Transient Simulation of Line-Focus Solar Thermal Power Plants

Abstract

Concentrated Solar Power (CSP) is a utility scale technology that pro duces electricity using the thermal energy of the sun. Due to the varying intensity of the solar irradiation, there is a constant change in the op eration point for solar thermal power plants. In order to optimize the process, a complex relation between irradiation intensity, fluid mass fl ow and collector focus must be considered and appropriate control strategies should take into account the transient situations. Therefore, detailed sim ulation tools are essential for the analysis and optimized operation of the power plant. In this context, the German Aerospace Centre (DLR), as a pioneering research institution of CSP, developed a model to simulate line-focus solar fi elds with single-phase heat transfer medium: the Virtual Solar Field (VSF). This simulation tool considers the hydraulic and thermal aspects of the plant, enabling to model the thermal condition effect of the field on the fl ow distribution among the parallel loops. Accordingly, the goal of the master thesis is to validate VSF under certain conditions and improve its applications. In addition, VSF is also used as a tool to enhance the control and improve the outcome of solar thermal power plants. The first phase of the project consisted of the validation of the simu lation tool by the comparison of the VSF model results with data from a real power plant. For that, data preparation was realized and a Validation method was developed, with further analysis of the results. The second phase of the project was based on the development of a broader use for the tool as an improvement for control. This was achieved by the application of a Fuzzy Logic Control (FLC) . This FLC implemen tation includes loop mass flow and collector focusing mode in the same algorithm, aiming to decrease defocusing instances while still maintain ing optimal temperature set-points. It considers control valves for each individual loop and also the period of the day, differentiating the phases of plant operation. The main advantage brought from fuzzy logic to this case is that the knowledge in the technology and in the expected behavior in transient situations could be fully applied in the control strategy. Consequently, VSF was successfully validated and used as a good sup port for the development of FLC. The results of FLC application Show that this unique approach can be very beneficial for the plant's operation, with a relative simple implementation. FLC performed as a robust and proactive controller, especially in transient situations, providing better energy performance and allowing less defocusing instances, with stable outlet fl uid temperature. In conclusion, the FLC is considered to be a proper strategy to be applied in combination with VSF simulation tool to enhance the control of a solar thermal power plant. This implementation represents an additional value for VSF, characterizing an innovative ap proach that considers dynamic valve control and collector focusing mode in a single strategy.