Reference Receiver Fig. 1 shows the principle of the solar dynamic reference receiver. It comprises 61 parallel cylindrical heat pipes each divided into three longitudial sections. The first receives the solar radiation. The second carries annular heat storage containers (subdivided by walls or not) and is protected from the hot environment of the first by a common radiation shield. The third provides for the heat exchange to the working gas of the Stirling engine (or alternatively a gas turbine). This heat exchange may be accomplished by round or flat tubes inside or mounted on the heat pipes and carrying the working fluid of the engine. The tubes chosen for the present calculations are described in the next section. In Case (2), the tubes do not enter the 61 individual heat pipes. They enter an intermediate common heat pipe into which the individual heat pipes are inserted on the other side. The aperture of the receiver is assumed to be covered by an insulated lid during eclipse. The heat pipes may be arranged as shown in Fig. 1 or at the inner periphery of the receiver. The latter version requires a larger receiver diameter but will provide a more equal distribution of solar radiation among the heat pipes. The theoretical predictions below are basically valid for both versions. The receiver was sized for a SDPS in a low Earth orbit of 94 min. with a 34 min. eclipse. There is also relevancy to terrestrial solar plants with cloud shadow phases of the order of 30 min. which require heat storage. This SDPS was supposed to include a Stirling engine plus generator for 25 kWe at a thermal-to-electrical design efficiency of 0.3.
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