# Economic Analysis of a Zero-Water Solar Power Plant for Energy Security
## 3 Results and Discussion
### Environmental and Social Considerations  
The environmental and social benefits of the Earth-CATs are not economically evaluated here, but a model to quantify them, in terms of revenues or funding by governments or other public administrations, would allow for a more thorough economic analysis. The social and environmental benefits of avoided water are significant not only in CSP plants but also in all thermoelectric plants, even more so if the efficiency of the power plant remains constant for zero-water operation, that is the case with Earth-CATs. Earth-CATs enjoy all the benefits of dry-cooling systems and more. The water saved would be available for other sectors, such as residential use or irrigation. The cooling system eliminates thermal and chemical environmental impacts of water-cooled power plants. Moreover, it allows for a reliable power generation by making the plant not vulnerable to water shortages and reducing the dry-cooling plant's dependency on the  
Figure 4: Effect of the water cost on the LCOE of the studied plant using wet cooling and comparison with the plant using Earth-CATs (dashed line). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Pipe Number** & **Pipe Unit Cost** & **Water Cost** & **NPV** & **PBP** \\ (-) & **(EUR/m)** & **(EUR/m3)** & **(MEUR)** & **(Years)** \\ \hline \multirow{4}{*}{10,965} & \multirow{4}{*}{30.76} & 1 & \(-\)139.59 & – \\  & & 5 & \(-\)99.83 & – \\  & & 10 & \(-\)50.14 & – \\  & & 15 & \(-\)0.44 & – \\  & & 20 & 49.25 & 13.9 \\ \hline \multirow{4}{*}{10,965} & \multirow{4}{*}{25.00} & 1 & \(-\)120.64 & – \\  & & 5 & \(-\)80.89 & – \\  & & 10 & \(-\)31.19 & – \\  & & 15 & 18.50 & 16.2 \\  & & 20 & 68.20 & 12.1 \\ \hline \multirow{4}{*}{8000} & \multirow{4}{*}{30.76} & 1 & \(-\)99.15 & – \\  & & 5 & \(-\)59.40 & – \\  & & 10 & \(-\)9.70 & – \\  & & 15 & 39.99 & 13.5 \\  & & 20 & 89.69 & 10.1 \\ \hline \multirow{4}{*}{8000} & \multirow{4}{*}{25.00} & 1 & \(-\)85.33 & – \\  & & 5 & \(-\)45.57 & – \\ \cline{1-1}  & & 10 & 4.12 & 17.8 \\ \cline{1-1}  & & 15 & 53.82 & 11.8 \\ \cline{1-1}  & & 20 & 65.82 & 10.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Influence of the water cost on the NPV of the Earth-CAT system. ambient temperature. These benefits would lead to sustainable plants with close to zero environmental implications. Therefore, the benefits of avoiding water use for cooling purposes must be analyzed with a life cycle assessment (LCA) throughout the whole life cycle of the plant. As mentioned, the cost of water should account for all relevant externalities: all of the required steps to make cooling water available to the arid region of the power plant (e.g., piping, desalination, transport supported by fossil or alternative fuels), the environmental impact on the qualitative and quantitative characteristics of the water/air used (the air used in air-cooling systems is returned to the environment at a higher temperature), as well as to account for the power reduction related to the use of high-temperature ambient air or cooling water availability shortages over the annual operation of the plant. A detailed LCA could lead to a more accurate estimation of annual savings due to the water avoided. Together with the potential governmental or other public administration support for sustainable operation, Earth-CATs could become more favorable economically. An important environmental concern of the Earth-CAT system that must be mentioned is the great volume of PVC material that would be required for the production of the pipes. Comparing different materials, not only based on their heat transfer properties and costs but also based on their environmental impact, would contribute to the optimization of the system. For example, compared to metal materials such as stainless steel, PVC has a higher impact because it takes a much longer time to degrade, it has a lower recycling rate, and may have a lower service life. On the other hand, it may consume less energy during its production and transportation [53].