"Selective coatings for new concepts of parabolic trough collectors"

The CSP technology based on parabolic trough solar collector for large electricity generation purposes is currently the most mature of all CSP designs in terms of previous operation experience and scientific and technical research and development. 

The current parabolic trough design deals with a maximum operating temperature around 400 degrees C in the absorber collector tube but some recent designs are planned to increase the working temperature to 600 degrees C increasing the performance by 5-10% to attain the improved productivity that the market demands. These systems are expected to be working during 20-25 years.

One of the key points of the receiver is the stack of layers forming the selective absorber coating. Typical optical values for this coating are >95% of absorbance and 10% of emittance at 400 degrees C. In the HITECO EU funded project a new modular concept of collector is being tested. With this new design the coating has to fulfill new requirements as the collector will be working at 600 degrees C and in a low vacuum of 10(-2) mbar. The authors from IK4-Tekniker have collaborated in the HITECO project building a sputtering system to upscale these new coatings to 4 meters long tubes for the application in a set of experimental collectors, being the project coordination done by ARIES Ingenieria y sistemas S.A.

However, there is a great lack of knowledge about the performance of the absorber coatings during the whole life of the receiver. So, it is necessary to establish characterization methods and standards to guarantee the performance, durability and quality control of high temperature coatings. For this purpose, a new EU funded project called NECSO, aims to design accelerated ageing protocols to test the evolution of these coatings under more aggressive conditions in the new designs.