Faced with the world’s environmental and energy-related challenges, researchers are turning to innovative, sustainable and intelligent solutions to produce, store, and distribute energy. This work explores the trend of using a smart sensor to monitor the stability and efficiency of a salt-gradient solar pond. Several studies have been conducted to improve the thermal efficiency of salt-gradient solar ponds by introducing other materials. This study investigates the thermal and salinity behaviors of a pilot of smart salt-gradient solar ponds with (SGSP) and without (SGSPP) paraffin wax (PW) as a phase-change material (PCM). Temperature and salinity were measured experimentally using a smart sensor, with the measurements being used to investigate the stabilizing effects of placing the PCM in the solar pond’s lower convective zone. The experimental results show that the pond with the PCM (SGSPP) achieved greater thermal and salinity stability, with there being a lesser temperature and salinity gradient between the different layers when compared to a solar pond without the PCM (SGSP). The use of the PCM, therefore, helped control the maximum and minimum temperature of the pond’s storage zone. The UCZ has been found to operate approximately 4 degrees above the average ambient temperature of the day in the SGSPP and 7 degrees in SGSP. Moreover, an unstable situation is generated after 5 days from starting the operation and at 1.9 m from the bottom, and certain points have the tendency to be neutral from the upper depths in 1, 3 m of the bottom.