How the founding team of Phytonics is harnessing the properties of a rose petal to revolutionize the photovoltaic market.
The tech spin-off Phytonics of KIT has a vision: to accelerate the energy transition by a technological leap in photovoltaics. "If we put it exaggeratedly, we can only achieve the European climate targets if legislations do not stand in their own way. Currently, on the one hand, we have a solar obligation for commercial locations and new buildings that are supposed to cover their electricity needs in the future with their own photovoltaic systems. On the other hand, there are regulations on the glare behavior of solar cells, which mean that such systems cannot be installed everywhere," explains Dr. Ruben Hünig, co-founder and CEO of Phytonics.
Blinded by reality
New ideas are needed so that these legislations do not continue to conflict. Photovoltaic systems today already achieve considerable energy yields, but to date they are not glare-free. "Solar panels are not allowed to emit more than 20,000 candela per square meter (cd/m²) of brightness. When you consider that the sun shines with a brightness of 1.6 billion cd/m², of which a one- to two-digit percentage is reflected off the solar modules, it becomes clear what a technological challenge the antireflection coating of the modules presents. Conventional solar glasses simply cannot achieve this anti-reflective effect," says Hünig, explaining the need for action. The Phytonics team has found a solution to this problem: An anti-reflective coating for photovoltaic modules. "The application principle is similar to that of a cell phone protective film for displays. Our film-like coating is an add-on for solar modules and is laminated onto the surface. This makes the anti-reflective film independent of the underlying technology and compatible with all solar module types. Above all, the coated module is thus absolutely glare-free," says Hünig, describing the innovation. The technology makes it possible to use photovoltaics in places where, for reasons of glare, none were previously allowed to be installed, for example around airports, near highways or on numerous house roofs with suboptimal alignment of the modules to the neighbor.
Inspired by nature
Behind this supposedly simple film are more than eight years of research and a complex solution. Hünig explains: "We took nature as our model, because plants are true masters of light management. For flowers to be pollinated, they have to produce a very strong color impression that looks the same to the insect from all directions. This can only be achieved if there is no reflection at the interface with the air, as the color impression would otherwise be overlaid by white ambient light. Therefore, most petals have a special combination of micro- and nanostructures on the leaf surface that can couple light of all wavelengths and from all directions of incidence approximately completely into the petal." To transfer this unique structure to solar cells, the founding team used electroplating to make a metallic print of rose petals strung together to transfer their micro- and nanostructure into metal.
Electroplating describes the electrochemical Separation of metallic deposits (coatings) on objects by an electrolytic bath. An electric current releases metal ions from an am Metal located on the positive pole and stores it by reduction on the object to be coated at the negative pole. The higher the current and the longer the bath, the more the coating falls of the item.
From roll to roll
"With this, we have created a molding tool that can subsequently be used many times for static hot stamping of polymer films. The tool is very suitable for development in the laboratory, but it is not efficient enough on an industrial scale. We therefore spent a lot of time and development effort on upscaling the process to the area of a solar module," says Hünig, describing the development steps over the past few years. Another challenge for the team was subsequently selecting a suitable manufacturing process. "We found a project partner who specialized in embossing nanostructures and with whom we were able to transfer the process to a low-cost roll-to-roll process," says Hünig. The roll-to-roll process is an embossing process in which the previously selected polymer film is clamped in the system, passed through two embossing rollers and the structure is continuously embossed into the film under pressure at high temperatures. In simple terms, the film passes from one roller to the other, acquiring its unique, non-glare surface along the way.
Special polymer films are long-term stable, scratch-resistant and particularly transparent for UV radiation. Thanks to these properties they are particularly good for outdoor use and thus for the technology of Phytonics.
Phytonics has been able to prove the film's anti-reflective properties both with measurements at its own test stand and via the evaluation of an official glare measurement. "The results have confirmed that we comply with all limit values and that we thus enable practically unlimited application possibilities for glare-free photovoltaic systems of the future," says Hünig. In addition to being absolutely glare-free and independent of the underlying photovoltaic technology, the film brings another key advantage. "At our test stand at KIT, using our anti-reflective film, we also achieve a relative additional yield of about five to ten percent, depending on the orientation and angle of incidence, compared to the test run with the same underlying technology without the coating. This means we achieve twice the additional yield of antireflective technologies available on the market. Not only do these achieve less yield, they also do not completely anti-reflect a solar cell," says Hünig, describing the advantages of the Phytonics technology.
In the long term, Phytonics would like to integrate antireflection coating technology into the production processes of photovoltaic manufacturers. "There is a lot of interest in the industry. We are already cooperating more closely with a few manufacturing companies. They are currently testing the film for long-term stability in accelerated aging processes. In 2023, these tests should be completed. In parallel, we are planning with the manufacturing companies to apply the film and integrate it into the existing process structure," says Hünig about the next steps. The fact that the technology is not only important for manufacturing companies, but also for end customers, is evident from extensive feedback: "We have a long waiting list of interested parties who would like to integrate the film on their existing solar system, including many private individuals with rooftop systems. This is also because there is an increasing number of legal disputes among neighbors due to glare from photovoltaic systems," explains Hünig.
By 2030, Phytonics wants to equip ten percent of the global market with the anti-reflective film. This is ambitious, but not unrealistic, because with their technology they are making possible what no one has been able to do so far: they are overcoming the legal hurdles of photovoltaics with a simple solution.
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