Assessment of Sandstorms to Develop an Accelerated Ageing Test for Solar Materials

Abstract

Concentrating Solar Power (CSP) systems are ad key technology for the future energy generation mix. Due to their ability to store energy thermally they are predestined to assure the uninterrupted supply with electrical energy even in times when other renewable power plants like photovoltaic or windmills do not have any significant power output. However, the long-term efficient operation of CSP plants depends heavily on the durability of the components. Especially optical materials like reflectors and absorbers of the solar radiation are prone to erosion by wind-blown particles during sand storms. At the current state of the art, there is no suited standardized test to assess the resistance of those optical materials against sand storms. The assessment of optical materials for particular plant sites is often carried out by standardized corrosion tests like the salt spray test according to ISO 9227 standard for marine environments, the ISO 11507 standard for long-term UV-radiation and cyclic condensation or the IEC 61215 standard for the simulation of thermal cycles. Though, the threat of sandstorms has not yet been dealt with within the framework of standardization testing. Since CSP plants are mostly situated in arid and semi-arid areas, erosion is a serious issue and both manufacturers and plant operators seek for methods to assess their materials. The hindering step towards the development of an accelerated laboratory test at the moment is the lack of field data about sandstorms. Preliminary testing of different groups in various laboratory setups gave rise to the most important parameters to be erosion determining. From current literature only very few of these parameters can be acquired satisfactorily. Therefore field campaigns need to be undertaken to give reliable information about wind speeds, particle concentration, particle size distribution, particle properties (hardness, roundness) at altitudes from one to five meters above the ground. By now the DLR has collected two years of data for total suspended particle concentration and wind velocity in Missour (Morocco). Furthermore the erosion damage caused by particle impact was analysed on exposed mirror samples in Missour and several other sites. Especially in Zagora (Morocco) the erosion effects on these mirror samples were significantly pronounced compared to samples from other sites. It is concluded, that in this area sandstorms are quite common. Therefore it was decided to achieve a more detailed view on the ongoing aeolian particle movement in Zagora by exposing a high volume air sampler in the course of 2016. Furthermore soil samples of different areas were analysed by sieving and microscopy and the results are presented in this work.