Progress in Development of High-temperature Solar-selective Coating

Improving the properties of the selective coating on the receiver represents one of the best opportunities for improving the efficiency of parabolic trough collectors and reducing the cost of solar electricity. Additionally, increasing the operating temperature above the current operating limits of 400oC can improve power cycle efficiency and reduce the cost of thermal energy storage resulting in reductions in the cost of solar electricity. Current coatings do not have the stability and performance necessary to move to higher operating temperatures. The objective of this effort was to develop new, more-efficient selective coatings with both high solar absorptance (α ≥ 0.96) and low thermal emittance (ε ≤ 0.07 at 400oC) that are thermally stable above 500oC, ideally in air, with improved durability and manufacturability and reduced cost. Using computer-aided design software, we successfully modeled a solar-selective coating composed of materials stable at high temperature that exceeded our property goals. In preparation for characterization of samples of these new coatings, a round-robin experiment was conducted to verify the accuracy of the selective coating reflectance measurements.