# Sustainable Approach of Generating Water and Energy:
## 1 Introduction  
Energy and water are precious resources and are essential for human well-being. Currently, around 759 million people lack access to energy [1], and 771 million do not have access to clean potable water [2]. The shortfall will widen owing to climate change and global population growth, which is anticipated to raise water and energy consumption by 50% and 100%, respectively, by 2050 [3]. The world's key supplies of energy and water are deteriorating and diminishing at an astounding level, which exacerbates this issue makes it even worse shortly. Even though desalination provides a long-term solution to compact the water shortage problem, most desalination procedures are energy-intensive which puts additional strain on the current energy supply. This necessitates the development of renewable-based, long-term desalination technologies, particularly in distant areas where energy generation from renewable sources has significant economic and environmental consequences. Arab Gulf countries seek to decarbonize their energy sectors by shifting to clean energy [4]. The path to reduce the reliance on fossil fuels and decarbonize the energysector is possible in the gulf regions due to massive solar energy resources. Saudi Arabia is among the top 15 countries globally that possess enormous potential in PV power generation [4]. With this, Saudi Arabia stated a clear goal to move away from conventional power generation plants that rely on fossil fuels to more sustainable options. Saudi Arabia aims to decarbonize half of the energy sector by boosting the renewable energy penetration by 2030 [5]. The transitions to renewable energy cannot be attained without addressing the high energy demand in the residential buildings and desalination industry, which consumes a large portion of the total energy produced in Saudi Arabia (KSA). Energy consumption for buildings in KSA accounts for 80% of the total electricity, with 50% consumed primarily by the residential sector [6]. In addition, energy consumption for desalination accounts for roughly 20% of the overall energy consumption [7]. A hybrid photovoltaic thermal energy system (PVT) is a promising technology that can provide heat and electricity, simultaneously. Due to the high sun radiance in water-scarce areas, solar energy is also an effective energy source for desalination. Most existing desalination systems, including multi-effect distillation (MED), reverse osmosis (RO), and membrane distillation (MD), may be powered by solar collectors either in form of electric energy, heat or both [8]. Among these technologies, direct contact membrane distillation (DCMD) has great potential due to its capability to be combined with low-grade solar thermal energy. For example, [PERSON] et al. experimentally investigated the possibility of integrating a concentered PVC with DCMD [9]. The results of the integrated system were promising, and their system was capable of generating power and purifying water simultaneously. [PERSON] et al. proposed a water desalination system that includes a DCMD and a solar pond [10]. Results show that increasing the feedwater temperature improved the produced water mass flux. [PERSON] et al. proposed a solar-assisted direct contact membrane distillation (DCMD) system with unique energy recovery techniques that can operate 24 h a day [11]. The specific thermal energy usage in the proposed system was 43% lower as a result of utilizing heat recovery. Another study proposed by [PERSON] et al. integrated a heat pipe solar system with DCMD [12]. The performance of their system was tested experimentally, and results indicated that the heat pipe solar system was capable of providing all of the required thermal energy for DCMD. In addition, a multivariable optimization technique of a combined solar power system with DCMD was presented by [PERSON] et al. [13]. [PERSON] et al. proposed a decentralized water/electricity degeneration system using a vacuum multi-effect membrane distillation system assisted with a concentrated photovoltaic thermal system [14].