Solid oxide fuel cell systems for combined heat and power production (SOFC μCHP) fueled by natural gas are attractive because of their high electrical and total efficiency even at small scale. The development of a hydrogen economy will increase the availability of distributed hydrogen as a pure gas. Alternatively, hydrogen may be blended with natural gas in the grid. This study investigates the performance of SOFC μCHP systems, while using a fuel varying from pure hydrogen to pure methane via mixtures of hydrogen and methane called Hythane. Flowsheet models of external as well as internal reforming fuel cell systems were developed in Cycle-Tempo simulation software. Results show that both the external as well as the internal reforming system can operated on all fuel gas compositions varying from pure hydrogen to pure methane, thus allowing for a transition towards a hydrogen economy via the mixing of hydrogen into the natural gas grid. Although the natural gas based systems have a higher electrical efficiency, the introduction of hydrogen into the gas leads to a higher total efficiency of the combined heat and power system. The addition of hydrogen into the fuel minimizes the problems of thermal stress and thermal shock associated with the use of methane in internal reforming fuel cell systems. The internal reforming system showed a higher performance compared to the external reforming system for all Hythane gas mixtures in terms of not only electrical efficiency but also in terms of thermal and total efficiency.

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In this paper we describe and analyze the results of experiments on a Solid Oxide ElectrolyzerCell with and without the supply of a fuel to the oxygen producing electrode. In theexperiments a 5 x 5 cm2 Solid Oxide Fuel Cell is used operating in electrolyzer mode. Wehave tested the influence of varying reactant utilization (i.e. steam utilization) and fuelutilization in fuel assisted electrolysis. In particular the effect of insufficient fuel supplywas studied experimentally as well as theoretically. In doing so we defined a turning pointat which all the fuel is utilized. It was shown that by supplying not enough fuel all the fuelis oxidized and as in conventional electrolysis, oxygen production will start and oxygen isleaving the cell. Moreover the cell performance approaches conventional electrolysis andthe effect of adding fuel on reducing the necessary amount of electric power almost vanishes.As in conventional high temperature steam electrolysis conversion efficiencies ofmore than hundred percent can be achieved also with fuel assisted electrolysis, under thecondition that sufficient fuel is supplied i.e. fuel utilization must be lower than hundredpercent.We have put the concept of fuel assisted electrolysis in the framework of multisourcemultiproduct energy systems (MSMP's) and emphasized for example the benefits of usingbio(syn)gas as the fuel in fuel assisted electrolysis. When using bio(syn)gas, the gas is defacto upgraded to pure hydrogen. This is an additional benefit next to the lowering of theelectric power consumption for producing the same amount of hydrogen in the fuelassisted electrolysis process. Furthermore the suitability of these flexible MSMP systems ina market with volatile electricity prices due to increasing penetration of intermittentrenewable energy sources is highlighted.@en