seals to isolate oxidant from the fuel, and this makes performance of tubular cell stacks very stable over long periods of times (several years). However, their areal power density is much lower (about 0.2 W/cm2) compared to planar cells (up to 2 W/cm2 for single cells and at least 0.5 W/cm2 for stacks) and manufacturing costs higher. The volumetric power density is also lower for tubular cells than for planar cells. To increase the power density and reduce the physical size and cost of tubular SOFC stacks, alternate tubular geometry cells, as illustrated in Fig. 3, are under development by Siemens.9 Such alternate geometry cells combine all the advantages of the tubular SOFCs, such as not requiring high temperature seals, while providing higher areal and volumetric power densities. The performance of these new design cells is higher than that of cylindrical tubular cells, but still lower than that of anodesupported planar cells.