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The sun shines on solar power

With installed capacities currently growing almost exponentially around the globe, it is extremely important to develop more efficient production methods for the solar modules that are essential to this ever more attractive market

3 Jun 2008 , Leverkusen : With installed capacities currently growing almost exponentially around the globe, it is extremely important to develop more efficient production methods for the solar modules that are essential to this ever more attractive market. There is definite room for improvement here, as employees of Bayer MaterialScience were recently able to demonstrate. Light-resistant thermoplastic polyurethanes (TPUs) make it much easier to manufacture solar modules. A film made from Desmopan® has been developed in collaboration with ETIMEX-Primary Packaging GmbH based in Dietenheim, Germany.
In the medium term, this will enable a continuous production process to replace the current batch production in certain areas, which could boost a module manufacturer’s output many times over with a comparatively low investment. The potential for improvement in cost-effectiveness should make solar power even more competitive in the future.

“It’s amazing how quickly solar power is expanding around the globe,” comments Faisal Shafiq, a Bayer MaterialScience expert on thermoplastic polyurethanes. According to the European Photovoltaic Industry Association (EPIA), the global market for solar power installations is currently growing at a rate of around 40 percent. Solar-Report 1/2008 from web service Solarserver.de reveals that the contribution of large solar power installations (at least 200 kW/a) to power grids has doubled every year since 2004. “And this trend is expected to continue,” says Shafiq.

As a result, the solar modules that generate solar power photoelectrically are very much in demand. “Yet they are still produced using a comparatively complex process”, explains Shafiq. Solar cells made from silicon wafers are put between a sheet of glass and a substrate together with an embedding film (primarily EVA films) and thermally crosslinked in a vacuum laminator for 12 to 20 minutes at temperatures of around 145 °C. This high temperature ensures that the EVA elastomer hardens to create a transparent layer. According to Shafiq, “This method has a number of disadvantages. For example, the time required for crosslinking prevents a higher throughput being achieved and solar module manufacturers have to factor in comparatively high downtimes and maintenance costs because the crosslinking agents added to the EVA can make it necessary to replace the filter membranes.”

This is where the solution developed by Bayer MaterialScience comes in. “Films made from our thermoplastic polyurethane Desmopan®, which are produced by our cooperation partner Etimex-PP and marketed under the name VISTASOLAR® TPU film, provide comparable results, but no crosslinking is required thanks to the higher melting point,” explains Shafiq. This speeds up module production and Bayer MaterialScience is predicting a significant reduction in cycle times. This is expected to have a positive effect on thin-film modules in particular. It will also result in better capacity utilization of the complex installation, making production more efficient and, at the end of the day, more cost-effective – despite the higher costs of TPU films.

The Desmopan® solution has a number of other benefits. For example, it is conceivable simply to return defective or damaged modules, which previously had to undergo time-consuming repairs, for repeat production. This is possible because thermoplastic polyurethanes can be remelted, enabling the expensive solar cells they contain to be used again. Storage would also appear to be simpler because Desmopan® films are much more robust than EVA films that already incorporate crosslinking agents.

“Weathering tests have proved that Desmopan® satisfies the relevant requirements in terms of service life”, states Shafiq. “TPU solar modules have also been certified as complying with the key IEC 61215 standard by TÜV Rheinland. In addition, our wealth of experience with other Desmopan® products makes us very confident of its weathering properties. Transparency is, of course, another crucial factor for the effectiveness of modules and here, too, this plastic more than holds its own against other embedding materials”, he adds.

The reduction in cycle time in the vacuum laminator is not the end of the story, though. Shafiq has another very special feature up his sleeve. “Because no crosslinking is required with Desmopan® films, there is no reason why the solar modules cannot be manufactured in a continuous process instead of being put into a furnace in batches”, he says. Initial tests at a plant construction company show that thin-film modules can be fused with TPU films in a heated roll laminator to form modules. “This enables production times to be halved or even cut to a third”, explains the Bayer MaterialScience solar expert. The resultant increased throughput with a much lower investment means that the sun is set to shine on solar power!

About Bayer MaterialScience:
With 2007 sales of EUR 10.4 billion, Bayer MaterialScience is among the world’s largest polymer companies. Business activities are focused on the manufacture of high-tech polymer materials and the development of innovative solutions for products used in many areas of daily life. The main segments served are the automotive, electrical and electronics, construction, and sports and leisure industries. At the end of 2007, Bayer MaterialScience had 30 production sites and employed approximately 15,400 people around the globe. Bayer MaterialScience is a Bayer Group company.

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