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 earl-stage ideas. Most importantly, it also showed off the breadth of ARPA-E's work: though the Department of Energy's early-stage grant program has at times been cast as an accelerator for renewable energy exclusively, ARPA-E projects span a variety of fuels and even include some non-energy projects whose application could save industry a significant amount of energy.

Flip through the gallery below to see what we mean.