Encapsulants in Photovoltaic Applications
by Christopher Reed
The growth of the photovoltaic (PV) industry in recent years has astounded even veterans of the original solar energy field. As PV has grown, so too have the technologies that generate clean energy from the sun. In the early years solar cells or “modules” were primarily based on crystalline silicon. Today there are polycrystalline modules (a variety of thin film technologies including amorphous silicon [a-Si]), cadmium telluride (CdTe), cadmium indium gallium selenide (CIGS) and various cell constructs including organic dyes and
Growth in the PV market has been significant in the last five years. Moreover, industry analysts estimate that overall PV production will increase nearly four times—from roughly 5 to 20 gigawatts—between 2005 and 2010. Since many of the modules produced for the PV market are comprised of laminated glass, this growth (much of which already has been realized) will lead to additional demand for raw materials and services from the glass
As PV technology developers rapidly move to capitalize on new science and breakthroughs, a variety of specialty chemical companies have increased development and introduction of modified materials that have been available for years. This phenomenon is most evident in the encapsulant area of PV. Encapsulants fuse a module together while simultaneously protecting the module from the outside environment. Ensuring that a module “sticks” together and maintaining performance over its rated useful life are critical. Many encapsulants also are designed to enhance overall module performance. Encapsulant providers are beginning to focus on developing products that reduce total module costs. These products can improve everything from panel efficiency to processing time and overall manufacturing
There are a variety of encapsulants available for module designers. Many of these materials originally were developed for application in laminated windshields and laminated architectural glass. Ethylene vinyl acetate (EVA) has the longest history in the PV encapsulant market. EVA is typically provided as a copolymer based sheet. Since it has been in use in PV applications for several decades, EVA has an established track record regarding module stability. EVA still is used in crystalline modules today and is found in some thin film
Polyvinyl butyral (PVB) recently has been used in certain segments of the PV market. PVB is typically provided to a module maker as a resin based sheet that can be trimmed to fit a given application. While it has been in use for decades in laminated glass applications, recent technology developments have made it a material of choice for certain PV module designs, including many thin film technologies.
Changes in formulations over the last 20 years have made PVB an ideal fit for photovoltaic applications. The development of formulas with strong edge stability and chemical compatibility provide module designers with a material that improves both manufacturing processes as well as long-term module durability. High yield, cost-effective encapsulation processes used for decades in traditional PVB-glass lamination applications now are being used to encapsulate thin film amorphous modules, increasing throughput, which in turn drops the cost per watt produced.
Encapsulants will continue to play a key role in the development of PV modules. Current and future innovation in formulations will lead to modules with longer useful lives and increased energy conversion efficiency. Co-development between encapsulant providers and innovative glass producers will lead to increased efficiency in producing and maintaining module constructs. Development in process technology will lead to more durable panels that are less expensive to make. These advances will result in reduced cost per watt for the module maker and end module user.
Christopher Reed is business director, photovoltaics, of Saflex, a unit of Solutia Inc. in St. Louis. Mr. Reed’s opinions are solely his own and not necessarily those of this magazine.
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