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Significance and Use
In many geographic areas, there is concern about the effect of falling hail upon photovoltaic modules. This test method may be used to determine the ability of photovoltaic modules to withstand the impact forces of hailstones. In this test method, the ability of a photovoltaic module to withstand hail impact is related to its tested ability to withstand impact from ice balls. The effects of impact may be either physical or electrical degradation of the module.
This test method describes a standard procedure for mounting the test specimen, conducting the impact test, and reporting the effects.
The procedures for mounting the test specimen are provided to assure that modules are tested in a configuration that relates to their use in a photovoltaic array.
Six or more impact locations are chosen to represent vulnerable sites on modules and general locations are listed in Table 1. Only a single impact is specified at each of the impact locations.
Resultant speed is used to simulate the speed that may be reached by hail accompanied by wind. The resultant speed used in this test method is determined by vector addition of horizontal wind velocity plus vertical ice ball terminal velocity.
Ice balls are used in this test method to simulate hailstones. Hailstones are variable in properties such as shape, density, and frangibility (for fracture characteristics, see Ref (10) in Practice E822). These properties affect factors such as the duration and magnitude of the impulsive force acting on the module and the area over which the impulse is distributed. Ice balls (with a density, frangibility, and terminal velocity near the range of hailstones) are the nearest hailstone approximation known at this time. Ice balls generally are harder and denser than hailstones; therefore, an ice ball simulates the worst case hailstone. Perhaps the major difference between ice balls and hailstones is that hailstones are more variable than ice balls. Ice balls can be uniformly and repeatedly manufactured to assure a projectile with known properties.
Ice balls are directed normal to the surface of a test specimen, which transfers the greatest kinetic energy to the test specimen, unlike a non-normal impact at a glancing angle.
Data generated using this test method may be used for the following: (1) to evaluate impact resistance of a module, (2) to compare the impact resistance of several modules, (3) to provide a common basis for selection of modules for use in various geographic areas, or ( 4) to evaluate changes in impact resistance of modules due to other environmental factors, such as weathering.
1.1 This test method provides a procedure for determining the ability of photovoltaic modules to withstand impact forces of falling hail. Propelled ice balls are used to simulate falling hailstones.
1.2 This test method defines test specimens and methods for mounting specimens, specifies impact locations on each test specimen, provides an equation for determining the velocity of any size ice ball, provides a method for impacting the test specimens with ice balls, provides a method for determining changes in electrical performance, and specifies parameters that must be recorded and reported.
1.3 This test method does not establish pass or fail levels. The determination of acceptable or unacceptable levels of ice ball impact resistance is beyond the scope of this test method.
1.4 The size of the ice ball to be used in conducting this test is not specified. This test method can be used with various sizes of ice balls.
1.5 This test method may be applied to concentrator and nonconcentrator modules.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements, refer to 5.1, Section 6, Note 8, and Note 9.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
E772 Terminology of Solar Energy Conversion
E822 Practice for Determining Resistance of Solar Collector Covers to Hail by Impact With Propelled Ice Balls
E1036 Test Methods for Electrical Performance of Nonconcentrator Terrestrial Photovoltaic Modules and Arrays Using Reference Cells
E1462 Test Methods for Insulation Integrity and Ground Path Continuity of Photovoltaic Modules
ICS Number Code 27.160 (Solar energy engineering)
UNSPSC Code 32111701(Photovoltaic cells)