10.07.2015   SonSolar

Contact to the PCB

The bus bar of the last solar cell is contacted to the PCB. Therefore the following two possibilities were examined: on the one hand the bus bar was contacted by soldering with a standard copper tab on the PCB, on the other hand an electrically conductive tape was used (see Fig. 4). After gluing the solar cells on the PCB the electrical parameters of the module were measured by contacting the bus bar of the last cell.

The adhesive film was applied manually and under light pressure to the solar cell and the PCB. After this step all electrical parameters of the module were measured again. The average loss in the fill factor (FF) caused by the connection with the PCB are illustrated in Fig. 5. The fill factor is a very good indicator for the series resistant in the module (the smaller the fill factor, the higher the series resistant).

Fig. 4: Schematic detail of the plated-through hole. The last front bus is contacted by copper tabs or conductive tape to the front of the PCB and led then by a standard plated-through hole on the back.

The results of the measurements which are illustrated in Fig. 5 show that by using the tape the average loss in the FF is about 1.5% higher than using soldered copper tabs. These 1.5% can be fully attributed to the higher contact resistance of the tape.

The measurements show that the conductive tape is not suitable for the use in high efficient solar modules. For the further modules soldered copper tabs were used.

solder conductive tape

Fig. 5: Fill factor loss (FF) caused by contacting a bus bar with the PCB by soldered tabs and conductive tape.

Encapsulation

Small test modules were manufactured to examine the suitability of different materials in the solar modules. In these test modules different cover and encapsulation materials were combined and measured on their electrical characteristics at standard test conditions. A special indication for the quality of the transmission of the packaging is the short circuit current of the module. A comparison of the short circuit current before and after the packaging supplies directly the portion of the transmitted radiation. The losses, which arise as a result of the encapsulation, are shown for the different material combinations in Fig. 6.

PC + EVA PET + EVA PMMA + EVA PVF + EVA PVF + PVB

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Fig. 6: Losses of the Isc caused by the lamination of the solar cells in dependence of the covering and encapsulation material.

The variation of the loss due to the change of the cover material can be recognised clearly. PC has the best cover material properties. Beside the higher firmness the examined PVB has the larger transmission in comparison to EVA. The material properties and a lamination process for PVB are shown in [SCHMIDHUBER01b].