The two main types of fuel cells being developed for micro CHP applications are PEM (Proton Exchange Membrane) and SOFC (Solid Oxide Fuel Cells).  The former are also being developed for automotive applications and historically formed the majority of systems.  However, SOFC units have the advantage of utilising Natural Gas directly, without the need for a separate reforming process, reducing the cost and complexity of the unit and raising conversion efficiency; balanced against this is the very high operating temperature of such fuel cells and their need for continuous heat output (even when there is no thermal demand) as well as their susceptibility to thermal shock.  Although this feature does raise some challenges, it has recently become apparent that the relatively low operating temperature of PEM fuel cells imposes limitations in domestic CHP applications with respect to the provision of hot water at a high enough temperature.  This, combined with the higher potential electrical efficiency of SOFC units, seems to favour SOFC in domestic CHP applications.

Over the past five years or so, several hundred fuel cell based micro CHP systems have been installed in Europe in the form of technology field trials.  So far, the majority of such fuel cell systems have, with notable exceptions, performed relatively poorly with electrical efficiencies and reliability failing to meet targets.  One such exception has been the SOFC product from Ceramic Fuel Cells (CFCL) which has not only out-performed any other fuel cell (and indeed any other form of gas fired generation technology at any scale), but has also regularly exceeded manufacturer's claimed performance.  With an electrical efficiency in excess of 60%, the CFCL Bluegen product is now being offered through distributors in UK, Netherlands and Germany, albeit at rather high capital cost.

Meanwhile in Japan, several thousand fuel cell micro CHP systems, both SOFC and PEM, have been installed as part of the ENE FARM programme, heavily subsidised by gas suppliers and the Japanese government.  These products are still very expensive, but are becoming widely adopted in the wake of the Fukushima disaster and the resulting power shortages which make some form of grid independence rather attractive to Japanese consumers at almost any price.  These same products are now in the process of being introduced to the European market although it is expected that this will take at least 2-3 years as the Japanese systems are currently configured to the peculiarities of the Japanese energy market, household energy consumption profiles and local manufacturing standards.

Although these installations have served to demonstrate the performance of fuel cell technology, there remain two major obstacles to commercialisation, namely cost and service life.  Unlike engine based technologies, fuel cells' life is characterised by continuous degradation of performance rather than catastrophic failure and economic viability may be determined by average rather than initial performance.

For further discussion of the relative merits of fuel cell types see section on papers, or click on links below for details of PEM and SOFC micro CHP products.