Overview
ISO 22975-4:2023 - "Solar energy - Collector components and materials - Part 4: Glazing material durability and performance" specifies definitions and standardized test methods for assessing the durability and optical performance of glazing used in solar collectors. It applies to glass covers for flat sheets and evacuated tubes, specifically soda lime silicate glass and borosilicate glass, and covers measurement of solar transmittance (0.3 µm – 2.5 µm, AM1.5).
Key topics and requirements
- Scope and terminology
- Defines terms such as specimen, solar transmittance, thermal shock, thermal shock resistance and endurance (see ISO 9488 for related vocabulary).
- Classification of solar glass
- Untreated glass (Classes U1–U3), single-side AR treated (S1–S3) and double-side AR treated (D1–D3) with specified solar transmittance values:
- Untreated: Class U1 τs = 0.900; U2 = 0.885; U3 = 0.870
- Single-side AR: S1 = 0.925; S2 = 0.910; S3 = 0.895
- Double-side AR: D1 = 0.950; D2 = 0.935; D3 = 0.920
- Optical testing
- Preparation of specimens (minimum five specimens; plate size ≥ 80 × 80 mm or tube fragments of specific diameters and length).
- Measurement of mean solar transmittance using a UV‑VIS‑NIR spectrophotometer with integrating sphere (requirements per Annex A).
- Thermal stability and thermal shock testing
- Apparatus requirements: hot oven (≥ 400 °C, ±3 °C stability), cold water bath (≈ 25 °C ±5 °C) and specimen basket.
- Specimen sets: 10 flat plates or tube fragments for thermal tests.
- Procedure: controlled heating, rapid transfer (≤ 6 s) to cold bath, inspection for cracks/breakage.
- Definitions and procedures for thermal shock resistance, progressive and high‑level tests, and determination of thermal shock endurance (temperature difference leading to 50% failures).
- Reporting
- Test reports must reference ISO 22975-4:2023 and include specimen counts, oven/cold bath temperatures and detailed failure statistics.
Applications and users
- Who uses it
- Solar collector manufacturers, glazing and glass suppliers, independent test laboratories, certification bodies, product designers and R&D teams.
- Practical value
- Ensures consistent assessment of glazing material durability, solar transmittance, and thermal shock performance for selection, quality control, warranty claims and certification of solar collectors.
Related standards
- ISO 9488 - Solar energy vocabulary
- ISO 22975-1 - Solar energy - Collector components and materials - Part 1: Evacuated tubes - Durability and performance
Keywords: ISO 22975-4, solar glass, glazing material durability, solar transmittance, thermal shock resistance, soda lime silicate glass, borosilicate glass, solar collectors, test methods.
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