ANTIREFLECTION OF GLAZINGS FOR SOLAR-ENERGY APPLICATIONS

Several antireflection treatments such as Teflon dipping, dipping in s ilica saturated fluosilic acid, have previously been tested. The films made with the fluosilicic acid showed an increased solar transmittanc e of up to 5%. Outdoor testing for more than 7 years indicated an exce llent long-term stability. The problem with this process is the involv ed chemicals, which are too harmful to permit a large-scale production in Sweden. Therefore, a dip-coating process has been investigated, wh ich uses silica sols, Two sols were investigated, one polydisperse and one monodisperse. The highest attained solar transmittance was achiev ed with the monodisperse sol. It is believed that the increase in the solar transmittance is connected to the size of the silica particles, the larger the smallest particles the higher the solar transmittance. A decrease by up to 5.2% in the solar reflectance has been noted. A pr oblem is the mechanical properties and especially the adhesion tends t o be low. It is, however, possible to improve these properties by baki ng the him at approximately 550 degrees C during 30 min. The solar tra nsmittance decreases when baking the film since it collapses partially , but the mechanical properties seemed to improve. During baking the t emperature is close to that of commercial tempering. It should therefo re be possible to bake and temper at the same time. The deposited film does not introduce any absorption. It is concluded that this process should be suitable for large-scale production, since the involved chem icals are harmless and the process is fairly rapid. Films were made at withdrawal rates of up to 1 cm/s. (C) 1998 Published by Elsevier Scie nce B.V. All rights reserved.