Rooftops could one day do much more than hold solar panels.
Scientists have developed a hybrid system that can produce electricity and heat while also providing cooling—all from the same surface and at the same time.
The technology, developed by researchers at the Karlsruhe Institute of Technology (KIT) in Germany, could help solve a major problem for energy-efficient buildings.
Solar panels need space to generate electricity, solar thermal collectors need space to produce heat, and cooling systems require additional energy.
On crowded roofs and building facades, fitting everything together can be difficult.
The new system combines three functions: photovoltaic electricity generation, solar heating and passive daytime radiative cooling.
The research was published in Cell Reports Physical Science.
At the heart of the design is a transparent cooling layer made from a silica base coated with a silicone polymer called polydimethylsiloxane.
Sunlight can pass through this layer, but the material can also release heat as infrared radiation.
That heat escapes through what scientists call the atmospheric window, a range of infrared wavelengths that can pass relatively easily through Earth’s atmosphere and travel toward space. Because outer space is extremely cold, this process allows a surface to lose heat without using electricity.
Below the transparent cooling layer is a Fresnel lens, which concentrates the incoming sunlight onto a much smaller photovoltaic-thermal collector. This collector uses the concentrated solar energy to generate both electricity and useful heat.
The arrangement solves a difficult engineering problem. Solar energy systems work best when they absorb large amounts of sunlight and become hot, while radiative cooling systems need to stay cool enough to release heat effectively.
By allowing sunlight to pass through the cooling layer before concentrating it onto a separate collector, the researchers were able to physically separate these competing functions.
Outdoor tests showed that the prototype could perform all three jobs simultaneously. It cooled a surface by as much as 6.5°C below the surrounding air temperature while generating 60.6 watts of electrical power per square meter. At the same time, its heating component reached temperatures as high as 110.8°C, or about 231°F.
The researchers describe the idea as harvesting both the “hot sun” and the “cold universe.”
The technology could eventually turn roofs and building facades into multifunctional energy surfaces. It may be especially useful in places that require large amounts of both electricity and cooling. One potential application is AI data centers, where powerful computing equipment consumes enormous amounts of electricity and generates large amounts of heat.
The team is now working to improve the system’s optical design, heat management and solar cells.
If the technology can be successfully scaled up, future buildings may no longer need separate surfaces for generating electricity, collecting heat and providing cooling.
Instead, one carefully designed surface could perform all three tasks—making much better use of limited space while reducing energy consumption.
