Solar energy is virtually limitless, generates no planet-warming greenhouse gases — and is useless between sunset and sunrise. Wind energy is also plentiful and emits no carbon, and it can be harvested day or night, but not when the air is calm.
A discovery announced in Thursday’s issue of Science may offer a way around these daunting problems, however. Chemists at the University of Calgary, in Canada, have found an efficient way to turn electricity from wind and solar energy into hydrogen, which itself can be used as a fuel, emitting nothing more harmful than water vapor, when the wind stops blowing or the Sun is below the horizon. “Essentially, we’re using hydrogen as a storage mechanism for electricity,” said co-author Curtis Berlinguette in an interview.
Without such a mechanism, electric utilities need to keep conventional power plants as backup, and if those plants burn coal or natural gas, they vent heat-trapping CO2 into the atmosphere. But the storage techniques energy experts have come up with so far — pumping water uphill when the sun is shining or the wind is blowing, then letting it flow down again to generate power, or storing the electricity in batteries, or using it to compress air that can run generators — are all quite inefficient.
Until recently, the same has been true of hydrogen storage. The way this technology works is that an electric current is run through water, splitting the H20 into oxygen (the O) and hydrogen (H). The downside, Berlinguette said: “It takes a lot of electricity.” You can speed the process by using a catalyst, which helps split water molecules, but so far, the best catalysts available have been made from rare metals with a layered, crystalline atomic structure.
That structure, however, keeps the water from making maximum contact with the catalyst. “It’s a bit like lasagna,” Berlinguette said. “If you pour sauce over layers of flat pasta [the crystalline metals], it has trouble penetrating all the way through.”
The chemists’ answer was to use cheaper metals, including plain old iron oxide (a.k.a. rust) in an amorphous, non-crystalline form. “It’s more like spaghetti,” Berlinguette said, and that makes the process far more efficient. It’s not nearly efficient enough if your end goal is simply to produce hydrogen: for that, an established process known as methane reforming is much better.
But if you’ve got a solar plant in the desert or a wind farm on the Nebraska (or Alberta) prairie, and you need somewhere to stash excess energy until it’s needed, hydrogen appears to be better than the other options. “The energy density of hydrogen,” — that is, the amount of energy it holds per pound of material — “is about a hundred times more than batteries or compressed air or the rest,” Berlinguette said.
The Calgary team’s new work improves upon a similar discovery made by MIT chemists a few years ago, and their new catalysts are the best available, doing the job better, and with cheaper materials.
While converting renewable electricity into hydrogen is currently far more expensive than these other methods, the higher efficiency and thousandfold-cheaper materials in this new process could finally make it competitive.
A company formed by the chemists to commercialize their new technology is planning to have a utility-scale working model on the market sometime next year, with a homeowner-size model, the size of a large refrigerator, by 2015. If that comes to pass, a house equipped with solar panels or a wind turbine could be entirely energy self-sufficient, around the clock.
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