# Economic Analysis of a Zero-Water Solar Power Plant for Energy Security
## 4 Conclusions  
This work presented the economic evaluation of a novel dry-cooling system based on earth-air heat exchangers (Earth-CAT system). The aim of the system is to eliminate the use of water for cooling purposes and support water-independent power systems that can operate securely under challenging future water-scarcity conditions. The proposed system was analyzed as part of a 20-MW solar power plant, and it was compared to both conventional air-based (dry) and water-based cooling systems.  
To analyze the economic performance of the plant, the TRR method was used. The levelized TRR and LCOE for an economic life of 25 years was found to be MEUR 40.48 and EUR 505.97/MWh, respectively. The total installed costs of the plant were EUR 13,728/kW. The use of Earth-CATs resulted in much higher levelized TRR and LCOE when compared to a plant using a conventional water-cooling system and approximately double the costs when compared to a plant using a conventional dry-cooling system. The proposed system is thus not currently competitive with conventional cooling systems.  
Earth-CATs could become competitive relative to a water cooling for a water cost higher than EUR 28/m3. In addition, a water cost of EUR 16/m3, result in a NPV and PBP of MEUR 9.51 and 17.4 years, respectively. Although this water cost seems high, when compared to current costs, forecasts of future costs in the power generation sector foresee even higher values. Nevertheless, for the system to become competitive with dry-cooling systems, further significant improvement should take place. From a technical point of view, improvements could include a closed-loop system to eliminate the dependency of the system on the ambient temperature. The number of pipes could be reduced though thermal performance improvement. An increase in the contact surface between the air and the PVC pipes or the study of the thermal response of the soil could a reduction in the number of pipes and land surface required. Such an optimized design could reduce the associated costs and make the system more competitive with existing cooling systems. Applying higher economies of scale would also play an important role in reducing the unit cost of the pipes. In addition, using more sophisticated economic methodologies such as using the Real Options Approach could enhance the accuracy of the analysis. Furtherresearch should include additional consideration of social and environmental benefits in terms of economic revenues, the implementation of energy policies, and a life cycle analysis of the overall plant.  
Conceptualization, F.P.; methodology, E.d.l.R.C., F.P.; validation, E.d.l.R.C.; writing--original draft preparation, E.d.l.R.C., F.P.; writing--review and editing E.d.l.R.C., F.P.; supervision, F.P. All authors have read and agreed to the published version of the manuscript.  
Fontain Petrakopoulou received funding from the Spanish Ministry of Science, Innovation and Universities and the Universidad Carlos III de Madrid (Ramon y Cajal Programme, RYC-2016-20971).  
All data are available upon request.  
The authors declare no conflict of interest.