Solar Power World

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By Laura Carrabine, Senior Editor

The process of transporting powerful yet fragile photovoltaic modules can be tricky. That is why specialists at Heckert Solar use the Rexroth TS solar transfer system to strategically position and transport modules.

Heckert Solar produces high-quality, powerful polycrystalline and monocrystalline photovoltaic units — modules with 54 solar cells that are encapsulated with film, a super-transparent 4-mm thick solar glass pan, and a warp-resistant aluminum frame. Installation of the cells on the glass pane and connections are performed on a fully-automated production line with a pane washing station, as well as soldering and laminating machines.

When the cells are delivered, employees examine and shake each unit to listen for defects such as micro-cracks. Then, visual and technical inspections take place. Meanwhile, the glass panes are washed, placed on the transfer machine, and covered with film. The panes may not come into contact with each other or the system, accumulate on the transfer system, or be stopped quickly under any circumstances, since the pre-stress would cause them to break immediately into many tiny shards.

Jens Bonitz, Heckert Solar technical manager, points out the hazards of working with glass panes. “If anything breaks after the cells have been installed, costs increase to replace damaged units and extra time is added for clean up. Additionally, there can be possible damage to the transfer belt and laminating machines that cause production downtime. Because of these issues, system builder Mondragon Assembly recommended we install the TSsolar transfer system. The system was delivered and commissioned just six weeks after design approval.”

Based on the TS 3plus technology, Rexroth developed a custom solution for the specific demands in the solar industry. As a result, each section element is equipped with its own drive. Frequency converters ensure soft starts and stops and the toothed belts have a closed surface and exhibit low wear and friction because of a densely woven textile coating. Lift transverse units adapted to the sections ensure a smooth change in direction when transporting parts. The system is silicone-free, which helps eliminate contamination by silicone, grease, or oil. An electro-static discharge (ESD)-compatible version also prevents electrostatic charging, which attracts dust particles that could cause problems when the cells are interconnected.

Bonitz says, “System automation would not work without this transfer system. This is why Mondragon Assembly precisely designed and programmed the TSsolar for our application.” Victor Maurer, project manager at Mondragon, adds, “We visualized all of the belt sections so users can call them up individually, activate them, and operate them manually during an emergency.”

The transfer system includes installed fixed stops with air nozzles. An air cushion quickly raises the film that protrudes just beyond the glass pane, enabling the stops to only grip the pane and properly align it. “This helps us attain the required precision of 5/10 of a millimeter with the stops and prevents the film from sliding or being pulled off the glass,” explains Bonitz. “This precise positioning is essential before the panes reach the laminating machines where the cells are laminated on the module.” This design is the result of a collaboration between Heckert Solar, Mondragon Assembly, and Rexroth’s technicians.

The shock-absorbing lift transverse units must also work with the same high level of precision. “The cells are placed on the glass at distances accurate down to the last millimeter, interconnected, and then laminated. Sliding of the individual cells due to imprecise stops or jerky movements in the lift transverse units would be immediately visible to the naked eye in the finished modules,” says Till Uhle, Heckert Solar’s head of sales and marketing. As a result, the seven changes in direction in the system present a special challenge. The TSsolar addresses this issue through optimum synchronization of the two belts used per lift transverse unit that directly support the glass panes. In addition, the maximum speed of twelve m/min is slowed down approximately 30% before the stops. Glass panes be raised and lowered with soft decelerations.

At the beginning of the process, six individual belt sections carefully transport the glass panes between the washing station and the two soldering machines, called stringers. Here, the solar cells are soldered to each other in single rows and positioned precisely on the prepared glass pane. Two transfer lift units distribute the panes to the stringers. Further belt sections and lift transverse units then move the glass panes from the stringers to the interconnection unit. After passing through a preparation section where the modules are inspected, they are then transported to two laminating machines working in parallel due to the longer processing time required. “For mass production of these modules, we needed a reliable transfer system that can be easily adjusted to the machines,” explains Bonitz. “This is the only way to ensure high production quality and the strong performance of the solar modules.”

The efficiency ratio of the modules in this application is the energy output by the sun and the amount of energy generated from it – which reaches 15% and is higher than the industry average of 13%. In addition, a handy module size of 1485 x 995 mm meets technician demands, and lets them lift the modules onto a roof without the need for an elevator. “Our complete system consisting of the module, inverter, cabling, and assembly system provides customers with a complete package,” summarizes Uhle. “Nevertheless, the high demand for this type of environmentally-friendly power generation can only be fulfilled with faultless production technology that includes safe transfer of the modules.”

Heckert Solar
heckertsolar.com

Bosch Rexroth
boschrexroth.-us.com

Mondragon Assembly
mondragon-assembly.com