Physical interpretation of impacts from a low cost manufacturing process on the surface microstructure of a novel solar absorber

A novel lower cost mechanical solar absorber manufacturing method has been developed. C/Al2O3/Al surfaces have been characterized with optical and microstructural methods. The surface consists of thin inhomogeneous matrix containing carbon and Al2O3 on Al-substrate. Manufacturing of the surface can be done by single phase manual or mechanical grinding with a silicon carbide grinding pad. A solar absorptance α = 0.90 and a thermal emittance ε = 0.22 have been achieved so far. Durability and aging mechanisms of the surface have been determined in laboratory and test field. The C/Al2O3/Al surface has passed accelerated aging tests recommended by IEA-SHC for high temperature and combined elevated temperature and condensation. The main degradation mechanism is hydration of aluminium oxide. The estimated service lifetime of the absorber (with an optical performance more than 95% of its initial) in normal use is in the range of 20 – 25 years, depending on the condensation frequency distribution on the surface. Computer simulations and solar collector testing at test field demonstrate some 5-17% lower annual energy yield compared to the commonly used collectors with nickel-pigmented and sputtered absorbers.