# Sustainable Approach of Generating Water and Energy:
## 1 Introduction
Results indicated that the solar collector cost and the electricity price have a tremendous effect on the specific cost of water $/m\({}^{3}\).  
Among various desalination technologies, membrane distillation (MD) is a promising one because it operates at a lower temperature, often less than 100 \({}^{\circ}\)C. Several studies have been conducted on MD when it is integrated with other renewable energy such as solar energy [8; 12]. One of the drawbacks of utilizing solar energy in MD technology is increasing the cost as compared with a conventional plant that uses fossil fuel. Among other sustainable energy sources, geothermal energy in MD is anticipated to lower the cost of producing water. For example, [PERSON] and [PERSON] proposed a small-scale solar-powered membrane distillation system for a rural area [15]. The cost of water in their study was 18 $/m\({}^{3}\). Another study proposed by [PERSON] and [PERSON] investigated the performance of sweeping gas membrane distillation driven by solar energy for coastal households [16]. The proposed system aims for supplying island and coastal families with a flexible and consistently fresh water supply. Results show that the solar collector area has a great impact on the system's performance. The cost of desalinated water in their system was 18.34 $/m\({}^{3}\). [PERSON] and [PERSON] performed economic and energy analysis of a hollow fiber membrane distillation powered by solar energy [17]. Results indicated that the cost of producing water is 16.88 $/m\({}^{3}\). The rate of growth of energy demand and portable water will likely continue to rise due to population expansion. Thus, many studies were conducted recently aiming to develop an energy-efficient hybrid system that can provide a sustainable energy source for residential buildings and the desalination processes. For residential buildings for example, a techno-economic optimization of hydrogen power production by using solar and wind was proposed by [PERSON] et al. [18]. The proposed system had investigated different climate conditions in the Kingdom of Saudi Arabia. The minimum levelized cost of energy (LCOE) in the study was $1.208/kWh. Another study developed a combination of solar PV and wind hybrid energy system for residential buildings in four cities located in different climate zone in Saudi Arabia, namely, Yanbu, Sharurah, Hafar Albatin, and Riyadh [19]. The study results demonstrated that the proposed hybrid energy system is economically viable in Yanbu, attributable to high renewable energy penetration. The main contribution of this study was reducing greenhouse gases as well as lowering energy costs. Furthermore, an evaluation and techno-economic design of a hybrid energy system for residential buildings communities in Juhail were investigated by [PERSON] et al. [20]. This hybrid energy system comprises PV/Wind/Diesel and PV/Wind with battery storage with an end goal to meet the electric load demands for three housing compounds. Using HOMER software, the technical and economic feasibility of different configurations has been evaluated. The minimum average LCOE for three compounds was $0.217/kWh. The minimum LCOE was $0.25/kWh for PV and wind turbine, coupled with energy storage, that provides 100 percent renewable energy penetration. Moreover, the ideal proposed system estimated to save 2800 tons of carbon dioxide annually. In addition, a hybrid system that consisted of Solar PV, WT, and a diesel generator was designed for a village in Saudi Arabia [21]. The proposed hybrid system expected to replace eight diesel types that were generated to meet the village's electric loads. The optimized results show that the energy cost is $0.212/kWh with 35% renewable energy penetration. Other studies minimized energy usage in a residential building using phase change material (PCM). Results from these studies revealed that energy usage associated with air conditioning dropped by 43.2% [22,23]. A cogeneration system that aims to decentralize water/electricity is proposed in this study.