MTS Group is also involved in a cooperative venture with U.S.–based Acumentrics Corp., maker of solid-oxide fuel cells (SOFC). The SOFC is a high-temperature ceramic device that converts fuel directly into electrical energy without intermediate combustion processes and mechanical conversion devices. Acumentrics engineers the SOFCs to be more than 45% efficient at making electricity, compared with the 25% efficiency level of polymer electrode membrane (PEM) fuel cells. The SOFC uses less fuel and produces less carbon dioxide than conventional power sources.
SOFCs are not as picky about fuels as other fuel cell technologies—it can reform a wide variety of fuels using steam created as a by-product of the reaction. PEM, on the other hand, needs hydrogen to operate, necessitating an external reformer and hydrogen separator. Solid-oxide cells are tolerant of CO and don’t need costly catalysts to remove CO traces.
The stack life of SOFCs has been shown in testing to be much longer than PEM fuel cells, remaining operational for over 16,000 hours without diminished power output. Acumentrics believes a stack life of 50,000 to 100,000 hours is feasible, compared with the 3000-hour average life of PEM fuel cells tested by the U.S. Army Corps of Engineers.
SOFCs are described as having the advantages common to all fuel cell types—low noise, low pollution, and high fuel-efficiency—but with other advantages specific to the technology. The cell elements are manufactured from reasonably inexpensive ceramic materials—anodes are composed of nickel oxide and yttrium-stabilized zirconia (YSZ), and tubes are coated with a YSZ electrolyte layer. A cathode of lanthanum manganite makes up the outer layer. All layers are manufactured using standard ceramic processes such as extrusion, dip coating, and sintering. The units run on a variety of hydrocarbon fuels—natural gas, ethanol, propane, reformed low-sulfur diesel, syngas, biofuels—and can run on pure hydrogen should it become widely available.
But it is their high operating temperature that makes these fuel cells effective for use in cogeneration cycles, resulting in overall energy efficiency nearing 90%.