Biofuels versus hydrogen
The article "Fuel Cells Rally" seemed not to appreciate several realities (C&EN, Jan. 31, page 18). Company sales staff may make claims that their technology allows fuel cells to be produced today for $200 per kW, but the facts are that vehicle-grade fuel-cell engines today still sell for at least $4,000 per kW. If fuel cells were really available for under $1,500 per kW, they would quickly put all other distributed power options out of business, and their sales would jump by two orders of magnitude within a few years. The fact that the major fuel-cell manufacturers' stocks are trading at or under 5% of their four-year highs suggests this is not likely to happen.
Hydrogen advocates may claim that hydrogen is clean and cheap, but again the facts are otherwise. Production of liquid hydrogen (which is required for practical distribution) from natural gas results in the release of more than 20 kg of CO2 for every kilogram of liquid hydrogen produced. Liquid hydrogen from coal, which is what we'll be using within 20 years, results in the release of 30 kg of CO2 per kg of hydrogen. After another decade of progress, with vehicle-grade fuel cells then getting 39% efficiency, making the fuel for hydrogen vehicles will cause over three times as much CO2 to be released per mile as advanced diesel hybrids, which will be getting more than 80 mpg.
The cost of pressurized hydrogen gas for the small industrial user has been rather stable at about $100 per kg for the past half century (1 kg of H2 has roughly the energy of 1 gal of gasoline). Large industrial users today in most parts of the country are paying $6.00 per kg for bulk liquid hydrogen delivered in 15,000-gal tankers, and realistic projections of minimum distribution and dispensing costs add at least another $4.00 per kg to its cost for the consumer, even when at the scale of 20,000 vehicles per city.
At 5,000 psi, the volumetric energy density of H2 is only 10% that of biodiesel. The mechanical energy alone stored in the hydrogen tank is five times that of a 50-caliber artillery shell. The risks associated with carrying this mechanical bomb around are probably two orders of magnitude greater than we are accustomed to accepting in our gasoline-powered cars today. For safety reasons, the recent National Academy of Sciences/National Academy of Engineering study concluded that both high-pressure tanks and cryogenic storage "have little promise of long-term practicality for light-duty vehicles."
The U.S. is facing a serious long-term energy crisis in the near future, but we do not prepare for it by ignoring basic scientific and engineering realities. And hydrogen hype is resulting in our limited research dollars being poorly used while real options in advanced biofuels get relatively little support.
It is true that corn ethanol is not an efficient use of food, and biodiesel from soy may make even less sense; however, Brazil is currently producing more than 5 billion gal of sugarcane ethanol per year at under 60 cents per gal, and production will likely quadruple over the next decade. There are a host of next-generation biofuels that make sense in other climates. The first of these is just hitting the market here--cellulosic ethanol. The cost of producing the cellulase enzyme needed to turn waste wood into high-grade fuel has been cut by a full order of magnitude over the past decade, and another factor of two is expected within a few years. Ethanol from waste wood will soon be half as expensive (per unit energy) as gasoline.
Ethanol, methanol, and biodiesel from efficient fuel crops such as switchgrass, eucalyptus, mustard, hemp, pines, algae, kudzu, and poplars will very soon be cheaper in the U.S. per unit of energy than gasoline at $2.50 per gal. At the end of the day, the death knell to the hydrogen dream is the practicality of clean, convenient, renewable biofuels coupled with advanced, high-efficiency hybrid engines.
F. David Doty