Clean Power

Published on September 9th, 2013 | by James Ayre


Stacked Solar Cells Can Now Operate At Solar Concentrations Of Up To 70,000 Suns Worth Of Energy Thanks To New Technique

September 9th, 2013 by  

A means of improving the connections between stacked solar cells — one capable of increasing the overall efficiency of solar energy devices, while also reducing associated costs — was recently devised by researchers at North Carolina State University. The new technique makes it possible for stacked solar cells to operate at solar concentrations of up to 70,000 suns worth of energy while still maintaining an optimal level of efficiency — rather than losing a larger and larger proportion of voltage as waste heat, as would otherwise be the case. The researchers think that this should help to reduce the cost of solar energy production.

For some background — stacked solar cells are simply a collection of multiple solar cells that are assembled on top of each another — they’re currently the most efficient type of solar cell on the market, reaching conversion efficiencies as high as 45%. In order for them to be effective, though, they need to be designed so that the connecting junctions in between these stacked cells don’t absorb any of the sunlight — in other words you need to make sure that the connections don’t siphon some of the voltage that the cells produce. The energy that is siphoned off ends up being “wasted” as waste heat.

“We have discovered that by inserting a very thin film of gallium arsenide into the connecting junction of stacked cells we can virtually eliminate voltage loss without blocking any of the solar energy,” states Dr. Salah Bedair, a professor of electrical engineering at NC State and senior author of a paper describing the work.

The discovery means solar cell manufacturers can create stacked solar cells that can handle high-intensity solar energies without losing voltage at the connecting junctions, potentially improving conversion efficiency. Image Credits: NC State University

The discovery means solar cell manufacturers can create stacked solar cells that can handle high-intensity solar energies without losing voltage at the connecting junctions, potentially improving conversion efficiency.
Image Credit: NC State University

The press release from North Carolina State University has more:

This work is important because photovoltaic energy companies are interested in using lenses to concentrate solar energy, from one sun (no lens) to 4,000 suns or more. But if the solar energy is significantly intensified — to 700 suns or more — the connecting junctions used in existing stacked cells begin losing voltage. And the more intense the solar energy, the more voltage those junctions lose — thereby reducing the conversion efficiency.

“Now we have created a connecting junction that loses almost no voltage, even when the stacked solar cell is exposed to 70,000 suns of solar energy,” Bedair explains. “And that is more than sufficient for practical purposes, since concentrating lenses are unlikely to create more than 4,000 or 5,000 suns worth of energy. This discovery means that solar cell manufacturers can now create stacked cells that can handle these high-intensity solar energies without losing voltage at the connecting junctions, thus potentially improving conversion efficiency.”

“This should reduce overall costs for the energy industry because, rather than creating large, expensive solar cells, you can use much smaller cells that produce just as much electricity by absorbing intensified solar energy from concentrating lenses. And concentrating lenses are relatively inexpensive,” Bedair concludes.

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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+.

  • JamesWimberley

    The photo looks like one of plain vanilla silicon solar panels, not the cutting-edge lab work being reported on, which may some day replace them – or maybe not.

  • Troy Frank

    I get that the concentration efficiency goes down if the focal point isn’t right in line with the sun. But being off-target a bit doesn’t mean you get no concentration does it? Is it really an all or nothing, or do you just get reduced concentration when you’re off-target?

  • Troy Frank

    I don’t see why this would mean that you need a tracker. Even without the tracker wouldn’t you still get some amount of concentration?

    • eject

      Because you have to keep the focal point of your concentration device (i.e. lens or mirror) right on the solar cell.

  • dcard88

    I don’t understand how you get from 1 solar energy to 4 or 5000 without some type of huge magnification. Maybe a 6 inch thick lens?

    • eject

      A parabolic mirror does this easily. 1m2 would bring the power of 10 000 suns on a 1cm2 pv cell.

      I personally think this is all rubbish anyway . way to complex. you need electrical motors and stuff to track the sun (hello, moving parts fail, they simply will). you loose a lot of space around those tracking devices. you need to put them somewhere far outside so the land is cheap enough. this means you need transmission lines. you are basically introducing many of the downsides of wind turbines to PV without getting the same yield as from a turbine. solar PV belongs on the roof. this way you loose no space. They will just sit there for 50 or more years. Nearly no maintenance

      • Stephen

        If your pants are loose, you’re going to lose them!

        • eject

          Dealing with the discrepancy between pronunciation and spelling requires attention at least for a non native.

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