The latest fallout from the April 2013 Metcalf incident: the unprecedented assault with high-powered rifles on PG&E’s Metcalf substation, in Silicon Valley, which disabled 17 of 20 large...
Fuel Cells: White Knight for Natural Gas?
conventional generation and other DG, perhaps in hybrid form.
Still, he says, "I don't think a lot of the fuel cell companies are looking in their rearview mirror. They're looking more for partnerships and for opportunities."
Regina R. Johnson is managing editor of Public Utilities Fortnightly.
Fuel Cells: A Technology Primer
Fuel cells are by no means a new breakthrough; the principle behind the technology was discovered in 1839. But their use in generating electricity began in the 1960s, when NASA began using fuel cells in the space program. The operating technology has continued to evolve since then.
Components and Types . Fuel cells generate electricity through the chemical reaction between hydrogen (or a hydrogen-rich fuel such as natural gas, methanol, propane, diesel or even biomass) and air. Their design generally consists of a fuel electrode (the anode) and an oxidant electrode (cathode) separated by an ion-conducting electrolyte material. When fueled with pure hydrogen, the preferred feedstock, heat and water are the only byproducts. Any hydrogen-rich fuel will do, however. Even when fueled with fossil fuels, fuel cells provide highly efficient, quiet generation with ultra-low pollution emissions.
For distributed generation, four main categories of fuel cells are being developed, as distinguished by the choice of electrolyte:
* PAFC. Phosphoric acid fuel cells,
* MCFC. Molten carbonate fuel cells,
* SOFC. Solid oxide fuel cells, and
* PEM. Proton exchange membrane fuel cells.
Cost and Efficiency. The PAFC is the only technology that has been commercialized to date, in a power plant application. According to the U.S. Department of Defense, which supports a great deal of fuel cell research, the PAFC operates at a fairly low temperature of 375 degrees F, with 40 percent to 50 percent efficiency. As with all fuel cell technologies, efficiency increases dramatically when the waste heat is used.
The MCFC, says the DoD, is expected to be more efficient and perhaps less expensive than PAFC technology. It operates at about 1,200 degrees F, with efficiency of 50 percent to 60 percent. It has potential primarily for large power generation.
Experts say that as compared with MCFC, SOFC technologies appear to be less expensive, less complex, more efficient, and capable of producing higher-grade useful heat. Their operating temperature is very high, about 1,830 degrees F, with about 50 percent efficiency.
PEM development is receiving the greatest amount of funding, with applications in transportation and power generation. PEMs are relatively simple, compact and operate at low temperatures. Recent advances may make it the least expensive of the technologies. - R.R.J.