Smart Windows Turn Into Solar Cells When Transitioning

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.