To improve the industry benchmark of solid oxide fuel cell systems (SOFC), we consider anode off-gas recirculation using a small-scale fan. Evolutionary algorithms compare the different system design alternatives with hot or cold recirculation. The system performance is evaluated through multi-objective optimization criteria, i.e. maximization of electrical efficiency and cogeneration efficiency. The aerodynamic efficiency and rotordynamic stability of the high-speed recirculation fan is investigated in detail. The results obtained suggest that improvements to the best SOFC systems, in terms of net electrical efficiency, are achievable.