Economic Chances and Technical Risks of the Internal Direct Absorption Receiver

Increased receiver temperatures of solar tower power plants are proposed to decrease the plants levelized electricity costs (LEC) due to the utilization of supercritical steam power plants and thus higher overall plant efficiency. Related to elevated receiver temperatures preliminary concept studies show a distinct LEC reduction potential of the internal direct absorption receiver (IDAR), if it is compared to liquid in tube (LIT) or beam-down (BD) receiver types. The IDAR is characterized by a downward oriented aperture of a cylindrical cavity, whose internal lateral area is illuminated from the concentrator field and cooled by a liquid molten salt film. The objective is the further efficiency enhancement, as well as the identification and assessment of the technical critical aspects. For this a detailed fluid mechanic and thermodynamic receiver model of the novel receiver concept is developed to be able to analyze the IDAR's operating performance at full size receiver geometries. The model is used to analyze the open parameters concerning the feasibility, functionality and performance of the concept. Hence, different system management strategies are examined and assessed, which lead to the proposal of a cost optimized lead-concept. This concept involves a rotating receiver system with inclined absorber walls. The spatial arrangements of the absorber walls minimize thermal losses of the receiver and enhance film stability. The centrifugal forces acting on the liquid salt film are essential to realize the required system criteria, which are related to the maximal molten salt temperature, film stability and droplet ejection. Compared to the state of the art at a 200 MW_el power level the IDAR concept can lead to a LEC reduction of up to 8%. The cost assumptions made for the assessment are quantified with sensitivity analysis.