% LCV) it is still significantly less efficient
than market leading CFCL (60%), although claiming to be the most
efficient micro CHP product in the world.
The Type S unit incorporates Kyocera SOFC
technology, Aisin generation unit (including the FC stack) and Chofu hot
water and heating supply components, in the now familiar two box
configuration.
Images below show a flat tubular SOFC
similar to that produced by Kyocera. |
JX are also collaborating with Kyocera to
produce a 700We SOFC based micro CHP package using Kyocera's flat
tubular cell components.
Although these cells are less efficient than
some others at only 45% (though significantly higher than many of the
European developers' products) it is considered a particularly robust
product capable of withstanding thermal and mechanical shocks.
However, as noted above, the need to cycle power output and the
consequent requirement to withstand thermal shock is only
necessary where the heat output is too high to be usefully recovered
continuously into the domestic hot water system. |
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In
addition to collaboration with Wärtsilä, the Finnish CHP company, Topsøe
also recently announced their collaboration with Dantherm, the Danish air
conditioning company on smaller, 1kWe units.
A
high temperature SOFC, the planar Topsøe cells are claimed to be extremely
robust. |
Acumentrics have developed a tubular cell, able to respond more
rapidly to thermal cycling than planar cells without damaging the ceramic components.
In late 2007, Acumentrics presented their
"wall-mounted" SOFC to a group of European utilities, and were expected to
trial their technology in 2008 in partnership with MTS, an Italian
boiler manufacture. This collaboration appears to have been
abandoned in favour of a range of stand-alone generators able to use
propane or natural gas fuels, albeit with rather low electrical
efficiencies.
The illustration shows generic tubular fuel
cell components similar to those used by Acumentrics. |
SOFCpower provides anode-supported, thin-film electrolyte, solid oxide
fuel cells produced in its pilot production line in Italy. The cells are
composed of a YSZ electrolyte
sandwiched between two electrodes, a porous perovskite cathode and the
anode support structure.
From these they have produced the ENGEN®,
a prototype wall-mounted micro CHP system in two power ranges, up to
500We and 1000We.
The low electrical efficiency (30-32%) is
explained by the poor gas utilisation in the stack; excess gas passes
through the stack and is then simply burned to produce additional heat
as in the Hexis product. |
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