PRODUCTLASER
asers are widely used for different kind of glass machining processes like cutting, marking, welding and glass inside engraving. Drilling of solar glass by laser is a very new approach with several advantages over conventional drilling techniques used in the thin film PV industry. Drilled holes are needed to feed the wires connected to the bus bars through the glass to the backside of the panels.
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At the backside of the panel these wires are connected to a junction box or just to connectors. Depending on the thin film layer structure (CdTe, a- Si/µ-Si, CIGS) the holes are drilled through the cover or through the coated substrate glass. Both variants are possible by laser drilling as described in this paper. Fig. 1 and Fig. 2 show divers geometries drilled by laser into float glass and into a coated glass substrate. Due to the flexible technique various three dimensional shapes are feasible like rectangles with conical edges.
Advantage of laser drilling
Fig. 1: float glass with different hole geometries drilled by laser
Conventional methods to drill holes into solar glass are mechanical drilling and sand blasting. Both techniques are non contact free methods inducing stress to the substrate during the process. Mechanical drilling often needs a liquid to cool and lubricate the drilling process which has to be followed by a washing process. In case of sand blasting the geometry mask has to be changed frequently (<50 panels) since the sand grains are very aggressive to the mask. This leads to varying hole geometries during production. The size and shape of hole 1 will be different as the shape of hole 20 blasted through the same mask.
The laser has the advantage that it is a contact free and dry method inducing minor mechanical stress to the glass substrate. Laser drilling does not effort any post processing like washing. Further advantages are: the laser drilling process is highly reproducible, the process is stable and the shapes of the holes are freely programmable.
Fig. 2: Mo-CIGS-TCO coated glass substrate with different hole geometries drilled by laser
From the economical point of view the initial investment for a laser drilling system is higher than the investment for a mechanical or sandblasting system. However, the total cost of ownership is
Fig. 3: principle of inducing single dots inside glass by focused laser beam
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www.solar-pv-management.com Issue II 2011
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