Thousands of inventors, engineers and entrepreneurs gathered in a suburban Washington convention center on Monday for the annual three-day meeting of Arpa-E, the Advanced Research Projects Agency – Energy. It wasn’t quite the Oscars. At the registration desk, attendees received a goody bag that included a report on clean energy from the Pew Charitable Trusts and a refrigerator magnet that showed the periodic table of the elements.

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But the breakout sessions held true to Arpa-E’s tradition: there were lots of swing-for-the-fence ideas. These included finding a high-efficiency, low-cost way to turn surplus natural gas into liquid fuel for cars and trucks, and identifying something to burn other than hydrocarbons so that carbon dioxide is not one of the byproducts.

One researcher proposed burning aluminum instead. One challenge is that the ashes, or oxidized metal, would be hard to recycle back into aluminum without big releases of carbon dioxide.



Arpa-E is the Energy Department’s effort to imitate the better-known Pentagon arm known as the Defense Research Projects Agency, or Darpa. Darpa laid the groundwork for the Internet and still finances high-potential ideas in their early speculative stages in the expectation that a few will be major breakthroughs; Arpa-E tries to do the same in energy.

So far the agency has invested $770 million in 285 projects, “and we’re proud of every single one of them,’’ said Cheryl Martin, the agency’s deputy director, in opening remarks to several thousand attendees. Although most will never be commercialized, the strikeouts are not as important as the home runs.

One particularly ambitious idea presented on Monday was to re-engineer plants so that their leaves reflect rather than absorb more light. In an age of global climate change, with shifting rainfall patterns, changing reflectivity holds appeal. The technology would save water, which means saving energy because the water that the plants need often must be pumped. It could prove a way to help crops grow with less rainfall.

Some of those crops can be used to produce energy as well. And increasing the amount of light that bounces back into space would help to limit global warming.

The notion is that crops will absorb light in the visible spectrum yet reflect some of the infrared and ultraviolet light, which heats the leaves. “Plants have a maximum efficiency of about 6 percent,’’ said Robert Conrado, an agency scientist. And plants regulate their temperature much the way people do, by giving off water, which cools as it evaporates. “All energy that is not able to be captured is dissipated as heat,’’ he said. “And that’s a lot of water.’’

In a hot climate, a cornfield can give off the equivalent of eight inches of rainfall in a month, he said, and agricultural irrigation accounts for 81 percent of water use in this country. The proportion is even higher in poorer places, which have fewer dishwashers and washing machines.

And some of that energy would radiate back into space, reducing global warming, Dr. Conrado said.Whether butterfly wings or fruits, he said, “nature has already evolved mechanisms for tailored light reflection.”