# Evaluation of the Coupling of a Hybrid Power Plant with a Water Generation System
## 1 Introduction
CSP-geothermal hybrids take advantage of the thermal energy beneath the surface of the Earth to produce electricity. The exact way to use this energy depends on the kind of the geothermal resource and the temperatures reached [14]. Located in Nevada (USA), Stillwater consists of a triple hybrid power plant that integrates 33.1 MW of geothermal energy with 26.4 MW of photovoltaic power and 2 MW of solar thermal capacity [15]. Furthermore, CSP-wind hybrids have been increasing their potential as an excellent renewable alternative for energy generation. Wind is available all over the world, and its low cost makes it attractive for hybridization processes [16]. However, the combination of wind energy with CSP is a field that has not being widely explored. This is primarily because the two renewable energies do not have great synergy in terms of successful share of infrastructure, contrary to other thermal energy sources [17]. Biomass also constitutes an attractive choice for the hybridization of CSP plants for continuous operation. Early proposals to combine CSP with waste materials using dish technology were briefly discussed in the 1980s but were not further considered for financial and technical reasons [18]. After approximately two decades the first operating commercial CSP-biomass plant, Termosolar Borges, was constructed in Lleida, Spain [6]. The plant has a capacity of 22.5 MW and an annual electrical production of 98,000 MWh. It has been in operation since December 2012, using the mature parabolic trough technology with thermal oil as the working fluid [19]. Despite the fact that biomass does not occupy a very significant place in the current renewable energy use in the country, especially if compared to wind and solar technologies, in 2011 biomass was used to generate 11.25% of the electricity in Spain [20]. Andalusia currently has a significant biomass wealth, largely originated from the olive cultivation and its surrounding industry. Olive oil industries produce 77.25% of the residual biomass, making the olive sector the greatest producer of biomass within this region [21]. At present, there are 18 electric biomass and cogeneration power plants in Andalusia with a total installed power of 257.48 MW and 19 biogas plants with 30.75 MW of power [22]. Several studies have analyzed the hybridization of parabolic trough plants with biomass [23; 24; 25]. Fresnel technology has also been investigated for the hybridization with biomass and other waste materials [24]. A significant advantage of these systems is the relatively high steam temperatures of up to 500 \({}^{\circ}\)C, which lead to higher conversion efficiencies. Nevertheless, no reference hybrid plants exist yet [25]. From the great variety of possible CSP-biomass hybridizations, solar tower and gasification have been reported to result in energy efficiencies of up to 33.2% [26]. However, no project has dealt with the use of these technologies within the same facility [27]. Increasing water demand, limited freshwater, and climate change make water reuse a necessary step to meet global water demand. Some recent studies on the combination of hybrid plants with desalination for water generation can be found in the literature [28; 29; 30]. In this work, the energy/water system is supported by a wastewater purification facility. Today, plans of wastewater management include not only the generation of sufficiently purified water to be returned to a natural water source, but also the further reuse of used water in downstream processes [31]. For this purpose, sewage undergoes different physical, chemical and biological processes to reduce pollutants according to its downstream use [32]. In the case of potable water, it is obtained by means of two fundamental procedures: Indirect (IPR) and Direct Potable Reuse (DPR) [33]. The major difference between these wastewater treatment plants (WWTP) is the use of an environmental buffer between the spillage and the collection point of water. The Goreangab Reclamation Plant has been a pioneer in DPR [34].