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ASTM Subcommittee Sets Solar Terminology
The ASTM E44.20 Subcommittee Glass for Solar Applications met in early July to further discuss the creation of standards and guides for the solar glazing industry.

The group began with a review of work item “Edge Classifications for Glass Used in Solar Applications,” led by Wayne Boor of PPG Industries. During the group’s last meeting it had heard a proposal to use SAE J673, a standard that describes the different edge types used in the auto glass industry, to define edges for solar glass. However, it was quickly realized that the architectural glass, solar module and even aluminum industries had different terms to describe various edge shapes, finishes and defects.

The group’s task is to provide names for these edge characteristics, rather than to provide information on edge strength, which should be a work item for the future, suggested subcommittee chair Doug Hall of Corning Inc. Hall noted that the point was to classify the terms, not set tolerances, in order to be able to have conversations with others about tolerances and specifications.

The group agreed on five edge shapes to begin to classify. The group will look to the Glass Association of North America’s Glazing Manual to gather terms already in use for these shapes, as well as for the finishes and defects.

A discussion of descriptions and terms for the treatment of glass corners began. “This is an area that’s new to the glass industry. Generally speaking, there really is no corner designation in any standard I’ve ever seen. However in the solar industry it is important,” Boor said.

The group came up with a list of the terms they’ve seen used to refer to corners and then whittled it down to two—dubbed and rounded—upon agreeing that most names agree to one of these two treatments.

Terms for glass classification came up again later in the meeting as the group met to discuss a guide to solar glazing terminology. The guide defines types of glass by its composition, but when it came to the portion of the outline setting out to define iron composition, specifically, what percentage of iron makes a glass mid-, low- or ultra-low-iron, the glass industry spoke out. Representatives of AGC, Cardinal and Guardian agreed that what customers request is a certain visible light transmittance, not iron content, and that to get to those specifics of the iron composition would be to share what sets their solar glazing products apart from competitors.

The subcommittee addressed several other issues. Daryl Myers with the National Renewable Energy Laboratory gave a presentation urging the group to support the reinstatement of ASTM E903, Standard Test Method for Solar Absorptance, Reflectance and Transmittance of Materials using Integrating Spheres. This test method, which essentially “died” in 1996 due to lack of re-balloting, covers the measurement of spectral absorptance, reflectance and transmittance of materials using spectrophotometers equipped with integrating spheres. Myers noted that these properties are important in all solar energy systems.

It also began the first steps in drafting a “New Guide for Durability and Reliability Issues of Glass and Coated Glass Used in Solar Energy Products.” The current work item is intended to serve as an educational document for manufacturers of solar energy products and to help E44.20 learn where future standards might be needed.
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