Logistically Speaking – The Role of PV Standards
Logistically Speaking – The Role of PV Standards
By: Shamsiah Ali-Oettinger, pv magazine
Logistics: From raw polysilicon to power generators: it takes a tremendous amount of effort to produce a high-quality PV module. Thus, it is rather embarrassing when it reaches the end customer cracked, scratched, broken or with the invisible enemy, micro-cracks due to bad logistics.
Every end-customer expects modules to be delivered in pristine condition. However, the path from production to warehouse to site is a long one.
When the module left the factory, it was in good condition. But when it reached the hands of the customer who wanted to install it on his rooftop, he saw that the sunny side up looked a little battered from the long journey. Whether it came by ship or was driven to the destination in the back of a container truck, the ‘crime’ happened ‘on the way.’ But who then pays for the damage?
The International Commercial terms (Incoterms) govern international commercial transactions. The core of the agreement remains between the end customer and the seller of the modules. There are some terminologies that govern such transactions. There are 11 rules in total for (a) any mode/s of transport and for (b) sea and inland waterway transport. The different codes, depending on the agreements between buyer and seller, separate the responsibilities of the parties involved. A brief overview can be seen in the table Incoterms 2010 (see p. 86).
Perhaps some sort of a standard for packaging and transport ought to be established? The photovoltaics industry, in comparison to other sectors like semiconductors and automobiles, is a rather young industry in the realm of packaging and transport. Consequently, there is no standard manual that says how PV modules ought to be packaged, loaded, transported and unloaded. This may be due to the fact that there are hundreds of photovoltaics manufacturers and thus hundreds of types of modules that all require their own special handling.
Head of Engineering Services at Adler Solar, Sönke Jäger tells pv magazine that having a such a standard ought to be the global aim. “However, it is not easy to implement. We have some ideas pertaining to this. It would be helpful to have some traceability as well as quality checks,” he says. Nevertheless, there is a long way to go before this standard materializes.
Product Manager of the Packaging Solution for Modules at Eckpack, Kai Hornberg says that a standard in the field of logistics is not easy to bring about as there is no standard product. Every manufacturer has his own set of rules of how the module ought to be packaged, with what type of packaging and, for example, whether they should be placed horizontally or vertically for transport in the containers. Adler Solar’s Tobias Brack agrees, saying that manufacturers will stay true to their solutions, with their own philosophies on packaging and transport.
The module’s behavior differs when subjected to various packaging and transport methods. The risks, to put it simply, are plenty. The journey for many modules is long. For example, think of modules manufactured in China, that then take a long sea route to Europe or the U.S. and thereafter, land in ports and are transferred to transport wagons to move further to their destination.
Sellers have to then ensure that the last journey the module makes to its final destination site is ‘accident-free.’ The modules might move, or even slip out of their packaging. The entire box of modules may fall off their pallet. Or being stacked on top of one another can cause stresses that can lead to the formation of micro cracks, something the end customer cannot instantly detect upon receipt.
There is no surefire way to go about this. The best way forward is to ensure that there is no quality compromise and the logistical costs remain low. But are the goals of low logistical costs and high quality diametrically opposed?
Checking transport vibrations
In the transportation process, there can be a certain amount of mechanical stress that gets exerted upon the module. The reasons can range anywhere from rough handling of the packed modules to vibrations that occur in the back of a lorry. At the end of last year, SEMI announced the publication of ‘SEMI PV23-1011 Test Method for Mechanical Vibration of c-Si Photovoltaic (PV) Modules In Shipping Environment: A new standard to reduce costs related to damage incurred during transportation of photovoltaic modules’.
The standard was primarily authored by the SEMI Taiwan PV Standards Committee and was thereafter vetted by the global SEMI PV Standards Committee.
Ivan Chen-Hsiu Liu from the Industrial Technology Research Institute (ITRI) in Taiwan tells pv magazine, “Before PV23-1011 was written, there had not been any international standard on packing and transport for the PV modules. Up to then the focus on qualification testing of PV modules, for example the standards IEC 61215 and 61730, were on other issues such as the temperature cycle, wet-leakage, and mechanical load, etcetera. However, the reliability of PV modules against vibrations and drops was not included at all in any standard document.” Liu also highlights that there were voices raised in the international PV community calling for such issues to be taken into consideration. “But drafting an IEC standard can easily take more than five years. This lengthy process certainly could not catch up to the fast-growing PV industry, and its urgent need for new standards. The platform provided by SEMI Standards is much better in this respect,” he adds.
The SEMI PV23-1011 serves to provide a common testing method to evaluate the damage to PV modules due to the mechanical vibrations that occur during transportation and shipping. SEMI sees this test as a springboard towards the development of better and safer module protection norms for transport.
The SEMI Vibration Test Method Task Force was formed to look into the problem of vibrations during transportation. The PV testing laboratory at the ITRI in Hsin-Chu, Taiwan, conducted tests that showed module performance drops due to such vibrations.
Liu explains, “Vibration comes in mainly three situations, during the manufacturing process, during shipping and on-site damages. To comply with the traditional scope of the SEMI Standards, which address mainly the issues in manufacturing and packaging, we put our focus on shipping. This is also when the modules receive the largest amount of vibration in a relatively short period in their lifetime.” The PV 23-1011 is a vibration test method that is done on already packaged PV modules. This makes it distinct from the other standards such as IEC 61215 or 61730. These tests are conducted on bare modules that are not packaged. Liu explains why, “This is because, in order to address shipping problems, one has to take the package design into consideration. It allows the manufacturers to evaluate their package design and how well it protects the modules.” The task force members worked together with module manufacturers as well as a reliability test company that specializes in vibration and impact testing. The tests conducted must also determine which locations inside the package experience the worst vibrations. Thereafter, these locations are focused on in the further series of performance and reliability tests.
Liu says that the most common damages due to transport are breakages and cracks of the solar cells in the modules. “Very often they are visible directly to the human eye. The less visible micro-cracks can be observed using the electroluminescence (EL) technique with an infrared camera. The damage of this type has direct impact on the power output of the PV modules. For thin film modules, which often come without metal frames, the whole panel sometimes breaks completely like shattered glass,” he adds.
Adler Solar, for example, apart from its laboratory tests, also offers on-site tests with its mobile service team. Jäger says that in both types of test, the same services are offered: visual checks and controls, flash tests and electroluminescence tests. Fundamentally, the whole overview on module quality can be checked on site. Perhaps it may make sense to test the modules the minute they are received by the buyer for any damages that could have occurred during transport?
Jäger points out that the demand for such mobile tests have been steadily increasing. “12 of the biggest 20 manufacturers are working with us. We can see that the demand is there,” he adds. However, he also cautions that defects in the module could have happened at any point of time, not just during transport, hence, it is essential to have some sort of comparison between the module as it left the warehouse of the manufacturer and the minute it gets unloaded.
The crack study
A study was undertaken by TÜV and the Institute for Solar Energy Research Hamelin (ISFH) to investigate a similar scenario. The study looked at different cracks that occur during transport and compared them to cracks that occur during a standard mechanical norm test. PV modules from different manufacturers with 60 mono- or multicrystalline cells were delivered in single module packages. The modules were sent directly from the manufacturer to the ISFH or TÜV Rheinland location. Again, the study recognized that additional damages not caused by transport could have occurred elsewhere.
A part of the experiment compared the statistical distribution of cracks for transported modules and for modules loaded in accordance with the standard IEC 61215 with the 5,400 Pascal (Pa) option.
The difference that was found between the two simulations with regard to the corners of the modules was rather significant. The transported modules showed only a small number of broken cells in the corners whereas the modules that underwent the 5,400 Pa component of IEC 61215 showed a higher number of cracks in the corners.
The researchers who presented this research paper, ‘Crack distribution of crystalline silicon photovoltaic modules’ at the 26th European Photovoltaic Solar Energy Conference and Exhibition, concluded that “a crack itself has no significant impact on the power of the module but the crack orientation determines the criticality of a crack”.
For crack orientation, the research gives the following designations: dendritic cracks, several cracks, parallel to busbar cracks, perpendicular to busbar cracks, cross cracks and 45 degree cracks (see Graph ‘Crack class bin definition for the crack sorting’, p.84).
The study concluded that handling and transport of a PV module should be reconsidered to reduce mechanical loads to the module as much as possible. The research pointed to the crack classes “cells with more than one crack direction” and “cells parallel to the bus bar” as the predominant ones.
Cracks parallel to the busbars, something that can degrade the module power the most, were discovered as one of the predominant crack classes for the transported modules. The core of the issue is to avoid mechanical stresses or at least, minimize them during transport to reduce the occurrences of such cracks that can degrade the module.
But what is a good package design that can protect the modules? For example, does a cardboard box with Styrofoam frames not suffice?
Liu explains that a good package design consists of buffer materials between and around the modules. “The handling of the whole package needs to be very careful such as using the forklifts and the type of vehicles.” If the packaging is not good enough, then there will be vibrations during the movement of the packaged modules. This can inevitably lead to damages like cracks in the cells.
Some manufacturers do not see their role ending the minute they move their modules from production to the warehouses for further shipment. Some see their role in logistics as well and actively involve themselves in the packaging, transport and tracking services. There are, however, also manufacturers who think otherwise. This depends on the buyer-seller agreements, as mentioned.
This is, of course, an important point for end-customers as they expect the module quality to survive the packaging and transport logistics. This is where manufacturers and their service providers have to decide on things like whether modules ought to be laid vertically or horizontally on top of one another, packed together or separately, or whether additional elements come into play in the packaging. Liu adds, “There are many factors that come into play. For example, the product design itself and the packing containers. Modules in both orientations can be equally damaged if the whole item meets the resonant requirement of the vibration.”
Rules for any mode or modes of transport
EXW: Ex Works
Requires the seller to deliver goods at his or her own place of business. All other transportation costs and risks are assumed by the buyer.
FCA: Free carrier
Requires the seller to deliver goods to a named airport, terminal, or other place where the carrier operates. Costs for transportation and risk of loss transfer to the buyer after delivery to the carrier.
DDP: Delivered duty paid
Requires the seller to pay for all of the costs related to transporting the goods and is responsible in full for the goods until they have been received and transferred to the buyer. This includes paying for the shipping, the duties and any other expenses incurred while shipping the goods.
Rules for sea and inland waterway transport
FAS: Free alongside ship
Requires the seller to deliver goods to a named port alongside a vessel designated by the buyer. “Alongside” means that the goods are within reach of a ship’s lifting tackle.
CIF: Cost, insurance and freight
Requires the seller to arrange for the carriage of goods by sea to a port of destination, and provide the buyer with the documents necessary to obtain the goods from the carrier.
Source: 2012 International Chamber of Commerce
A large number of modules today still arrive in cardboard cartons. There are also a number of PV module manufacturers who are promoting recycled cardboard packaging or the use of lesser packaging material as the ‘greener’ solution for logistics. But how fail-proof is good, old cardboard?
Enlog is a company that has been serving photovoltaic module manufacturers since 1995. The company’s crystalline PV matrix includes packaging and shipping as service solutions. The company’s Eckpack solution’s Product Manager Kai Hornberg explains how cardboard packaging poses a problem, especially when they get wet.
“An example: In 2007, it rained a lot in Spain. The cardboard packages holding the modules at the installation sites got wet. After installation, they noticed that the plants did not perform as well; single strings were not functioning as expected. Then they realized that cardboard residue was sticking to some parts of the glass. This was a huge problem.” Secondly, Hornberg also explains the problem with paper waste. When the modules are unpacked from the cardboard packaging, waste is inevitably generated.
The third issue that Hornberg highlights is ‘paper dust’ that is airborne and can potentially contaminate production, should it be within the vicinity of the production areas as well. Cardboard boxes stacked or worked on in a section next to the production lines can lead to contamination. “You then have microscopically small issues,” he adds. This translates to a power loss and, accordingly, monetary loss.
The fourth reason Hornberg presents is that manual cardboard packaging of modules can lead to frame damage, especially with regard to black frames. These were the primary reasons for the development of the recyclable Eckpack.
The Eckpack solution
The Eckpack Trio is an intelligently designed plastic corner that replaces the cardboard, fitting into the module frame. With four corners covered, the modules can then be stacked onto one another and each module carries its own weight without exerting any pressure on the module below. Every 120 gram element can carry up to 250 kilograms and all module sizes can be fitted. The packaging density can also be increased to 32 modules on one pallet, with six millimeter spaces in between. “We had to decouple the load from the modules, getting it away from the corners. That was when we developed the packaging solution,” Hornberg adds.
With this solution, is there then an answer to the question of vertical or horizontal transport? Hornberg explains that the name Trio itself implies that it allows three solutions: vertical long side, vertical high and horizontal. He adds that modules that are placed horizontally tend to be subjected to more mechanical vibrations. He says a lot of companies and customers are not very confident about vertical packaging despite other PV companies having employed this configuration with the Eckpack Trio without problems. In any case, he recommends vertical loading.
Open or closed packaging?
The modules, when they are given over to the transport freights, are then in the care of the drivers and loading/unloading crew. When using the Eckpack solution, a transparent wrapping is used around the stack of modules. Hence, the crew is able to see that what the goods are and that they are valuable. An important point as Hornberg points out.
He says that with ‘closed packaging’ people are unable to see the product beneath and thus sometimes, other elements like inverters are loaded on top. Container truck drivers also perhaps have multiple jobs to complete and this means a few different shipments to arrange and stack in their containers. With transparent wrapping, the risk of having a heavy object placed on top is lesser as they know that modules can potentially break if this is done. “That is why we decided on ‘open packaging’,” he concludes.
The Eckpack is not just a packaging solution, but it also offers a service. At PV plant sites, the corners are removed from the modules and thereafter they are placed in big bags provided by the Eckpack Service. The installer notifies the service when the bags are full and they get picked up by freight and forwarded back. The corners are then sorted, washed, checked, stacked and are ready for the customer again, staying true to the promise of reduce, reuse, recycle. Multiple usages are also a more cost-effective method than one-time packaging that is discarded after use.
There are no absolutely perfect solutions, though better alternatives for packaging exist on the market. What the PV 23-1011 offers is a test and evaluation method for the product and packaging design. ITRI’s Liu elaborates: “Their credibility is achieved by successive use of the same standard each time when a new product and packing design is made. The reports from the tests should show an improvement on the performance and reliability.” The Eckpack Trio is but one example of an improved packaging design.
With the PV 23-1011 standard test procedure, the task force concluded an almost nine percent fall in the maximum power output of the modules. This means an immediate decrease of module performance and also a likely effect on reliability and thereby a shorter lifetime in the long run. Liu concludes, “With the improvement of the package design, the damage was reduced to only about one percent. Therefore, the cost savings are made, and the profit maximized, for both the manufacturer and the customer.”
This article was
reprinted with permission from pv magazine.
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