Researchers at the National Renewable Energy Laboratory (NREL) have developed a new type of window that can switch between transparency and solar energy generation—potentially transforming buildings and vehicles into distributed power plants.
Windows are everywhere: in homes, offices, skyscrapers, and cars. They let in daylight and connect indoor spaces with the outside world. But what if they could also generate electricity when sunlight is abundant? That possibility is now closer to reality thanks to advances in a promising material known as perovskite.
Traditionally, windows and solar cells serve opposite purposes. Solar panels are designed to absorb as much sunlight as possible, while windows are meant to transmit it. Overcoming this fundamental contradiction has long been a technical challenge.
To address it, NREL researchers used a specialized perovskite material—part of a broad class of crystalline ceramics whose chemical composition can be finely tuned. This flexibility allows scientists to engineer materials with highly specific optical and electronic properties. In this case, the team created a device that can function both as a clear window and as a solar panel, achieving a solar conversion efficiency of 11.3 percent.
“There is a fundamental tradeoff between a good window and a good solar cell,”
“This technology bypasses that. We have a good solar cell when there’s lots of sunshine and we have a good window when there’s not.”
— Lance M. Wheeler, lead author of the study.
When operating in its transparent mode, the smart window allows 68 percent of visible sunlight to pass through. When switched into solar-collection mode—a process that takes about three minutes—it becomes much darker, transmitting only around three percent of visible light while converting the remainder into electricity.
The implications for urban environments are significant. In dense cities, the vertical surfaces of buildings vastly exceed the available rooftop area. Harnessing sunlight from façades could dramatically increase renewable energy generation. At the same time, cities struggle with so-called “urban heat islands,” where asphalt and brick surfaces absorb and retain heat. By converting a portion of incoming solar radiation into electricity rather than heat, smart windows could help reduce cooling demands.
With air-conditioning costs rising worldwide, such dual-purpose technology could provide both energy savings and electricity generation—effectively turning sunlight from a burden into an asset.
The automotive sector could also benefit. Vehicle windows could generate power when cars are parked, helping charge batteries in electric vehicles without additional infrastructure.
For companies aiming to transition to 100 percent renewable energy, the technology presents an attractive alternative to covering buildings entirely with conventional solar panels. Instead of sacrificing window space for rooftop installations, businesses could integrate both functions into a single device.
However, commercialization is not imminent. One major challenge remains durability. The researchers observed that the performance of their switchable solar windows declines after about 20 switching cycles. By comparison, conventional photovoltaic panels typically maintain around 80 percent of their original efficiency for up to 25 years. Improving longevity is now a primary focus of the research team.
The study, titled Switchable Photovoltaic Windows Enabled by Reversible Photothermal Complex Dissociation from Methylammonium Lead Iodide, was published in the journal Nature Communications.
Reference:
Lance M. Wheeler, David T. Moore et al. (2017). Switchable Photovoltaic Windows Enabled by Reversible Photothermal Complex Dissociation from Methylammonium Lead Iodide. Nature Communications. DOI: 10.1038/s41467-017-01842-4.