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4.2.1 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.

4.2.2 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.

4.2.3 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.

4.2.4 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.

4.2.5 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.

4.3.1 This test method requires analysis of visual effects, as well as electrical measurements. Visual effects are generally more sensitive than the electrical measurements; therefore, the absolute values for voltage and current are not critical, but repeatable conditions for before and after tests are required for determining electrical changes.

4.3.2 A range of observable effects may be produced by impacting various types of photovoltaic modules. Physical effects on modules may vary from no effect to penetration by the ice ball. Some physical changes in the module may be visible when there is no apparent electrical degradation of the module.

4.3.3 Electrical changes may vary from no effect to no output. All effects of the impacts must be described in the report so that an estimate of their significance can be made.

4.4.1 If the testing is being performed to evaluate impact resistance of a single module, or several modules, it may be desirable to repeat the test using several sizes and velocities of ice balls. In this manner, the different effects of various sizes and velocities of ice balls may be determined. However, no point shall be impacted more than once (see 7.10).

4.4.2 The size and frequency of hail varies significantly among various geographic areas. If testing is being performed to evaluate modules intended for use in a specific geographic area, the ice ball size should correspond to the level of hail impact resistance required for that area. Information on hail size and frequency can be found in Appendix X1 of Practice E822 and footnotes 3 and 4 of this test method, or may be available from local historical weather records.

4.4.3 When testing modules that are designed to be in a stowed position during hail storms, additional impact locations should be chosen accordingly.