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See Inside March 2010

Readers Respond on "A Path to Sustainable Energy by 2030"

Letters to the editor from the November 2009 issue of Scientific American


Winds of Change
I found it surprising that in “A Path to Sustainable Energy by 2030,” Mark Z. Jacobson and Mark A. Delucchi do not mention the effects of the suggested energy sources on climate. The authors propose to absorb about six terawatts of energy from about 60 terawatts available in the wind, or about 10 percent of its total energy. Because the winds, at least near the U.S., usually flow around highs or lows, where the speed and related Coriolis force tend to maintain the pressure difference, I can easily envision that absorbing the energy will change the rate at which the pressure centers collapse. How this would change the weather, I do not know, but it must make a change to give us some of the energy. Possibly, the weather change would be an improvement, but as a believer in Murphy’s Law, I would be surprised. About 100 years ago dumping garbage into the ocean was justified because the oceans were infinite compared to the effect, so no one calculated how much was allowable. Let’s be smarter this time! Why not do the calculations before we cause more problems?
Paul Roetling
Grand Island, N.Y.

Jacobson and Delucchi have a bold vision and a generally balanced account of the opportunities and difficulties. Three matters of concern should be explored further, however. First, vast solar arrays in deserts would suffer from serious loss of efficiency in sandstorms. Second, extensive studies were published in the 1970s on the design of liquid-hydrogen-powered aircraft, the massive energy systems needed at major airports and the difficulties of servicing aircraft whose systems are at three kelvins. Although these problems might eventually be solved, it is very optimistic to think this could be done by 2030. Third, and probably the biggest worry of all, is the rate of construction of these new energy systems that the plan would require. All new global energy systems have grown over a century or so at an average of 1 to 2 percent a year; the article implies a rate of 5 percent a year. Admittedly, the authors compare previous novel construction rates to their proposals, but these were not on the global scale. New technologies that do not reach about 2 to 3 percent of the market lose momentum, fall into the “snake pit” and are forgotten.
John E. Allen
Kingston University
London

THE AUTHORS REPLY: Sandstorms are limited primarily to the Sahara, Persian Gulf states and Gobi Desert but hardly contribute to reduced solar radiation in North or South America or Australia in comparison. During severe events, solar power is reduced in sandstorm regions, but the solar radiation reaching the ground in the annual average in such regions is still large because the events occur periodically. With respect to the second point, we propose that most transportation modes use electricity. Only in cases where electricity cannot be used do we propose hydrogen or hydrogen-electric hybrid vehicles. Air transport is probably the most difficult sector to address; however, a recent European Commission report suggests that there are “no critical barriers to implementation” of a liquid-hydrogen aircraft fleet (http://ec.europa.eu/research/transport/news/article_786_en.html). Although liquid hydrogen requires more than four times the volume of jet fuel, it is about one-third the weight of jet fuel for the same energy, which more than makes up for the additional weight of the fuel tank. As a result, a fully fueled liquid-hydrogen plane will produce more drag but weigh less than a jet-­fueled plane. With respect to the third point, our plan is for governments to mobilize infrastructure changes at a rapid pace. The examples given in the letter are based on typical market penetrations, not on aggressive efforts.

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