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Date: 18-10-13

Heat converted to infrared to increase solar PV efficiency

There is lot of heat generated when sunlight falls on the solar PV cells, researchers at Stanford University have tried to convert that heat into infrared and then make the solar cells absorb that infrared emission to convert into electricity. The heat-resistant thermal emitter converts heat into infrared light. This technology is known as thermophotovoltaics. Nano material based thermal emitter design by Stanford researchers remains stable at temperatures as high temperatures up to 2,500 F.

Shanhui Fan, a professor of electrical engineering at Stanford University and his colleagues at the University of Illinois-Urbana Champaign (Illinois) and North Carolina State University collaborated on the project. Their results are published in the Oct. 16 edition of the journal Nature Communications. Shanhui Fan said "This is a record performance in terms of thermal stability and a major advance for the field of thermophotovoltaics".

"In theory, conventional single-junction solar cells can only achieve an efficiency level of about 34 percent, but in practice they don't achieve that," said study co-author Paul Braun, a professor of materials science at Illinois. "That's because they throw away the majority of the sun's energy."

"Essentially, we tailor the light to shorter wavelengths that are ideal for driving a solar cell," Fan said. "That raises the theoretical efficiency of the cell to 80 percent, which is quite remarkable."

So far, thermophotovoltaic systems have only achieved an efficiency level of about 8 percent, Braun noted. The poor performance is largely due to problems with the intermediate component, which is typically made of tungsten – an abundant material also used in conventional light bulbs.

Though this concept is quite old, what these researchers have done is, they have used better material with higher thermophotovoltaic efficiency and also ability to withstand extremely high temperatures. They have used three-dimensional structure made up of coated tungsten emitters in a nanolayer of a ceramic material called hafnium dioxide. They could withstand temperatures above 1,800 F (1000 Deg C), and also displayed better performance at higher temperature.

As per the report the ceramic-coated emitters retained their structural integrity for more than 12 hours. When heated to 2,500 F (1,400 C), the samples remained thermally stable for at least an hour.

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