Steady State Analysis of Direct Thermal Energy Storage in Solid Oxide Fuel Cells (SOFC)

Abstract

This study explored the potential for TES in solid oxide fuel cells (SOFCs) by investigating the steady state fuel cell performance with a one-dimensional numerical model. The effect of including TES was simulated by increasing and decreasing the mass of the interconnect, stainless steel 441, as the storage medium. Using a model previously developed and tested in MATLAB Simulink®, the interconnect mass was varied from 42% to 99% of the total SOFC mass under the same initial and inlet conditions. The SOFC fuel studied was syngas derived from coal. As the size of the TES increased for constant cathode air mass flow, the heat capacity increased, resistance to heat conduction decreased and the temperature profile through the fuel cell became more uniform. As temperature gradients decreased, thermal stresses and the chance of cell failure reduced. Larger interconnect masses resulted in higher cell voltage and thus yielded higher efficiencies. The cathode air mass flow was also adjusted to control two different temperature conditions: constant average temperature and constant solid temperature difference across the cell. Instead of minimizing the size of the interconnect to reduce the cost of the SOFC, the interconnect material can be increased to add sensible heat storage directly to the fuel cell, increase heat and electrical conduction, and improve the efficiency of the fuel cell for hybrid systems as well as stand-alone fuel cells.