Encapsulant Lowers Solar Cost Through Materials and Process
In its efforts to become the material house for the photovoltaics industry -- from ingot to module and perhaps installations as well -- Dow Corning Corp. has developed an encapsulant that enables increased solar module efficiency along with a manufacturing process that significantly increases the production rate of solar panels, further lowering the cost per watt of solar power.
Aaron Hand, Executive Editor, Electronic Media -- Semiconductor International, 8/29/2008 12:21:00 PM
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The PV-6100 Series encapsulants, which protect solar modules from the elements, depart from the typically used ethyl vinyl acetate (EVA) resin to provide a substantially more durable and transparent solution through a silicone-based polymer. To put a number on it, Chad Steiner, program manager for encapsulants at Dow Corning’s Solar Application Center in Freeland, Mich., estimates that today’s systems screen out ~3% of the light that hits the solar cells. “Because of ultra-transparency and our ability to allow UV light to go through the silicone ecapsulant, we believe that we can pick up about 1.5% relative efficiency gains in module efficiency,” he said. “To translate that, if it’s a 15% efficient module, we believe that we can get it to somewhere around 15.2 to 15.3% efficient using a silicone solution.” In the solar cell industry, even a 0.1% efficiency gain is significant in trying to maximize the energy available from the sun’s light.
The photovoltaics industry is in the process of benefitting from the production knowledge of other industries, particularly semiconductor and flat panel display manufacturing. In this case, Dow Corning is also able to bring its construction industry knowledge into play, recognizing silicone-based materials as inherently UV-stable and ultra-transparent, as well as extremely reliable over time.
Although Dow Corning will divulge little more about its chemistry than the fact that it is a liquid silicone two-part material, the key factor is that silicone is the only polymer that doesn’t suffer from UV, according to Gaëtan Borgers, global industry director, Dow Corning Solar Market Business Unit. “The very backbone of our polymer has natural resistance to UV, so we don’t have to use UV blockers, for instance, to the contrary of incumbent products.” Other polymers require additives to block out the part of the sun’s light that is aggressive to them, but then of course that part of the light does not get collected by the module, he explained. “With silicone, because it is basically inert to light, you don’t have to block any part of the spectrum, and so you can collect more light in the cell.”
Dow Corning is not only introducing an encapsulant series, but a process as well, helping to improve production efficiencies through knowledge gained from the electronics industry. “We’re going to use a liquid silicone dispense system that we believe is much more efficient in the manufacturing area than traditional lamination,” Steiner said. In fact, he estimates a time savings of about 2× and perhaps even 4×. “Today, when you use EVA, the cure times for EVA encapsulation or lamination is somewhere around 16-18 minutes. So if you have a four-place laminator, you can basically create a laminate every four minutes,” he said. “In our solution, because of our cure chemistries, we’re trying to be able to place a laminate between every one and two minutes.”
Also, an EVA laminator is by default a batch process, Borgers noted. “We have a process which looks much more like a continuous approach. And so the overall manufacturing approach is much more suitable for automation and continuous process.”
The process and encapsulant series are being piloted by solar customers in the Dow Corning Solar Application Center, which opened in May. According to Steiner, the 27,000-square-foot, state-of-the-art facility has been an important part of Dow Corning’s ability to bring the new encapsulant to market. “Given the shift in technology — moving away from a sheet of EVA to a liquid silicone solution — we’re really going to need to bring in customers’ components and be very collaborative in our efforts.” The application center and pilot line gives Dow Corning the ability to produce laminates at an industrial scale, showing customers that the encapsulant will work in volume production, and on 72-cell panels, he added.
“What we are proposing has, we believe, a lot of merit, but it’s also a significant change compared to what the industry is doing today,” Borgers said. “And so being able to demonstrate our value proposal is extremely important.”
Although a silicone-based encapsulant applied with a liquid dispense system is a significant departure from what the photovoltaics industry knows today, Borgers added, that is likely to be true with any innovation. “That’s where an application center like Freeland is very useful.”
So until the encapsulant series and process are made more widely available around mid-2009, Dow Corning and its solar partners are fine-tuning the process steps for each customer’s approach, Borgers said. Not only is Dow Corning addressing the needs of both crystalline and thin-film photovoltaic techniques, but also all the variants within those processes — back and front contacts, monocrystalline and multicrystalline, thick and thin wafers. “And so what we are learning now with our customers is how to tweak and adjust the value steps of our process to deliver a solution that works for each customer,” he said.
