SECTION I INTRODUCTION The paraboloid of revolution (parabolic dish) is one type of solar energy concentrator that uses two-axis tracking. The other major two-axis tracking system uses a field of heliostats focusing on a central receiver (Ref. 14). The parabolic dish solar collector can achieve relatively high concentration ratios (500 to 2000), and as a result rather high potential temperatures; values in the range of 500°C to 1400°C are achievable. The thermal energy collection efficiency is also quite high; for example, the efficiency is estimated to be 70% at 800°C for a reasonable cavity receiver design. These characteristics indicate both the strength and weakness of the parabolic dish solar collector. The high concentration ratio and high heat fluxes at the focal zone make it difficult to design a receiver with low temperature differences between tube wall and fluid. Heat pipes, spiral fluid tubes in insulated cavities, and porous ceramics are examples of design approaches for a suitable receiver. A three-dimensional surface (dish) with sufficient surface accuracy and structural rigidity is difficult to achieve at low cost. Also the structural anchoring needed to withstand winds due to the large area cross section is a major design concern along with accurate two-axis tracking. The high potential temperatures and efficiencies are extremely attractive for driving a heat engine, but the high temperature makes it difficult to collect heat from a large field of dish collectors and to bring the heat to a central power plant. Two approaches have been considered in the application of the parabolic dish for electric power production. The first is central generation where heat is collected from a field of dishes and transported to a central site either through thermal transport or chemical transport for eventual energy conversion. Large central steam Rankine engines are efficient even at moderate temperatures (500°C) and
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