# Economic Analysis of a Zero-Water Solar Power Plant for Energy Security
## 1 Introduction
According to [PERSON] (2015), water acquisition costs vary from USD 0.03/m\({}^{3}\) in India to USD 2.1/m\({}^{3}\) in the Middle East [9]. For example, [PERSON] and [PERSON] (2010) assumed a water cost of USD 0.26/m\({}^{3}\) to analyze the performance and costs of a coal power plant using wet and dry cooling with and without carbon capture and storage [31]. [PERSON] et al. (2016) studied the potential to approximate the use of air-cooled condensers to wet cooling technologies, indicating that the cost of dry cooling systems is 3.5-5 times higher. The difference of the two technologies reduces with the increasing value and price of the water [32]. In the present paper, the idea of cooling ambient air before it is used in the condenser of a thermoelectric plant is tested. The novel concept is based on earth-cooling air tunnels (Earth-CATs), inspired by smaller-scale EAHEs. With Earth-CATs, air driven by fans is cooled down in large-scale pipes buried underground at a depth where the temperature of the soil remains relatively constant [18]. The fans are powered by electricity generated in the plant, increasing, on the other hand, its parasitic power. In addition, the system emptied the exhaust of the air into the environment at the same temperature that it was introduced into the system. This technology has, thus, zero environmental impact. The performance of open-loop and horizontal Earth-CATs has been technically evaluated in Ref. [16] for a 20-MW solar power plant located in the Iberian Peninsula. In that study, the viability of the system was analyzed through computational fluid dynamics (CFD), and sensitivity studies of the geometric characteristics of the pipe (diameter, length, distance between pipes, thickness, and material) and the flow conditions of the air (velocity and inlet temperature) were realized. From the results, a cooling system for cooling the air from 35 \({}^{\circ}\)C down to 25 \({}^{\circ}\)C was proposed. This work estimates and evaluates the economic viability of the construction and operation of the proposed Earth-CAT system for use in a 20-MW solar tower power plant. The economic analysis of the system includes the cost of the PVC pipes of the Earth-CAT system, the fans, the filters, and dryers, together with the excavation, drilling, and O&M costs. The integration of the system in the power plant is evaluated using the total revenue requirement (TRR) method, obtaining both the total installed costs and the levelized cost of electricity (LCOE). The obtained results are compared to plants with conventional dry- and wet-cooling systems. Additionally, the NPV of the Earth-CAT system is calculated accounting for the benefits of zero-water use, and the results are compared to wet-cooling systems. A sensitivity study of the parameters influencing the total costs of the novel system is also presented. Finally, the environmental and social benefits are highlighted and future research steps for the implementation of Earth-CATs are proposed. Along with the use of renewable energy sources, this novel technology aims to contribute to sustainable and reliable power generation.