Smart windows lower indoor temperature without power and generate electricity from raindrops

The increasing demand for cooling due to global warming has significantly boosted energy consumption in buildings. One major culprit of energy loss is traditional windows, which tend to absorb solar heat rather than reflect it.

To address this challenge, energy-saving windows are emerging as a practical solution. These advanced windows not only provide thermal comfort but also help reduce reliance on conventional cooling systems, contributing to a more sustainable future.

In order to optimize energy savings in buildings, windows must integrate efficient cooling technologies that don’t rely on electrical power, known as Zero Energy technologies, alongside energy-harvesting methods that ensure a steady power supply, called Plus Energy technologies. While doing so, windows should still maintain their essential transparency, even in cold or foggy weather.

A research team, led by Professor Seung Hwan Ko from Seoul National University, has developed multifunctional smart windows that push the boundaries of what windows can do.

These innovative windows perform three critical functions. They provide radiative cooling, which lowers indoor temperatures on sunny days without consuming electricity. On rainy days, the windows generate electricity using raindrops. Furthermore, they incorporate a transparent heater that can quickly defrost or de-ice the surface in colder weather.

These multifunctional windows demonstrate how technology can evolve to address multiple challenges simultaneously. Instead of focusing solely on keeping buildings cool, these windows also generate energy and provide clear visibility in adverse weather conditions. This breakthrough has the potential to revolutionize how buildings manage their energy consumption, paving the way for more energy-efficient, self-sustaining structures.

Buildings are significant consumers of energy, particularly for temperature management. The rise in global temperatures has dramatically increased the demand for cooling, and traditional windows, with their high solar absorption rates, contribute heavily to energy loss. As a result, researchers worldwide are focusing on creating smart windows that can maximize energy savings.

While many smart windows today can adjust their opacity to regulate temperature, this method has drawbacks. By becoming opaque, the windows lose their primary function—transparency. The challenge is to develop windows that can manage heat without sacrificing visibility.

Professor Ko's team has made strides in maintaining transparency while enhancing energy efficiency. The new smart window technology uses a Zero Energy approach with “transparent radiative cooling,” which allows the windows to cool buildings without consuming electricity. These windows reflect near-infrared light while allowing visible light to pass through, keeping the interior cool and well-lit.

In addition, the team developed a Plus Energy technology that harnesses the energy generated by friction when raindrops hit the windows. This approach surpasses traditional Zero Energy models by actively contributing to a building's energy production. The windows also feature a transparent heating element, which quickly melts frost or ice, ensuring clear visibility during cold weather.

These smart windows achieve their multifunctionality by using a layered structure made of silver and indium tin oxide (ITO). These materials are known for their excellent electrical conductivity and optical properties.

The radiative cooling technology minimizes the absorption of sunlight while emitting radiant heat outward, which reduces indoor temperatures without using refrigerants.

On rainy days, the friction between raindrops and the window surface generates electricity, thanks to the conductive properties of the silver and ITO layers. Moreover, the windows use Joule heating to remove frost or ice during cold conditions, ensuring clarity and enhancing safety.

The smart windows developed by Professor Ko’s team offer substantial improvements in performance over conventional windows. Under direct sunlight, these windows maintained indoor temperatures about 7 degrees cooler than regular windows. In a simulation of rainy weather, the windows generated 8.3 watts of power per square meter from a single raindrop. Additionally, they cleared frost twice as fast as regular windows due to the Joule heating feature.

These results highlight the potential for these multifunctional windows to transform the building industry by providing a sustainable, energy-efficient alternative to traditional systems. This technology supports the growing trend of Plus Energy Buildings, which not only minimize energy consumption but also actively generate power.

As global temperatures continue to rise, the demand for cooling in buildings will only increase. The smart windows developed by Professor Ko and his team offer a promising solution to both reduce energy consumption and generate clean power. By integrating three key functions—radiative cooling, energy generation, and frost removal—into a single device, these windows are setting a new standard for energy efficiency in buildings.

This innovation could lead to significant energy savings, particularly in hot or humid climates, while also reducing the environmental impact of cooling systems. As the technology is refined and scaled up for broader use, it could play a key role in shaping the next generation of energy-efficient buildings.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

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