COVERSTORY
turns out to be the hidden defects rather than the obvious visual problems. Hidden defects in solar production include micro/large cracks and low efficiency areas (shunt and dark regions).
ESCAD Automation approoach was to apply an electroluminescence technique with their ELC pinpoint product in order to visualise those invisible defects hidden inside the mono/multi Crystalline solar cells through automatic inspection software. ESCAD extends the capability to detect grid interruptions (finger interruption) and string connection failures to micro/large cracks and low efficiency areas (shunt and dark regions) inspection.
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Micro/large cracks in solar cells are invisible but gradually increase the breakage rate of the solar cell during the production as well as handling steps. These cracks impact the efficiency of the solar cell area.
Low Efficiency Area (Shunt) generally means to the non-conductive area over the solar cell surface. When they appear the low efficiency area could affect the impact of Microcracks that cut-off the flow of electron through conduction grids. On the other hand, electrons could also be blocked from conduction once grids (Fingerprint) are interrupted. This problem is called by the general term as “Grid Interruption (Finger Interruption)”.
eSYS Photovoltaic eCI-005 ELC Pinpoint M1080 Measurement Unit
Maintaining the flow
Manufacturers might have different methods to perform the test on their solar cell production due to their specific manufacturing layout. Some may choose to apply the electroluminescence test at the end of the solar module production line in order to improve the solar module quality and assure proper guarantee period to their customer.
A number of manufacturers try to keep their module production constant by performing the inspection process after
the solar cell stringing but before lamination. In this case, manufacturers will also have the possibility to check for the string junctions soldered to the solar cell bus bars prior to those three defect types. This reduces the possibility to gain low efficiency module since module manufacturers will be able to replace defect solar cells in time before the lamination process takes place.
Beside the production line, research and development engineers try to improve their solar cell fabrication process. Defects could also be identified and kept statistically in the production database in order to improve the quality of solar cell fabrication by analyzing single cells.
Tracing the inspection results from number of defects, type of defects, positions of defects, etc. could improve the understanding of current production process and points to be improved or maintained.
Full automatic inspection (inline/offline)
eSYS Photovoltaic eCI-005 ELC Pinpoint Machine Solution (SUNNY Side Up/Down)
Defects are required to be recognised, processed and classified automatically. The inspection software employed by ESCAD is able to synchronize itself to the machine automation routine in order to start the module inspection process once the module is fed in to the machine and
www.solar-pv-management.com Issue III 2010
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