## 1 Introduction  
In the coming decades, the major challenge will be accessing fresh drinking water, especially in isolated sites. Social scientists predict that by the year 2025, at least 70% of the Earth's population is likely to suffer from freshwater scarcity [1]. Therefore, a solution to prevent a foreseeable crisis is in place. Scientists suggest that the answer to this problem is to make saline water fresh through environmentally friendly mechanisms such as the use of solar power. Using other forms of energy, such as fossil fuels, will worsen the situation owing to global climate change and the heavy use of fresh water to cool the industry [2]. These novel methods have not yet been put in place as they are under development [3; 4]. Besides, the solar desalination method is known to produce small amounts of water that may be insufficient to sustain the population. The production of the solar-based system (SBS) has been compared with other sophisticated methods, such as multi-stage flash distillation (MSF), multiple-effect distillation (MED), vapor-compression desalination (VC), and reverse osmosis (RO). Therefore, various scientists have tried to improve the productivity of the solar-based system owing to its cost-effectiveness, timeliness, and friendliness to the environment. [PERSON] et al. [5] modified the closed-air open-water (CAOW) humidification and dehumidification (HD) system by incorporating recovery options that depend on heat. The option is made possible through the following two steps: a mixing chamber step and a heat exchanger step. To be able to assess the efficiency of the system, scientists have designed a scale (low, moderate, and high) to measure the effectiveness. Other scholars, such as [PERSON] et al. [6], came up with another technique based on innovativeness. In their model, the Maisotsenko cycle-based air saturator was used to increase air humidity. In their new model, [PERSON] et al. were able to increase the rate at which desalination took place by up to 30%. In the same model, the recovery ratio increased by 46%, while the gain output ratio increased by 11%. The gain output ratio was compared with that of other sophisticated methods that had been used previously. Further studies on the modification of solar-based desalination were done by [PERSON] et al. [7]. They designed and tested different versions of the system to check which modification would do better so that it would be adopted. After their experiments, the authors suggested that the modification that worked well was the solar-based system with a closed-air open-water design (CAOW) [3,8]. Moreover, [PERSON] et al. [8] introduced another parameter in the solar-based system, which they referred to as the enthalpy pinch. The new variable was designed to balance the system with random numbers in its stages [9]. On the basis of the results, the authors concluded that pinches increased the effectiveness of the system by 55%. A couple of authors consolidated the solar-based system with a heat pump to increase its effectiveness in desalination [10, 11, 12, 13, 14]. In the new system, heat is preserved because heat lost in one stage is used in the next stage. [PERSON] et al. [11] investigated the performance of the desalination method coupled with a thermal pump. The authors found that the combined system had an efficiency of 22.26 kg/h. This value was higher than that of the single solar-based system. Similarly, research conducted by another group of researchers, [PERSON] al. [15], involves coupling the SBS with a heat pump in a random manner, yielding positive results. They employed the HYSYS(r) simulator software to conclude that, when the SBS is integrated with the heat pump, the system's efficiency is enhanced. Thus, as shown by this brief literature review, a few improvement methods and techniques were adopted by investigators to boost the performance of HD solar desalination systems.