One of the most interesting approaches to the large scale development of solar energy for electric power production is the Central Receiver System Concept. The Central Receiver System contains a large number of individually guided heliostats that reflect sunlight towards a central receiver high above the field of heliostats. The system resembles a giant Fresnel mirror and provides a substantial concentration of the solar beam. If high concentration is desired, a terminal concentrator may be included. The terminal concentrator is a device designed to increase the concentration of solar flux reflected from the collector field. Our study depends on two assumptions: (1) the beam width formula for the reflected beams and (2) the uniformly bright collector field which is a gross simplification allowing us to deal with the terminal concentrator. We obtained the necessary design relations, including a lower bound for the rim angle φm, the average fraction reflected f{hook}(φm), a radiative stagnation temperature for the aperature, and the concentration ratios. The temperature and concentration ratio curves determine the optimum rim angle φm for each of several designs. When designed to provide maximum concentration, the terminal concentrator becomes excessively large. Consequently, we consider a design which produces 90 per cent of the maximum concentration and reduces the size of the conical reflector by 5-6 times. The effectiveness of this compromise design permits us to conclude that a practical terminal concentrator of the conical variety can almost double the concentration without any appreciable loss of total power. There will be losses due to reflectivity but not due to beam spillage because of the reduced aperture. The terminal concentrator will be economically desirable for small central receiver systems if it is cheaper than the incremental cost of the heliostat field due to the additional focusing required to produce the same concentration. © 1979.
