Luxor modules must
With the holistic quality approach of German engineers
How well a solar module works is shown not only on the roof, but already during manufacturing. That’s where we start with our know-how.
We can assert the unique quality of the Luxor modules with a clear conscience. It shows in all locations where the modules are tested for low-light behaviour, degree of cross-linking, temperature coefficient and module performance. For example at the TÜV Rheinland, the TÜV Süd, or in the Photovoltaics Institute in Berlin. Our strict quality controls begin already in production. For this purpose, we have developed our own manufacturing guideline, using our years of experience and the complete technical knowledge: Monitoring by our own engineers on site. 100% pre-sorting of the cells by current, voltage and optically. 100% check of the modules for micro cracks, before and after lamination through an electroluminescence procedure. High-quality flashers with parameters checked and monitored by Luxor for precise measurement results. This results in a quality, which we at Luxor guarantee with comprehensive warranty.
100% cell receiving inspection
The cells are, so to speak, the heart of our solar modules – that’s why a careful receiving inspection is especially important. Because already at this step it will be decided whether a module will really meet our expectations regarding performance and yield. And these expectations are uncompromising. In the first step of the production process, the cells go through a visual check and the so-called electroluminescence procedure. This procedure facilitates the check for micro cracks. Cells with micro cracks, misprints, or colour differences are rejected immediately. Cells meeting our high quality standards are accepted.
Before the cells are processed further, we sort them such that they have approximately the same current. The rationale for this is as follows: In the solar module, the cells as well as the current sources are interconnected in series. As in every other aspect of life, so here too: each chain is only as strong as its weakest link. With regard to solar modules this means: The current of the weakest cell reduces the overall performance of the module. The more the current of the cells interconnected in the module differ, the more negative the impact on the module performance. Therefore, Luxor only uses cells with similar current intensities in a module. We form so-called module classes, which are marked in colour. Due to this helpful marking, the modules with approximately the same currents can be combined quickly and without a lot of effort into strings during assembly of the photovoltaic power plant system. And this generally has a positive effect on the yields of the system.
Manual or machine soldering – that’s the question. Both procedures have their advantages.
Since the very beginning of the solar industry in the 1970s, soldering in the solar module has been carried out manually. If this soldering is performed correctly and quality consciously, “manual work” is highly suited for creating the conductive connections. The best proof for this are the photovoltaic solar power plants with manually soldered modules, which provide electric current reliably since the 1970s – without any major failures.
But machine soldering today is just as good, provided the quality is right. By now, there are very precise automatic soldering machines which work reliably and produce both high-quality and durable solder connections. Soldering by machine has two advantages: The production of solar modules becomes more efficient and guarantees larger numbers of modules of consistently high quality.
However, soldering by machine also has risks, since in the recent past some companies had a lot of problems with incorrectly soldered solar modules (one speaks of “cold” solder connections, which do not conduct at all or only insufficiently). A risk is the use of old or improperly designed automatic soldering machines, and another source of risk is human error. If one of the employees in charge of the automatic soldering machine neglects to check critical parameters, dangerous bulk batch errors may occur.
Luxor knows these risks and ensures uncompromising quality through specially developed strict manufacturing guidelines. Thus, for example, we make sure that workers at our lines are trained for at least 3 months at their main work place. The employees in charge of the soldering robots are trained just as long, and by the qualified experts of the manufacturing companies. In addition, we sensitise the employees of all other stations with regard to the integral understanding of the manufacturing process.
As an additional quality assurance measure, Luxor checks all solar modules BEFORE lamination for the correctly executed solder connection (see steps 5 and 6). This way, possibly erroneous connection can be fixed quickly, although this reduces productivity. That’s why Luxor focuses on complete check from the very beginning. Only process-stable and high-quality soldering is good enough for our branded solar modules.
Flashing every string after layout and soldering
After all the solder connections between the cells and the strings were carried out – manually or by machine – the first flashing takes place. This means: The performance of every string is measured by a flash. If the current or the voltage do not meet strict standard values, the module is checked very carefully during the electroluminescence test, to find out where the error lies. In the subsequent repair step any possible soldering defects are eliminated before lamination.
During the electroluminescence measurement the solar module becomes a kind of LED. We apply electric current to it and record the light emitted by it with a camera. This way we can recognise damaged areas of solar cells very well, because they light up more weakly in the module than others. Using the electroluminescence measurement, besides micro cracks, contact finger defects (these are erroneously printed land patterns having no conducting connection to the main string of the current discharge) in a solar module can also be made visible in an optimal way. This is an important measure for quality assurance, because even the finest micro cracks reduce the performance and lifetime of a module significantly.
This repeated procedure for checking for possible micro cracks is currently not used by all module manufacturers. But we from Luxor place great importance on this important quality assurance measure before lamination, where the silicon cells are energised. The areas through which the current passes emit light which can be made visible through a special camera. This way, micro cracks, solder connections conducting poorly or not at all, or areas not conducting any current can be detected easily. If there are no problems, the lamination process may start. However, should anything still not meet our demanding criteria, we take the laminate out of the line and have it reworked if necessary.
Checking and recording the lamination times for each lamination run
Luxor controls the parameters of the lamination process for each lamination run according to the manufacturer’s data for EVA (abbreviation for ethylene vinyl acetate; a transparent plastic layer), since the parameters differ from manufacturer to manufacturer. What is decisive for us is a test, which checks the cross-linking of EVA. EVA protects the solar cells against corrosive influences from outside. The solar cell is so to speak “encapsulated” and thus protected against water ingress.
What exactly happens during lamination? In this production step, the following layers are stuck together:
Backside laminate – EVA – solar cell – EVA – pasted glass, namely through the cross-linking which takes place at process temperatures of approx. 145 °C and usually lasts 16 minutes. In this step, long-chain polymers are cross-linked by adding additives. What is important here is the degree of the achieved cross-linking. Each batch supplied to production is checked chemically by us when it reaches the laboratory, to see whether the achieved degree of cross-linking is at least 80%. When storing the EVA, a dry and air-conditioned environment (25°C) is also important, otherwise the capacity for cross-linking will suffer. A critical situation is reached if the cross-linking degree is below 80%. In that case, there is a risk that the laminate will permit the ingress of water and other corrosive influences within a few years – which would ultimately destroy the module.
After lamination, the solar module is cooled to about 40°C, so that the cross-linking can be completed. This is done either by waiting for a sufficient period, or by using the so-called “curing oven”, meaning a drying or hardening furnace.
Transporting the laminates and turning them by machine
The modules are then transported through conveyor belts, and turned by machine. This way, any possible stress to the still warm laminate and the still fragile structure of the modules, the cells and the connections is prevented, which could easily happen through manual handling. Manual processing is again possible after the framing and the hardening of the frame bonding (silicone adhesive or adhesion through sealing tape).
Laminate trimming and framing on the rotary table
The EVA (ethylene vinyl acetate) “flows” during the lamination process, expanding slightly during this time. The result of this is that it extends laterally beyond the glass. Therefore, the laminate must be trimmed before framing is carried out. This production step takes place on a rotary table, which minimises the mechanical stress in this procedure, and thus ensures the quality.
Machine-framing of the stuck frame through a compressed air framing station
During the assembly, the framing by machine – using compressed air – has many advantages over the manual procedure: It takes place gently, avoids a possible shock, presents important comparisons, and is easily reproducible. In addition, the constant contact pressure during the attachment of the frame parts guarantees the high processing precision desired by Luxor. The precise orientation on the framing device, carried out by machine, also plays a role in this.
Attaching the ventilated socket
Luxor uses sockets from different manufacturers. There are good reasons for this. Our experts know what standards a socket must meet in order to carry out its task for a long period and, more importantly, without defects. Therefore, the manufacturer’s brand name is not really decisive for us. Only the quality of the socket counts. And also if the following important parameters are available:
1. Ventilation of the socket
Through ventilation, the humidity within the socket can disperse; otherwise, it could easily lead to corrosion on the power contacts within the socket.
2. Minimisation of the contact resistance between the module strings and the cable
For a better understanding, let us provide some background knowledge regarding the assembly: During the assembly, the strings of a module are introduced into a so-called terminal block. On the other side, the same happens with the cables. It is important that the cable is already crimped into the terminal block in the factory (attached mechanically) and that the connection is made through welding. Or that it was inserted into the terminal block with a suitable cable lug. We at Luxor prefer a high-quality variant, where the plug-in connection is additionally secured by a screw. The cable itself is protected against a possible withdrawal by an extra screw connection with a cable relief, but many craftsmen unfortunately tend to take the modules out of the package by pulling on the cables. Or they suddenly yank on the cables, to prevent the module falling from the roof.
Luxor has developed its own criteria for the selection of components: In the matter of selecting a component for our high-quality modules, what is most important is not necessarily the brand name. We know what the features of a good component are. And these are more than just a name. Our years of experience has shown us what is really important. We use this advantage for more flexibility and better pricing.
Let’s take a behind-the-scenes look at some brand manufacturers: Of course, one might assume that brand manufacturers pay great attention to high-quality design and manufacturing of their products. Unfortunately, however, this is not always the case. Therefore, a brand name alone is no guarantee for a really high-quality component. We found out that even brand manufacturers often neglect important aspects during design. And because we know which few criteria are really decisive for a socket, we prefer to select “our” component manufacturers.
What is important for us when selecting components: Only high-quality plug-in connections guarantee the best power contact in every weather. In addition, they are extremely durable. What is decisive here is the nature of the connectors, which is checked through the TÜV certification and other independent tests (e.g. in the test laboratory of the specialist journal Photon). The application is carried out manually, because only this way an optimal fitting of the module contacts can be guaranteed.
Measuring the modules with flashers from Berger or Pasan, strictly according to STC (standard test conditions)
For us, only high-quality flashers with suitable technology, checked multiple times, as well as the corresponding lamps guarantee accurate measurement results – thus also the plus tolerances of the Luxor branded solar modules. In addition, every power measurement must be carried out according to the “standard test conditions” (STC). A decisive factor: the precisely maintained surface temperature of 25°C. Each flash is monitored by a qualified employee at Luxor. Furthermore, the proper calibration of the flasher is essential. It is carried out every 4 hours by a module, calibrated by TÜV Rheinland with a precision measurement. Naturally, this process is also constantly monitored by a Luxor employee. A normal measurement has a measurement tolerance of +/-5 %. Depending on the used flasher, a precision measurement – before which a spectral analysis of the used solar cell is carried out - differs from such a measurement and is characterised by a markedly better measuring accuracy of up to +/-2.5 %. For a module with a proven rated power of 190 Wp, the measurement may fluctuate between 185.36 and 194.75 Wp. Not to mention the manufacturers who deliver their module with a rated power tolerance of +/-5 %.
Due to these measurement tolerances, which can hardly be avoided, Luxor delivers every module with a minimum power of 1.5-6.5 Wp beyond the proven rated power – we’ve been doing this already since 2009. Even before that, our plus tolerances since 2008 have generally been 0-5 Wp above the rated power.
100% final check
Before our solar modules are packed and delivered, we once again take sufficient time for the “finishing Luxor touch” of each module. Only by doing this can we honestly guarantee our high quality standards. We want to make 100% sure that each of our modules on the roof delivers optimal performance – and that something did not go wrong in spite of all the checks. At this last check at the end of the manufacturing process, we pay particular attention to the cleanliness of the module and its gaskets and washers, the symmetrical and uniform layout of the cells, keeping all distances according to IEC 61730 and the dimensional accuracy. In addition, we check the relevant components, such as the correct assembly of the socket and the cable, one more time. Only then we send off our branded products to their destination with a good feeling.
Luxor special packing to avoid micro cracks in the cells
Our solar modules are shipped in a standing position in a packing specially developed by Luxor, in order to avoid the formation of micro cracks during transportation. If the modules were transported in a lying position, this would facilitate the formation of resonance vibrations. To be more precise: The modules can be damaged by the constant up-and-down vibrations, which also facilitates the formation of micro cracks in the cells. A further advantage of the custom-made Luxor packing: The pallet can be stacked in threes without any problem. This saves spaces when storing the modules, and at the end of the day cash too.