Engineers invent transparent coating that cools solar cells
Every time you stroll outside, you emit energy into the universe: Heat from the top of your head radiates into space as infrared light.
Now three Stanford engineers have developed a technology that improves on solar panel performance by exploiting this basic phenomenon. Their invention shunts away the heat generated by a solar cell under sunlight and cools it in a way that allows it to convert more photons into electricity.
The group’s discovery, tested on a Stanford rooftop, addresses a problem that has long bedeviled the solar industry: The hotter solar cells get, the less efficient they become at converting the photons in light into useful electricity, Physorg wrote.
The Stanford solution is based on a thin, patterned silica material laid on top of a traditional solar cell. The material is transparent to the visible sunlight that powers solar cells, but captures and emits thermal radiation, or heat, from infrared rays.
“Solar arrays must face the sun to function, even though that heat is detrimental to efficiency,” Shanhui Fan, a professor of electrical engineering at Stanford, said. “Our thermal overlay allows sunlight to pass through, preserving or even enhancing sunlight absorption, but it also cools the cell by radiating the heat out and improving the cell efficiency.”
The Stanford team tested their technology on a custom-made solar absorber — a device that mimics the properties of a solar cell without producing electricity — covered with a micron-scale pattern designed to maximize the capability to dump heat, in the form of infrared light, into space. Their experiments showed that the overlay allowed visible light to pass through to the solar cells, but that it also cooled the underlying absorber by as much as 23°Fahrenheit.
The researchers said the new transparent thermal overlays work best in dry, clear environments, which are also preferred sites for large solar arrays. They believe they can scale things up so commercial and industrial applications are feasible, perhaps using nanoprint lithography, which is a common technique for producing nanometer-scale patterns.
Lensless imaging with
extreme ultraviolet light
Researchers from the Friedrich Schiller University Jena, Germany, have pushed the boundaries of a well-established imaging technique, using ultrafast beams of extreme ultraviolet light streaming at a 100,000 times a second. Not only did they make the highest resolution images ever achieved with this method at a given wavelength, they also created images fast enough to be used in real time. Their new approach could be used to study everything from semiconductor chips to cancer cells.
The researchers wanted to improve on a lensless imaging technique called coherent diffraction imaging, which has been around since the 1980s. To take a picture with this method, scientists fire an X-ray or extreme ultraviolet laser at a target.
The light scatters off, and some of those photons interfere with one another and find their way onto a detector, creating a diffraction pattern. By analyzing that pattern, a computer then reconstructs the path those photons must have taken, which generates an image of the target material, all without the lens that’s required in conventional microscopy, according to osa.org
“The computer does the imaging part, forget about the lens,” explained Michael Zürch, Friedrich Schiller University Jena, Germany and lead researcher. “The computer emulates the lens.”
The table-top machines are unable to produce as many photons as the big expensive ones which limits their resolution. To achieve higher resolutions, the detector must be placed close to the target material, similar to placing a specimen close to a microscope to boost the magnification.
Given the geometry of such short distances, hardly any photons will bounce off the target at large enough angles to reach the detector. Without enough photons, the image quality is reduced.
Zürch and a team of researchers from Jena University used a special, custom-built ultrafast laser that fires extreme ultraviolet photons a hundred times faster than conventional table-top machines.
With more photons, at a wavelength of 33 nanometers, the researchers were able to make an image with a resolution of 26 nanometers, almost the theoretical limit.
“Nobody has achieved such a high resolution with respect to the wavelength in the extreme ultraviolet before,” Zürch said.