A multistage solar receiver: The route to high temperature

A high-temperature solar thermal receiver is subject to temperature-dependent emission and convection losses. Minimizing these losses is essential to realization of high temperature, high efficiency systems. Dividing the aperture into separate stages according to the irradiance distribution has been shown theoretically to significantly reduce these losses. In such a partitioned system, the working fluid is gradually heated as it passes through a sequence of receiver elements with increasing irradiance levels. An experiment to demonstrate this principle using two heating stages has been constructed at the Weizmann institute's Solar Tower. The high-temperature receiver stage is the Directly Irradiated Annular Pressurized Receiver (DIAPR). The low-temperature stage is implemented as a partial ring of intermediate-temperature cavity tubular receivers (Preheaters) surrounding the central high-temperature stage. Following initial concentration by a part of the Weizmann Institute heliostat field, the light enters the receivers via secondary concentrators constructed as approximate CPCs. We present recent test results with the two-stage system. Air exit temperatures of up to 1000 degrees C were obtained, with the low-temperature stage supplying up to 750 degrees C. The power output was up to 55 kW(th). Heat transfer in the high-temperature receiver, losses due to the partitioning, and future plans for partitioned receivers are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.