2011-12-02

Co.Exist

Harnessing The Sun's Heat For Power By Mimicking The Greenhouse Effect

The planet’s atmosphere gets heat from the sun and then traps it. A new breakthrough from MIT lets objects do the same thing, so that we can use the sun to heat things to astronomically high temperatures and then generate power from them

Solar panels have come a long way. Their rapidly lowering cost is part of what brought down Solyndra. And they’re also getting more efficient. But solar still makes up just a tiny percentage of our overall power, because the panels are not yet as efficient and cheap as they need to be. But by copying the Earth’s ability to let heat in but not let it back out, MIT researchers might have made using the sun’s heat much more efficient.

Many big solar projects, like the the $2.2 billion Ivanpah Solar Electric Generating System, which is still under construction in the Mojave Desert, are relying on something called concentrated solar technology, a technique where mirrors focus the sun’s heat onto a specific area. The heat drives a steam turbine (or other heat engine), which generates electrical power.

But concentrated solar is expensive to deploy (look at that Ivanpah price tag). And photovoltaic prices are dropping rapidly, making it look even less enticing. Researchers at MIT, however, think that concentrated solar can be deployed simply and on the cheap—by using energy from the sun’s heat and something called thermophotovoltaics (TPV).

TPV devices take heat and convert it to electricity by using the same mirrors found in a concentrated solar plant to direct heat directly onto a TPV panel—forgoing the complicated mirror to steam to turbine process. The technology has been around since 1980s, but it’s never been efficient enough to be deployed commercially. And it’s never quite worked for solar, because while the sun is quite hot, it’s not hot enough to get TPVs up to a temperature where they could generate a lot of power (about 1,600 degrees Fahrenheit).

MIT scientists now think they can lose the mirrors and still use the thermophotovoltaics, with a little help from a photonic crystal—an array of microscopic holes placed on a top layer of the material. It’s a technique that mimics the greenhouse effect. The sun’s heat goes into the panel, but then it can’t come out. So, instead of losing that heat back into the air, it stays really hot and generates a lot of power.

MIT Researcher Peter Bermel breaks it down: Instead of a large, complex system to get something hot, we can now take a standard black object and "in practice, we can get it extremely hot, and not reradiate much of that heat."

On a large enough scale, this technique could compete efficiency-wise with conventional forms of power. The only problem: It’s still mostly theoretical. So perhaps years down the line we’ll see the thermophotovoltaic method deployed throughout the world’s deserts, but for now, traditional concentrated solar reigns.

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