Ultrahigh Concentrations

9.1 CONCENTRATION LIMITS FOR NONIMAGING TERMINAL CONCENTRATORS IN Central RECEIVER APPLICATIONS

9.1.1 Introduction

In this chapter, a preliminary analysis that carries out various performance trade-offs involved in the design of a two-stage central receiver plant that could achieve ultrahigh concentrations with a nonimaging CPC type secondary is presented. It should be noted that the study was carried out in the context of using a solar central receiver plant to generate hydrogen from the direct thermo­chemical splitting of water. However, the analysis is independent of that context and applies to any and all central receiver (or the so-called power-tower) configurations. This analysis shows that such a two-stage central receiver plant can achieve geometric concentrations approaching the maximum theoretical limits and provides a methodology for evaluating various geometrically dependent per­formance trade-offs. The concept of using a secondary (terminal) concentrator in central receiver systems has been around for some time (Rabl, 1976a; Athavaley, Lipps, and Vanthull, 1979) but has not been seriously investigated until relatively recently (Spirkl, Timinger, Ries, Kribus, and Mus – chaweck, 1998; Kribus, Huleihil, Timinger, and Ben-Mair, 2000; O’Gallagher, and Lewandowski, 2005).

The objective is to design a large-capacity (multimegawatt) plant, and it is clear that such a large scale with >1 MW power requirements can only be delivered by some kind of central receiver. We wish to consider the incorporation of a nonimaging secondary into such a configuration. In CPC designs, the geometry known to be optimal is a cylindrical, axially symmetric configuration, which, for a central receiver has a central tower surrounded by a circular area containing heliostats (Athavaley, et al., 1979) such as illustrated schematically in Figure 9.1a.

Updated: August 20, 2015 — 6:40 am