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the big picture
By Jeremy Harrison
Photo book

SOFC | PEM fuel cell

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.


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.


Electrical efficiency 30-35%

1.8kWt (+20kWt supplementary modulating condensing burner)

Bluegen (DHW plus power)

Electrical output 1.5kWe

Thermal output 600Wt

Electrical efficiency 60%

Thermal efficiency 25%

1kWe 1kWe; 1.7kWt


Field trials in DE, CH 2005

Laboratory re-design 2006

Callux field trial 2012


Bluegen 1.5kWe available now in UK, NL, DE (€25,000)

Packaged micro CHP version field trial 2012




2013 Participation in German Callux field trial


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.

700We 700We 700We; 40kWt supplementary boiler


2012 Japan



2012 Japan

JPY 2.75 million (~£21,000) retail

2014 Germany field trial


2012 Japan

$31,000 retail


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.


250We ~25%

500We ~30%

1500We up to 35%






Prototype packaged micro CHP system of larger (20kWe) product





Prototype packaged micro CHP system

Page update 23rd February 2014


the big picture
By Jeremy Harrison
Photo book



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This site was (partially) last updated on 12th August 2017 © Jeremy Harrison