Optimisation of a Photovoltaic-Thermal (PV-T) panel for Desalination

Water stress levels are rising due to industrialisation and the increase in population. With the freshwater supplies depleting at a rate faster than the refreshment rate, there is a need to look into unconventional and sustainable sources of water. Desalination technology is a reliable solution for the future water requirement; however, it is an energy-intensive process. Desalination is mostly powered by fossil fuels and there is a need to move away from these. For this reason, a Photovoltaic Thermal (PV-T) powered desalination plant which uses the Multi-effect Distillation (MED) coupled with Mechanical Vapour Compression (MVC) technology, is investigated. A novel design of the PV-T module is used wherein a water reservoir is attached directly to the back of a PV module.The PV-T module produces electrical and thermal energy simultaneously, which are the required inputs to a MED-MVC desalination system. To have the desalination system working efficiently, it is important to predict the output from the module with respect to its design and the location weather parameters. To predict the output water temperature with varying weather conditions, a PV-T model was built using COMSOL Multiphysics. The model was validated using experimental data from the location of Dubai. It is found that the water outlet temperature and the total efficiency of the module vary with its inclination angle and flow rate of water through it. With a sensitivity analysis for the outlet water temperature and the total efficiency with respect to tilt angle and flow rate, optimum values for these parameters are obtained for summer and winter days. A maximum water outlet temperature of 91o C in summer and 58 o C in winter is predicted from the model, for the Dubai location, for these optimum values. Using experimental and simulated results, output parameters such as water outlet temperature at a given flow rate is predicted using dimensionless numbers which characterises the PV-T design and the surrounding environment that the system is placed in. The hot water from the PV-T array which consists of 400 PV-T panels is used to produce steam using flash evaporation, for thermal input to the MED vessel. Sensitivity analysis for the temperature and quantity of the hot water produced from the array showed that a maximum amount of steam of 1782 kg can be produced on a summer day with a water outlet temperature of 85 o C. Due to lower water outlet temperature in winter, heating elements should be used to raise the water temperature to 85 o C. The maximum amount of steam produced, as a result of 85 deg C water temperature, will lead to 6058 kg of distilled water per day when used as input to the MED with 4 effects. According to water requirement, additional steam can be produced by the MVC.