With the rise in severe weather events, it is more important than ever to assess PV systems for hidden damage that can affect performance and potentially be hazardous, writes Dr Michelle McCann from PV Lab Australia.
The incidence of severe weather events in Australia is on the rise. Science tells us it should be true and many of us have witnessed first-hand events that certainly make it feel like wild weather is happening more frequently.
When severe weather events such as strong winds and hail hit a PV system, they may cause visible damage. In these cases, the system owner has an obvious course of action: they collect evidence of the damage and file an insurance claim. The result is repair or replacement of their PV system.
However, in some cases, severe weather events cause visible damage to the surrounds of a PV system, or to neighbouring systems, but the PV system itself appears unaffected. The owner of the system would be right to question whether there could be hidden damage in the form of microcracks that are not visible to the naked eye, but are potentially very damaging to the panel.
Such damage may take the form of:
- A loss in power from the system, although often this is not immediate.
If the silicon solar cells can hold together despite the presence of cracks, there may be no power drop at all until the silicon pieces move apart during the heating and cooling cycles that occur daily and seasonally. At this point, power loss could be substantial. - Hot spots. These are regions of a panel that get particularly hot. Over time, these can lead to a loss of power and, in very extreme cases, a risk of fire.
- Cracked backsheets. These are a concern because once the backsheet is cracked, water can enter the panel and may lead to electrical shorts from parts of the panel that should not be live, mainly the outside bits. This carries the risk of electrical hazard and fire.
Installers to the rescue
Until recently, hidden damage to PV systems was hard to spot. The losers were system owners as they experienced a delayed loss in output power – and potentially some of the aforementioned hazards – when drawing a link between it and a previous severe weather event had well and truly passed.
A small but growing group of installers is changing this situation and giving their businesses a boost in the process. It works like this:
- Step 1: Experience a severe weather event that is likely to cause hidden damage to a PV system. A good indicator of likely hidden damage is there are either some panels with cracked glass in nearby areas, and/or visible damage to surrounding infrastructure. For example, dents on the building’s rooftop.
- Step 2: When it is safe to go outside again, approach PV system owners with a request to remove a small, random selection of their panels for testing (or to test in-situ on the rooftop). The sample size depends on the size of the system. For 26 to 50 panels in total, five is sufficient. For 91 to 150 panels, eight is a good number. The total cost of testing is $750 to $1200 for these two examples.
- Step 3: The results of the testing will show either no damage; damage present and consistent with hail, or another severe weather event; or somewhere in the middle, with further testing recommended. Statistical sampling can be used to infer the extent of any damage across the whole system. In most cases, system owners are interested in knowing that less than one – or three to five depending on system size – of the panels is damaged.
- Step 4: Present results of the testing report to the system owner and their insurance provider together with a quote for a replacement system. If the quote is accepted, the returns to the installer are in the range of 10 to 20 times any investment in testing costs. Often returns are even higher because the insurer will agree to cover the cost of the testing.
- Step 5: Sit back after a good few days’ work installing a new system for a happy customer who has been saved from future loss of power, from having a potentially dangerous system, and receiving 10-plus times return on your initiative.
Below: The same cells under electroluminescence imaging. Even the very severe microcracking evident here is not visible with a naked-eye inspection.
Testing technology
In order to detect microcracks in panels, electroluminescence (EL) or photoluminescence is used. EL applies a current, typically ISC (the short-circuit current) to the panel and taking a long-exposure photograph in the near infrared. The images above show a comparison of the same cell photographed with a regular camera, and with an EL system.
Once the photograph is taken, images are analysed cell-by-cell and the table below shows some real testing results.
The insurance industry
The insurance industry is coming to understand that EL testing is appropriate for detecting cracks, but at PV Lab we have seen a wide variety of responses from the industry to the problem of looking for hidden damage in PV systems.
Some insurers are already across the technology and will pay for comprehensive testing work. However, we’ve also seen insurers commission other tests, some of which look very high tech, but ultimately do not detect microcracks and, unfortunately, usually show a system with no issues. This is good for the insurer, but leaves the system owner unprotected.
Downside and solution
The downside of chasing storms and saving system owners is that, inevitably, some functional PV panels will be replaced before their true end of life. A smashed panel or a panel at risk of fire should absolutely be replaced immediately under insurance.
But should a damaged panel that still has some good years in it – albeit with a reduced power output – be thrown out and replaced with a new panel? Or could it be more closely monitored and replaced only when necessary?
At PV Lab, we believe a deeper understanding of the issue by the insurance industry is needed in the future, including how to use statistical sampling methods for PV systems together with appropriate testing technologies, and a flexible insurance payout scheme that may include options for a partial refund on lost revenues when the system is safe but functional.
In cases where the system must be replaced, the industry should develop standards for reuse – possibly supported by refurbishment of panels in a secondhand market – and further support and possibly mandate a viable recycling option for panels that cannot be saved.