Tubular cells perform satisfactorily for extended periods of time
under a variety of operating conditions with less than 0.1% per 1000
hours performance degradation and have a power density at 1000o
C
of about 0.20-0.25 W/cm2
. To date, the tubular design has progressed
the most and power generation systems of up to 250 kW size have
been produced and operated using such cells. To construct an electric
generator, individual cells are connected in both electrical parallel
and series to form a semi-rigid bundle that becomes the basic
building block of a generator. The cell bundles are arrayed in series
to build voltage and form generator modules. These modules are
further combined in either series or parallel to form SOFC
generators. Using this scheme, Siemens Westinghouse fabricated a
100 kW size and a 250 kW size atmospheric power generation
system. The 100 kW system was successfully operated for over two
years in the Netherlands and Germany on desulfurized natural gas
without any significant performance degradation.