Enlarge / A crop monitoring robot: Like a Roomba, but with more sensors and responsibility. (credit: Megan Geuss) NATIONAL HARBOR, MD—Last week's ARPA-E summit was full of big ideas about the future of energy, and nowhere was that more evident than on the summit's show floor. In the basement of the sprawling Gaylord Hotel and Convention Center, dozens of academic institutions and companies set up booths to show off what they had been working on with their grant money. From cars to recycling to electricity-generating turbines to biofuels, the warehouse temporarily turned into a montage of early-stage ideas.