## 2 Special Issue Findings
The study focused on control circuits used in the thermal storage system of a parabolic trough power plant during the charging/discharging cycle. In the charging phase, the heat transfer fluid (Therminol VP-1) from the solar field at a temperature of 393 \({}^{\circ}\)C heated the molten salt (sodium and potassium nitrates), which was pumped from a cold tank into a hot tank and stored in a temperature of about 386 \({}^{\circ}\)C. The charging phase continued until the maximum capacity of stored thermal energy of about 1025 MW\({}_{\text{th}}\) h was reached. During the discharge phase, the hot molten salt heated the heat transfer fluid (Therminol VP-1), to be used in the power block via the heat exchangers. The molten salt left the heat exchangers and entered the cold tank at a temperature of approximately 292 \({}^{\circ}\)C. Accordingly, the thermal storage system provides the thermal power at the nominal load (125.75 MW\({}_{\text{th}}\)) for about 7.5 h in the evening time. The authors stated that the main results of this study should help researchers and designers understand the advanced control structures used in parabolic trough power plants. For more studies on the dynamic simulation of solar power plants, see this review paper [11]. * 7. The seventh article in this Special Issue addressed an important topic currently under research as an effective technology for the gasification of solid fuels such as biomass and refuse-derived fuels to produce valuable products, e.g., methanal or Fischer-Tropsch synthesis (see Figure 2). Here, recent developments related to the biomass-based chemical looping gasification process were reported by the authors ([PERSON]; [PERSON]; [PERSON]; and [PERSON], from the Technical University of Darmstadt, Germany, and Can Theo University, Vietnam) [12]. The influence of process parameters such as gasification temperature, steam-to-biomass ratio, oxygen-carrier-to-biomass ratio, and biomass characteristics on the performance of the chemical looping gasification process was discussed. Furthermore, improvements in syngas purification technologies were shown to reduce problems associated with breakdowns and plugging, as well as efficiency losses. The latest experimental and simulation/modelling studies and their basic assumptions were described in detail. The authors pointed out that the proof of concept has been carried out for a pilot scale system from a few kW up to one MW. This is the basis for the scaling up of the process, which is required for commercial power plant and syngas production together with CO\({}_{2}\) capture. Finally, the review paper emphasised current research topics, highlighted research gaps, and identified opportunities for future applications of the biomass-based chemical looping gasification process. * 8. The authors of the eighth article ([PERSON]; [PERSON]; [PERSON]; [PERSON]; and [PERSON], from the Technical University of Darmstadt, Germany, and the University of Technology, Iraq) presented a detailed dynamic model of an existing parabolic trough solar power plant using the advanced process simulation software (APROS) [13]. The authors claimed that the developed model is the first in the literature that analyses the dynamic interaction of all parts of a parabolic trough solar power plant, including the solar field, thermal storage system, and power block (see Figure 3), and described the heat transfer fluid and steam-water  
on the hydrodynamic characteristics of the sieve tray. While increasing the inlet gas flow rate up to a certain value improved the liquid retention capacity, raising the inlet gas flow rate above this value did not increase the liquid holdup. There was a relationship between absorber performance and the liquid holdup on the sieve tray. The performance of the CO2 absorber increased due to the rise in liquid holdup caused by the increase in inlet flow rate. The interface between the gaseous and liquid phases varied with a change in gas flow rate.