Reversible solid oxide cells (rSOC) can convert excess electricity to valuable fuels in electrolysis cell mode (SOEC) and reverse the reaction in fuel cell mode (SOFC). In this work, a five – cell rSOC short stack, integrating fuel electrode (Ni-YSZ) supported solid oxide cells (Ni-YSZ || YSZ | CGO || LSC-CGO) with an active area of 100 cm2, is tested for cyclic durability. The fuel electrode gases of H2/N2:50/50 and H2/H2O:20/80 in SOFC and SOEC mode, respectively, are used during the 35 reversible operations. The voltage degradation of the rSOC is 1.64% kh−1 and 0.65% kh−1 in SOFC and SOEC mode, respectively, with fuel and steam utilisation of 52%. The post-cycle steady-state SOEC degradation of 0.74% kh−1 suggests improved lifetime during rSOC conditions. The distribution of relaxation times (DRT) analysis suggests charge transfer through the fuel electrode is responsible for the observed degradation.@en

The objective of the current work is to support the design of a pilot hydrogen and electricity producing plant that uses natural gas (or biomethane) as raw material, as a transition option towards a 100% renewable transportation system. The plant, with a solid oxide fuel cell (SOFC) as principal technology, is intended to be the main unit of an electric vehicle station. The refueling station has to work at different operation periods characterized by the hydrogen demand and the electricity needed for supply and self-consumption. The same set of heat exchangers has to satisfy the heating and cooling needs of the different operation periods. In order to optimize the operating variables of the pilot plant and to provide the best heat exchanger network, the applied methodology follows a systematic procedure for multi-objective, i.e. maximum plant efficiency and minimum number of heat exchanger matches, and multi-period optimization. The solving strategy combines process flow modeling in steady state, superstructure-based mathematical programming and the use of an evolutionary-based algorithm for optimization. The results show that the plant can reach a daily weighted efficiency exceeding 60%, up to 80% when considering heat utilization.@en

Power-to-chemicals driven by solar energy for methane, methanol and gasoline are evaluated thermo-economically for three locations in Europe with high solar irradiation, and with two daily product demands and seasonal product storage. The electricity sources considered are molten-salt solar power tower technology (MSTP), photovoltaic (PV) with daily electricity storage, and the electrical grid as complementary technology to satisfy the targeted daily product demand. A bi-level optimization employs (i) mixed-integer linear programming at the lower level with heat and mass integration for optimal sizing of technologies and utilities, and (ii) genetic algorithms at the upper level for optimizing the involved technologies themselves, e.g., MSTP. Particularly, since the capital investment of MSPT contributes significantly to the levelized product cost, the optimization of the heliostat field is coupled for a potential cost reduction. The results show that (1) high local solar irradiation to ensure long annual operation hours of MSPT and PV is the most important aspect for the location selection; (2) high thermal storage capacity for ensuring long full-load operating hours of MSPT is beneficial for reducing levelized production cost; (3) PV is generally not preferred as a power source, due to the short operating hours and expensive electricity storage; (4) the plant size affects significantly the final product cost, indicating that a compact, small-scale system is far too expensive; (5) the levelized methanol and gasoline product costs per kg are lower than that of hydrogen and methane and less affected by the plant size as well as the annual power contribution of MSPT; (6) comparing with the market prices for all the three chemicals considered, solar fuels can hardly be competitive in terms of cost in the near future.@en