Advanced heat-pump architectures for PV-battery powered HDH desalination: performance, reliability, and cost analysis

A stand-alone photovoltaic (PV)-battery-powered open-water closed-air water-heated humidification-dehumidification (OWCA WH HDH) desalination system integrated with three heat-pump configurations: baseline vapor-compression (BHP), ejector-expansion (EEHP), and ejector-subcooled with an internal heat exchanger (ESCHP) is developed and evaluated. The integrated framework couples steady-state thermodynamic models of the HP-HDH system with a PV-battery subsystem to assess desalination performance, renewable-energy reliability, and freshwater production cost. The governing coupled HP-HDH model was validated against measurements from a pilot-scale open-water open-air (OWOA) HP-HDH experimental facility, while the HDH, advanced heat-pump, and PV sub-models were independently benchmarked against published studies. The model reproduced the measured HP-HDH performance with deviations within ±0.6–8% for GOR, recovery ratio, and freshwater productivity. The validated framework was subsequently used to compare the three heat-pump architectures under identical desalination operating conditions. The ESCHP configuration consistently exhibited the best thermodynamic performance. Under the principal operating conditions, GOR varied from approximately 0.85 to 8.1, with optimum performance near MR = 1.30–1.35. Under literature-based high-effectiveness conditions (ε_H = 98.7% and ε_D = 99%), the predicted GOR increased to approximately 10.6, 13.1, and 14.1 for the BHP, EEHP, and ESCHP configurations, respectively. The recovery ratio reached up to 4.8%, while the minimum specific electrical energy consumption decreased to 69.6 kWh/m³ for the best-performing configuration. The PV-battery subsystem supplied more than 99% of the annual electrical demand, with battery state of charge maintained between 10% and 100%, and the highest monthly loss-of-power-supply probability limited to 0.029 in September and 0.008 in October. Economically, the freshwater cost decreased to 5.55, 5.34, and 5.30 cent/L after 20 years for the BHP, EEHP, and ESCHP configurations, respectively, reaching approximately 5.12 cent/L after 30 years for the ESCHP configuration. Overall, the validated integrated modelling framework predicts that the ESCHP configuration offers the greatest potential for efficient, reliable, and economically competitive PV-powered HDH desalination while supporting sustainable decentralized freshwater production consistent with the objectives of the United Nations Sustainable Development Goals, particularly SDG 6 (Clean Water and Sanitation) and SDG 7 (Affordable and Clean Energy).