Excess energy recovery from a stand-alone PV system for freshwater production using RO unit: Techno-economic analysis

A techno-economic assessment of electricity and freshwater cogeneration system powered by a standalone solar PV system is investigated under weather conditions of Al-Khobar City, Kingdom of Saudi Arabia. The excess electricity generated by the PV system is used to operate Reverse Osmosis (RO) desalination unit using three alternative storage types: Battery, Water-Tank, and hybrid Battery/Water-Tank storage system. The RO desalination plant is mathematically modeled, and its hourly specific energy consumption is predicted by taking into consideration variations in pressure and temperature for one full year using Engineering Equation Solver (EES) software. Then, a MATLAB code is developed and used to optimize the PV array with the three alternative storage options. A novel indicator called the Shortage of Water Supply Probability (SWSP) is introduced and used to optimize the storage size and to ensure satisfying water demand. Results showed that the lowest levelized cost of water (LCW = 1.874 $/m³) is obtained when operating the RO desalination plant with a hybrid Battery/Water-Tank storage system. However, LCW is 2.892 and 2.647 $/m³ when battery or water-tank storage systems are used, respectively. From an environmental point of view, utilizing renewable energy to run the cogeneration system saved 131 tons/year of CO₂ emissions.