Friday 18 April 2014

New “solar thermal fuel” has energy density of lead batteries

Science Focus

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Right now, photovoltaic devices are the cheapest, most efficient way to harvest the energy in sunlight. The problem is that this energy ends up in the form of electricity, which we have difficulty storing in a cost-effective manner. An alternative approach, solar thermal energy, converts solar energy to heat and can use that heat to continue generating power for several hours after the Sun goes down. But that's not enough to make solar an around-the-clock energy source.

Researchers are apparently working on a third option, one that could potentially store energy indefinitely. It goes by the name of "solar thermal fuel," but it's not a fuel in the traditional sense. Rather than breaking apart the fuel molecule through combustion, solar thermal fuels release heat by rearranging bonds within a molecule, leaving all the atoms in place. As a result, they can be recycled repeatedly—in the example that introduced me to solar thermal fuels, a research team ran theirs through more than 2,000 cycles with no loss in performance.

How do you get energy into and out of a molecule without breaking any bonds? In this case, the authors worked with derivatives of a chemical called azobenzene, shown below. The double bond between the two nitrogens forces the remaining bonds into one of two forms: either both of the rings can be on opposite sides of the molecule (top, called the "trans" form) or they can be on the same side (bottom, called "cis").

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original post: http://feeds.arstechnica.com/~r/arstechnica/science/~3/fMXY00uIx98/
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