Power Loss Attributable to Solar Module Degradation

Solar modules are prone to other changes as well, which, though non-hazardous, can result in power loss as time goes by. A study of such changes was conducted in the autumn of 2009 under the auspices of the EU’s PV Servitor project. Figures 4.108-4.110 show changes in the M55 module, which was frequently used in the 1990s and at the time was still being made by US-based Arco Solar, which merged with

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Figure 4.106 This fire apparently originated at the soldering point of string no. 3, which either was not properly soldered or underwent gradual moisture-induced ageing. Heat gradually built up over the years, until finally arcing occurred during a brief power surge secondary to a cloud enhancement event (see Figure 7.19), causing a fire to break out

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Figure 4.107 Generator junction box damage in a PV installation (Vmpp ~ 100 V) in the absence of arcing. The damage was halted by a fused bridge on the left side, whereupon installation operation resumed but at only at 50% of normal output (see thermographic image on the right). The damage here was minor as the arcing’s potential combustion of 20 V was relatively low

Siemens in 1990. Siemens continued making the M55 for a few years into 2000 and it was used in numerous early PV installations in Europe. Thus relatively extensive long-term experience has been acquired with this device (Figure 4.108 displays a brand-new M55).

Initially marketed as a device with 53 W of nominal output, the M55 manufacturing process was modified in about 1988 and the M55 became a device with 55 W of nominal output. Unfortunately, as a result of this change in the production process, after a few years of operation many of these devices exhibited long-term degradation, which mainly took the form of delamination, notably around the contact strips (see Figure 4.109). Moreover, the M55s rarely exhibited their rated output. After the Siemens merger, beginning in about 1991 the manufacturing process improved and later devices were far less prone to delamination. However, such modules frequently exhibited lesser delamination after around 10 years of use.

Figure 4.108 displays a brand-new M55, Figure 4.109 displays an M55 degraded by delamination around the contact and Figure 4.110 displays a close-up of this delamination.

As Figure 4.111 shows, such delamination is not merely an aesthetic defect (as was initially claimed by the vendor) but also appreciably reduces module output.

The M55 also exhibited another type of long-term degradation, which mainly took the form of clouding that spread inwards from the edges of the cells and that likewise induced power loss, albeit to a lesser degree.

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Figure 4.108 Brand-new Siemens M55 module from the small stock of backup devices at the Bern University of Applied Sciences PV Lab (129.7 cm x 32.9cm, made in around 2000; vendor’s then specified nominal output: 55W ± 10%). Being new, this module has never been exposed to light for very long

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Figure 4.109 Arco Solar M55 (made in 1988; vendor’s then specified nominal output: 55 W ± 10%) with severe delamination around the contact strips. The picture shows the module in a cleaned state prior to characteristic curve measurement as in Figure 4.111. The device was operated at the MPP in a solar generator for around 18 years

Looking back at these events, it is amazing that the products of the then market leader exhibited these types of problems. Hence caution is in order when production processes are modified, and the potential impact of such changes on long-term device stability should be taken into account.

Updated: August 8, 2015 — 11:31 am