October, 2000 Energy Services Bulletin

Have you called Western's Power Line lately? It offers information on nearly any energy-related topic. Here's an example of a recent question and answer.

Q. Can you give me information concerning fuel cells, specifically power production costs and Web sites listing distributors and manufacturers?

A: To give you a broad overview, I am including a section on fuel cell operations and the major types of fuel cells either currently available or being commercially developed.

What is a fuel cell?
Fuel cells are electrochemical devices that convert a fuel's energy directly to electrical energy. Fuel cells operate much like continuous batteries when supplied with fuel to the anode (negative electrode) and oxidant (e.g. air) to the cathode (positive electrode). Fuel cells forego the traditional extraction of energy in the form of combustion heat, conversion of heat energy to mechanical energy (as with a turbine), and finally turning mechanical energy into electricity (e.g. using a dynamo).

Instead, fuel cells chemically combine the molecules of a fuel and oxidizer without burning, dispensing with the inefficiencies and pollution of traditional combustion.

Types of fuel cells
Phosphoric Acid. This is the most commercially developed type of fuel cell. It is already being used such diverse applications as hospitals, nursing homes, hotels, office buildings, schools, utility power plants, and an airport terminal. Phosphoric acid fuel cells generate electricity at more than 40-percent efficiency-and nearly 85 percent if steam from this fuel cell product is used for cogeneration-compared to 30 percent for the most efficient internal combustion engine. Operating temperatures are in the range of 400 degrees F. These fuel cells also can be used in larger vehicles, such as buses and locomotives. Currently, phosphoric acid fuel cells are the only commercialized technology.

Phosphoric acid technology does not lend itself well to small-scale applications due to the support systems required to manage liquid acids at such high operating temperatures, the use of more expensive materials, and greater maintenance requirements.

Proton Exchange Membrane. These cells operate at relatively low temperatures (about 200 degrees F), have high power density, can vary their output quickly to meet shifts in power demand, and are suited for applications where quick startup is required (such as in automobiles). According to the U.S. Department of Energy, "they are the primary candidates for light-duty vehicles, for buildings, and potentially for much smaller applications such as replacements for rechargeable batteries in video cameras." PEM fuel cells offer a number of advantages over other fuel cell technologies for many market applications because of the compact size, low weight, low operating temperature, low noise level (due to the relative simplicity of the support systems required), relatively quick start up and desirable load response characteristics.

Molten Carbonate. Molten carbonate fuel cells promise high fuel-to-electricity efficiencies and the ability to consume coal-based fuels. This cell operates at about 1,200 degrees F. The first full-scale molten carbonate stacks have been tested, and demonstration units were tested in California in 1996. Molten carbonate is best suited for dispersed power applications in the 1-20 MW capacity range. There are a limited number of MCFC demonstration sites around the world.

Solid Oxide. Another highly promising fuel cell, the solid oxide fuel cell could be used in big, high-power applications including industrial and large-scale central electricity generating stations. Some developers also see solid oxide use in motor vehicles. A 100-kilowatt test is being readied in Europe. Two small, 25-kilowatt units are already on line in Japan. A solid oxide system usually uses a hard ceramic material instead of a liquid electrolyte, allowing operating temperatures to reach 1,800 degrees F. Power generating efficiencies could reach 60 percent. One type of solid oxide fuel cell uses an array of meter-long tubes. Other variations include a compressed disc that resembles the top of a soup can. Solid oxide technology operates at even higher temperatures than MCFCs. Due to these extremely high operating temperatures, design and operation issues are very challenging.

This wind turbine at Jefferey Energy Center in Manhattan, Kan., effectively showed participants in a July wind energy conference how to capture this resource. More than 200 people attended the conference sponsored by the American Wind Energy Association.