Bright prospects for photovoltaics

Bayer MaterialScience is committed to developing sustainable technologies and materials, particularly when it comes to utilizing energy from renewable sources such as the sun and wind energy. With photovoltaics (PV), for example, the focus is on customer-specific solutions featuring higher energy efficiency, lower manufacturing costs and a broader range of applications.

"The current development portfolio offers a variety of innovations, including polyurethane sheathing for solar modules with an integrated assembly system, a sandwich composite of polycarbonate sheets with solar cells, and flexible solar modules with higher efficiency," says Dr. Frithjof Hannig, who is responsible for the coordination of photovoltaics activities at Bayer MaterialScience.

Innovations and visions with thermoplastic films

At present, crystalline solar cells are leading the way worldwide in terms of solar technology. These are encapsulated by Platilon® hot-melt adhesive films made of thermoplastic polyurethane (TPU), which have proved to be superior to other materials used for the same purpose. This is particularly true of their flexibility in bonding with relatively hard materials such as polycarbonate and glass. The TPU film facilitates continuous, vacuum-free processing without cross-linking and, therefore, also without emissions. "This is a clear advantage in terms of productivity in the manufacture of photovoltaic modules. What’s more, the film can be recycled and enables complete solar modules to be repaired," adds Hannig.

When it comes to novel thin-layer solar cells, Makrofol® polycarbonate encapsulation films can make it possible to produce flexible photovoltaic modules. A current target is to produce flexible, lightweight modules using reel-to-reel processing. At present, Bayer MaterialScience is working with partners to improve the product’s barrier properties against oxygen and water, in order to protect the active layer. This solution could lead to a replacement of glass which was used so far for this application.

But the developments don’t stop there. In the area of portable electronic devices such as laptops and cell phones in particular, the call for a power supply without a power pack and socket is growing all the time. Flexible organic solar cells made of plastic film could prove a viable economic solution in this area, provided that the utilization level and service life of solar cells could be increased in line with requirements. For the photovoltaic layer – the crucial part of the thin sandwich composite – the company is using inorganic quantum dots (Q-dots). In this way, PV cells could be applied to films in a simple printing process, resulting in a cost-effective solution for mobile electronic devices.

Soccer stadium as a power plant

Sheets made of the transparent polycarbonate Makrolon® also make it possible to integrate solar modules in roof constructions. One example is the sandwich composite developed by Sunovation GmbH in cooperation with Bayer Sheet Europe GmbH, which comprises floating silicon cells embedded between a Makrolon® solid sheet on the one side and a Makrolon® triple-wall sheet on the other. The composite is shatterproof, flexible and boasts a long service life thanks especially to the load-bearing properties of the multi-wall sheet. As a result, it provides optimum protection for the sensitive silicon cells and meets the fire safety regulations of the construction industry.

One impressive application of Sunovation’s photovoltaic solution is installed in the Weserstadion in Bremen, which currently boasts the biggest photovoltaic system of any sports stadium in Germany. One part of this construction is the roof’s inner ring, which is seven meters deep and fitted with special modules from Sunovation over an area of 3,000 square meters. Instead of being attached to the roof, these modules actually form part of the stadium’s construction. This solution was also preferred due to the existing construction’s static load limit. Glass was not a viable option in this case due to the weight. In fact, polycarbonate cuts the weight of the structure by around 60 percent, which in this case is equivalent to some 60 metric tons. The judging panel of the European Polycarbonate Sheet Extruders (EPSE) organization was so impressed by the solution that it awarded it first place in the "Best Innovation" category.

Cost-effective assembly thanks to polyurethane sheathing

The SOLON® Black 160/05 in-roof module from SOLON SE has also won several awards. It is equipped with an intelligent system frame with an integrated assembly system based on the Bayflex® polyurethane system from BaySystems. The solar module is fitted in the roof without the need for conventional installation systems. Thanks to fastening elements integrated into the plastic, the module can be screwed directly onto the roof battens. What’s more, the system’s overlapping polyurethane frame ensures that rainwater runs off easily and does not penetrate the roof. "In other words, this module is one of only a few genuine in-roof solutions in which the surface acts as a water-bearing layer, which means that costly substructures are no longer necessary. As a result, this innovative product delivers a low-cost, all-in-one solution", explains Dr. Hannig. In addition to the simplified substructure, the polyurethane coating of solar modules also opens up a whole range of design opportunities.

A polyurethane electrical encapsulation system based on Baydur® E is recommended for insulating the sockets of solar modules. It fills even narrow gaps and cavities very quickly and offers reliable protection against external influences. To this end, the polyurethane systems house BaySystems, Denmark, and Isotherm AG, Switzerland, have developed a cost-effective process based on reaction injection molding (RIM) technology, which makes it possible to enclose electrical parts in a single step. This electrical encapsulation system has been tailor-made for this application and exhibits flame retardance in line with the requirements of UL 94 V-O.

Multilingual and cosmopolitan

In future, photovoltaic applications could extend far beyond traditional solar modules. One such visionary application is a "translator shirt" for traveling salesmen and other people who travel a lot. During a conversation, voice recognition software would be used to display the translated words on the shirt. "The surfaces of certain textiles can be equipped with photovoltaic elements, while other areas exhibit the properties of batteries. This would provide the power supply for the shirt," explains Eckard Foltin from the Creative Center at Bayer MaterialScience. Then, all the user would have to do is start the program and enter the target language via a label with integrated microphone and translation unit. "This application could help overcome language barriers," says Foltin.