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Smart buildings 04/11/2020

Smart Windows Turn Into Solar Cells When Transitioning

Sun as a source of energy is both seemingly of infinite value, and comes with limits. (credit: Dennis Schroeder, NREL)

Researchers have managed to create PV films that can keep buildings cool while still producing electricity.

By definition, it is intermittent. But it is also, in the case of solar windows, a kind of energy “paradox:” when the very electricity the sun produces is consumed more rapidly when it shines too strong and bright.

Buildings in the US, whether they are residential or commercial use 74% of the country’s electricity; and among the energy-hungry applications is air-conditioning, which is most often switched on to cool down interiors because the sun shining through the windows generates heat.

By applying to solar windows a color-changing — or transition — technology that darkens glass when heated by the sun, researchers have managed to create PV films that can keep buildings cool while still producing electricity. In a new study published in Nature Communications, scientists from the US Department of Energy’s National Renewable Energy Laboratory (NREL) present this next-generation “thermochromic photovoltaic” technology, which could ultimately help reduce the need for air-conditioning even on the sunniest days.


Here are the key points of their breakthrough:

  • The windows are made from three different materials, a thin film of the emerging solar cell material formamidinium metal halide perovskite (MHP), sandwiched between two panels of glass and a solvent vapor that is injected in between.
  • As long as the light is not too strong, the humidity stays low and the film remains transparent. But when temperature reaches between 95 and 115 °F (35 and 46 °C) and creates vapor, perovskite crystals rearrange into three different shapes, inducing a different shade of color and light-blocking degrees, from yellow to brown.
  • As soon as the film is colored (within seconds), the electricity generation starts, power conversion efficiency rising to 4.69%.
  • The team aims to develop a prototype window using the new technology within a year, though additional research will be conducted to determine the number of times the thermochromic window can be cycled into an electricity-generating operating mode.

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