Round robin on accelerated life testing of solar absorber surface durability

As degradation by ageing of solar absorber surfaces was identified to be an important quality factor, the Working Group MSTC (`Materials in Solar Thermal Collectorsʹ) of the IEA-SHCP (International Energy Agency-Solar Heating and Cooling Programme) worked out a general test procedure for accelerated lifetime testing (ALT) of these materials, based on methods established by the former Task X of the IEA SHCP. The qualification test procedure was adopted by ISO and is presently dealt within ISO/TC 180 `Solar Energyʹ. The standard proposal in detail describes a procedure how to test the long-term stability of an absorber surface for the use in flat plate collectors for domestic hot water systems. The collectors service lifetime is assumed to be 25 years, at least. Degradation caused by thermal loads, high humidity and condensation and sulphur dioxide are regarded. In order to examine the feasibility and reproducibility of the test method the Working Group MSTC initiated a round robin test in accelerated life testing of solar absorber surfaces. The test was performed according to the ISO standard proposal dated January 1997. In total, five different industrially manufactured absorber coatings were available to the three participating laboratories. Tests concerning the thermal stability as well as the resistance to high humidity and condensation were performed by all three laboratories. The test for determining absorber surface corrosion resistance to air of high humidity containing sulphur dioxide was carried out by one lab only. The outcome of the round robin test shows very good agreement of the results of the different coatings tested for all of the laboratories. The feasibility and reproducibility of the method was fully confirmed.