Volume 44, Issue 7 - July 2009

Solar Insights

“Clean” Energy 
Transitioning Washers to Solar Glass 

by Jen Didyk 

Developments in photovoltaic (PV) technology have pushed this field to the forefront of glass applications, raising demand for substrate processing equipment. Because of the stringent demands of solar glass as compared to traditional architectural glass products, the demands on the processing equipment may also be tougher than normal. For example, solar glass processors require washers that handle a smaller variety of lite sizes than they typically may process—and they must also be able to achieve cleanliness standards at the molecular level. 

Architectural glass producers may run a wide variety of lites in different shapes and thicknesses, all frequently on one machine. Water volume, heat and nylon brushes typically are used to process their materials. If glass doesn’t meet cleanliness requirements, every process afterwards, be it drilling, coating, grinding or laminating, is also compromised. This results in lost time, material and profit. 

New Requirements with Solar Processing 
While glass washing has always been critical, PV has pushed the glass processing industry to redefine the very metrics of “clean.” Ideal solutions for architectural glass washing may not necessarily be suitable for solar glass substrates.For example, minute traces of ionic particles on solar glass can compromise energy transference, directly affecting the function of the end product. These ions may be deposited by previous processes or transferred from machine component corrosion, abrasive washing processes, ineffective drying or imprecise machine function. Solar customers typically use sonar-like time-of-flight secondary ion mass spectrometry (TOF-SIMS) to measure molecular contaminants other techniques may miss. The “echo” from an ionic beam projected onto the substrate reveals the presence of oils, particles and residues. There is a lot the glass processor can do to prevent these problems. 

Proper Solar Glass Washing
Proper glass washing can begin with choosing the appropriate equipment. The solar industry requires standard use of stainless steel washer components. Aside from the reduced cost of ownership that comes with increased durability and uptime is the more important fact that, unlike mild steel, stainless steel dramatically reduces atmospheric and hydro-corrosion, which release ions that may contaminate the substrate. Next, it’s important to be aware that the standard mechanical brush cleaning method preferred for architectural processes may leave unacceptable levels of carbon on a PV substrate. For this reason, many solar customers request contact-free cleaning. Proven techniques for chemical cleaning, including increased velocity atomized cleaning through two-fluid spray nozzles and greater fluid agitation through ultrasonic rinsing to avoid molecule transference and remove microscopic impurities, are a good fit for this market segment. 

Finally, drying directly impacts an architectural glass washers’ line speed and product visual quality. The higher sensitivity of PV processing over architectural glass processing means even minute amounts of remaining moisture can deposit particles on the substrate. A thorough drying technique really is required for both markets, but is that much more critical for PV processing. 

Evaluating the End-Product
In relation to architectural applications, the sensitive nature of PV glass substrates requires more extensive failure mode and effects component analysis, as well as constant data tracking. By continuously monitoring the processing and making changes based on collected data, the glass washer operator can allow for instantaneous adjustments to processing parameters, reducing energy and water consumption and increasing uptime. 

Jen Didyk is spare parts coordinator of Benteler Mechanical Engineering in Fort Wayne, Ind. Ms. Didyk’s opinions are solely her own and not necessarily those of this magazine.

USG
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