# Economic Analysis of a Zero-Water Solar Power Plant for Energy Security
## 1 Introduction
It was found that the EAHE systems were not financially viable, in spite of the energy savings when compared to conventional systems. [PERSON] et al. (2020) realized an economic analysis of an EAHE system in severely cold regions and compared it to a conventional air-handling unit [23]. They obtained a static PBP of 2.08 years for an IRR of 8%, in addition to other economic and environmental benefits. Excavation work charges were USD 732.9 for one day, each pipe with a diameter of 0.25 m and a length of 36 m had an estimated cost of USD 3225, the blower had a cost of USD 109.9, the heat recovery unit set USD 879.5, and accessories, such as vents and indoor pipes, were estimated to cost USD 703.6. [PERSON] et al. (2021) evaluated the combination of EAHE with indirect evaporative cooling to reduce the water consumption of evaporative cooling systems, in arid and semi-arid regions [24]. Their analysis estimated a total investment of USD 2500, achieving electricity (in summer) and natural gas (in winter) savings of USD 112 and USD 104, respectively. Additionally, a PBP between 5.5 and 6.4 years was estimated. A methodology to minimize the costs of a GCHP system was presented by [PERSON] and [PERSON] (2014) by calculating the NPV for a 20-year lifetime with an interest rate of 6% [25]. The excavation and drilling costs were CAD 42 and CAD 40 per meter, respectively, while the piping cost was CAD 42 per meter for a standard diameter used in such applications. With the objective of minimizing the costs, their optimal design showed that 62% of the total cost was related to operating costs (i.e., energy consumption for heating) and 38% was related to the initial investment (i.e., heat pump, drilling, excavation, and pipes). [PERSON] et al. (2020) studied the economics of a GCHP system producing air conditioning or heating together with hot water [26]. Assuming a 20-year lifetime, a discount rate of 4%, and an annual performance degradation of 1.5%, they found that the initial investment for a residential building was compensated by electricity savings after an operational period of three years. Other published studies in literature focused on the cost of the pipes that seem to be the most influential parameter in the economic performance such systems. [PERSON] et al. (2011) analyzed the PBP of an EAHE system for the Italian climate and estimated excavation and refilling costs for different types of soil and pipe materials [27]. For a PVC pipe and unleashed soil, the excavation and refilling costs were estimated equal to EUR 2.4/m3 and EUR 2.0/m\({}^{3}\), respectively. The cost of plastic pipes with diameters of 160 mm, 315 mm, and 400 mm was estimated to be EUR 8.0/m, EUR 28.0/m and EUR 44.0/m, respectively. An additional 20% was assumed for the installation of the tubes, while the costs of metallic and concrete pipes were estimated to be much higher. They concluded that EAHEs are economically viable (PBP of 5-9 years) only when excavation and refilling works are easy and cheap. [PERSON] et al. (2017) listed the cost of pipes used in their simulations of shallow geothermal energy depending on dimensions and materials [28]. They considered a price of EUR 1.92/m for a PVC-U pipe with a diameter of 32 mm and a thickness of 2.4 mm, and a price of EUR 4.65/m for a pipe with a diameter of 63 mm and a thickness of 4.7 mm. Additionally, they expected an average service life of 70 years. [PERSON] et al. (2016) considered a PVC pipe cost of USD 61.92/ft (USD 203.15/m) for a 24 in (0.61 m) diameter together with a 50-year service life and a repair cost of USD 1000 per year and per mile [29]. This literature review is complemented with published studies on the cost of water use in power generation. In a typical coal power plant in the United States, power generation will start to be curtailed when the price of water exceeds USD 1.22/m\({}^{3}\) and it will shut down for a price of USD 1.70/m\({}^{3}\)[30].