A German institute is developing a hybrid rooftop system that generates electricity, heat, and cooling

A German research institute has developed a compact rooftop technology that generates solar electricity, provides hot water and indoor cooling in one integrated system. According to the institute's information service, the system combines solar cells, photovoltaics and passive daylight radiative cooling technology.

In a press release issued by the German Karlsruhe Institute of Technology on August 14, 2026, a research group led by Gan Huang announced the development of a hybrid system capable of generating electricity, heat, and cooling simultaneously on a single surface, taking advantage of the heat of the sun and the cold of outer space.

The system relies on a transparent cooling layer made of silica and polydimethylsiloxane. This layer allows light to pass through while releasing heat into space through what is known as an atmospheric window.

An atmospheric window is a natural physical mechanism that allows the surface on Earth to shed its heat directly into outer space without the atmosphere hindering this process. There is a certain range of infrared wavelengths (between approximately 8 and 13 micrometers) in which the atmosphere is very transparent to heat, and does not absorb heat emanating from the surface. When the surface emits heat within this range, it passes through the atmosphere and goes directly into space, which leads to natural cooling without consuming energy or electricity. The heat exits directly into space as if there is an “open window” allowing it to escape.

The presence of a cooling layer made of silica (with a substance called polydimethylsiloxane) is important in this hybrid system because it is specially designed to release heat within that range, allowing it to remain cool during the day despite the presence of the sun, and provides natural cooling without electricity, while the solar cells underneath produce electricity and heat.

Cell Reports Physical Science explains that this layer allows for natural cooling without consuming energy, while a Fresnel lens focuses sunlight on a small solar collector to produce heat, and there is a thermal photovoltaic collector to produce electricity.

The prototype demonstrated the ability to achieve cooling that reached 6.5 degrees Celsius less than the ambient air temperature, produce 60.6 watts/m² of electricity, and reach 110.8 degrees Celsius of heat.

Ivan Alberto Cruz Garcia, a researcher at the Institute of Microstructure Engineering, says that separating the cooling zone and the heating zone was the biggest challenge.

Gan Huang describes the system as a combination of “fire and ice,” capturing sunlight to produce energy, while emitting heat into space to provide cooling. He points out that the technology may be ideal for applications such as artificial intelligence data centers that require high power and continuous cooling.

Professor Shanhui Fan from Stanford University, one of the leading experts on passive diurnal radiative cooling, participated in the study. The scientific paper confirms that the combination of sun and space paves the way for the emergence of a new generation of multi-functional building roofs.