plate, and transfer to the fluid by convection) or darkened (allowing

Recent solar central receiver designs emphasize direct absorption receiver. (DAR) concepts primarily because of their ability to absorb high flux densities. An attractive design utilizes molten salt as the transport /storage fluid, which is pumped to the receiver and allowed to flow over a hightemperature absorber surface. As the salt runs down the absorber surface in a thin film, concentrated solar flux heats the salt to 900°C, either directly (blackened fluid) or by convective heat transfer with the irradiated absorber (clear fluid). The feasibility of such a design depends on the optical efficiency of the absorber /fluid combination. The optical properties of candidate absorber materials and transport fluids are therefore required at appropriate elevated temperatures. Because such salts can be extremely reactive at high temperatures, it is important to measure optical properties as a function of exposure history of the salt /absorber. Optical characterization of a clear molten carbonate salt