Or take energy storage — which could enable greater use of wind and solar power. As renewable energy becomes more widespread, utilities will have to grapple with the fact that their energy production can fluctuate significantly on a daily or even monthly basis. In theory, batteries or other energy storage techniques could allow grid operators to soak up excess wind energy during breezy periods for use during calmer spells. But the current generation of lithium-ion batteries may prove too expensive for large-scale seasonal storage.

It’s still not clear what set of technologies could help crack this storage problem. But the agency is placing bets on everything from novel battery chemistries to catalysts that could convert excess wind energy into ammonia, which could then be used in fertilizer or be used as a fuel source itself.

At the summit, Michael Campos, an ARPA-E fellow, also discussed the possibility of using millions of old oil and gas wells around the Midwest for energy storage . One idea would use surplus electricity to pump pressurized air into the wells. Later, when extra power was needed, the compressed gas could drive turbines, generating electricity. A few facilities like this already exist, though they typically rely on salt caverns . Using already-drilled wells could conceivably reduce costs further.

“This is a very early stage idea,” Dr. Campos told the audience. “I’d love to hear from you if you have ideas for making this work — or even if you think it won’t work.”

Other projects focused on less-heralded problems. A company called Achates Power showed off a prototype of a pickup truck with a variation on the internal combustion engine that it hoped could help heavy-duty trucks get up to 37 miles to the gallon — no small thing in a world in which S.U.V. sales are booming. Several other ventures were tinkering with lasers and drones to detect methane leaks from natural gas pipelines more quickly. Methane is a far more potent greenhouse gas than carbon dioxide.