In September 2011, an EPC installed some 8,800 Chinese-manufactured PV panels in southern France. A mere three months later, more than 90% of the modules had snail trails. The investor informed the EPC of the problem. The EPC countered that the snail trails had no influence on the quality or yield of the modules. In August 2012, the investor contacted the module manufacturer directly about the snail trails and has yet to receive a response, despite numerous calls to China.
As harmless as it sounds, this case illustrates how one problem led to another and grew ever more complicated and disastrous. It was not until mid-2013 that the investor, who also operates the solar farm, noticed grave problems for the first time. The investors analysis of monitoring data revealed that the energy the PV farm was yielding was 5??6% less power, which in his estimation was due to module damage. According to the investor, an on-site inspection and thermographic study of the farm revealed that some 450 modules had hotspots with temperature differences of 30 kelvins, or more, in thermographic images. According to the investor, some 70% of the affected modules had brown cell areas indicating overheating. Some even had scorched busbars. While there were other modules where some of the backsheets had significant blisters or even melted areas.
Damage tripled within a year
This damage only became increasingly severe. By the time the operator repeated the thermographic measurement in October 2014, approximately 1,500 modules some 17% of the original delivery volume were affected. The damage to the backsheets had spread significantly. Overall, the damage nearly tripled within a year. The investor said that the yield of the farm had plummeted by 10 to 12%.
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The laminate had smoldered or even caught fire in some cases, said the investor who contacted pv magazine as part of our Bring out Your Black Sheep series. This creates a fire risk in the dry summer months if the defective modules are not actively analyzed ahead of time and replaced. Electroluminescence inspections of 100 sample modules also revealed that nearly all of the modules had clearly identifiable microcracks and cell breakage.
The investor suspects that the cracks could be what is causing the other damage. Microcracks can grow over time and create contact problems. The faulty contacts then cause areas in the modules to overheat, which are the so-called hot spots. In these areas, temperatures increase so much that backsheets begin to blister, melt or even catch fire, which leads the investor to believe that the problem will in all likelihood get worse.
At this point, random thermographic tests have confirmed this suspicion. The next full inspection is scheduled for this spring.
EPC company cover up
In this case a number of problems converged. The conflict of interest arising from letting EPCs handle operations management has been a subject of discussion among experts for some time. In the first two years of the farms operations, the EPC company also acted as the general contractor for plant maintenance.
During this period, the investor claims that the damage was already visible and that he is able to prove this was the case. But, he says, the EPC covered up the information at the time.
After two years, just as the warranty was about to expire, the investor took over the maintenance and operation of the solar farm. The drop in yield the investor had already noticed was explained away by the EPC in falsified service records as one-off incidents, such as failed strings. However, a visual inspection of the farm quickly revealed that this could not be the true cause of the drop in yield. After many long, angry letters, the EPC finally admitted that it had performed a thermographic inspection prior to handover, according to the investor.
The result: At least 500 of the modules were damaged at the time the O&M services were transferred. Such conduct is, of course, criminal, says the investor, who plans to take the company to court.
Too few and unsuitable modules
Currently, the investor is purposely refraining from asserting any claims against the performance guarantee (90% of capacity within the first 10 years of operation). His communication with the EPC and manufacturer is therefore focused primarily on the product warranty because, from the investors point of view, the damage was most likely caused by faulty products. Furthermore, in the event of a fire hazard, European product liability law comes into play. Strictly speaking, the manufacturer and/or the EPC company must issue a recall and replace all of the modules.
The EPC company also acknowledged the faults within the agreed-upon product warranty period and is therefore liable for damages, in the investors view. The investor is unaware of the details of the product warranty the EPC company negotiated with the manufacturer. Nevertheless, the EPC had tried to get the modules replaced, and the dispute continued.
After two years of disputes, in which the investor, the EPC company, and the module manufacturer all carried out thermographic inspections, the Chinese manufacturer finally delivered a container with 840 new modules to the construction site instead of the 1,500 modules actually damaged and did so only as a token of goodwill. The manufacturer refused to admit to any product faults.
The investor explained that the trade dispute between Europe and China was an additional complication for the manufacturer. In order to comply with import regulations and minimum price rules, the Chinese manufacturer had to import the replacement modules and certify that it had exported an identical number of damaged modules. The customs processing cost both the manufacturer and the investor a good deal of work, and took several days.
The hotspot problem
The module manufacturer justified the low number of replacement modules by stating that only modules that had hotspots with a temperature difference of more than 45 degrees Celsius relative to the rest of the module would be replaced. This solution was problematic for the investor for several reasons. First off, temperatures generally tend to be higher in southern France, which means that smaller differences in temperature can damage the modules. Also, the assumption is that the problem stems from a product fault and that damage to the modules will increase over time. Not every hotspot with a temperature difference of 30 kelvins is a problem, says the investor. But in our case, the hotspots will most likely continue to heat up and thus result in more damage to the modules. Development of the problem over the first three years has demonstrated this, he says. Another critical point is that the temperature differences in hotspots fall as soon as the cell fails, in whole or in part, and less current flows in the module. The manufacturer does not take such module damage into account, even though it is visible to the naked eye.
Another problem with the replacement modules was that both their capacity and their dimensions differed from the original panels. That meant that all of the new modules had to have new module clamps attached. Furthermore, there are now gaps in the module rows due to the new dimensions. This also resulted in additional costs because some of the strings had to be rewired.
The investor said that he personally approached the manufacturer at Intersolar Europe 2015. At this point, the manufacturer rather unabashedly offered to deliver the remainder of the modules if the investor was willing to use the manufacturers modules for subsequent projects. Outrageous business practices, says the investor, particularly in view of the fact that the manufacturer is still subject to product liability. Other cases in our Black Sheep series indicate that such behavior is common.
Could have done better
First, the investor would have appreciated a faster delivery of replacements for all of the damaged modules. But only some of the modules were replaced, and then only after significant delays. Because the module replacement took about two years due to the disputes, the investor would also like to be compensated for lost yield. He is not holding his breath. Even German manufacturers refuse such compensation these days.
The removal of the old modules and installation of the new modules were not covered under the manufacturers warranty. The investor did appreciate the manufacturer delivering the modules to the construction site and removing the old modules at the same time. However, we had to pack the old modules and load them on to a freight forwarders truck, said the investor.
The EPC company is European and in this specific case acted as a general contractor, selling the PV farm to the investor as a turnkey project, including modules. According to the maintenance contract, regular yield checks were to be performed using flasher tests of predefined reference modules. According to the investor, the tests were not performed and the module damage was covered up.
In my eyes, the company is liable for all damages, including the installation and removal of the broken modules and compensation for lost yield, explained the investor. After all, he said, the EPC company knew about the damage within the warranty period and failed to notify the investor. The modules should have been replaced immediately with panels of equal value from another manufacturer once the damage had been discovered to
prevent lost yield. Our primary interest is in maintaining the level of power generation we promised our investors. The EPC company could then have cleared up the legal situation with the module manufacturer at a later time.
What the investor foresees
Due to the high number of microcracks in the module cells, the investor assumes that yield will continue to drop in the future. We might have to replace all 8,800 modules at some point, he says. Whether that is worthwhile depends on how module prices develop. Maybe well get a container of replacement modules from the manufacturer or modules paid for by the EPC company and procured elsewhere. Everything depends mainly on the outcome of the negotiations still pending or the legal dispute with the EPC company. If, in fact, the product warranty route fails in the end, the investor intends to file a claim based on the manufacturers promised performance warranty. To that end, extensive performance testing of individual modules, in addition to the thermographic inspections, will be performed.
Topics to be discussed
This case illustrates themes that will be discussed at the pv magazine Quality Roundtable at SPI.
- How relevant is temperature variation in the evaluation of hotspots? How pronounced can temperature variation be?
- What can investors do in order to prevent EPCs, who also serve as the plant operator, from concealing issues until after the initial warranty period has expired?
- When do product liability warranties come into effect and can they be relied on?
- What conditions should be included into a contract when buying modules?
- Could such a case apply to US investors?
How would you answer these questions? Please share your thoughts with pv magazine at roundtable@pv-magazine.com
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I wasn’t there for the round table discussion, but I can answer this question:
“How relevant is temperature variation in the evaluation of hotspots? How pronounced can temperature variation be?”
If the topic at hand is warranty claims against power degradation, the fact that there are hotspots at all is proof that the module is producing 33% less than full power. Hotspots only happen in conditions of reverse-bias, which means the bypass diode associated with the hot cell is shunting the current around that third of the module. The other (undamaged) cells in the bypassed sub-string are pumping electrical power into the damaged cell, causing the heat. A current clamp and a voltmeter will show the voltage is less than 2/3rds Vmpp (the bypass diode forward drop is negative relative to the output voltage).
Regarding micro-cracks: snail-trails are the result of micro-cracks. Virtually all solar cells are subject to reverse-bias at regular intervals due to partial shading, and a micro-crack concentrates current near the “V” of the crack, creating a small, intense hot spot. The heat melts the EVA film, creating the tel-tale snail trail. The heat also distorts the crystal, lengthening the crack; the snail trail follows the propagating crack. The point is: it is not necessary to do E-L testing for micro-cracks on a module with visible snail trails. The snail trails mean there are micro-cracks, whether naked-eye visible or not.
Regarding the fire danger from damaged modules, certainly the plastic can catch on fire, but of far greater danger is possible electrical fire. String voltages run to several hundred volts, and the cells in modules near the high-voltage end of the string are particularly prone to throw a spark to the grounded frame. Once that occurs, a direct-current, self-feeding plasma arc begins “eating” the array, often dropping flaming material onto the ground or roof below and igniting further fires. Prime examples of this happening were seen in the numerous Walmart string fires earlier this year (2019).