Performance analysis of a flexible PV-MD-Electrolysis system for co-production of ultrapure water and green hydrogen

This thesis investigates membrane distillation (MD) as a route to produce ultrapure water from saline/brackish feeds and analyses its thermal integration with a photovoltaic (PV) module and an electrolyser for co-production of freshwater and green hydrogen. A dual modelling framework is developed: a 0D physics-based analytical model and a 2D Simulink model that closes the thermal balance between PV rear side losses and the MD feed channel, linking distillate flow to the electrolyser’s water demand. The work also offers a critical review and operating guidelines for pre/post-treatment and membrane cleaning across diverse industrial effluents. Simulations considering a flat sheet DCMD module show that the axial temperature field governs the vapor pressure gradient and thus flux: at 40 °C and 60 °C with a feed velocity of 0.1 m/s, fluxes of 3.1 and 9.2 kg h-1m-2 are obtained, with a peak near the feed inlet. A parametric study identifies an optimal feed velocity of 0.3 m/s, maximizing yield per energy (3.76 kg h-1m-2 at 40 °C) by limiting pressure drop while enhancing shear induced antifouling. Salt comparison indicates the productivity hierarchy KNO3 > NaNO3 > NaCl, consistent with water activity and the nonlinear temperature dependence of flux. PV rear side heat losses provide useful input to MD (485 Wm-2 at 40 °C and 192 Wm-2 at 60 °C), with a trade-off as cell temperature rises. In the simulations conducted at 100 g/L NaNO3 and the optimal velocity across 40-70 °C, the AEM electrolyser (50 cells, 144 cm²) delivers 0.036-0.187 kg/h of hydrogen requiring 1.85-9.54 kW from 40-70 °C. At system level, overall PV-MD-EL system efficiency is 50-60% , showing a concave-down trend due to PV thermal penalties. With appropriate thermal integration, particularly through recovery of electrolyser waste heat, MD can meet the stack’s water demand and deliver a meaningful surplus, thereby simplifying system operation by removing the need for dedicated cooling infrastructure.