Smart glass coating could cool glass buildings

Researchers at the Fraunhofer Institute have developed a smart coating for building glass that can automatically darken in sunlight. This technology combines electrochromic and thermochromic materials, responding to both electrical stimuli and temperature changes. In modern buildings with extensive glass curtain walls, the coating effectively reduces indoor overheating caused by solar radiation, thereby decreasing reliance on energy-intensive air conditioning systems.

The construction industry is one of the major sources of global greenhouse gas emissions. In Germany, for example, according to statistics from the Federal Environment Agency, the building sector accounts for approximately 30% of the country's carbon dioxide emissions and 35% of its energy consumption. Buildings with large glass facades and roofs, especially office structures, experience sharp rises in indoor temperatures during strong summer solar radiation. Traditional shading devices such as blinds and curtains often compromise visual aesthetics and obstruct views. As a result, such buildings commonly rely on air conditioning for cooling, leading to high electricity consumption and an increased carbon footprint.

To address this issue, the Fraunhofer Institute for Silicate Research (ISC) and the Fraunhofer Institute for Organic Electronics, Electron Beam, and Plasma Technology (FEP) jointly led the EU-funded "Switch2Save" project. They collaborated with universities and industry partners across several European countries to advance the development and application of smart window coating technology.

In this smart coating system, the electrochromic component is based on a transparent conductive film. Applying voltage to the film triggers the migration of ions and electrons, enabling the glass to reversibly transition from transparent to dark. The thermochromic coating, on the other hand, automatically reflects solar heat when the ambient temperature reaches a specific threshold, operating without external power as a passive response mechanism.

The electrochromic elements can be integrated with sensors and a control system to monitor light intensity and temperature in real time. When values exceed set parameters, the system sends an electrical signal to the conductive film, gradually darkening the glass. This effectively blocks heat input and provides anti-glare functionality. On cloudy days or at night, the glass returns to full transparency, maximizing the introduction of natural light.

The technology has already been implemented in practical building applications. For instance, this smart glass system has been installed in the pediatric clinic of a large hospital in Athens, Greece, and an office building in Uppsala, Sweden. Researchers will conduct a year-long energy consumption monitoring study to compare electricity usage of air conditioning systems before and after retrofitting, verifying energy-saving performance under real climatic conditions.

In terms of manufacturing, the team employs wet chemical processes and vacuum coating technology. The electrochromic coating is integrated onto a flexible polymer film, while the thermochromic layer is prepared on an ultra-thin glass substrate. Roll-to-roll production methods enable economical and scalable manufacturing. The final product is only a few hundred micrometers thick and weighs less than 500 grams per square meter, making it easy to install in existing building windows without structural modifications.

Currently, the project team is focused on further enhancing the technology’s applicability. Efforts include combining electrochromic and thermochromic units to improve regulatory flexibility, developing coating processes suitable for curved glass, and expanding color options beyond gray and blue to meet diverse architectural aesthetic needs.

As global warming and the EU Green Deal advance, the demand for energy-efficient building technologies is growing rapidly. All buildings in the EU are expected to achieve carbon neutrality by 2050. Smart window technologies like Switch2Save are poised to play a key role in promoting the low-carbon transformation of the construction industry.