PV Lab Australia has introduced a static mechanical load test for solar panels to see how they stand up to severe weather events, writes Dr Michelle McCann.

At PV Lab Australia, we recently introduced a static mechanical load test into our suite of offerings. It is designed to assesses how panels will stand up to specific conditions, and these might include mounting configurations, snow load or wind.

If you are a system designer or owner and are interested in questions such as, “Can our system withstand a one-in-100-year wind event?” the test is for you.

The static mechanical load test was developed in our laboratory by Gabriel Nelson and Lawrence McIntosh, and is conducted according to IEC 61215, test number MQT16. According to Mike Home, technical sales manager from solar mounting systems manufacturer Schletter, mounting configurations (one in vertical, two in horizontal, etc) are generally specified by the engineering, procurement and construction (EPC) or developer.

Racking manufacturers consult the data sheet of the chosen module, taking note of clamping points and module dimensions and then design the racking system accordingly. If the system is being installed in an area of particularly high-wind loading, Home recommends extra testing.

“Measuring and understanding the pressures on the modules allows Schletter to go beyond standard modelling and make specific alterations to the racking design to ensure the longevity of the panels,” he says.

Before starting the test

In order to perform a useful static mechanical loading test, there are a few questions to consider: How will the panel be mounted? Is it portrait or landscape? How many rails and clamps are used? What kind of mounting equipment should be used in testing? What are the clamping zones and clamp sizes? What is your design load and what is your test load?

The test load is equal to the design load multiplied by the safety factor. The IEC standard, 61215, states both a minimum design load (1600 Pa) and a minimum safety factor (1.5). Design loads may be different for the front and rear sides.

PV Lab Australia test co-developer Gabriel Nelson with a broken (shattered and deformed) panel. Photo at top of page: Dr Michelle McCann with a broken (shattered and deformed) panel.

You also need to know what you want to track through the testing. At a minimum, the standard requires both a visual inspection before and after, and a wet leakage test before and after the static mechanic load test.

Other options are to include power performance, electroluminescence and insulation resistance to assess module performance after mechanical stressing.

In the testing room

The test proceeds by applying the test load. We use water as the test load, but other possibilities include sandbags, pneumatically controlled suction cups, and pressurised air bladders.

The weights are substantial. For a panel with an area of 2.2 square metres, application of 2400 Pa is equivalent to approximately 540kg. Load is applied for one hour, during which time the electrical continuity of the module is monitored. The module is then flipped and the process is repeated.

At the end of the second hour, one cycle is complete. Full testing requires three cycles so it takes a minimum of one day to process one panel.

The electrical continuity is monitored by applying a small current across the panel and checking it is continuous for the duration of the test – just like the continuity tester in a multimeter. If a panel fails the test, we observe a drop in current.

Panels bow considerably under load during the test. In our experience, it is not uncommon to see deflections of several centimetres across a two-metre panel length. Deflection amounts are dependent on mounting configurations. While unnerving to observe, deflection is predominantly elastic and seen in panels that pass the test.

Sometimes a panel will break. Inside the laboratory, this is somewhere between a minor thrill – as a place for quality control, we are not usually into breaking our subjects – and a sad occurrence, requiring a stop-work and clean up.

The static mechanical load test is a destructive test. Once complete, panels should be thoroughly checked before reuse or recycling.

Building the rig

In past years, PV Lab has been approached several times with requests to provide static mechanical load testing, however readying the laboratory to provide a new test is far from trivial.

Considerations range from those that might be considered obvious, such as fully understanding the requirements of the standard and working out how to safely and repeatedly apply loads of many hundreds of kilograms in a uniform way to a solar panel, to less obvious considerations such as where to put the thing – the static mechanical load test is a low-throughput test (one panel per day) that takes up a lot of floorspace.

Clockwise from top left: “Skywhale Junior” from below; “Skywhale Junior” from above; Panel deflecting under static load – the silver band is the edge frame of the module. When undeflected it would be parallel to the wooden beam above.

However, we are keen to respond when the solar industry in Australia is missing an important capability such as this testing so we stepped up to the challenge. We considered a couple of different options for the actual load, eventually settling on water as it conforms nicely to the panel surface as it bends.

Our final design contained a number of flexible troughs all suspended and loaded with water. In a fitting tribute to our hometown of Canberra, we affectionately call it “Skywhale Junior”.

PV installations are increasingly moving to the remote fringes of Australia, and as with all things climate related, it is likely that wind loading will become more of an issue in the coming years.

“Skywhale Junior” and the team at PV Lab Australia will be happy to weigh down your panels and keep our fingers crossed for a gentle bowing in the breeze with no signs of broken glass.

Dr Michelle McCann is a co-founder and director of PV Lab Australia.