ID readers aid solar panel quality control

Seamless quality assurance requires the glass plates to be assigned to individual inspection stations by means of DataMatrix code identification.

Wurth Solar has been producing solar modules using CIS technology since October, 2006.

It has collaborated with AIT Gohner , a Stuttgart-based integration partner of Cognex, to implement data tracking using In-Sight ID readers to boost productivity and optimise product quality.

Current production yield is at 90% and rising.

The modules from Wurth Solar are made up of multilayer copper/indium/selenium solar cells in series, with a coating thickness of four microns.

Even in poor light conditions, they guarantee a high output.

It is important in production of these cells to collect all the quality data from the substrate plates in each production machine.

However, the individual quality results arrive only at the end of the production process, when the performance of the 1200 x 600mm modules is tested in the solar simulator.

Therefore, it is only at this point that it becomes clear whether a module really will have the desired output of around 80W.

This means that Wurth Solar engineers only discover how good their results are at the end of the complex coating processes.

If quality data has not been collected beforehand, it is too late to determine the origin of defects.

Seamless quality assurance requires the glass plates to be assigned to individual inspection stations by means of DataMatrix code identification.

Quality data is recorded every third or fourth step of the production process.

The DataMatrix code is used to test whether the plate assigned to the data collected to date, really has been processed.

Glass breakage can be one of the reasons for data sets being created for a plate which no longer exists.

DataMatrix coding prevents any confusion.

The code is applied as an engraving using a laser system.

The challenge came in the form of selecting a suitable vision system to read the codes.

The real difficulty with lasered DataMatrix codes on glass is the low contrast between the engraving and the surrounding surface.

After various products had been tested, it was decided to use Cognex ID readers - the In-Sight 5400/5100 vision sensors.

The ID readers detect and decode even difficult codes on problematic surfaces, achieving read distances of over 2m in the process.

Nineteen processing steps follow the lasering, the so-called "birth" of the plate including the application of the base coating plus subsequent laser structuring giving the plates their cellular shape.

A quality inspection is important at this point, as the key production step follows once the plate has been washed.

The plates have their CIS coating applied at 600C.

After a chemical treatment to apply a buffer coating, the DataMatrix code is checked again.

Zinc oxide is then applied, forming a light-permeable front contact for the solar cell, completing the photodiode.

In the final finishing stage, the plates are given additional bores for the guide electronics for the contacts.

Finally, the coated substrate glass is permanently bonded to the cover glass.

Thus combined, the CIS solar panel is ready for applications, ranging from classic sun collectors and electricity generation on roofs and house facades, to integrated product and standalone solutions.

This brief outline of the complex production process shows the many factors affecting the quality of CIS solar modules.

The seamless tracking of production data using the Cognex ID reader created the basis for perfecting individual workstations.

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