Leuze electronic’s sensors and machine safety products are an essential part of the World’s most modern solar module factory – Conergy’s Frankfurt factory has merged together all three production stages, from wafer production to cell and finally module assembly. A benefit of this approach is that it allows for gentler transportation of the very sensitive wafers and cells, which reduces the breakage rates. To achieve this Förster & Krause installed a fully automatic, factory transport system in which optical sensor systems from Leuze electronic contribute to a reliable and gentle material flow.
The high level of technology and intense cost pressures involved are apparent even at the start of the process, during wafer production. Extremely thin wafers are produced from so-called silicon ingots, which are rectangular blocks, about the size of a slice of bread.
Even though the earth is approximately 15 percent silicon by weight, making it the second-most common chemical element after oxygen, it is referred to as "grey gold", not only on account of its grey-black colour.
Aside from the pure raw material value, the cutting times and the materials necessary for performing the cutting are also considerable. As if with an egg slicer, a block is sawed into approximately 1,000 slices – each just 200 micrometres (0.2 mm) thin, considerably thinner than a CD. This takes approximately five hours. Per ingot, 250 kilometres of wire and 5000 litres of cutting fluid and coolant are required. Furthermore, the wire, which has a diameter of 140 micrometres, results in a very high level of material consumption with respect to the wafer thickness.
The very valuable, extremely thin blanks are, due to the material properties, sensitive to damage and breakage. Handling and transport from process to process must be performed with appropriate care. "The merging of all production steps, from wafer production to cell manufacture to module assembly, has opened the door to installing a fully automatic, inter-factory transport system", explains Dieter W. Krause, who, together with his team, Förster & Krause GmbH, undertook planning and implementation of the transport system. – A production area of 35,000 m2, handles up to 60 million cells, which are assembled into 1.2 million modules per year. "From ingot to finished module, around 1,000 metres of conveyor belt connect the process stations".
With that, he puts into terms of numbers a fully linked solar module production system unlike anything before. Special transport boxes were developed for this purpose that not only satisfy the requirements of multiple machines, but that are also appropriate for transport and storage. "Synchro drives enable gentle acceleration and gentle deceleration of the extremely sensitive wafers", explains Krause.
More than 80 vertical conveyors connect the machines with the conveyor belts, which travel at a height of 2.70 m for the empty boxes and at a height of 3.30 m for the full boxes. Two, 12-metre high vertical conveyors connect the system between the building storeys passing through two fire-protection collars.
At each junction within the material handling system, which includes approximately 100 belt changers are Leuze’s PRK 3B retro-reflective photoelectric sensors or, if due to space reasons, no reflector can be mounted, HRTR 3B diffuse reflection light scanners ensure reliable detection of the wafer boxes. In addition to their compact construction, Krause praises both products above all for their excellent background suppression: "In the modern, well-lit rooms, strong sunshine can, at times, result in a very bright environment. The Leuze electronic sensors reliably master this requirement, even at high production speeds", attests Krause.
In addition to position detection on the conveyor belts and space monitoring at the transfer interfaces and turning stations, optical data transceivers from Leuze are also used. They are used to communicate between the high-bay storage devices of the small-parts stores and the store management system. Optical data transmission with infrared laser light to and from the moving high-bay storage devices occurs free of both contact and wear. The DDLS 200 optical data transceivers are likewise characterised by low interference susceptibility to noise from light sources.
Optical data transceivers consist of a device pair and communicate bi-directionally, with each device functioning as a combined transmitter and receiver unit. Network data is transmitted over a distance of up to 500 metres and benefits from being highly resistant to electrical interference as well as being contact-free and therefore wear-free.
Any linked system designed for fully automatic operation must have a means for manual intervention, to allow employees to manually load or remove products, even if only for removing samples for quality control purposes. Therefore, on some of the process systems, the short conveyor belts at the transfer heads to the vertical conveyors are not fully enclosed but are instead open on one side and equipped with SOLID-2E safety light curtains from Leuze. "Due to the narrow conveyor belts, the safety light curtains are necessary in order to prevent employees reaching across into the vertical conveyors located on the other side", explains Krause.
Leuze electronic is proud to play such a key element within the World’s most advanced solar cell factory.