# Evaluation of the Coupling of a Hybrid Power Plant with a Water Generation System
## 1 Introduction
The plant started operation in 1968 with the aim of averting water shortages in Windhoek, Namibia. However, throughout the years, its treatment train has been continuously evaluated and upgraded to find the most effective processes and barriers for safe drinking water [35]. More recent DPR projects include the Wichita Falls River Road and the Big Spring (2013) facilities, both located in Texas, USA [36]. The first began its operation in July 2014 as an emergency potable water supply in response to severe drought conditions. The latter has been operating since 2013, blending treated and raw water resources before their further processing and distribution within the region. In Spain, renewable energy and water reclamation systems are increasing, not only due to technological developments but also due to the increase of political commitment and awareness of the population [37]. The Spanish energetic scenario has changed during the past years, evolving from a centralized generation system based on fossil energies, towards a more efficient system of distributed generation [38]. In terms of installed solar capacity, Spain had 1,950 MW shared among 43 facilities by the end of 2012. Most of the plants use parabolic troughs, while three plants use central receivers and one Fresnel reflectors [37]. However, the wider adoption of RES suffered a significant slowdown during several years, mostly as a consequence of the recent economic crisis and the technological immaturity and over-capacity of the system. It was only in 2018 that the renewable sector started to recover, driven by energy bids and costs reduction, which resulted in a 70% growth, with respect to 2007 [39]. The published Plan of Renewable Energy predicts that CSP plants will be generating 3% of the Spanish electricity by 2020 [40]. Furthermore, the lack of rain in Spain, along with the rising temperatures, has resulted in a reduction on the availability of freshwater reservoirs, leading to emergency levels especially in several areas of the Iberian Peninsula [41]. During the last decade, several aspects have enhanced the development of water reuse at the national level, primarily regulated by the Royal Decree 1620/2007 of December 7 th [42]. This Decree establishes the basic quality requirements of water for different non-potable applications in Spain. Since 2008, the country has been working on the improvement of the treatment trains to meet current standards. Nowadays, the most common treatment trains in any reuse application in Spain include specific disinfection methods such as physical-chemical treatments followed by sand filtration together with ultraviolet (UV) radiation or chlorination [43]. The potential combination of hybrid power plants with water recycling can constitute a unique and innovative alternative for emerging energy/water global problems; yet an important research gap exists in this field. This paper studies the design, thermodynamic and economic characteristics of a system coupling a hybrid solar/biomass plant (20 MW central receiver power plant with a biomass support system) with an advanced wastewater treatment facility. It must be mentioned that this study constitutes a simplified, steady-state analysis that does not consider the hourly dynamic behavior of the plant. The main objective is to reveal the potential of the continuity of energy supply, the economic viability and the contribution of renewable energy through a detailed simulation and analysis of the proposed plant. This project is designed to be installed in Fuentes de Andalucia, a town located 57 km away from the Spanish province of Seville, to evaluate the viability of this kind of plants in one of the most water and energy demanding areas of the Iberian Peninsula. The solar block consists of a heliostats field that concentrates the incoming radiation towards a fixed receiver located at the top of a solar tower. Molten salts passing through the central receiver work as the heat transfer fluid collecting the thermal energy used to generate electricity.