Test lab verifies high break resistance of solar PV modules

1st February 2013

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Independent solar-module testing and certification organisation, Kiwa NV (Apeldoorn, The Netherlands) was unable to break TULiPPS’ new 120-cell/500-watt-peak prototype modules during exploratory testing of two units subjected to rigorous industry-standard Hail Impact and Module Breakage tests at facilities in Legnano/Milano, Italy.

COSMOS frameless solar photovoltaic modules are the first to use a unique composites-based frameless construction method and lightweighting design techniques borrowed from the automotive industry in combination with special 2mm/0.08inch toughened solar glass from Ducatt NV (Lommel, Belgium) produced via the patented tempering process developed by LiSEC Group (Hausmening, Austria). 

“You have confidence in a technology and believe it will work as you have designed it,” says TULiPPS Solar BV Founder and Managing Director, Paul Stassen, “but you can’t be sure until and unless you test it. Only then do you find out if all your plans and assumptions were correct or completely inadequate.” 

Each module uses a 3.2-square-meter/34-square-foot, single-layer sheet of tempered glass that is 60 per cent larger than glass typically used on 72 cell/280-watt-peak conventional aluminium-framed PV modules – the largest commonly available commercial modules – but is half the thickness.

The combination of thin, strong glass and lightweight design techniques from the automotive industry provides a level of break resistance not previously seen in solar modules subject to aggressive industry tests.

Kiwa is an independent accredited certification organization providing inspection, testing, training, and consulting work.  The company maintains strict independence and is not involved in manufacturing, trading, or other activities that might affect its impartiality. 

Already the reference certifier within the building/construction and energy sector through its Energy Products Division’s accredited testing laboratory, Kiwa offers testing and certification services for solar thermal collectors and systems as well as PV modules according to International Electrotechnical Commission (IEC) standards.

During exploratory testing of two 500-watt-peak COSMOS modules at Kiwa/IRcCOS in Legnano/Milano, Italy, Ing. Fabio Lo Castro, Ph.D., laboratory manager, performed two very-challenging tests.  One module was subjected to the Module Breakage Test (IEC EN 61730-2:2009 10.10) in which a 45.5-kilogram/100-pound ball is suspended above and at a distance out from the module (the latter can be varied) and then released.  T

he test is designed to break the module (simulating a worker falling onto it during installation or maintenance) with the goal of seeing how the glass fractures and the size pieces it breaks into after impact. 

A second 500-watt-peak COSMOS module was subjected to the Hail Impact Test (IEC EN 61215:2006 10.17). Here, ice balls, which are 25 mm/1.0 inch in diameter and weigh 7.5 grams/0.3 ounces, are projected from a pipe mounted 0.5 meters/20 inches from the module at specific target locations.

During two full days of testing at the Kiwa/IRcCOS facility, a preliminary investigation was conducted to evaluate durability of the prototype modules. Since it was important to understand the limitations of the face glass that protects underlying PV cells, tests were modified slightly to select the most severe settings available.  For instance, the impact ball in the Module Breakage Test has three height settings of 30, 50, and 122 centimetres/12, 20, and 48 inches above and out from the module.  During normal certification testing, the ball is dropped from the lowest setting first; if the module survives, then it is impacted again from the next highest setting, and so forth.  However, for TULiPP’s module, the test was started at the most severe setting of 122 centimetres.

For the Hail Impact Test, ice balls were shot at locations considered to be the most severe (in the centre and along edges). Furthermore, these locations were hit using peak kinetic impact energies that were five-times higher than are normally used during certification testing (51.5 meters/second (10 Joules)/115 miles/hour (7.4 foot-pounds of force) instead of 23 meters/second (2 Joules)/51.5 miles/hour (1.5 foot-pounds of force)).

Before formal testing began, baseline electrical output for each module was established by 'Flash testing' with sunlight-simulating test equipment according IEC 60904-09. At exactly 25˚C/77˚Fahrenheit, a module is exposed to a light flash of 1,000 watts/square-metre (0.64516 watts/square-inch) intensity per American Society for Testing & Materials (ASTM) Air-Mass (AM) 1.5 terrestrial references spectra for PV performance evaluation, and the amount of electrical power it generates is measured and recorded.  This quantitative test is typically conducted on modules before and after Hail Impact tests to determine if there has been any output loss, with modules being required to sustain no more than 5 per cent output loss/retain 95 per cent of their electrical output.

In the case of the COSMOS modules, since no one knew how much energy the thin glass could absorb before breaking or causing the PV cells underneath to fracture, a second qualitative examination was also conducted on both modules. This procedure – essentially the opposite of Flash testing – is called Electroluminescence testing and it identifies cracked or broken cells visually by feeding normal electrical power into a PV module positioned in a dark room. When cells in the module begin emitting/radiating light, a special photograph is taken. By comparing 'before' and 'after' images, it is possible to see damaged cells, which do not light up but remain dark/black.

“Normally, when Kiwa does its rigorous Module Breakage Test on conventional aluminum-frame solar modules with 4mm glass,” notes Stassen, the 45-kilogram ball not only cracks the glass and destroys the cells beneath, but the entire module is damaged beyond repair during the test. 

When they impacted our new 500-watt-peak module, the first hit – which was conducted at the highest, most-severe impact height – did no damage to the glass. 

To see how tough the module really was – because these results were so exceptional – Dr Lo Castro repeated the test twice more on the same module at the same impact location at the maximum impact height and still there was no damage to the tough 2mm glass. 

You would expect glass this thin to be very fragile, but instead it performed beyond expectations.  Since modules never are functional after the Module Breakage Test, they aren’t usually subjected to Flash testing and Electroluminescence examination afterward, but we were able to do that with our unit. 

Even after three hits at maximum impact, the module retained 95% of its original output, which is something Kiwa had never seen before.  In addition, our second 500-watt-peak prototype module sailed through the Hail Impact Test, even though it was performed at five-times higher than normal impact energy. 

Flash testing confirmed there was zero output loss and Electroluminescence testing showed there were no cracked or broken cells. Given these results, we suspect the glass could handle even higher impact energy, which is very positive indeed.”

Noting the unusual nature of these results in a follow-up report, Leendert van der Marel, commercial director-Energy Products Division, Kiwa NV, wrote: “You requested us to evaluate the performance before and after the Module Breakage and Hail Impact tests of the two TULiPPS PV-module prototypes. We can inform you that, with respect to the thin glass, very-large surface, and high number of cells of the COSMOS 120 cells/500-watt-peak module, the test results of the Module Breakage test and Hail Impact tests are very exceptional in a positive sense. Where average modules with smaller sizes, glass of double thickness, and less number of cells do break, your COSMOS module did not show any damage or spots.”

Solar Modules Nederland (Kerkrade, The Netherlands) manufactured the PV laminates used in the COSMOS prototype modules. John van Laarhoven, R&D manager at the company noted, “Despite their unusual large size, manufacturing the 500-watt-peak laminates was very easy to do.  I feel it would be no problem at all for us to implement this technology on a commercial scale.”

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