Melting backsheets, broken cells, and hotspots


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 investor’s 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 farm’s 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 investor’s 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 investor’s 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.