The hotter it gets, the less efficient photovoltaic solar panels tend to become. Typically, as photons hit the panels, the solar cells convert some of them into electricity. The remaining photons produce heat energy, which escapes the power generation process.
Engineers from Stanford University, however, have found away to capture both the light and heat energy produced by the sun. Published this week in the journal Nature Materials, their research demonstrates that coating a solar cell's semi-conducting material with cesium allows the cell to use both light and heat to make electricity.
The process called photon-enhanced thermionic emission, or PETE, could theoretically use waste heat to improve photovoltaic efficiency by 50 percent. The image above shows the cesium-coated gallium nitride PETE device within a vacuum chamber. The researchers are also looking into other conductive materials, such as gallium arsenide.
Concentrated solar systems also harness the solar heat energy via strategically placed mirrors. The mirrors direct concentrated solar reflections to heat liquid that produces steam, which then power turbines.
Many photovoltaic solar cells become less effective in conditions over 212 degrees Fahrenheit (100 Celsius). But PETE reaches peak efficiency at well over 392 degrees F (200 C), according to researchers. This bodes well for PETE's potential for solar concentrators, such as parabolic troughs. The troughs, sometimes used in hybrid solar-thermal operations, can reach temperatures higher than 1,472 F.
PhysOrg quotes study author Nick Melosh:
What we've demonstrated is a new physical process that is not based on standard photovoltaic mechanisms, but can give you a photovoltaic-like response at very high temperatures. In fact, it works better at higher temperatures. The higher the better.
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Image: Nick Melosh, Stanford University