Experimental and numerical Investigation of an integrated PVT–TEC–VMED system for off-grid freshwater production

Existing off-grid solar desalination systems are often constrained by inefficient thermal-energy utilization, inadequate waste-heat recovery, and unstable operation under fluctuating solar conditions, resulting in reduced freshwater productivity and overall system efficiency. To address these limitations, this study experimentally evaluated a thermally integrated hybrid freshwater production system. The system integrates a photovoltaic–thermal (PVT) collector, a thermoelectric module (TEM), a vertical multi-effect diffusion (VMED) desalination unit, and thermal and electrical energy-storage subsystems. The proposed configuration simultaneously harnessed solar energy for electricity generation, thermal-energy recovery, saline-water preheating, atmospheric moisture condensation, and desalination under fully off-grid operating conditions. System performance was experimentally investigated at feed salinity levels of 10,000, 20,000, and 30,000 ppm over a 12-day test period. The maximum freshwater productivity reached 23.05 kg/day at a feed salinity of 10,000 ppm, whereas the minimum productivity was 14.50 kg/day at 30,000 ppm. Year-long TRNSYS simulations predicted an average daily freshwater productivity of approximately 35.03 kg/day under continuous autonomous operation with thermal and electrical energy storage. The experimental results were compared with predictions from the TRNSYS model, yielding an R 2 of 0.805, an RMSE of 1.383 kg, and a maximum deviation of approximately 11%. Water-quality analysis confirmed effective salt removal, and the produced freshwater met the World Health Organization (WHO) drinking-water standards. Furthermore, the minimum freshwater production cost was estimated at 0.0025 USD/kg under favorable operating conditions. Overall, the results demonstrate that the synergistic integration of PVT cooling, TEM waste-heat recovery, and VMED desalination substantially improves freshwater productivity, thermal-energy utilization, and operational stability, offering an effective approach to sustainable and decentralized freshwater production.