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Material Could Harness the Sun’s Power

April 15, 2014 By William Opalka

SolarjpgThe greatest barrier to solar power’s adoption is pretty obvious. Power can’t be generated in the dark.

So energy storage has been a promising avenue for research, and a team at MIT and Harvard University has come up with a way around that by creating a material that can absorb the sun’s heat and store energy in chemical form, on demand. A report in MIT News describes the process.

The technology could produce electricity, but inefficiently. However, when only heat is required, for buildings or industrial processes, this source of solar energy could be used. A paper describing the new process is in the journal Nature Chemistry.

Some molecules called photoswitches can assume either of two different shapes. Sunlight causes them to absorb energy and jump from one configuration to the other. But a jolt of heat or light can trigger the photoswitches to return to the other configuration, releasing heat.

The new work is a follow-up to computer analysis done three years ago, but creating a material has been time-consuming. To reach the desired energy density packing the molecules close together became necessary and problematic. The team tried attaching the molecules to carbon nanotubes (CNTs), but getting those molecules packed onto a CNT in that kind of close packing was hard.

After additional analysis the photoswitching molecules, called azobenzene, protrude from the sides of the CNTs like the teeth of a comb. While the individual teeth were, indeed, twice as far apart as the researchers had hoped for, they were interleaved with azobenzene molecules attached to adjacent CNTs. The net result: The molecules were actually much closer to each other than expected.

While previous modeling showed that the packing of azobenzenes on the same CNT would provide only a 30 percent increase in energy storage, the experiments observed a 200 percent increase.

There are many applications where heat, not electricity, might be the desired outcome of solar power. Solar cooking could alleviate the need to burn wood, eliminating a pollution source, for example.



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