S. Furbo1* and J. M. Scultz1

1 Department of Civil Engineering, Technical University of Denmark, Brovej, Building 118, DK-2800 Kgs.

Lyngby, Denmark

* Corresponding Author, sf@byg. dtu. dk
Abstract

Outdoor long-term side-by-side laboratory measurements during a Danish summer elucidate how much the transmittance for a glass cover can be improved in practice by antireflection treatment of the glass surfaces. The influences of water caused by rain and dew and dirt on the glass surfaces are included in the measurements.

During the test period the solar transmittance for the glass is increased by 8% due to the antireflection treatment of the glass surfaces. The measured transmittances are 2-3% lower than calculated transmittances based on measurements for the clean glasses. The antireflection treatment has no significant influence, negative or positive on the transmittance reduction caused by water and dirt attached to the glass surfaces during the summer period.

Keywords: Cover glass, antireflection treatment, solar transmittance, long term measurements

1. Introduction

Investigations have shown that the transmittance of a clean glass cover is increased by 5-9% by equipping the glass cover with antireflection surfaces by means of a liquid-phase etching by Sunarc Technology A/S [1]. The increase from 5 to 9% depends on the incidence angle. The investigations were carried out for different incidence angles in an outdoor solar tracker.

The surfaces of glass with the antireflection treatment are hydrophilic, which influences the time it takes for water caused by rain or dew to disappear from the surfaces. The hydrophilic surfaces might also influence the amount of dirt attached to the glass surfaces. The transmittances for cover glasses with and without antireflection treated surfaces might therefore in practice be different than the transmittances for the glass covers calculated based on measurements for clean glasses.

This paper describes long term measurements of the transmittance for an antireflection treated glass and a normal glass carried out as side-by-side tests in an outdoor laboratory test facility. The measured transmittances are compared to theoretically calculated transmittances based on transmittance measurements for clean glasses.