Hail Stress Sequence

The increase in PV sites being deployed to extreme hail prone regions is prompting concern for many in the solar industry. Aside from the hail risk, some of these locations are ideal for large utility-scale solar sites due to the excellent solar resource, available land and economies of scale. Both developers and investors are enticed by these benefits, but hail mitigation methods must be implemented to ensure successful long-term operations.

These mitigation strategies include selecting modules that have higher hail resistance and implementing weather monitoring and tracker stowing practices. They no longer include relying on big insurance payments if the site is severely impacted by hail. In the current insurance landscape for hail claims, insurers are requiring large deductibles, are implementing limits that significantly reduce payouts, and/or are adding exclusions to insurance policies such as not covering modules with cell cracks. This has essentially pushed hail damage risk on to the other project stakeholders.

Kiwa PVEL’s field team has performed field EL on over 2 GW of sites with hail damages in the past few years. This testing was initially used to identify modules with underlying cell damage and helped size the insurance payment. But as insurance coverage for hail damages grew more restrictive, mitigating hail damage became increasingly important for site owners. Kiwa PVEL’s HSS test goes well beyond the minimum requirements of IEC 61215 and is providing critical data for site developers and investors in determining which modules should be considered to help lower hail damage risk.

Modules with hail damage. Those without broken glass may have extreme cell cracking, but it is no longer likely that insurance will pay for their replacement.	A module with over 25 cracked cells due to hail, which was not eligible for insurance coverage due to changes in insurance policies.

 

These materials determine how well or poorly a module can withstand hail impacts:

Cells Encapsulant Glass Rear Glass Frame Module Size

 

The test sequence is specific to the module design and includes testing four modules:

• • • For modules with non-fully tempered glass (such as 2.0 mm glass//glass modules), two modules are subjected to hail testing using 40 mm lab-manufactured ice balls at terminal velocity in 11 different locations at a 0° angle as indicated by IEC 61215. These hail strikes deliver an impact energy of 12.9 joules. If neither of the initial modules experience glass breakage, the second two modules will be subjected to hail testing using 45 mm ice balls at terminal velocity, which deliver an impact energy of 20.7 joules. However; if one of more of the initial modules experience glass breakage, the second two modules will be subjected to hail testing using 35 mm ice balls at terminal velocity, which deliver an impact energy of 7.7 joules.
    • For modules with fully tempered glass (such as 3.2 mm glass//backsheet modules), two modules are subjected to hail testing using 50 mm ice balls at terminal velocity. If neither of the initial modules experience glass breakage, the second two modules will be subjected to hail testing using 55 mm lab-manufactured ice balls at terminal velocity, which deliver an impact energy of 46.1 joules. However; if one of more of the initial modules experience glass breakage, the second two modules will be subjected to hail testing using 45 mm ice balls at terminal velocity, which deliver an impact energy of 20.7 joules.

Following hail testing, the module manufacturer can opt-in to having the non-broken glass modules proceed through DML, TC50 and HF10 testing (as described in the MSS testing procedure). This is particularly encouraged for modules with a significant amount of cell cracks following hail impacts. The DML is designed to articulate any existing cell cracks, creating inactive areas or increased series resistance in susceptible modules. This is followed by TC50 and HF10 to simulate an acceleration of natural, daily temperature changes and other environmental conditions that may cause hail-induced cracks to propagate through cell metallization.