## 2 Methodology  
A numerical simulation under a system advisor model (SAM) based on direct normal irradiance (DNI) with real and satellite data was carried out to optimize the parameters characterizing these performances. The influence of these parameters on each other made it possible to choose an optimal CSP configuration. In the research, SAM software (Version 2017.9.5, National Renewable Energy Laboratory. Golden, CO, USA, 2017) was used. The SAM is a software to model and simulate the performance of energy parameters and the economics of systems to facilitate the decision-making process in the field of renewable energies [25]. The solar radiation intensity is an important factor in the evaluation of CSP plants. Direct normal irradiance is the amount of direct normal solar radiation received per unit area. There are three techniques to assess the evolution of DNI over time for a given location [26; 27]. Optimization of the design of the heliostats field is a trade-off between optical performance and cost, so this process includes both optical and economic analysis. This implantation can be performed by determining the optimum values of the radial spacing \(\Delta R\) and the azimuth spacing \(\Delta A_{Z}\). There are various optimization procedures to establish these two geometric position parameters. One of the most effective procedures is the radial offset arrangement [28]. The evaluation of the radial and azimuthally distance can be evaluated by empirical Equations (1) and (2) [29]. These parameters also depend on the angle (\(\alpha\)) between the heliostat, the ground, and the tower, as shown in Figure 1[30; 31],  
\[\Delta RHM=63.0093-0.587313\cdot\theta+0.018423909\cdot\theta^{2}+\left(2.808 733-0.1480498\cdot\theta+0.001489201\cdot\theta^{2}\right)\cdot\cos\alpha \tag{1}\]  
\[\Delta A_{Z}WM=2.46812-0.0401054\cdot\theta+0.000923594\cdot\theta^{2}+\left(0.17344593-0.009112590\cdot\theta+0.00012761\cdot\theta^{2}\right)\cdot\cos\alpha \tag{2}\]  
where \(\Delta R\) is the radial distance between heliostats (m), \(HM\) is the heliostat height meters, \(\theta\) is the receiver elevation angle from heliostat, \(\alpha\) is the heliostat loft angle in degree, \(\Delta A_{Z}\) is the azimuthal distance between heliostats (m), and \(WM\) is the heliostat width meters (m). Table 1 shows the location parameters for different regions. The size of the heliostat field influences the optical performance and depends on the desired power and temperature of the heat transfer fluid at the output. The total incident thermal energy is given by the following Equation (3):  
\[Q_{h}\ =\ I_{d}\cdot A_{h}\cdot N_{h} \tag{3}\]  
where \(I_{d}\) is the direct normal irradiation, \(A_{h}\) is the surface of the heliostat, and \(N_{h}\) is the number of the heliostat, and 144 m\({}^{2}\) was considered the surface of the heliostat field. The efficiency of the field \(\eta_{h}\) is defined by the following Equation (4):  
\[\eta_{h}=\frac{Q_{rec}}{Q_{inc}}=\frac{Q_{rec}}{I_{d}\times A_{h}\times N_{h}} \tag{4}\]  
where \(Q_{rec}\) is the heat flow of the receiver and \(Q_{inc}\) is heat flow of the incident. The efficiency is calculated considering losses due to different effects (cosine, shading, blocking, overflow, reflection, dispersion) and it is given by the following Equation (5) [32]:  
\[\eta_{h}=\eta_{cos}\cdot\eta_{omb}\cdot\eta_{bloc}\cdot\eta_{deb}\cdot\eta_{ ref}\cdot\eta_{disp} \tag{5}\]  
where \(\eta_{cos}\) is the losses due to cosine effect, \(\eta_{omb}\) is the losses due to shading effect, \(\eta_{bloc}\) is the losses due to blocking effect, \(\eta_{deb}\) is the losses due to overflow; \(\eta_{ref}\) is the losses due to reflection and \(\eta_{disp}\) is the losses due to dispersion. The model of the receiver of the present study is an external type. It consists of a large number of vertically disposed pipes through which a heat transfer fluid is pumped in the vertical direction. Inside the pipe three types of heat transfer are identified (convection, conduction, and radiation) and