Take a look at this video. See the little bubbles racing to the water's surface? What you're looking at is an "artificial leaf," unveiled yesterday by a team of researchers at MIT. On either side of this leaf are specially-designed catalysts that, with the help of a little sunlight, allow it to convert the water that its submerged in into hydrogen and oxygen.
The leaf is the most recently developed example of what have come to be known as "solar water-splitting cells" — a technology that some scientists think may one day provide a solution to one of solar power's biggest shortcomings: solar panels can only generate electricity when the sun is shining; if you want to be able to use solar-derived energy when it's dark or cloudy outside, you need to be able to store it.
Solar water-splitting cells, like MIT's artificial leaf, take the incoming energy from the sun and store it in the bonds of the diatomic hydrogen molecules generated in the water-splitting reaction. Assuming this hydrogen can be collected and stored (the technologies for which don't really exist yet), it could prove to be an immensely valuable source of recoverable energy.
That is, if we can do it affordably. Your average plant leaf converts just 1% of the energy received in the form of sunlight into chemical bonds, which is hardly a number to engineers to shoot for. In fact, MIT's artificial leaf can reportedly achieve an efficiency of almost 5%. Nevertheless, some estimate that energy efficiencies will need to reach percentages in the teens before we can really start to consider how we might use technologies like this in real-world applications.