Direct Absorption Receiver System Studies

The DOE Solar Thermal Program has funded a number of projects in high temperature, central receiver technology. These projects aim at identifying efficient and low-cost receiver concepts, as well as conversion systems. The direct absorption receiver (DAR) concept offers several potential advantages. It is clear, however, that the component and system advantages of DAR systems have not beenadequately assessed. The DAR concept may greatly extend the range of operating temperatures compared to metal tube receivers of conventional design. Pressurized metal tube receivers become less practical beyond about 600 degrees C because of the low material strength. Low pressure, metal alloy tube receivers may be used at temperatures up to 750 degrees C, but the alloys are very expensive andmore reactive to corrosive environments. Ceramic tubes can be used at high temperature, but this is an emerging technology whose feasibility has not been established. Overall, the DAR concept, where the concentrated solar flux is absorbed by the working fluid with no intermediate tube heat transfer surface, is a potentially very simple design. The simplicity of the design may result in goodperformance and both low capital and operating costs. The candidate working fluid, molten eutectic carbonate salt, can be used as the storage medium, thus eliminating one heat exchanger in the system design.