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Wednesday, 26 October 2011

Solar Energy Shines brightly: Tapping that energy cost-effectively remains a challenge

MIT News
Oct 26, 2011

The sunlight that reaches Earth every day dwarfs all the planet’s other energy sources. This solar energy is clearly sufficient in scale to meet all of mankind’s energy needs — if it can be harnessed and stored in a cost-effective way.

Unfortunately, that’s where the technology lags: Except in certain specific cases, solar energy is still too expensive to compete. But that could change if new technologies can tip the balance of solar economics.

The potential is enormous, says MIT physics professor Washington Taylor, who co-teaches a course on the physics of energy. A total of 173,000 terawatts (trillions of watts) of solar energy strikes the Earth continuously. That’s more than 10,000 times the world’s total energy use. And that energy is completely renewable — at least, for the lifetime of the sun. “It’s finite, but we’re talking billions of years,” Taylor says.

Since solar energy is, at least in theory, sufficient to meet all of humanity’s energy needs, the question becomes: “How big is the engineering challenge to get all our energy from solar?” Taylor says.

Solar thermal systems covering 10 percent of the world’s deserts — about 1.5 percent of the planet’s total land area — could generate about 15 terawatts of energy, given a total efficiency of 2 percent. This amount is roughly equal to the projected growth in worldwide energy demand over the next half-century.

Such grand-scale installations have been seriously proposed. For example, there are suggestions for solar installations in the Sahara, connected to Europe via cables under the Mediterranean, that could meet all of that continent’s electricity needs.

Because solar installations of all types are modular, the experience gained from working with smaller arrays translates directly into what can be expected for much larger applications. “I’m a big fan of large-scale solar thermal,” says Robert Jaffe, the Otto (1939) and Jane Morningstar Professor of Physics. “It may be the only renewable technology that can be deployed at very large scale.”

And we do know how to harness solar energy, even at a colossal scale. “There’s no showstopper, it’s just a matter of price,” says Daniel Nocera, the Henry Dreyfus Professor of Energy at MIT.

Nocera foresees a time when every home could have its own self-contained system: For instance, photovoltaic panels on the roof could run an electrolyzer in the basement, producing hydrogen to feed a fuel cell that generates power. All the necessary ingredients already exist, he says: “I can go on Google right now, and I can put that system together.” Nocera’s own invention, a low-cost system for producing hydrogen from water, could help over the next few years to make such systems cost-competitive.
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