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Scientists Discover Way to Send Information into Black Holes Without Using Energy

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‘Smart Windows’ Darken to Cool & Generate Power Like Solar Panels When Hot

New NREL technology darkens to reduce heat and converts sunlight into electricity

Imagine a window that not only keeps your home cool under the blazing summer sun but also turns that same sunlight into clean, usable energy. It sounds futuristic—but it’s already here. Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have developed a groundbreaking technology known as “smart windows.” These windows darken automatically when heated by sunlight to keep interiors cool, while simultaneously functioning as solar panels to generate electricity.

This innovative approach could revolutionize the way we cool and power our buildings—offering a double dose of sustainability: reducing the need for air conditioning and producing renewable energy.

The Problem: Cooling Without Compromising the Planet

In hot climates, keeping buildings cool is a challenge that often comes with environmental costs. Air conditioners consume massive amounts of electricity, much of it generated by fossil fuels. According to the International Energy Agency (IEA), cooling accounts for nearly 10% of global electricity use, and demand is expected to triple by 2050.

Traditional blackout blinds or tinted windows help block sunlight, reducing heat indoors. However, they waste one major resource—the sunlight itself. Instead of merely blocking the sun’s rays, what if we could use them to our advantage?

That’s exactly the question NREL scientists set out to answer.

A Window That Works Smarter

The research, published under the title “Reversible Multicolor Chromism in Layered Formamidinium Metal Halide Perovskites,” describes a new thermochromic photovoltaic technology. This term may sound complex, but the concept is surprisingly simple: the material reacts to heat by changing color, and at the same time, it produces electricity from sunlight.

The core of the window’s technology lies in perovskite, a special material already popular in the solar energy world. Perovskite solar cells are known for their efficiency, flexibility, and low cost compared to traditional silicon panels.

In the smart window design, a thin layer of perovskite is sandwiched between two panes of glass. A solvent vapor is introduced between them, which triggers a fascinating chemical transformation when the temperature rises.

How It Works: The Science Behind the Shade

When the window heats up under direct sunlight—typically between 95°F and 115°F (35°C to 46°C)—the perovskite crystals begin to rearrange themselves. They move through different structural forms: first as chains, then as sheets, and finally as cubes.

Each of these crystal structures absorbs and reflects light differently, causing the window to gradually darken. The transition isn’t just aesthetic—it’s functional.

  • Transparent mode: When it’s cool outside, the window lets in natural light, maintaining brightness indoors.

  • Tinted mode: As the sun’s intensity increases, the window darkens automatically, reducing heat entry and glare.

  • Solar mode: While darkened, the perovskite layer starts harvesting sunlight to generate electricity, effectively turning the window into a mini solar panel.

This transformation happens in just seven seconds, making it fast enough to respond dynamically to changing sunlight throughout the day.

Cleaner Cooling for a Warming World

The environmental impact of this innovation could be huge. By blocking heat, smart windows reduce the need for energy-hungry air conditioning systems. At the same time, they generate power that can help offset a building’s overall electricity consumption.

According to Bryan Rosales, a postdoctoral researcher at NREL and lead author of the study, a prototype of this smart window could be ready within a year. The team’s latest model shows remarkable improvement over earlier prototypes, which operated at lower temperatures and took longer to switch.

In regions where heatwaves are becoming more frequent and intense, this technology could help buildings stay cool without increasing carbon emissions.

The Double Benefit: Energy and Efficiency

One of the most compelling advantages of these smart windows is their dual functionality. Traditional solar panels often require large rooftops or separate installations. With smart windows, the solar cells become part of the building’s structure itself—what’s known as building-integrated photovoltaics (BIPV).

This means that even skyscrapers with limited roof space could produce renewable energy simply through their windows.

Let’s break down the benefits:

  1. Reduced Cooling Costs – By blocking heat, buildings need less air conditioning.

  2. Energy Generation – The same sunlight that warms the glass also produces electricity.

  3. Lower Carbon Footprint – Less reliance on fossil-fueled power sources for cooling.

  4. Enhanced Comfort – Dynamic shading keeps indoor environments more stable.

  5. Aesthetic Flexibility – The window’s color changes—yellow, orange, red, and brown—could even enhance architectural design.

In short, smart windows promise comfort, efficiency, and sustainability—all in one elegant package.

A Step Toward Greener Cities

As urbanization increases, cities are becoming heat islands—areas where concrete and glass trap heat, raising local temperatures. Air conditioners, in turn, pump out even more heat into the environment, creating a vicious cycle.

Smart window technology could help break that cycle. By reducing the energy required for cooling and capturing solar power, it aligns perfectly with the goals of net-zero energy buildings—structures that produce as much energy as they consume.

If widely adopted, smart windows could contribute to massive energy savings at the city level, especially in commercial buildings, which have large glass surfaces exposed to the sun.

Beyond Windows: Future Applications

The science behind these smart windows could extend far beyond office towers and homes. Researchers envision potential uses in cars, greenhouses, and even wearable tech.

  • Automotive industry: Imagine car windows that tint automatically under bright sunlight, keeping interiors cool while charging the vehicle’s battery.

  • Agriculture: Greenhouses could regulate light and temperature while generating solar power to run irrigation or lighting systems.

  • Consumer electronics: Small versions of the technology could one day power portable devices through self-shading screens.

Such versatility demonstrates the potential of thermochromic perovskites to reshape multiple industries.

Challenges on the Horizon

Of course, no new technology is without hurdles. Perovskite materials, while efficient, are sensitive to moisture and oxygen, which can degrade their performance over time. Researchers are actively working on improving their durability and stability, ensuring that smart windows can withstand years of weather exposure.

Another challenge lies in scaling up production. Manufacturing perovskite layers uniformly on large glass panels requires precision and consistency—something that is still being refined.

Cost is also a factor. While perovskites are cheaper than silicon, integrating them into double-paned glass systems with vapor layers may initially be expensive. However, as production scales up, prices are expected to drop significantly, much like what happened with solar panels over the past decade.

Complementary Clean Cooling Innovations

Smart windows are part of a growing wave of innovations aimed at cleaner cooling. For example, researchers have recently developed “cold tube panels,” which allow buildings to stay cool while keeping windows open. These systems radiate heat away from the body rather than cooling the air itself, reducing energy use.

Together, these technologies suggest a future where air conditioning doesn’t have to be an environmental burden. Instead, buildings could use a combination of passive cooling, smart shading, and renewable power generation to stay comfortable and efficient.

The Road Ahead

The NREL team’s next goal is to move from laboratory prototypes to real-world applications. According to Rosales, the technology is now stable enough to be integrated into a working window design. “A prototype window using the technology could be developed within a year,” he said.

Future versions may also include customizable color transitions and integration with smart home systems, allowing users to adjust transparency or monitor energy production via an app.

Imagine a future where your home automatically optimizes itself—tinting windows when it’s hot, generating electricity during the day, and brightening up in the evening—all without you lifting a finger.

Toward a Sustainable Future

As the effects of climate change intensify, innovations like smart windows represent a crucial step forward. They embody the essence of sustainable design: using natural resources intelligently rather than fighting against them.

Instead of relying solely on air conditioning, we can turn our buildings into active participants in the energy system, harvesting power from the same sun that heats them.

Smart windows may start as a laboratory innovation, but their potential to reshape architecture, urban planning, and energy consumption is enormous. With continued research, investment, and collaboration between scientists, architects, and policymakers, this technology could soon become a standard feature of the buildings of tomorrow.

Final Thoughts

The vision of smart, energy-generating windows combines science, sustainability, and design into one elegant solution. As cities grow and temperatures rise, technologies like these remind us that innovation doesn’t just mean doing more—it means doing better.

By transforming sunlight into both shade and power, NREL’s smart windows illuminate a brighter, cooler, and greener future for us all.

Reference: Rosales, B.A., Mundt, L.E., Allen, T.G. et al. Reversible multicolor chromism in layered formamidinium metal halide perovskites. Nat Commun 11, 5234 (2020). https://doi.org/10.1038/s41467-020-19009-z

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