The Effect of Size on Optimization of Solid Oxide Fuel Cell/Gas Turbine Hybrid Cycles

The coupling of solid oxide fuel cells (SOFCs) and recuperated gas turbines (GTs) in a hybrid system has the potential to lead to efficiencies exceeding 60%. SOFC/GT hybrids have been proposed at power outputs from 20 MW down to power outputs as low as 25 kW. The optimum configuration for high and low power outputs is therefore likely to be significantly different. This paper proposes a simple model of the SOFC/GT hybrid to investigate the desired flow rate and pressure ratio for optimum hybrid efficiency with varying component performance and, hence, varying inferred size. The overall hybrid specific power will be dominated by the fuel cell and is therefore of secondary importance when matching with a gas turbine. The results presented suggest that hybrid cycles with total power output of the order MW or greater are preferable.