American Scientist

To the Editors:

As someone who was, until recently, directly involved with the engineering side of the fuel-cell industry, I disagree with some aspects of Henry Petroski's article on the subject (Engineering, September–October).

In his battery comparison, there are unsafe (and unstated) assumptions: How much power is being delivered and at what efficiency? Misinformation about fuel-cell efficiency has been a characteristic of the industry's public face for many years. Although it is true that, theoretically, the energy conversion is 80-percent efficient, the value hardly ever exceeds 40 percent in the real world.

In addition, so-called "balance of plant" expenditures (motorized valves and blowers that control fuel and air delivery to the cell) do not scale well with reduced size, and they consume an inordinate amount of energy in gaseous fuel-cell systems below 50 kilowatts. The overall efficiency is so low that the value of such systems is dubious.

Dr. Petroski also notes that fuel cells cannot deliver high peak loads. In fact, neither of the common mechanisms for medium-power fuel cells is suited to the types of varying loads that are used in automotive or domestic service—even when these loads lie entirely below the steady-state rating of the unit. This limitation exists because the rate of a chemical reaction in any fuel cell is directly related to the amount of current being drawn from the cell. So the amount of water and heat produced at the cell surface is proportional to the instantaneous electrical demand. Under varying load conditions, the control of critical water content in proton-exchange-membrane systems becomes extremely difficult, and in solid-oxide fuel cells, the sudden heat changes at the cell surface can fracture the brittle ceramic membrane. In both cases the result is likely to be premature degradation or total cell failure.

The one-kilowatt co-generation unit proposed for domestic use is no more than a toy, given that it would hardly power the lights in an average home. Candles would be more practical. A 10-kilowatt generator would provide enough power to allow independence from the grid, but a system of this size presents other issues: These same variable load problems increase as a function of output power, not to mention that the capital and operating costs would be prohibitive for individual families. There is considerable interest in the concept of home generators, but right now even focus groups are surprisingly prudent about the overall costs of installation and maintenance. And nobody wants a basement full of lead-acid batteries to smooth the electrical load.

Finally, nowhere in Dr. Petroski's article is there any mention of the problems of handling, and later disposing of, these devices. All fuel cells use catalysts, some more dangerous than others, and solid-oxide fuel-cell systems also use potentially hazardous materials to insulate the device, which operates continuously at 1,350 degrees Fahrenheit. Add in the fact that the cell membranes do not last forever—indeed, they have to be replaced quite regularly—and there is real potential for the release of these materials into the environment.

Campbell Kelly Gleichen, Alberta, Canada