Retrofittable Electrochromic Films for Windows and Glass Facades

Controlling light and heat radiation through windows and glass facades at the push of a button, saving energy and still maintaining a clear view? Switchable electrochromic films that turn dark but remain transparent are expected to make this possible in the future.

The fact that this can also be retrofitted in existing buildings is to be demonstrated by the joint project “EnOB: FLEX-G 4.0 – Technologies for innovative switchable films as a retrofit solution for energy-saving windows and glass facades” (funding reference: 03EN1048), which is funded by the German Federal Ministry of Economic Affairs and Climate Action BMWK.

Coordinated by the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, the project will work with six other partners to advance the state of the art to the prototype stage over the next four years. In doing so, the project aims to kill two birds with one stone – on the one hand, the windows of a Dresden school are to be retrofitted, and on the other, the pupils are to be actively involved in the technology development as a contribution to promoting career orientation.

The new FLEX-G 4.0 project aims to develop a cost-effective retrofit solution with innovative switchable films which can be applied to existing glass surfaces as simple as possible. In the previous FLEX-G project, crucial technological fundamentals have already been investigated, culminated in electrochromic films on a laboratory scale. These films are now to be further developed for industrial production.

“The switchable films can significantly reduce the overall energy transmittance of windows, the so-called Solar Heat Gain Coefficient, and thus the energy demand of the building,” said Dr. Cindy Steiner, project coordinator at Fraunhofer FEP. “We are strongly interested in demonstrating the results of the project in a real environment and involving young people for this purpose – pupils from a Dresden school who will also benefit from the project in their lessons!”

The main objective of the project is transfer of research results into suitable system designs and manufacturing technologies for large-area electrochromic films to be installed directly on the construction site. Furthermore, robust processes for “easy” on-site application of these films to windows and facades in existing buildings are to be developed.

For demonstrating and monitoring purposes, it is planned to integrate the retrofit films at an existing building, the 46th Dresden Secondary School, as well as in the newly constructed laboratory building of Fraunhofer FEP. In addition, the Fraunhofer Institutes FEP and ISC will provide teaching materials for science subjects and offer internships for pupils. Involvement in the measurements and evaluation of the results together with the pupils is also planned.

To optimize and enhance electrochromic films and, in particular, to create a retrofit solution, the project partner tesa SE, Fraunhofer ISC and Coatema are working on the lamination processes required and will optimize the electrochromic cell by using suitable materials. Specifically, materials and roll-to-roll (R2R) application processes for a polymer electrolyte are being researched.

Its purpose is to adhere two films of the electrochromic cell to each other like an adhesive being ion-conductive and electrically insulating at the same time, which is crucial for the switching process. For the application of the electrochromic film to window glass, a laminating adhesive with a long lifetime is also being developed. A robust application process suitable for construction sites will complete the project.

Fraunhofer FEP and ISC contribute their extensive know-how and equipment technology for R2R processes for applying the electrochromic layers and the protective layers to the films. The R2R processes are based on both vacuum thin-film processes and coatings under atmospheric pressure. Further integral part of the project is development of characterization techniques for the electrochromic films, its quality and related process control of the manufacturing technologies. The project partner Coatema is taking care of specific plant engineering issues for transferring the processes to industrial production.

In order to be able to switch the optical properties of the films at the end, solutions are being developed for grid-independent energy supply, e.g. via solar cells. For this matter, the project partner Enerthing is working on IoT systems (IoT = Internet of Things), the design of the energy supply, sensor technologies for wireless and automated control of the switching state and the integration of the sensor technology into the existing building management system. The aim of this system is to optimize energy savings.

The finished retrofit films will first be applied to the two buildings in Dresden to determine the actual energy-saving potential. For this purpose, close coordination is taking place between the developers of the consortium, the state capital Dresden and the school in order to implement the integration of the electrochromic film, as well as the unification of this with the IoT systems later.

Over a period of 12 months, the savings potential in terms of cooling and heating energy demand in the two demonstration buildings will be determined. At this point, the pupils will also be involved in the research work of the FLEX-G 4.0 project. The project partners’ learning materials for the lessons and the offer of orientation internships additionally support the project consortium’s efforts to strengthen environmental awareness and interest in new technologies among pupils of all educational backgrounds, from secondary school to university entrance qualification.

Project partners:
• Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP
• Fraunhofer Insitute for Silicat Research ISC
• Hochschule für Technik Stuttgart
• tesa SE
• Coatema Coating Machinery GmbH
• Enerthing GmbH
• Landeshauptstadt Dresden