# Techno-Economic Analysis of a Solar Thermal Plant for Large-Scale Water Pasteurization
## 4 Cost Estimation Model
### Capital Costs  
The estimation of the capital cost for the simulated solar thermal pasteurization plant can be obtained using either the typical cost estimations methods available in the literature or the communicated costs from possible suppliers.  
First, the cost analysis proposed by [PERSON] et al. [47] has been considered for the costs of the tank, heating coils, pumps and gas burner. The overall installation cost, which includes direct and indirect expenses, for each component can be estimated as  
\[C_{BM}=C_{p}^{0}\left(B_{1}+B_{2}\,F_{M}\,F_{P}\right)\frac{I_{2018}}{I_{2001}}, \tag{22}\]  
where \(B_{1}\) and \(B_{2}\) are coefficients depending on the type of component, while \(F_{M}\) and \(F_{P}\) are corrective factors related respectively to construction materials and operating pressure. While for the heating coils and pumps these parameters are provided separately (see Table 1), the cost of the tank and gas burner is given as a function of \(F_{BM}=B_{1}+B_{2}\,F_{M}\,F_{P}\). The ratio \(I_{2018}/I_{2001}\) is used to take into account the changing value of money over time, and allows to estimate the current capital expenses using the purchase cost curves valid for a reference year (i.e., 2001 in this case [47]). The values \(I_{2018}\) and \(I_{2001}\) are obtained based on the chemical engineering plant cost index (CEPCI) of 567.5 (for 2018) and 397 for the reference year. The base cost \(C_{p}^{0}\) of each component has been evaluated as  
\[\log C_{p}^{0}=k_{1}+k_{2}\log A+k_{3}\big{(}\log A\big{)}^{2}, \tag{23}\]  
where \(k_{1}\), \(k_{2}\) and \(k_{3}\) are factors depending on the equipment type, while \(A\) is a parameter related to the size of the component (see Table 1).  
Second, the cost of the solar field has been considered equal to 335 EUR m\({}^{-2}\), as provided by the manufacturer (Sky Pro 18 Advanced CPC, by Kloben Industries). The unit price of the plate heat exchanger, instead, has been considered to range from 506 EUR m\({}^{-2}\) to 230 EUR m\({}^{-2}\) depending on the considered size of the plant, as indicated by a possible supplier (T25-B  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline
**Component** & \(\mathbf{k_{1}}\) & \(\mathbf{k_{2}}\) & \(\mathbf{k_{3}}\) & \(\mathbf{B_{1}}\) & \(\mathbf{B_{2}}\) & \(\mathbf{F_{P}}\) & \(\mathbf{F_{M}}\) & \(\mathbf{F_{BM}}\) \\ \hline Tank & 4.8509 & \(-\)0.3973 & 0.1445 & - & - & - & - & 1.10 \\ Heating coils & 4.1884 & \(-\)0.2503 & 0.1974 & 1.63 & 1.66 & 1.00 & 1.00 & - \\ Pumps & 3.3892 & 0.0536 & 0.1538 & 1.89 & 1.35 & 1.00 & 1.00 & - \\ Gas burner & 2.0829 & 0.9074 & \(-\)0.0243 & - & - & - & - & 2.19 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Coefficients used for the capital cost evaluation of some components of the solar thermal pasteurization plant. Note that, for the tank and gas burner, \(F_{BM}\) is directly provided [47].  
Figure 5 shows the contribution of the different components to the overall capital cost of a plant with 250 L s\({}^{-1}\) capacity and different solar multiples (SM = 0.5, SM = 1.0, SM = 2.0 and SM = 3.0). In all the four cases, the duration of the thermal energy storage has been considered equal to 12 h. The most expensive component of the facility is found to be the solar field, which contributes for a percentage between 49.3% and 85.2% to the total capital cost. Other important contributions to the total cost are represented by the thermal storage system and gas burner, while the economizer and pumps account for a minor share.