Non-uniform characteristics of solar flux distribution in the concentrating solar power systems and its corresponding solutions: A review

In this paper, the non-uniform characteristics of solar flux distribution and the consequent challenges in concentrating solar power (CSP) systems including parabolic trough system, linear Fresnel reflector system, solar power tower, and solar dish system are summarized. The corresponding solutions proposed to tackle the challenges caused by non-uniform solar flux distributions are particularly reviewed. Meanwhile, the authors' previous work is also introduced. It is can be seen that the solar flux distributions in both tubular receiver and volumetric receiver are extremely non-uniform for the 4 types of CSP systems. The non-uniform solar flux leads to the non-uniform temperature distributions in the absorber. There exist high local temperature and large temperature gradient, which can causes great challenges for the safety and high-efficiency operation of CSP systems. The selective coating and the heat transfer fluid tend to degrade in high temperature environment; and the absorber also could be burned out in the hot-spot area. Thermal stress and thermal deformation resulted from large temperature gradient can cause damage of the key components of solar receivers. Then the authors pointed out the reason that the non-uniform solar flux distribution could cause the above challenges is attributed to the mismatching between the non-uniform solar flux distribution in the absorber and the uniform heat absorption capacity of the heat transfer fluid, which leads to the non-uniform temperature distribution. Accordingly, the existing solutions for tackling the challenges caused by non-uniform solar flux distribution can be classified into 2 groups: (1) Optimizing the heat absorption capacity to match the non-uniform solar flux distribution; (2) Homogenizing the solar flux distribution in absorber/receiver to match the uniform heat absorption capacity. Finally, the guiding principle of matching between the collecting process and the absorbing process is proposed for solving the problems caused by the non-uniform characteristics of solar flux distribution. The solar collectors and solar receivers in CSP systems should be optimized under the guidance of this principle to improve the safety and efficiency of CSP systems.