NEWS Researchers at Umeå University have developed new sustainable coatings that improve the performance of solar thermal collectors – strengthening solar heat's position as a climate-smart energy source. Using nanomaterials and simple manufacturing methods, the technology can become both more efficient and more accessible.
The research results could lead to more efficient solar thermal collectors that have the potential to compete with fossil energy sources.
ImageAbsolicon“Solar thermal has great potential to contribute to the green transition, especially as a source of industrial process heat. But the technology needs to become even more competitive to gain broader traction,” says Erik Zäll, doctoral student in experimental physics at the Industrial Doctoral School at Umeå University.
In his doctoral thesis, he demonstrates how optical coatings – thin films that control how light interacts with surfaces – can be tailored to improve both efficiency and durability. His work focuses on two key components of solar thermal collectors: the cover glass that allows sunlight to enter, and the receiver that absorbs the light and converts it into heat.
Erik Zäll, doctoral student at the Industrial Doctoral School and the Department of Physics.
ImageHans KarlssonFor the glass, Erik Zäll has developed an anti-reflective coating made of silica with small, hexagonally ordered pores. By adjusting the size and shape of the pores, as well as the thickness of the coating, he has succeeded in increasing the light transmitted through the glass. At the same time, the coating’s resistance to scratches, dirt and moisture is improved – factors that would otherwise reduce performance over time.
For the receiver, the thesis presents two solutions. One is an electroplated cobalt-chromium coating that absorbs light thanks to its surface structure. It is produced using a type of chromium that is far more environmentally friendly than those previously used. The second solution is a composite film made of carbon nanotubes and silica, spray coated on annealed stainless steel using ultrasonic technology. The thermal treatment of the steel creates a thin oxide layer that improves both optical properties and heat resistance.
Both coatings absorb most of the sunlight while emitting very little thermal radiation. They can be manufactured using low-cost, environmentally friendly methods suitable for large-scale production.
The research has been carried out in close collaboration with Swedish solar energy company Absolicon Solar Collector and is directly adapted to their collector technology. The results have led to two patent applications and may eventually lead to more efficient solar thermal collectors, boosting Absolicon’s competitiveness in the global solar thermal market.
“Our work shows that it’s possible to combine sustainability, cost-effectiveness and high performance in optical coatings – a key to making solar heat a viable alternative to fossil fuels on a larger scale,” says Erik Zäll.
On Friday 23 May, Erik Zäll of the Department of Physics at Umeå University will publicly defend his doctoral thesis titled Heating a sustainable future: Optical coatings for solar thermal collectors. The defence will take place at 9:00 a.m. in Lilla Hörsalen, KBC Building. The faculty opponent is Professor Ewa Wäckelgård from Dalarna University.
The Industrial Doctoral School is based on collaboration between the University, researchers and businesses or organisations. The aim is to combine benefits for both society and the external party while training new high-quality researchers. The doctoral student also receives a tailored academic course package. The doctoral school is open to all disciplines and the doctoral student is employed at Umeå University.
