Analysis of a conical terminal concentrator



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One of the most interesting approaches to the large scale development of solar energy for electric power-production is known as the Central Receiver System Concept. The Central Receiver System consists of a large area covered with heliostats referred to as a collector field. Each heliostat is individually guided to reflect some light towards a central receiver atop a tower. The system resembles the Fresnel lense and provides substantial concentration of the solar beam. If higher concentration is desired, a terminal concentrator may be included. A terminal concentrator is a device designed to increase the concentration of solar flux reflected from the collector field. Our work depends on two assumptions, viz. 1) the beam width formula, and 2) the uniformly bright collector field. We obtained the necessary design relations, the lower bound to choose the rim angle [Phi][lowered m], the average fraction reflected f([Phi][lowered m]), the radiative stagnation temperatures for the aperture and for the conical skirt and concentration ratios. The temperature and concentration ratio curves determine the optimum rim angle [Phi][lowered m] for each of several designs. We conclude that under certain circumstances the terminal concentrator can almost double the concentration without losing the 20% of the total power which would be lost if the aperture size were simply reduced.