Accelerated life testing for service life assessment of solar absorbers

With the view of establishing the use and limitation of accelerated life testing for assessing the service life of materials used in solar heating and cooling applications, a joint case study was undertaken within Task X "Solar Materials Research and Development" of the IEA Solar Heating and Cooling Programme. The work of case study involved the development of both experimental and theoretical tools to aid the assessment of service life of solar absorber coatings in collectors for domestic hot water, DHW, systems. This entailed performance analysis, failure analysis, microclimate characterization, environmental resistance testing and life date analysis. Predicted in-service degradation of coatings from accelerated life testing was found to be in fairly good agreement both qualitatively and quantitatively with what was actually observed on coatings installed and tested for three years in solar collectors working under typical DHW conditions. As the result of case study, also, the relative importance of the different degradation mechanisms of coatings was clarified. For the anodized aluminium coatings of the case study, the design of the solar collector with respect to ventilation was found the most crucial factor for the service life