Monday, 04 June 2012 07:57
June 4, 2012
When scientists and policymakers talk about distributed electricity generation, generally what they are referring to is some form of renewable energy. Usually, people think of solar power first, but sometimes wind will get a nod.
One group of researchers at the Department of Energy's Pacific Northwest National Laboratory, however, wants to bring fuel cells into the discussion. And the group has the engineering research to back their argument up, having successfully developed a new type of solid oxide fuel cell (SOFC) that could provide efficient power for a neighborhood, or even a single house.
Fuel cells and their challenges
Fuel cells operate by using a chemical reaction between oxygen and fuel to produce electricity, rather than through combustion.
SOFCs are designed to make use of certain types of ceramic as the electrolyte in which the reaction occurs, allowing them to operate at higher temperatures, which helps to dramatically increase efficiency. Some SOFCs can reach efficiencies of 60 percent, compared to around 18 percent for combustion engines in portable generators.
However, these high operating temperatures - often in the range of 1,100 to 1,800 degrees Fahrenheit - also represent one the biggest restrictions on the use of fuel cells, generally limiting them to industrial and power-generation purposes.
Scaling down industrial fuel cells
Led by Vincent Sprenkle, PNNL's chief engineer for SOFC research and development, the group of researchers has been working on making fuel cells for neighborhoods that maintain the high efficiency of their large-scale cousins.
"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 power plants," Sprenkle explained. "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."
What the PNNL's team came up with was an SOFC that makes use of methane, the largest part of natural gas, and a process known as steam reforming. This process exposes the methane to steam, breaking it down into other components that can react more efficiently with the oxygen.
Steam reforming can sometimes weaken the ceramic electrolyte of the SOFC, so PNNL moved the process to an external chamber. They then increased efficiency even further by heating this chamber through the use of hot exhaust from the fuel cell reaction in a heat exchanger, which pass two fluids through separate but touching pipes. A set of microchannels within the heat exchanger, which increase the surface area for heat transfer, further increase efficiency.
Impressive early results
The first prototype of this new design was able to produce up to 2.2 kilowatts at 48.2 percent efficiency, and reached as high as 56.6 percent efficiency when it was scaled back to 1.7 kilowatts. The researchers think that with a few tweaks, that number could hit 60 percent.
More importantly, though, the system was specifically designed so it could be scaled up to anywhere from 100 to 250 kilowatts. The current model would power the average American home, but the larger versions could run anywhere from 50 to 100 homes.
"There still are significant efforts required to reduce the overall cost to a point where it is economical for distributed generation applications," said Sprenkle. "However, this demonstration does provide an excellent blueprint on how to build a system that could increase electricity generation while reducing carbon emissions."
Meanwhile, Bloomberg reports that FuelCell Energy Inc., which produces large-scale natural gas-powered fuel cells, has finally approached a profit with gas prices plunging to decade lows, offering some strong support for the technology as a whole.