Direct Absorption Receiver

The Solar Energy Research Institute (SERI) is conducting research for high temperature solar thermal receiver concepts. A good candidate for a receiver heat transport and a thermal storage medium is molten salt, and molten carbonates are the primary candidate salts for applications requiring temperatures of 850 degrees C (1562 degrees F) or higher. The receiver absorbs concentrated solarradiation directly on a salt film flowing down a wall in a cavity. The molten salts being investigated are carbonates and chlorides. Although sodium hydroxide is the cheapest medium, it has the highest corrosion rate on containment materials and, thus, does not warrant further study at this time. Chlorides have low corrosion rates on ceramics but high rates on metals, and carbonates have low ormodest corrosion rates on both metals and ceramics. A ternary eutectic of lithium, sodium, and potassium carbonate has been selected as the primary salt mixture for the direct absorption receiver and thermal storage system concept. Figure 1 illustrates the receiver concept. Low-temperature salt at 425 degrees C is pumped to the receiver in the riser, and a manifold distributes that salt over thetop of the absorber surface. The molten salt runs down the absorber surface and is heated by the concentrated solar flux to a temperature of 900 degrees C. The salt then returns to ground level through the downcomer, a metal pipe. Solar radiation enters the cavity through an uncovered opening and is absorbed in either a blackened salt or a black surface with a relatively clear salt.