Video: MIT Researcher Explains New "Third Way" Solar Innovation

We tend to think of solar power as coming in two possible forms: photovoltaics, which convert sunlight into electricity, and solar thermal systems, which use the sun's heat to warm water or a home, or which can be concentrated on a fixed spot to boil water or oil and turn a turbine, thereby generating power.

Of course, the sun's energy could theoretically be used in any number of ways. In fact, most of the forms of energy we recognize are, in some way, "solar" power. This includes coal and oil, which as fossil fuels contain ages' worth of the sun's energy accumulated as rich carbon over time. The same goes wind power, as heat from the sun is what drives wind currents.

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Recently there have been some exciting advances in one decades-old idea for capturing and utilizing the sun's energy, thanks to a team of MIT researchers lead by Jeffrey Grossman. The so-called "thermo-chemical approach" is described by MIT News Office's David Chandler like so:

"solar energy is captured in the configuration of certain molecules which can then release the energy on demand to produce usable heat. And unlike conventional solar-thermal systems, which require very effective insulation and even then gradually let the heat leak away, the heat-storing chemicals can remain stable for years.

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Basically, the team has discovered this incredible molecule: fulvalene diruthenium. That cute little molecule (pictured on the left) will change its shape when it absorbs heat and, later, with the help of a still-to-be-determined calalyst, will release the heat and snap back to its original shape.

Here's a video that probably describes the process better than I do:

[youtube]http://www.youtube.com/watch?v=sbLF2u2XBYc

Grossman says this of the thermo-chemical approach:

...it takes many of the advantages of solar-thermal energy, but stores the heat in the form of a fuel. It’s reversible, and it’s stable over a long term. You can use it where you want, on demand. You could put the fuel in the sun, charge it up, then use the heat, and place the same fuel back in the sun to recharge.

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There are still a few significant sticking points—ruthenium, one of the elements in the molecule, is rare and prohibitively expensive, so they're going to have to figure out a different molecule that will perform the same basic task. But that seems possible. The big advance announced here is that the concept was proven. This molecule “is the wrong material," Grossman said, "but it shows it can be done.”