Experimental and numerical study of passive solar membrane distillation driven by the heat recovered from a photovoltaic module

This thesis investigates the possibility of coupling the photovoltaic (PV) technology with an innovative desalination technique based on passive multi-stage distillation, which is driven by low-temperature heat. The term "passive" distillation is here intended as a process that relies only on evaporation and capillarity without requiring any mechanical or electrical devices. The aim is to demonstrate the possibility to cogenerate both electricity (from the PV module) and distilled water (from the passive distiller). Instead of exposing the distiller to direct sunlight, the necessary heat is recovered from the back side of the PV module. Therefore, other than the cogeneration of electricity and distilled water, a synergic effect can be eventually achieved, since a gain in efficiency of the PV is sought due to the reduction of the panel’s temperature. Laboratory experiments are carried out to evaluate the performance and thermal properties of both PV and desalination technologies. Both 1D and 3D modelling approaches are used for interpreting the observed experimental results. In the thesis, also the prototyping work made of design and manufacturing steps is presented, which followed simplicity and cost reduction as main guidelines. The result is a desalination rate of up to 2 l/m2h under one sun (1000 W/m2) constant irradiation, and around 1.3 l/m2h during continuative operation along five consecutive days. Furthermore, a relative photovoltaic efficiency gain of 4.5% is obtained by reducing the panel’s temperature by 8 °C. The results are promising for a hypothetical scale-up of the prototype; in fact, the possibility to implement a high-yield, low-cost and easy to use device able to cogenerate both electricity and distilled water by PV and membrane distillation process has been demonstrated. Despite some current issues with reliability and long term performance, this work paves the way to floating installations made of such passive cogeneration units, which could rapidly provide energy and safe water in off-grid areas, especially in case of emergency conditions (e.g. after natural disasters).