Performance analysis of solar desalination unit coupled with latent heat energy storage tank for stable freshwater production

Solar desalination systems commonly suffer from intermittent freshwater production due to the transient nature of solar radiation and the absence of effective thermal buffering during low- or off-sunshine periods. This study develops and optimizes a hybrid solar desalination system integrating flat-plate solar collectors, a packed-bed latent heat thermal energy storage (TES) tank filled with encapsulated RT65 phase-change material, and a four-effect solar still. A transient numerical framework is developed to describe the coupled thermal interaction among the collector loop, PCM storage tank, heat exchanger, and multi-effect still. The heat-transfer fluid flow is divided between direct heating of the solar still and TES charging, creating a trade-off between immediate freshwater production and delayed thermal supply. Response surface methodology is employed to optimize the total system flow rate Qsys and the TES flow fraction γ. The optimum operating conditions are obtained at Qsys=0.87 m3/h and γ=11%, yielding a distilled water production of 53.30 kg/day. Compared with the optimized conventional system under the same solar radiation profile, collector area, still geometry, and operating duration, the PCM-assisted configuration increases freshwater productivity by 21.97%. The solar-to-evaporation thermal efficiency increases from 50.68% to 62.20%, corresponding to a 22.73% relative improvement. The results demonstrate that optimized latent heat storage can stabilize thermal delivery, extend desalination operation, and improve freshwater productivity in solar-driven multi-effect desalination systems.