Results of Durability Testing of Antireflective Glazing

Andreas Gombert, Markus Heck, Volker Kübler & Michael Köhl, Fraunhofer Institute for Solar Energy Systems
Bo Carlsson, Kenneth Möller, SP Swedish National Testing and Research Institute
Stefan Brunold, Institut für Solartechnik SPF
Michele Zinzi, ENEA

Over the past decades, different attempts have been made to enhance the solar transmittance of glazing. The potential for improving solar facade components is rather high. The main difficulty in developing efficient broadband antireflection (AR) layers is the need for layers with a refractive index lower than 1.3 . Conventional multi-layers with alternating high and low refractive indices are very effective in the visible region but cannot be used for the solar spectrum. The principle to achieve the necessary low refractive indices is always the same substrate material is mixed with air on a sub-wavelength scale. This results in layers with sufficiently low effective refractive indices.

Porous sol-gel coatings are produced by dipping a glass pane into a sol containing very small SiO2 particles. The etching technology using HF and H2SiF6SiF4 includes in reality not only etching but also re-deposition of SiO2.

The goal of this work performed in the framework of Task27 "Performance of solar facade components" of the Solar Heating and Cooling Programme of the International Energy Agency was to analyse potential failure modes and to develop suitable qualification testing in order to enable us to service life estimation based on the test results and the comparison with monitored long-term outdoor exposure at different climatic sites.

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The Authors