‘We have demonstrated the very first electrochromic device that can switch between solar heating and radiative cooling.’
Researchers from Duke University, North Carolina, US, have developed a ‘smart window-like technology’ which they say can be used to either harvest heat from sunlight, or at the flip of a switch allow an object to cool.
Based on electrochromic technology; the researchers demonstrated a thin device that interacts with both spectrums of white light while switching between passive heating and cooling modes. In the heating mode the device darkens to absorb sunlight and prevents mid-infrared light from escaping. In the cooling mode the darkened window-like layer clears, simultaneously revealing a mirror that reflects sunlight and allows mid-infrared light from behind the device to dissipate. The researchers say that because the mirror is never transparent to visible light, the device would not replace windows in homes or offices, but it might be used on other building surfaces.
Reporting their work in the journal American Chemical Society Engineering Letters, the research team describes a technique where a thin grid of gold is placed on top a one atom thick layer of graphene to act as a highway for electricity. The researchers then integrated a phenomenon called plasmonics, which exploits the unique optical properties metallic nanostructures to enable the manipulation of light at nanoscale. This allowed the switching back and forth between absorbing light and heat, or allowing it to pass through.
The research team says that this development could have a significant impact for HVAC, potentially cutting energy usage in the US by nearly 20%. ‘We have demonstrated the very first electrochromic device that can switch between solar heating and radiative cooling,’ said Po-Chun Hsu, Assistant Professor of Mechanical Engineering and Materials Science at Duke University.