Harnessing the sun's energy for use at night.

• Position: Solar Fuel

Solar energy long has been used as a clean alternative to fossil fuels such as coal and oil, but it only could be harnessed during the day when the sun's rays were strongest. Now, researchers led by Tom Meyer at the Energy Frontier Research Center at the University of North Carolina, Chapel Hill, have built a system that converts the sun's energy not into electricity, but hydrogen fuel, and stores it for later use, allowing for the powering of devices long after the sun goes down.

"So called 'solar fuels' like hydrogen offer a solution to how to store energy for nighttime use by taking a cue from natural photosynthesis," says Meyer, professor of chemistry. "Our new findings may provide a last major piece of a puzzle for a new way to store the sun's energy--it could be a tipping point for a solar energy future."

In an hour, the sun puts out enough energy to power every vehicle, factory, and device on the planet for an entire year. Solar panels can harness that energy to generate electricity during the day, but the problem with the sun is that it goes down at night--and with it the ability to power homes and cars.

If solar energy is going...