High-temperature flat plate collector with glass capillary modules

An improved flat plate collector with a newly developed Transparent Insulation Material made from glass capillaries has been built. Stagnation temperatures of 261 degree C were measured. From outdoor efficiency measurements the U-value of the collector has been determined to be F' U is equal to (2.30 plus 0.0035DeltaT Khighminus1) W mhighminus2 Khighminus1 and the optical efficiency is F' Etasub0 is equal to 0.72, where both values are based on the absorber area. Possible improvements are discussed.