Modelling and Control of Transients in Parabolic Trough Power Plants with Single-Phase Heat Transfer Fluids

Kurzfassung

Optimizing solar field operation and control during transient processes, like passing clouds and solar field start-up, is key to improve the competitiveness of line-focus solar thermal power plants in comparison to other renewable energy technologies. Although Simulation tools play a significant role in the design and optimization procedures, common solar field computational models cannot predict the behaviour of such a system exposed to high degrees of, both, temporal and spatial variability in the energy input. Some very detailed tools can only simulate parts of the system within acceptable time and computational power, and hence, they are not utilized as platforms to test new concepts under realistic operation conditions. On the other hand, tests in pilot or full-sized solar fields not only are too costly to prove a concept, but it is also nearly impossible to reproduce a transient test case with exactly the same disturbances to provide fair comparisons. Thus, a novel transient solar field model, the Virtual Solar Field (VSF), is developed within the scope of this thesis. The model couples a static hydraulic flow model with a detailed dynamic loop model making use of the different time scales in the system. This results in an accurate and computationally efficient simulation tool for commercial power plants scale, such that, for example, 10 hours of Andasol-III solar field operation can be simulated in under 10 minutes. VSF has been validated against solar field operation data from Andasol-III as presented in the thesis. Also new control schemes that use direct normal irradiance (DNI) maps from nowcasting systems, as well as single loop valve control have been implemented and tested in VSF. A controller performance assessment scheme based on energy output and conversion efficiency has been developed to estimate the expected revenues of the solar field within the simulated time. This provides information to quantify the benefits of using one control strategy over another. The availability of the simulation tool also paves the way for developing model-predictive control strategies to optimize the field operation and production.