Clean Power

Published on November 28th, 2012 | by James Ayre


New Way To Create Electricity Out Of Sunlight Discovered, A Solar Energy Funnel

November 28th, 2012 by  

The discovery of a revolutionarily different way to generate electricity from sunlight has been made by researchers at MIT. The new technology, which is essentially a solar energy funnel, is able to use a much broader spectrum of sunlight’s energy than conventional solar does, by utilizing materials under elastic strain.


“We’re trying to use elastic strains to produce unprecedented properties,” says Ju Li, an MIT professor and the lead author of a paper describing the new concept.

The ‘funnel’ in this case is a metaphor, though — it is electronic forces creating the funneling effect, not gravity as in a literal funnel. “Electrons and their counterparts, holes — which are split off from atoms by the energy of photons — are driven to the center of the structure by electronic forces.” But, interestingly, as the process occurs, the material actually assumes a funnel shape. The material is a stretched sheet of “vanishingly thin” material, pushed down at a center point with a microscopic needle, producing a curved shape similar to a funnel.

The pressure from the needle creates an elastic strain that increases toward the needle point. Because of the variation in the strain, the atomic structure is changed to the point where different sections are ‘tuned’ to different wavelengths of light. Making it possible to make use of not only visible light, but also the rest of the spectrum, most of which is invisible. The majority of the energy in sunlight is invisible.

The material used is a thin layer of molybdenum disulfide, which is a semiconductor that can form a film just a single molecule in thickness. And it possesses a ‘crucial characteristic’ called bandgap, which allows it to be formed into solar cells. But unlike the material used in most solar cells, silicon, “putting the film under strain in the ‘solar energy funnel’ causes its bandgap to vary across the surface, so that different parts of it respond to different colors of light,” the MIT press release notes.

“It turns out that the elastic strain, and therefore the change that is induced in electrons’ potential energy, changes with their distance from the funnel’s center — much like the electron in a hydrogen atom, except this ‘artificial atom’ is much larger in size and is two-dimensional.”

The funnel will also lead to better charge collection, the researchers think. In typical solar cells, the excitons randomly move throughout the material after they’ve been generated by photons. But in the funnel, the characteristics of the material direct them to the collection site at the center, which should lead to more efficient charge collection.

“People knew for a long time that by applying high pressure, you can induce huge changes in material properties,” Li says. But more recent work has shown that controlling strain in different directions, such as shear and tension, can yield an enormous variety of properties.

The work was just published this week in the journal Nature Photonics.

Source: Massachusetts Institute Of Technology
Image Credits: Yan Liang; Creative Commons Attribution Non-Commercial No Derivatives license

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About the Author

's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy. You can follow his work on Google+.

  • Dave

    Progress gotta love it. However good solid ideas are sometimes overlooked in the rush forward.

    How is it that the world has almost completely ignored the most promising solar tech of all (IMO), Solar Updraft Towers, AKA Solar Chimneys. A 200MW plant of this type is being built in Arizona. It is unique among solar power plants in that it also generates some electricity at night, at a reduced rate of course. Base loads anyone?

    Solar Chimneys are a combination of well known, tried and true technologies and are far more reliable than PV or CSP. With the added advantage that they scale *economically* from 50KW (the test plant, 30 years ago in Spain) to 400MW. The operation is simple enough, a large greenhouse collection area collects sunlight, which warms the air beneath it. The warm air is funneled to the center where a turbine or turbines are situated at the base of a large chimney. The height of the chimney keeps the warm air from diffusing too quickly, harnessing its buoyancy to provide power. Basically a combination of greenhouses, wind turbines, and we already know how to make chimneys and large cooling towers. Making a hollow chimney is much easier than building an inhabited sky scraper, the chimney doesn’t have to hold up anything besides itself.

    As for the nighttime power, the sunlight also warms the ground under the greenhouse during the day. At night the ground warms the air and the process goes on at a reduced rate.

    Even better, using 2/3rds or more of the collection area for orchards or other agricultural uses will produce far more income than the electricity by itself. Almost any crop, year round, frost free. In larger plants, the inner 1/3 is too hot to grow anything.

    • Bob_Wallace

      I’m going to guess that most people who have cranked through the numbers didn’t find the idea so hot. Now that someone is building one we should have some real world numbers which can be used to determine if solar chimneys make sense.

      Seems to me that there is an awful lot of structure being built to run one or two turbines. There are likely many places to get cheaper electricity.

    • Ronald Brak

      In the past solar towers had to compete with other solar thermal designs and they had the drawback of needing to be very large to hope be cost effective which means they had a drawback when it came to attracting money. A proposed one in Australia couldn’t get out of planning because of the reasonable fear that its cost would escalate, something that is extremely common for large new projects. Nowadays all forms of large scale solar thermal have been hurt by the huge drop in solar PV prices. In places like Australia and Germany no form of grid only electricity can now compete with point of use solar PV.

  • JMin2020

    This actually compete ditectly with the Caimbridge Rainbow full spectrum seperation and conversion technology. Different technique ; but same objective. Full Spectrum Conversion. This one can deliver from what I read in the origional article cited from MIT. Cambridge has not developed the actual conversion at all seperations of rhe spectrum as yet. This MIT Tech has achieved this conversion at al levels of spectrum seperation with respect to the visible light spectrum.

  • This sounds extremely promising, although it looks like a completely new class of solar PV technology, so current production equipment may not be re-usable at all.

    • Yeah, quite an interesting development. Curious if it can get out of the lab.

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