New small, solid oxide fuel cell could lead to efficient, local power generation

June 3, 2012

Pacific Northwest National Laboratory’s new, small-scale solid oxide fuel cell system can achieve up to 57 percent efficiency, thanks to microchannels etched onto the heat exchanger’s shim (credit: PNNL)

Individual homes and entire neighborhoods could be powered with a new, small-scale solid oxide fuel cell system that achieves up to 57 percent efficiency, significantly higher than the 30 to 50 percent efficiencies previously reported for other solid oxide fuel cell systems of its size.

The smaller system, developed at the Department of Energy’s Pacific Northwest National Laboratory, uses methane, the primary component of natural gas, as its fuel.

“Solid oxide fuels cells are a promising technology for providing clean, efficient energy,” said Vincent Sprenkle, a co-author on the paper and chief engineer of PNNL’s solid oxide fuel cell development program.

“But, until now, most people have focused on larger systems that produce 1 megawatt of power or more and can replace traditional power plants

“However, this research shows that smaller solid oxide fuel cells that generate between 1 and 100 kilowatts of power are a viable option for highly efficient, localized power generation.”

Efficiency with microchannel technology

The key to the efficiency of this small SOFC system is the use of a PNNL-developed microchannel technology in the system’s multiple heat exchangers. PNNL’s microchannel heat exchangers have multiple walls created by a series of tiny looping channels that are narrower than a paper clip.

This increases the surface area, allowing more heat to be transferred and making the system more efficient. PNNL’s microchannel heat exchanger was designed so that very little additional pressure is needed to move the gas through the turns and curves of the looping channels.

The system also recycles. It uses the exhaust steam and heat byproducts coming from the anode to maintain the steam-reforming process. This recycling means the system doesn’t need an electric device that heats water to create steam. Reusing the steam, which is mixed with fuel, also means the system is able to use up some of the leftover fuel it wasn’t able to consume when the fuel first moved through the fuel cell.

These characteristics help the system use as little energy as possible and produce more net electricity. Lab tests showed the system’s net efficiency ranged from 48.2 percent at 2.2 kW to a high of 56.6 percent at 1.7 kW. The team calculates they could raise the system’s efficiency to 60 percent with a few more adjustments.

The PNNL team would like to see their research translated into an SOFC power system that’s used by individual homeowners or utilities.

The research was supported by the DOE Office of Fossil Energy.

Ref.: Mike Powell, Kerry Meinhardt, Vince Sprenkle, Larry Chick, Gary McVay, Demonstration of a highly efficient solid oxide fuel cell power system using adiabatic steam reforming and anode gas recirculation, Journal of Power Sources, 2012, DOI: 10.1016/j.jpowsour.2012.01.098