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Stacked Solar Cells Efficient up to 70,000-Suns, North Carolina State University

Solar Cell Connections Fixed by NCS Innovation
Solar Cell Connections Fixed by NCS Innovation

In order to increase the output associated with a certain area of solar cells exposed to sunlight, various methods have been tried, such as stacking, concentrating, or spectrum tuning, even nanotechnology.

For example, the most efficient solar cells are about 45% efficient, that is, they can convert 45% of the sun’s energy into electricity. The other 55% is lost to reflection and heat. Efficient solar cells make use of a combination of methods, such as combining stacked solar cells with concentrating lenses. Concentrating lenses are fairly inexpensive and abundant which, by concentrating the sun’s rays up to 5,000 times, can increase the output of solar cells exponentially. Stacked solar cells allow various layers to convert solar energy into electricity, as each individual layer cannot convert the light that ends up passing through it.

There’s still one catch to maximizing solar cell efficiency, which actually isn’t in the cell itself, but in solar panels that are made up of many individual solar cells. The connections in between solar cells were a point of focus by researchers at North Carolina State University [NCS]. The problem is that, while the solar cell itself can be up to 45% efficient, the connection between two cells is 0% efficient, converting solar energy, not into electricity, but into heat. Heat loss is one thing, but in electrical terms, can be detrimental to output as a whole. The higher the temperature gets, the more resistance is generated, siphoning off voltage in the connections instead of passing it on to the collector at the end of the panel.

The effect is barely noticeable if no concentrating lens is used, but once the concentration hits about 700 suns, the voltage drop across the connection between solar cells starts to impede the efficiency of the whole panel. The more connections overheating in the panel, the less efficient it becomes. Researchers “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 NCS.

In addition to eliminating the voltage-drop problem brought on by heat generated up to 1,000 suns concentration, NCS researchers were able to prove the effectiveness of the change up to 70,000 suns. Since even the best concentrating lenses max out at around 5,000 suns, the new coating is more than sufficient to assure highly efficient solar cells and the connections between them for improved efficiency in the entire solar panel.

Image © Wikimedia

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