Another PV Breakthrough

If it seems like solar technology has been improving almost by the day, well that’s probably because it has. It takes some serious effort these days to keep up with all the reports about newer and more efficient ways to harvest the sun’s rays. But this latest development takes an approach that seems especially ingenious.

Many photovoltaic arrays attempt to boost their efficiency by changing the angle of their panels as the sun shifts position in the sky. However, there are a number of drawbacks to such “trackers”, including their expensive installation and maintenance, as well as the possibility of damaging the PV cells through overheating, and keeping them cool requires the installation of even more expensive technology. So scientists have begun to develop and experiment with devices called Lumiscent Solar Concentrators (LSCs), which capture the sun’s rays before focusing them on the solar cell regardless of the angle from which they arrive, thereby improving efficiency.

These devices, a throwback to technology initially developed during the 1970s, are essentially plastic sheets laden with dye molecules that absorb light and are similar in principle to fiber optic cables, trapping and bouncing photons (particles of light) between the plastic surfaces while steering them towards the cell. But determining the right amount of dye molecules is still tricky business. Too many leads to greater heat loss through dye absorption, hence greater inefficiency, and too few means less sunlight captured.

But one new LSC innovation could conceivably triple the efficiency of these devices, and make them cheaper to manufacture. As reported in a recent issue of Science (see abstract) , two MIT researchers have introduced a radical wrinkle by getting rid of the plastic sheet and spraying a pane of glass with a combination of dyes and an aluminum compound called tris (8-hydroxyquinoline) aluminum. This novel combination joins two phenomena. First, the glass and dyes act together to capture light and prevent its escape. Second, the dyes and tris aluminum in tandem create a quantum effect (called Forster energy transfer) that re-emits the photons at a different wavelength, preventing their loss by dye molecule absorption. Together, these combined effects also mean that the solar cells can be significantly smaller and need only be placed at the edges of the glass pane rather than spread over a large surface area, further minimizing costs and installation difficulties.

Finally, by adding a second treated glass panel on top to absorb rays of shorter wavelength such as ultraviolet light, these LSCs are made even more efficient. This way the panel underneath will not only catch the longer wavelengths that elude the first, but will also recover any incidental photons lost after their initial capture. The end result is a prototype device with an efficiency potentially ten times greater than that of conventional solar cells. And they’re apparently so simple to manufacture that they could be on the market within three years. The future continues to gain speed…

Sources: “Breakthrough in solar energy: ten times more effective solar power may be available in three years”, www.mongabay.com; “MIT opens new ‘window’ on solar energy”, MIT News;“High Efficiency Organic Solar Concentrators for Photovoltaics” (abstract), Science; “Guiding Light”, The Economist; “Forster resonance energy transfer”, Wikipedia.


Posted on Friday, July 18th, 2008 at 2:52 pm | Tagged in Energy Efficiency, Green Building, Photovoltaics, Sustainability, Technology | posted by Bill

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