Update: Evonik, microstructure expert see bright future for photovoltaicsUpdate: Evonik, microstructure expert see bright future for photovoltaics
(This update contains more details on the 10X technology for creating a micro-structured surface on plastic sheet, and reasons its creator says his technology beats injection molding for surface structuring).
February 12, 2010
As reported here earlier this week, acrylic sheet and compounds supplier Evonik Cyro LLC has formed an alliance with 10X Technology LLC (Libertyville, IL), which develops micro- and nano-structured polymer substrates, to commercialize surface-enhanced acrylic materials for the photovoltaic market. First up will be co-development of lenses that improve the performance of energy-related products such as solar energy systems and interior lighting.
Products the companies will co-develop include solar concentrator lenses, which improve the efficiency of solar cell systems by focusing sunlight on a selected area of semiconductor material. These concentrated photovoltaics (CPVs) are a rapidly emerging field within the solar power industry as they work to greatly increase the relative energy output for a given area of space.
MPW has heard back from Robert Pricone, president of 10X Technology and the inventor of its patented micro-structuring technology, on more specifics of his company's process, and it is clear that photovoltaics are not the only plastic application for which it may be of interest. He says that the 'micro-replication' technology his company uses to fabricate precision solar concentrator lenses, or other products, is established technology used for more than 20 years to manufacture precision optical products. He also claims the technology, applied to extruded sheet, is a much better method for these and other applications than injection or compression molding.
With his company's technology, explained Pricone, the surface structures are formed after extrusion of plastic sheet by maintaining a very high temperature (somewhere above the extrusion temperature but below decomposition) to achieve minimum polymer viscosity. The sheet is then pressed into the microstructures on a cylindrical mold, which his company develops, and cooled below the glass transition temperature before removal. In that way the features cool to take their final shape before removal from the mold.
In answer to MPW questions, he wrote, "In a sense it's the same concept as injection molding only we are making rolls of film—hot polymer pressed against a mold and then cooled before removal to insure replication. The advantage is it runs continuously 1 meter or more wide, replicates more precisely than injection molding or compression molding, and the finished structures do not have any residual stress. The absence of stress means the features won't change or anneal over time, maintaining optical tolerances for 20 years or more."
10X's technology is established already on road signs throughout the world. The roll-to-roll process was used to make the first micro-prismatic reflective film for traffic signs, and since has been used to manufacture millions of square meters of signage, and is used for "virtually every traffic sign" made, he reports.
Evonik and 10X want not only to develop but also to market photovoltaic lenses, and claim that because of their ability to link research and production, they will be able to offer a stronger warranty than other suppliers which are focused solely on production of these lenses.
"One of the great challenges for industry today is to increase the relative efficiency of the material we produce and consume," said Pricone. "Plastic or glass can function as the exterior surface of a solar cell system, but just imagine if that same surface could also concentrate sunlight. In the same dimensional space, we could increase energy production by several multiples. This is a great example of how to improve the efficiency of renewable energy sources while also reducing the carbon footprint." —Matt Defosse
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