Silica low-reflection coatings for collector covers, by a dip-coating process

A procedure for the deposition of antireflection coatings onto collector cover plates, by means of a dip-coating process using an ethanol-based colloidal silical sol, is described. By use of this process the solar transmittance of such cover plates can be increased by an increment 0.05 thus eliminating over 60 per cent of the reflectance losses. This increased transmittance increases the daily heat output for a single-glazed flat plate collector by a factor of approximately 1.1, and for double-glazed units by a factor of approximately 1.2. These antireflection films can be deposited on glass and on some types of plastic substrate. The abrasion resistance of the deposits on glass can be improved greatly by baking to 500°C. Outdoor weathering tests have shown the films probably have adequate stability for use in solar collector applications.