Loop-wise control valves application in molten salt parabolic trough solar fields

Abstract

Parabolic trough power plants use collectors to concentrate direct sunlight onto an absorber tube containing a heat transfer fluid (HTF). The thermal energy is used to generate electricity in a steam cycle power plant. In almost all commercial power plant designs, the HTF is distributed homogeneously to all loops with a fixed opening for the manual loop inlet valves. This work presents an approach with individually controlled mass flow distribution to all loops. The objective is to achieve a more stable outlet temperature in the event of non-homogeneous irradiation. The control concept includes a controller for the total mass flow at the HTF pump, the focus rate of each collector and the opening of the individual loop inlet valves. The suggested control concept is tested using the Virtual Solar Field (VSF) dynamic simulation tool for a 38-loop molten salt parabolic trough field. This simulation tool uses highly discretized irradiance data to reproduce realistic irradiance boundary conditions. A total data set of 940 days of operation recorded at CIEMAT’s Plataforma Solar de Almería are used. Furthermore, different artificial soiling scenarios are implemented to test the concept under non-homogenous heat input. The new control concept is compared with the state-of-the-art control schemes based on loop inlet valves with fixed opening. For normal soiling conditions, the simulation results show an average increase of 0.85 % in the net electrical energy produced.