## 2 Technical Solution
### Definition of Scenarios
#### 2.2.1 Baseline Configuration: Scenario I  
The Gemasolar power plant, located in the municipality of Fuentes de Andalucia, Sevilla (37\({}^{\circ}\)33\({}^{\prime}\) N, 5\({}^{\circ}\)19\({}^{\prime}\) W [26]), is the first commercial-scale solar thermal power plant to utilize a central tower and molten salt thermal storage system [27]. This facility has been  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Scenario** & **Type of Storage** & **Integration of Energy Curtailment** \\ \hline I & & No \\ II & & Yes \\ \hline III & & No \\ IV & Solid particles & Yes \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of the scenarios studied.  
Figure 1: Distribution of electrical surpluses in the 2016–2021 period and their normalized values.  
selected as the basis for designing Scenario I in this study. The main characteristics of the plant are summarized in Table 2.  
The selection of Gemasolar is justified by its recognition as a standard reference for tower solar thermal plants with molten salt storage [13] and its extensive use in various studies where it has been considered a benchmark facility [28; 29; 30].  
In this plant, a field of mirrors, known as heliostats, reflects sunlight onto a receiver located at the top of a central tower. In the receiver, the concentrated heat is absorbed by a heat transfer fluid, which in this case is a molten salt mixture of 60% NaNO\({}_{3}\) and 40% KNO\({}_{3}\). This fluid is stored at high temperature in a dedicated tank. When required, the fluid transfers part of its heat--reducing its temperature--to a working fluid, specifically liquid water, which is converted into superheated steam. The generated steam is then used to produce electricity through a subcritical Rankine cycle [13; 31].  
These solar thermal power plants offer numerous advantages in electricity production, particularly their ability to generate dispatchable energy. This capability arises from the potential to store excess solar energy during the day, extending electricity production even during periods without solar irradiation, such as cloudy days or nighttime.  
However, one of the main challenges of these plants is the need to maintain the heat transfer fluid above 220 \({}^{\circ}\)C [31; 32; 33; 34] to prevent solidification, which necessitates the incorporation of an electric tracing system. Table 3 outlines the primary characteristics of the solar salt.  
A summary of the typical efficiencies achieved in each section of the plant, as reported in the literature, is presented in Table 4. This table includes the primary zones, excluding the heliostat field, as it is pre-simulated using SAM with a model specifically developed for the Gemasolar plant [35]. These efficiencies will be subsequently used in Section 3 for the plant simulation.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Characteristics** & **Amount** \\ \hline Number of heliostats & 2650 \\ Total reflective area (m\({}^{2}\)) & 306,658 \\ Tower height (m) & 140 \\ Receiver power (MW\({}_{\text{th}}\)) & 120 \\ Turbine power (MW\({}_{\text{e}}\)) & 19.9 \\ Storage size (hours of operation without sun radiation) & 15 \\ Storage tank dimensions (height \(\times\) diameter (m)) & 10.5 \(\times\) 23 \\ Mass of salts (tons) & 8500 \\ Generated electric energy (MW\({}_{\text{he}}\)/year) & 110,000 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Gemasolar project main characteristics [27].  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Value** \\ \hline Composition [by weight] & 40\% KNO\({}_{3}\) \\  & 60\% NaNO\({}_{3}\) \\ Specific heat capacity [J/kg\({}^{\circ}\)C] @ 300 \({}^{\circ}\)C & 1899 \\ Melting point [\({}^{\circ}\)C] & 220 \\ Maximum service temperature [\({}^{\circ}\)C] & 585 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Key properties of solar salt adapted from [31; 32].