Sealing The Deal: Why Encapsulation Matters
Posted on 03/09/2018 at 12:00 AM by Ryan Jeffrey
Say you are in the market for a solar panel. You buy two competitive options and begin to test different aspects.
You stage a test and determine what product has the most real-world output.
You then see which repels water and stands up to the elements best.
Finally, you determine which has the most flexibility and makes sense for your application.
Think you’ve taken all important factors into account?
Lamination affects every single thing you tested and is an incredibly important piece of the solar-build puzzle -- one that is often neglected or not understood entirely.
It is a balancing act in ensuring the qualities needed in a particular product while maintaining as many other desirable traits as possible.
Important factors in lamination are optical transmission, lifetime, ease of maintenance, ease of manufacture, and cost. In some applications, the dimensional stability in various temperatures is also a critical factor.
The most common premium top film for solar is ETFE, a Teflon like material with a high optical transmission (typically above 96%). Its Teflon-like characteristics make it self cleaning and very environmentally stable, leading to long service life.
It is, however, among the most expensive potential laminates and the same characteristics which make it self cleaning make it difficult to bond to the solar cell, requiring special treatment and adhesives. It balances having relatively poor dimensional stability by being quite soft and easily held in place by other layers of the panel.
On the other side of the spectrum is PET or basic polyester. Cheap, plentiful, and easy to bond to, polyester is a go-to top film for lower cost products and applications.
Polyester has considerably lower optical transmission (typically 85-90%), poor environmental stability leading to yellowing and cracking after prolonged outdoor exposure, and minimal self-cleaning characteristics leading to higher maintenance needs in some environments.
While these are the two most common top films, there are a variety of other options for top films with their own strengths and drawback, including PVDF and FEP with similar characteristics to ETFE but different challenges in workability and material cost.
Yet another option, PEN, a type of polyester which is durable but also more expensive and challenging to bond to.
Further, while the top film is of critical importance, other layers in the lamination stack also have a great impact on the cost and performance of the module, including the top and bottom adhesives and the bottom protective laminate.
Optical transmission is critical for the top adhesive as well as its ability to adhere to the top film, solar cell, and bottom adhesive. Top adhesives also frequently have UV blockers and stabilizers to protect layers below them from degradation by UV light and ensure the longevity of the adhesive layer itself.
Other important characteristics include laminating temperature, thermoplastic vs. thermal-set, damp heat resistance, and of course cost. Lower layers in the laminate stack typically don't require high optical transmission or UV resistance due to protection by the layers above but need to hold up to humidity and other environmental factors.
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Categories: Solar Education