A symmetric bifacial photovoltaic-membrane distillation system for simultaneous freshwater and electricity generation

A novel three-channel membrane distillation (MD) unit coupled with bifacial photovoltaic (PV) system (two monofacial PV cells), intended to deliver freshwater and electricity at the same time, is examined here through joint experimental testing and numerical modelling. Two PV modules (200 mm × 100 mm) were considered in the numerical model (on the upper and lower faces of the MD unit), whereas two electric heaters with a total power input of 95.4 W were used experimentally to reproduce the thermal behavior of the upper and lower PV cells. The numerical predictions showed good agreement with the measured data, with a mean relative error below 3.5%. Under representative daytime steady-state solar irradiance conditions, the simulated quantities comprised permeate flux, thermal efficiency of the system, gained output ratio (GOR), specific energy consumption (SEC), and the temperature polarization coefficient (TPC), defined as the ratio of the transmembrane temperature difference to the corresponding bulk-fluid temperature difference. The productivity was markedly higher for the bifacial system: as velocity climbed from 0.01 to 0.05 m s −1 , its permeate flux moved from 8.52 to 21.18 kg.m −2 .h −1 , compared with 5.76–14.66 kg.m −2 .h −1 recorded for the monofacial system. GOR likewise reached 0.39 for the bifacial unit and 0.49 for the monofacial one, while a parallel rise in TPC pointed to a stronger thermal driving force. The peak thermal efficiency rose to 72.3% for the bifacial system versus 64.7% for the monofacial system. The SEC decreased from 1562.11 to 468.54 kWh.m −3 for the bifacial system and from 949.13 to 365.17 kWh.m −3 for the monofacial system as the feed flow velocity increased. For the single PV module tested, the peak output power reached 6.93 W (346.5 W.m −2 ) for the bifacial system and 3.82 W (191.0 W.m −2 ) for the monofacial system. The results demonstrate the potential of the integrated PV-MD configuration for simultaneous freshwater and electricity generation, while the relatively high SEC indicates the need for further optimization of heat recovery and energy utilization.