High‐temperature electrolysis has been shown to be a promising technology for the so‐called Power‐to‐Liquid processes. However, to reach the full potential of high‐temperature electrolysis regarding process efficiency, by‐product recirculation and heat utilization are of vital importance. Herein, the possibility to perform internal reforming of by‐products within the electrolyzer to again obtain syngas can be advantageous. This mode of operation is demonstrated in electrolysis lab tests on cell and stack level, showing the ability to convert methane. However, the recycled gaseous product stream from a Fischer–Tropsch synthesis is much broader in its composition and longer‐chained hydrocarbons may lead to issues such as carbon formation, thermal stress, and catalytic stability. Herein, the Power‐to‐Liquid process, consisting of high‐temperature co‐electrolysis and Fischer–Tropsch synthesis, is implemented in a laboratory‐scale plant to study the possibility of internally reforming by‐products within the electrolyzer. Herein, the importance of by‐product recirculation is highlighted by the results of the investigation, as it allows for a significant increase in carbon efficiency and subsequently in energetic efficiency, but especially the potential of high‐temperature electrolysis for integrated process concepts applying internal reforming.

A simple thermodynamic system model for the analysis and evaluation of possible SOFC system concepts with regard to reachable electric efficiency is presented. All reforming concepts, various available fuels and anode off‐gas recirculation are included in the model. Furthermore, the model allows the characterization of the reforming conditions necessary to reach the calculated and desired electric efficiencies by the use of two dimensionless energy flow ratios, which are introduced. It is presented how to quickly assess system concepts and identify system concepts that are particularly interesting due to a simple process, high electric efficiency, or preferably a combination of those. Within the experimental section, the model is used to support the system design process of a biogas‐driven SOFC system with partial oxidation as reforming concept, without anode off‐gas recirculation. Since adjustable operating parameters are input into the model, the parameters' influence on efficiency and reforming conditions can be analyzed. With the model real system effects are investigated making it possible to reach a maximum gross electric efficiency of 0.55 with the real designed system.

Contracted by the company h2e Power Systems Pvt. Ltd. based in Pune, India, Fraunhofer IKTS has developed a 1 kW(el) solid oxide fuel cell (SOFC) power generator during a three year system engineering and technology transfer project. The fuel cell system is based on the CFY stack technology by Plansee SE and IKTS, which incorporates state-of-theart ESC with Scandia-doped Zirconia electrolytes. For the SOFC power generator, a chromium based interconnects (CFY) stack was integrated with a pre-reformer, a tail-gas oxidizer and heat exchangers into a HotBox-module following a novel concept for least-space-demanding reactor integration and flow distribution. The applied system concept aimed at a very compact and robust, yet highly efficient power generator with optional heat extraction. Two major design decisions have been introduced in the process layout, i.e., a rated fuel utilization in the stack of 85% as well as a POX-air pre-heater for reducing the reformer air flow to lowest possible values. This approach lead to a waterless SOFC system with a net electrical efficiency above 40%. Two proof-of-concept (PoC) prototype systems were commissioned and tested for system concept validation. Based on the operating experience, three improved prototype units were built at IKTS and shipped to India for initial demonstration projects and field trials at the customer's site. At the same time, the technology transfer to the customer was initiated, in order to enable for a local manufacturing and deployment of SOFC systems in India. This paper outlines the system development approach and major technical achievements demonstrated on PoC prototype level.

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As SOFC microCHP systems come closer to commercial application, Vaillant GmbH as one of Europe's largest heating appliance manufacturers and their development partner Fraunhofer IKTS focus on system development for large scale demonstration.