Designed for Automation

Today’s junction box requirements focus not only on production-relevant topics like process reliability or production rate, but also on operating characteristics in the PV system itself. Modules must operate for at least 25 years – which is what the end-consumer expects. Very careful choice of materials and continuous quality control are required in order to fulfill expectations. Although the junction box is mounted on the back of the modules, it must withstand the effects of the same weather and environmental conditions – e.g. humidity, UV, ammonia, and temperature – as would be expected on the “sunny side” of the module.

Automated or manual assembly

Automation is the keyword in modern module manufacturing facilities. Assembly is performed by robots or linear positioning systems. The process is very similar for crystalline and thin film modules. As a general rule: Cycle time and output are deciding factors.

The choice between automated and manual assembly is not easy. Both have their advantages and disadvantages. While automation has a very high repeatability, manual assembly shows a much better flexibility regarding tolerances in the layout of the ribbon – the conducting flat connector that is embedded in the layers of a PV module.

One thing is sure: an increase in production capacity for crystalline modules, with cycle times of 30 s or less, can only be achieved with an automated line. Depending upon the degree of automation, up to 20 s are needed just for the handling –picking and placement. The remaining 10 s must be enough for contacting of the ribbons. That is not much time for a connection that has to remain mechanically stable for 25 years or more. Hence the electro-mechanical connection persists as a challenge.

Fast connection technology

The most common kind of crystalline PV module has four contacts coming out of the module’s backsheet and leading to the contacts of the junction box. Before the lamination process starts, these ribbons are laid flush to the backsheet. In most cases they are also covered by an additional sheet of Teflon to prevent lamination membrane damage. After lamination, this Teflon sheet is removed and the ribbons are again adjusted to a defined position. This is essential – otherwise the junction box would be mounted on top of the ribbons and electrical contacting would not be possible.

The new connection technology called “grapple contact” is specially designed for production lines with a high level of automation. The main idea of the technology is based on the spring connection concept. It enables contacting of all ribbons simultaneously in less than two seconds – excluding machine movement.

This is realized by delivery with opened contacts. To complete the connection, the spring merely has to be pushed down. Time-consuming assembly steps such as opening the clamps, arranging the ribbons, dispensing the solder, or soldering itself, can be omitted.

Another benefit is the flexibility of the contact. It can be used several times without increasing the contact resistance. For example, this may be necessary if there is a functionality upgrade like an emergency shut-off or a replacement after malfunction. These steps can be performed by removing the inlay; the junction box housing remains on the module. There is no need to use a new box or even a new module.

The junction box can be mounted in various ways. Simple automation with a gripper and a pressure unit will suffice. Use of the grapple contact can reduce the cycle time commonly required for automated soldering by a factor of 3. Cost-intensive manual assembly can be eliminated.

Sunclix grapple contact – technical data

As a new member of the Sunclix family, the grapple contact has been specifically developed for PV modules that are based on wafer technology. It is able to handle high currents of up to 25 A, and can contact ribbons of up to 10 mm width and a thickness of 0.1 to 1.0 mm. The contact of the spring connector is compliant with the standards specified in IEC 60999 and follows normative recommendations for industrial plug connectors.

All junction box component parts fulfil the relevant normative requirements. The plastics are RoHS compliant and meet the requirements for ammonia and flame resistance and protection class IP 67. All features are continuously tested at the company’s certified laboratory under normative conditions.

The prices of commodities such as copper have increased considerably during recent years. These price hikes have a significant effect when purchasing cabling and ribbons for PV components. With the new Sunclix grapple contact it is possible to reduce the length of ribbon material required, making ribbon lengths of 10 mm sufficient for a reliable connection. In a module factory with an annual capacity of 100 MWp – e.g. 425 000 modules of 234 Wp each – there is potential to save approximately 50 km of ribbon material. This is calculated on the basis of an average ribbon length of 2 640 mm per module with a typical excess length of 40 mm per contact. This represents an overall saving of 4.5 per cent of the annual ribbon requirement.

Useful Accessories

The junction box can be attached to the backsheet of the module using 1- or 2-component silicone adhesives or adhesive pads. The overall height of the box is 26.0 mm after attachment to the module. To reduce power losses in cases of shadowing or module failure the junction box is equipped with bypass diodes. The actual diodes used will depend on the specified forward current and the required reverse voltage.

In most cases module manufacturers decide to use a junction box with cable and plugs included. The Sunclix junction box for crystalline silicon modules is suitable for use with cable diameters of 5.0 to 7.5 mm, corresponding to cable cross-sections of 2.5 to 6.0 mm² and also satisfying UL and Multinorm cable requirements.

The cable and plugs are mounted in a pre-defined position in secure holders on each side of the box. This provides a higher safety level during handling in the assembly and simplifies the transport of the modules. For example, unfixed plugs can damage the module during transport. Another benefit of having the fixed cable and plug holders concerns the final power classification, i.e. flash testing. The defined position of the plugs enables an automated power measurement.