Solar Builder

JAN-FEB 2019

Solar Builder focuses on the installation/construction of solar PV systems. We cover the latest PV technology (modules, mounting, inverters, storage, BOS) and equip installers/contractors with tips and tools to make informed purchasing decisions.

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Page 20 of 51

SOLARBUILDERMAG.COM | 21 night-vision goggles detect. Normally this form of cooling doesn't work well for some- thing like a building because Earth's atmo- sphere acts like a thick blanket and traps the majority of the heat near the building rather than allowing it to escape, ultimately into the vast coldness of space. Holes in the blanket Fan's cooling technology takes advantage of the fact that this thick atmospheric blan- ket essentially has holes in it that allow a particular wavelength of infrared light to pass directly into space. In previous work, Fan had developed materials that can con- vert heat radiating off a building into the particular infrared wavelength that can pass directly through the atmosphere. These materials release heat into space and could save energy that would have been needed to air condition a building's interior. That same material is what Fan placed under the stan- dard solar layer in his new device. Zhen Chen, who led the experiments as a postdoctoral scholar in Fan's lab, said the researchers built a prototype about the diameter of a pie plate and mounted their device on the rooftop of a Stanford building. Then they compared the temperature of the ambient air on the rooftop with the tem- peratures of the top and bottom layers of the device. The top layer device was hotter than the rooftop air, which made sense because it was absorbing sunlight. But, as the research- ers hoped, the bottom layer of the device was significantly cooler than the air on the rooftop. "This shows that heat radiated up from the bottom, through the top layer and into space," said Chen, who is now a professor at the Southeast University of China. What they weren't able to test is whether the device also produced electricity. The upper layer in this experiment lacked the metal foil, normally found in solar cells, that would have blocked the infrared light from escaping. The team is now designing solar cells that work without metal liners to cou- ple with the radiative cooling layer. "We think we can build a practical device that does both things," Fan said. 50 Year Itch A team of solar energy researchers from Case Western Reserve University has been awarded $1.35 million from the U.S. Department of Energy Solar Energy Technologies Office to continue its work toward increasing the efficiency and lifetime of photovoltaic modules — specifically aimed at pushing their lifespan to 50 years. Led by Roger French, the Kyocera Professor in the Materials Science and Engineering Department at the Case School of Engineering, the research is expected to help determine the relative value of two different kinds of module construction for encapsulating photovoltaic cells: 1) double-glass construction and 2) glass/backsheet, where the backsheet is instead a multilayer polymer laminate. Each type of PV module construc- tion has its advantages and disadvantages. Double-glass better protects the structural integrity of the PV cells but can also trap corrosive degradation elements inside, whereas the glass/backsheet breathes better so that cor- rosives leak out but offers less physical protection to the inside compo- nents. "My background is in chemistry, so I'm looking at the chemical degra- dation of polymers inside the solar panels, especially in the glass-glass construction, as many manufacturers are starting to use that method," said Laura Bruckman, an associate research professor at the center. And while Bruckman peers into the innards of the solar panel to look at chemical degradation, Jennifer Braid, postdoctoral researcher at the SDLE Research Center, will be considering the relative effect of that degradation on the PV cells and their electrical performance. "One of the big problems is corrosion," Braid said. "In the glass-poly- mer construction, those corrosive materials can escape; while in the glass- glass module, not so much. We'll be measuring and comparing the effects of corrosion and other degradation modes on module power loss." Case Western wants to push PV modules to 50 years

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