## 4 Economic Evaluation  
In this section, the EL-FC system is economically analyzed for comparing the usefulness of this from a different point of view, which is followed by the economic comparison with the conventional system with a battery. Some parameters have been considered such as the Levelized Cost of Energy (LCOE), which is used for evaluating the cost of the system; the LCOE value can be calculated through the [PERSON] et al., equation [59; 60]:  
\[\text{LCOE}=\frac{\text{IC}\cdot\text{CRF}+\text{OM}}{\text{EO}} \tag{8}\]  
where IC is the installation cost, OM is the operation and maintenance cost, CRF is the capital recovery factor, and EO is the average annual overall energy output from the system. The CRF factor is calculated according to the next equation:  
\[\text{CRF}=\frac{(1+\text{i})^{\text{n}}\cdot\text{i}}{(1+\text{i})^{\text{ n}}-1} \tag{9}\]where p is the interest rate and n is the amortization period. In this case, the interest rate is 10% and the amortization period is twenty years. Furthermore, two economic parameters have been calculated for clarifying the financial part. On the one hand, the Net Present Value (NPV) is an economic tool used to equate the total cost of a project over a specified period to the total cost today, taking into account the time value of money. On the other hand, the Internal Rate of Return (IRR) is a financial parameter to estimate the profitability of potential investments [27; 61]. \[\text{NPV}=\sum_{0}^{n}\frac{C}{\left(1+\text{i}\right)^{n}} \tag{10}\]  
where C is the net cash flow; i and n were previously defined. The technical specification of the photovoltaic panel, electrolyzer, fuel cell, and battery were mentioned in the corresponding section of each equipment, and the economic specifications are summarized in Table 2. The hydrogen tank investment was calculated in order to measure the amount of carbon steel required (see Equation (11)). The equipment investment is shown in Table 3, and the total investment of the system is similar to other reports [18; 62]. \[\text{m}=\rho\cdot\text{S}\cdot\left(\frac{4\cdot\text{V}}{\text{D}}+1.04\cdot \text{D}^{2}\right) \tag{11}\]  
where m is the amount of carbon steel, \(\rho\) is the carbon steel density, S is the thickness, V is the volume, and D is the diameter of the tank. \begin{table}
\begin{tabular}{c c c} \hline \hline
**System** & **Component** & **Data Specification** \\ \hline \hline  & **Photovoltaic Panel** & \\  & Size (Wp/module) & 109 \\  & Lifetime (years) & 20 \\  & Capital Cost (\(\mathbf{\xi}\)) & 3052 \\  & O\&M Cost (\(\mathbf{\xi}\)/year) & 5 \\  & **Electrolayer** & \\  & Size (cm\({}^{2}\)) & 50 \\  & Lifetime (years) & 20 \\  & Capital Cost (\(\mathbf{\xi}\)) & 5493 \\  & O\&M Cost (\(\mathbf{\xi}\)/year) & 10 \\  & **Fuel Cell** & \\  & Size (W) & 1013 \\  & Lifetime & 15,000 \\  & Capital Cost (\(\mathbf{\xi}\)) & 2436 \\  & O\&M Cost (\(\mathbf{\xi}\)/year) & 4 \\  & **Hydrogen Tank** & \\  & Size (m\({}^{3}\)) & 0.91 \\  & Lifetime (years) & 20 \\  & Capital Cost (\(\mathbf{\xi}\)) & 1846 \\  & O\&M Cost (\(\mathbf{\xi}\)/year) & 3 \\ \hline  & **Photovoltaic Panel** & \\  & Size (Wp/module) & 106 \\  & Lifetime (years) & 20 \\  & Capital Cost (\(\mathbf{\xi}\)) & 3562 \\  & O\&M Cost (\(\mathbf{\xi}\)/year) & 6 \\
**Conventional** & **Battery** & \\  & Nominal Capacity (kWh) & 32.3 \\  & Lifetime (years) & 1 \\  & Capital Cost (\(\mathbf{\xi}\)) & 7273 \\  & O\&M Cost (\(\mathbf{\xi}\)/year) & 12 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Economic and technical specification for the components of EL-FC/conventional system. Once the equipment investment is known, the rest of the investments are calculated by the Vian Method (see Table S3 in Supplementary Materials); following it, the total investment is 15803 \(\upcels\) and 13348 \(\upcels\) for the EL-FC system and conventional system, respectively. The datasheet of the battery indicates that the efficiency of 90% is only maintained for a year of use.