## 5 Conclusions  
A large number of works can be found regarding parabolic trough power plants; however, few studies focus on the dynamic behaviour of the secondary systems--e.g., the TSS, taking into account stable electrical power and capacitance factor enhancement. A particular focus is placed on the modelling of the SF. Most works refer to the use of a simplified steady-state model instead of a comprehensive dynamic model of these power plants. In order to understand the dynamic behaviour of the secondary systems (SF, TSS, and PB) with high accuracy, more consideration should be devoted to the thorough modelling of the power plants.  
In this study, detailed solar field and thermal storage system models for a parabolic trough power plant are implemented based on the specifications from data obtained from Andasol II, located in Spain. In this work, the components of these models have been accurately modelled using APROS software.  
A detailed SF model was modelled with 156 collector loops, as well as implementing many control circuits to regulate the operation processes. Therminol VP-1 was used as an HTF in the SF. The reference solar field was designed to operate with maximum HTF mass  
Figure 12: Hot tank control valve (during discharge mode) (simplified).  
flow (1170 kg/s) at the design outlet temperature (393 \({}^{\circ}\)C). Hereby, the solar field operates with a total capacity of useful thermal energy of approximately 280 MW\({}_{\text{th}}\).  
A comprehensive TSS was implemented using hot and cold insulated drums and, between them, heat exchangers. Moreover, the control circuits of this system are described. The thermal storage system was operated with two operation modes--namely, charge mode and discharge mode. During charge mode, the HTF from the solar field at a temperature of 393 \({}^{\circ}\)C heats the molten salt (sodium and potassium nitrates) that is pumped from the cold tank to the hot tank and stored with temperature of approximately 386 \({}^{\circ}\)C. This process continues until achieving a maximum capacity of stored energy of about 1025 MW\({}_{\text{th}}\) h. This thermal storage provides high operational flexibility and stable electricity generation.  
On the other mode, the hot salt heats the thermal oil via the heat exchangers. The molten salt exits the heat exchangers and is sent into the cold tank at a temperature of about 292 \({}^{\circ}\)C. Accordingly, the thermal storage system will provide the thermal power at the nominal load (125.75 MW\({}_{\text{th}}\)) for a period of approximately 7.5 h in the evening period.  
The purpose of this work was to provide reference models for the SF and TSS. This, in turn, will help researchers and designers to understand the advanced control circuits of these stations. In addition, these models can determine the best manner of power plant operation.  
Future studies will be focused on a detailed description of the power block controllers.  
This research received no external funding.  
Not applicable.  
We acknowledge support from the Deutsche Forschungsgemeinschaft (DFG --German Research Foundation) and the Open Access Publishing Fund of the Technical University of Darmstadt. The first author would like also to thank the University of Technology, Iraq.  
All authors declare no conflict of interest.