Innovative lifetime testing protocol for high-temperature secondary reflector materials used in concentrated solar thermal energies

The actual energy market based on fossil fuels is the responsible of more than half of the greenhouse gases generated worldwide. Renewable energies play a fundamental role to lead the transformation towards an energy market less damaging for the environment. Concentrated solar thermal (CST) energy is essential to achieve this objective because it is the most profitable renewable technology to store energy in the form of heat. In recent years, solar tower (ST) systems are the most installed CST plants thanks to their high operating temperatures that allow reaching greater efficiency. Developers are presently considering the integration of secondary concentrators on the top of the tower to improve its optical and thermal behavior, and hence, to increase the performance and feasibility of the system. However, no commercial high-temperature secondary reflector materials for ST systems are marketed because their durability is currently unpredictable. In this work, a new methodology based on accelerated aging tests is developed to predict the lifetime of secondary reflector materials in short time. Additionally, operating conditions that typically take place on a ST are simulated in a solar furnace to validate the reliability of the aging tests. The protocol developed was applied to a novel secondary material recently developed. According to the results obtained for this exemplary material, the main degradation is suffered due to the high temperature during operation. The correlation was validated under representative operating conditions with deviation of 0.2% of the reflectance comparing the accelerated aging and the operating conditions tests.