Secondary Reflectors tested at High Temperatures and High Radiation Intensities

A prototype secondary reflector demonstrator for a solar power tower was designed, constructed, and tested at the synthetic sun facility in Jülich Germany "Synlight". The concept was a secondary reflector system that avoided water cooling. The entire construction was steel, where highly polished steel panels coated with a high reflectance silver coating were formed into channels and simply mechanically connected to a steel frame. In simulations it was revealed that an active fan-driven air-cooling system was necessary for this designed system when in use at a solar power tower where it would be exposed to "high" temperatures and "high" radiation intensities. Testing was taken to account where standard operating conditions of the secondary would be below temperatures of 350 ˚C and radiation intensities of 250 kW/m2. Maximum test regimes went up to values of 450 ˚C and 300 kW/m2. The testing regimes was based on real heliostat field data simulated for different aiming strategies at a solar power tower fitted with a secondary reflector. Modelling in advance of testing allowed the design for the prototype system with specified optical and thermodynamic properties. As well as the cooling concept and design, the durability and the high reflectance of the coating system were critical parameters which were developed during the project.