Corrosion of Second Surface Heliostats Used in Coastal Environments

Le résumé fourni par la source

Understanding heliostat durability under typical operating conditions is crucial for ensuring long term stability of the heliostat field within a concentrated solar energy plant. Not only from the perspective of impact to available power input/output to the system but also in regard to economic impact to operation and maintenance (O&M) and plant replenishment. Knowledge of localized climatic and environmental conditions are important in both heliostat design and installation for a given plant location. Heliostats deployed to semi-arid areas will experience strongly contrasting conditions to those in humid sub-tropical coastal environments. In our study into these impacts to the heliostat fields designed for the National Solar Energy Centre (NSEC) at Mayfield West, Newcastle we observe significant impact from the coastal environs and surrounding industry to the mirrored glass surface as well as the supporting structure and actuators. In this study we use scanning electron microscopy (SEM) to examine corrosion to the second surface mirrors. We observe failure to the rear mitigation layer(s) of the mirror can occur during installation or as a result of imperfections during manufacture. These defects provide sites for corrosion initiation at the reflective silver (Ag) layer. Over time the corrosion spot grows and after 4 years of field deployment has been observed up to 35mm in diameter. We further illustrate environment effects impacting the supporting structure and discuss design changes implemented to minimise influences from the local conditions.

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