A new paper out of Pacific Northwest National Laboratory reminds us that alternative energy technologies are systems composed of many elements, and that the supporting elements of the system can affect overall efficiency as much as the energy conversion technology itself. In this case, the researchers gained record efficiencies of nearly 60 percent for small solid oxide fuel cells through a clever design of the fuel delivery system.
The PNNL team led by Vincent Sprenkle, chief engineer of PNNL’s SOFC program, built a pilot system that could generate about 2 kilowatts of power, enough to power a typical American home. This approach is different from the usual SOFC development tack. In a press release from PNNL, Sprenkle says, “Solid oxide fuels cells are a promising technology for providing clean, efficient energy. But, until now, most people have focused on larger systems that produce 1 megawatt of power or more and can replace traditional [utility] power plants.” With this research, the group was interested in SOFC-generated power that could be scaled in a distributed-power model for a neighborhood of 50-100 homes.
Methane is used the fuel source, and the group developed an external steam reforming process to convert the methane to hydrogen and carbon monoxide. The heat required to drive the steam reforming process is harvested from the exhaust from the SOFC, which is fed through a microchannel heat exchanger. The microchannels are narrower than a paper clip wire, and by using several of them, the surface area of the heat exchanger is maximized, making the process more efficient. Also, any fuel that passes through the SOFC is captured and recirclulated through the system, also increasing efficiency.
According to the paper’s abstract, “the single-pass fuel utilization is only about 55 percent, [but] because of the anode gas recirculation the overall fuel utilization is up to 93 percent.” The demonstration system achieved power outputs ranging from 1.65 kilowatts to 2.15 kilowatts. The maximum efficiency of 56.6 percent occurred at 1.72 kilowatts output. The group expects that the system’s efficiency can be pushed to over 60 percent with the use of properly sized blowers.
For full details, see “Demonstration of a highly efficient solid oxide fuel cell power system using adiabatic steam reforming and anode gas recirculation,” M. Powell, K. Meinhardt, V. Sprenkle, L. Chick and G. McVay, Journal of Power Sources, Volume 205