Gap & Parallelism Measurement in Photovoltaic Applications

Maintaining uniform and parallel gaps

Coater Gap Measurement in Photovoltaic Applications

According to the European Photovoltaic Industry Association (EPIA), the driving forces in the photovoltaic industry are the reduction of cost per kilowatt-hour and module efficiency.

Keithley Instruments 2009 survey published in PV Society.com states “Overall, the survey showed the industry is focused on improving device efficiencies as its dominant development priority. Manufacturing costs reduction was the second most important among the respondents, although substantially less significant than the need to boost device and panel performance.”

Capacitec has been on the forefront of assisting engineers at PV Solar panel and module manufacturers as well as PV Manufacturing Machinery and Equipment to enhance this efficiency. This is achieved by providing non-contact displacement, gap and parallelism sensor solutions to enhance module efficiencies and reduce cost in the following applications:

1. Gap/parallelism of CVD coater head to metal roller

Capacitec is supplying high temperature gap sensors to a European producer of Flexible Solar Cell Laminates. These foot wide laminates are lightweight, unbreakable, very pliable and well suited for integration in to other products such as roofing materials.

A roll-to-roll production process is used in the deposition of various active and non active ultra thin layers onto the PV media. This process offers important cost saving advantages in large scale production. There are a number of roll-to-roll steps from the deposition of the transparent top layer and the silicon layers to the final reflective metal backing.

Capacitec high temperature non-contact displacement sensors are used in one of these layer deposition stages which is produced with CVD equipment that deposits the coatings at the elevated temperature of 1,100°F (600°C). In this process it is very important to set and maintain the gap between the coater head and the roll positioning the media. If the gap is too big the coating will be too thin, too small a gap would produce coatings that are too thick. An unparallel head would distribute the coating unevenly across the width of the substrate. The challenge in this application is that the producer cannot set the gap at ambient temperature before the start of the process. This is due to the fact that, once heated to over 600°C during production, the roll diameter thermally expands.

To control the position of the coater head, Capacitec supplies four high temperature non contact displacement sensors combined with high temperature displacement sensor cables that are positioned next to the coater head on a custom fixture that measure both the gap and parallelism between the coater head and the metal roller at production temperatures. This constant measurement ensures that the gap and parallelism are maintained during very long production runs.

2. Control Slot Die Coater Gap for liquid coating

For the past 15 years Capacitec has been working closely with leading global manufacturers of specialty film and tapes as well as slot die coater suppliers to develop systems to precisely measure coater gaps. These new systems have made dramatic improvements over traditional gap measurement methods such as feeler gauges and micrometers. The Capacitec “electronic feeler gauge” solution achieves coater gap uniformity of > 10 microinches (0.25 microns) with gaps as thin as 433 microinches (110 microns) across the full length of the coater die. A typical non-contact capacitive gap measurement solution includes sensor wands, special wand holders, and signal conditioning electronics and software as seen in the figure to the left. This technology is now being transferred to Solar Panel manufacturers looking to maintain uniform gaps along the full length of their slot dies used in liquid coating operations.

"Maintaining Gap Uniformity in the Application of Liquid, Anti-reflective and CVD coatings onto Flexible and Flat Glass Solar Panels"Presented at the 8th European Coating Symposium, September 7-9, 2009, Karlsruhe

3. Gap/parallelism of Slot Die coater head to media

During OPV (Organic Photovoltaic) panel fabrication, a slot die coater gap measurement system is used to maintain organic material coating uniformity. Capacitec non-contact gap and parallelism systems are also used to maintain parallelism between the slot die coater and the metal roller.

This is accomplished by installing model HPC-150 non-contact displacement sensors on to special fixtures on both ends of the slot die coater in line with coating head. The signal from each of these sensors is transferred through the Capacitec electronics and onto Capacitec Bargrafx^® linearization and display software. The display graphically shows whether the slot die coater is parallel to the metal roll before liquid coating operations of the OPV layers begin.

4. Gap/parallelism between rollers

Gap/parallelism measurement between lamination rollers

A Capacitec Gapman portable non-contact gap measurement system that works like an "electronic feeler gauge" can be used to set the gap distance and parallelism between metal rollers used during the encapsulation stage of OPV and other flexible solar panels. Please send in an inquiry form with your roller diameters and other in formation found in the form and we will get back to you with a technical and price proposal.

5. 800°C proximity sensor for absence/ presence

Capacitec was contacted by a PV Module manufacuterer who was unable to find a supplier of very high temperature proximity switches to track the absense/presence of glass panels entering a vacuum furnace for processing. Capacitec was successful in developing a custom very high temperature non-contact displacement sensor with special high temperature vacuum thruput cables that allowed the producer to track the location of thier Solar PV modules in the 800°C furnace.