Building Envelopes as a Triple Energy Surface

August 17, 2026

Source: E & M powernews

A hybrid system developed by KIT combines electricity, heat, and cooling within the same building space. Researchers at the institute have tested a prototype in the field.

To date, several technical systems have been competing for limited space when it comes to supplying energy to buildings. Photovoltaic systems generate electricity, solar thermal systems provide heat, and air conditioning systems handle cooling. A research group at the Karlsruhe Institute of Technology (KIT) aims to combine these functions within a single area. At the Institute of Microstructure Technology, the team led by Dr. Gan Huang has developed a hybrid radiant cooling and solar system for this purpose and tested it under field conditions. Huang heads the “Hybrid Solar Technologies Lab” at KIT.

The researchers’ primary goal is to use roofs and facades more efficiently. Instead of installing separate systems side by side, a multifunctional building envelope is intended to simultaneously provide electricity, usable heat, and cooling. KIT sees potential applications wherever energy and cooling are needed simultaneously. Huang cites AI data centers as a possible example, as they require a lot of electricity and also have high cooling loads.

Space-Age Cooling Complements Solar Energy

Technically, the system combines photovoltaics with passive radiative cooling, known as “Passive Daytime Radiative Cooling” (PDRC). A translucent silicon dioxide plate emits heat as infrared radiation toward space, thereby cooling itself. At the same time, it allows sunlight to pass through. A flat lens then focuses this light onto a small solar collector, which generates electricity and heat from it. In this way, the same surface area can simultaneously contribute to cooling as well as to electricity and heat generation.

According to KIT, in a field test, the prototype cooled down to 6.5 degrees Celsius below the ambient temperature. At the same time, it achieved an electrical power density of 60.6 watts per square meter and temperatures of up to 110.8 degrees Celsius for heat utilization.

According to the researchers, the challenge lies in combining two conflicting requirements: While the solar collector is designed to absorb as much solar energy as possible—and thereby heat up—the cooling layer above it must remain as cold as possible. The physical separation of the two areas makes this possible. Sunlight first passes through the cooling layer. Only below that does the lens focus the light onto the solar collector. “We bring ‘fire’ and ‘ice’ together,” says Huang, describing the principle.

From Cooling Material to Hybrid System

The project builds on the research group’s earlier work. According to KIT, in 2024 the team introduced a transparent material capable of passively cooling buildings while allowing daylight to pass through. Building on this, the researchers have now expanded radiative cooling to include the use of solar energy.

Next, the research group plans to optimize, among other things, the guidance of sunlight, thermal management, and the solar cells. The study was conducted in collaboration with Professor Shanhui Fan of Stanford University in the United States, an expert in passive radiative cooling.

The study, titled “Co-harvesting universe coldness and solar energy for tri-generation of cooling, electricity, and heating,” is available on the website of the journal *Cell Reports Physical Science*.

Author: Davina Spohn