Surface Damage to Mirrors used in Concentrated Solar Power Plants

by Jincy Varughese

In Concentrated Solar Power (CSP) plants, 30% of investment costs are attributed to the installation, maintenance, and replacement of mirrors. In order to ensure high yield at a CSP plant, the solar specular reflectance of these mirrors must be maintained at high standards. However, several environmental factors such as temperature, humidity, and windstorms contribute to the degradation of these panels. The latter, is of particular interest to Karim and a team of researchers from Morocco who, over the course of two years, evaluated the effect of windstorms on surface erosion of CSP mirrors.

Karim et al. (2014) utilize both natural aging tests and erosion tests in a sandblasting chamber to observe the effects of windstorms on mirror roughness and performance. The natural aging tests occurred on a desert and a seaside site. The sandblasting chamber allowed natural aging conditions to be stimulated but in a controlled environment. Climatic parameters such as wind speed and direction as well as geological parameters such as size distribution, shape, and hardness of sand particles were recorded for these sites. During these different conditions, the specular reflectivity was also measured using a portable reflectometer.

The researchers found that the optical performance of CSP mirrors decreased with increasing wind speed and found that even low wind speeds were associated with ring cracks. The study demonstrated that roughness, impact, and losses in specular reflectivity increased for CSP mirrors with increasing tilt for angles between 20 and 90 degrees. The study also found that particle properties have significant effects on mirror degradation. When controlling for wind velocity and particle size, desert areas with hard sand had mirrors with high roughness parameters whereas mirrors in seaside areas with sharp sand had lower roughness but higher impact parameters. Additionally, course sand was found to contribute to a higher loss in specular reflectivity than fine sand. In conclusion, Karim et al. found that wind velocity, mirror angle, particle hardness, and particle sharpness affect the optical performance of CSP mirrors and can contribute to their degradation in natural conditions.

Karim, M., S. Naamane, C. Delord, and A. Bennouna. “Study of the Surface Damage of Glass Reflectors Used in Concentrated Solar Power Plants.” SolarPACES 2014. [GSSS: Karim Naamane surface damage concentrated solar] http://www.researchgate.net/publication/266077905_Study_of_the_surface_damage_of_glass_reflectors_used_in_Concentrated_Solar_Power_Plants.

s.naamane@mascir.com

christine.delord@cea.fr

 

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