Analysis and improvement of solar flux distribution inside a cavity receiver based on multi-focal points of heliostat field

The strong flux variations distributed on the surfaces of receiver during its service life can intensify material aging and thus deteriorate the thermal performance of material. Generally, the single focal point heliostat field, i.e., focusing at the centre of the aperture of a cavity receiver, could possibly result in an irregular flux distribution, which would have a very high peak value of flux density on the inner sides of the cavity receiver at a certain time of sun tracking. In order to give a maximum protection to the central receiver, in this paper, by taking the 1 MWe DAHAN solar tower power plant as the investigating subject, a multi-focal point model for finding the optimum configuration of focal points using an arbitrary heliostat has been developed. Based on the model, the pattern of solar flux distribution for different zones of the heliostat field is investigated to study how the pattern changes with date and time. From the simulation results, a new grouping method for the layout of the focal points of a heliostat field inside the cavity receiver is proposed. Then a popular optimization algorithm based on the TABU meta-heuristic method is developed to find the optimal flux distribution on the receiver surface. The objective is to flatten the flux distribution as much as possible by changing the aiming points of different groups. Simulation results show that the new multi-focal points system can provide a more secure way to safeguard the operation of the receiver system comparing to the traditional single focal point system. (C) 2014 Published by Elsevier Ltd.