Development of a spatially resolved reflectometer to monitor corrosion of solar reflectors

• A prototype of a specular reflectometer for solar mirrors is developed and validated.
• The specular reflectance can be measured with spatial resolution.
• Image processing permits to create a specular reflectance map of the mirrors’ surface.
• The measuring spot size of more than 5 cm in diameter is large compared to commercial reflectometers.
• Degradation of the reflector surface can automatically be detected and monitored.

Solar reflectors for Concentrating Solar Power (CSP) concentrators require a high reflectance and high specularity over the whole solar spectrum. During their lifetime of at least 20 years, the reflectors must withstand harsh outdoor conditions without loosing their reflective properties. Currently, there are not many devices available to measure the specular reflectance. In this work a prototype of a specular reflectometer with spatial resolution has been developed. The major advantage of the prototype compared to other reflectometers is the possibility of measuring the specular reflectance on an extended measuring spot of more than 5 cm in diameter with a spatial resolution of 37 pixel/mm. Additionally, measurements can be taken at three different acceptance half angles (φ = 3.5, 6.0, and 12.5 mrad) and at three different wavelengths (λ = 410 nm, 500 nm, and 656 nm). This lab scale instrument can be employed to monitor degradation effects, such as corrosion spots, and evaluate their influence on the specular reflectance of solar mirror materials.