Tremendous market growth within the solar power industry, together with the soaring pressure to increase manufacturing efficiency and reduce the associated production costs, are forcing producers of photovoltaic modules to automate their fabrication processes. In addition, these photovoltaic (PV) modules have to survive twenty-five year customer warranties and maintain high standards of performance throughout their lifetime.

Two important factors will be driving the future of PV module interconnections—assembly cost and connection reliability. The automated fabrication of PV modules improves efficiencies, product integrity and reduces production overhead. By using automated production lines, assembly time of a junction box to a PV panel can be reduced considerably. The introduction of new automated systems inevitably results in changed requirements in design of a mounting mechanism for an electrical junction box.

In a PV module, the quality of the interconnections is often the most critical point for the performance and lifetime of the module. Many of the potential problems only show up after several years. If lower quality is employed, defective electrical connections may lead to a fire in the junction box. The Molex SolarSpec PV junction boxes are soldered to the PV panel ribbons, as in this case soldered connections are the safest and most reliable connection, rather than relying on clamped joints as they are still used in many manually assembled junction boxes.

Uli Schoettle, European industry marketing manager for the industrial market at Molex, introduces the SolarSpec junction box with an innovatively designed mounting mechanism. To address the issues relevant to the solar industry, Molex can call on a variety of well-established in-house technologies and solutions that have already met the challenging requirements in many other industries, such as telecom and data systems, the automobile and commercial vehicle sector as well as in the factory and process automation segment.

Molex has already developed a range of interconnection products designed specifically for the solar industry. The SolarSpec range of solar-rated, UV-protected connectors and cordsets offers complete solutions for solar applications like solar panels, tracking systems and inverter connection systems.

Working closely with leading photovoltaic module manufacturers, Molex has added a PV junction box to its SolarSpec range developed specifically to ease assembly and to limit risks associated with process variation. This SolarSpec junction box is designed for fully automated module production. The primary goal is to offer a product that is universal, reliable and able to address a wide diversity of customer requirements while still allowing any customer-specific requirements to be implemented.

To achieve these objectives, Molex designed a completely new board termination system for the base part of the two-piece junction box. In the socket of the junction box there are solder terminals, which make direct contact with the exposed conductors of the PV panel. This enables the part to be easily positioned to the PV module by a pick and place machine or industrial robot. The contact springs are then soldered to the conductor by means of an automated solder process. The Molex patented Solder Charge™ SMT technology is an additional integrated feature that allows simplification of the solder operation. Manual interventions such as up-righting, isolating and pre-positioning of the panel-side conductor strips are no longer required.

Molex Solder Charge™ SMT technology is tailored to connectors with contacts being in-line and gives much better reliability when it comes to solder joints and mechanical resistivity. The solder charge entails a flat, riveted terminal onto which a solder mass is stamped to provide a dense envelope for adhesion to a PCB or a conductor as used in a PV panel. During the soldering operation, the solder charge will melt completely around the terminal to create a conical joint. At the same time, solder adheres within the riveted hole in the contact for added retention forces.

The cover of the Molex SolarSpec junction box, which contains the bypass diodes connections, can simply be placed on top of the base that has already been installed on to the PV module. This operation can likewise be automated as part of the production sequence.

The cover and the socket of the SolarSpec junction box interlock via a clip mechanism positioned on the left and right-hand side of the unit. This assembly can be opened simply with a flat bladed tool, such as a screwdriver. The clip mechanism also serves as a pre-centring aid so that the upper and lower sections can be easily brought together and securely interlocked during automatic placement. Furthermore, the asymmetrical polarised arrangement of the locking clips prevents the upper section from being incorrectly fitted.

An optimised component layout within the Molex SolarSpec junction box ensures a smooth and uninterrupted component feed during the pick and place process, and the compact overall design guarantees precise positioning of the junction box on to the PV module. Another important factor in the design of the SolarSpec junction box is the optimisation of its external dimensions. Furthermore, reduced weight and a minimised component count also provides for an elegant and cost-effective solution and help to avoid the associated heat dissipation problems often encountered in less efficient assemblies.

The adhesion and sealing of the junction box on to the PV module is conventionally achieved by using silicone, which must be applied prior to mounting. In order to simplify the automated assembly of the box to the PV panel, Molex can pre-assemble a double-sided adhesive tape so that only the protective foil needs to be removed prior to mounting. This eliminates the time consuming application of silicone and, above all, the time required for the silicone to cure.

The Molex junction box complies with DIN EN 50521 for PV connectors and VVDE 0126-5 for PV junction boxes. The product has been approved by TUEV and UL. The ingress protection is IP65.