Growing concerns over climate change and energy security have kicked research on alternative energy sources into high gear. The list of options continues to expand, yet few papers have comprehensively reviewed them. And fewer still have weighed the pros and cons in as much depth as a new study published earlier this month in the journal, Energy & Environmental Science. The results are a mixed bag of logical conclusions and startling wake-up calls.

The review pits twelve combinations of electric power generation and vehicular motivation against each other. It is a battle royal of nine electric power sources, three vehicle technologies, and two liquid fuel sources. It rates each combination based on eleven categories. And it was all compiled by one man, Mark Jacobson, professor of civil and environmental engineering at Stanford University.

"I felt a need to pull together all the information we had plus that from other sources to quantify and rank... the best and worst proposals,” Jacobson told Ars.

The results of his mathematical ranking are both rational and unexpected. Wind power emerged as the overall victor. When teamed with battery electric and hydrogen fuel cell vehicles, it claimed the top two spots by winning seven of the eleven categories. Photovoltaics are an unexpected also-ran, failing to make the top five. Politically favored ethanol stands out as the big loser of the study, falling behind "clean coal," a technology many consider a dead end. Ouch.

Such an undertaking suits Jacobson. He and his research group have broad experience in the alternative energy field. They have covered a variety of topics, from wind power to aerosol pollution to health and vehicle emissions. A few years ago, he dipped his toe into the policy arena. This study is his latest contribution.

"My hope is that policy makers will use this information and begin to focus on the best solutions to climate change, air pollution, and energy security," Jacobson said.

He's off to a good start. Two major alternative energy plans—RePower America and the Pickens Plan—already use information from Jacobson's compendium to bolster their proposals. He has also presented his results to New Mexico Senator Jeff Bingaman, Chair of the US Senate Energy and Natural Resources Committee, and shared early findings with the US House of Representatives Select Committee on Energy Independence and Global Warming.

An alternative energy encyclopedia

Jacobson's success with policy makers should come as no surprise. He has created an encyclopedia of current knowledge on alternative energy sources for the 21st Century. In addition to evaluating many proposed sources of "green" electricity and fuel, he summarizes the technologies with respect to several categories. His ranking covers everything from water usage to terrorism to a proposed solution's effect on wildlife.

The breadth of these categories may have precipitated some of the unanticipated results. Jacobson emphasized two categories over the others—global warming emissions and mortality. The latter appears to be a novel addition to the ranking system, quantifying deaths caused both by pollution and war or terrorism. Nuclear and ethanol fared poorly in both categories.

Nuclear power, while clean at the point of generation, suffered from high emissions in this study. Nuclear pollutes throughout its lifespan. It starts with pollution from ore mining and continues through to plant decommissioning and waste storage. Nuclear also dropped in the rankings—although not by much—due to the risks posed by nuclear proliferation. Jacobson made an intriguing assessment of nuclear power’s mortality score. First, he envisioned a nightmarish, but not inconceivable, scenario—a “limited nuclear exchange,” or the detonation of 50 fifteen kiloton bombs. He estimated the deaths directly resulting from the bombings, and then calculated the number of deaths caused by soot and pollution from the burning cities. To arrive at the final result, he tempered this worst case scenario with a probability score, a number that attempts to gauge the likelihood of such an event.



Bad news for Eddie Ethanol

Cradle-to-grave emissions also sunk corn and cellulosic ethanol. While ethanol's direct tailpipe emissions are offset by subsequent crops, much of the carbon released early in the process is never recaptured, the paper said. With the expansion of farmed fuel, lands once considered marginal would fall under the till. The carbon stored within these targeted ecosystems is enormous, and its release would be extremely difficult to offset. And while ethanol attempts to address carbon emissions, it does nothing to reduce other gases responsible for climate change and respiratory diseases.

The pace of climate change may be unpredictable, but experts agree that significant warming will occur by the end of the century. Many scientists are urging quick action, so any delays in addressing the problem will further compound the issue. Wind, for example, is a proven and commercially available technology. It would be responsible for zero emissions due to delays in bringing the technology to production capacity. "Clean coal," on the other hand, is anything but proven, and so it drops in rank.

As is common in reviews, Jacobson relies on findings from previous studies. Some may consider this a deal breaker, but the paper is remarkably straightforward. All numbers, assumptions, and formulae that form the ranking’s backbone are listed in a detailed appendix (PDF).

With the economy currently in shambles and gas prices well below $2 a gallon, alternative energy sources may be the last thing people want to think about. But now may be the best time to act. The US labor market shed another 58,000 jobs last week alone, so plenty of workers await employment. And installing the capacity to power all road-going vehicles with electricity would be surprisingly easy. By comparison, the United States put 300,000 planes into the air during World War II. For that same effort, Jacobson says we could install between 73,000 and 144,000 five megawatt wind turbines. Doing so would prevent 15,000 pollution-related deaths a year and trim U.S. carbon emissions by nearly a third. This alone would not suffice to curtail US contributions to global warming, but it would be a start.

Energy & Env. Sci, 2008. DOI: 10.1039/b809990c