## 2 Literature Review
### SHTES Systems in Greenhouses
#### 2.2.3 Rock Bed as SHTES System
[52] heated the ambient air in a Canarian-style greenhouse using a solar-energy-storing rock bed to maintain the ideal plant-growing environment. This device stores excess heat from the greenhouse during the day and releases it at night. The results of the experimental measures showed that the interior air temperature of the greenhouse with the rock bed was, at night, 3 \({}^{\circ}\)C higher and, during the day, 1.9 \({}^{\circ}\)C lower than that of a typical greenhouse. The solar energy storage greenhouse naturally had higher relative humidity during the day and lower relative humidity at night since it was heated during the day and cooled during the night. Additionally, this method positively impacted tomato  
Figure 31: The schematics of the proposed system by [PERSON] et al. [51]; (**a**) the considered greenhouses, (**b**) the details of the experimental setup, and (**c**) the performance of the proposed rock beds in two modes of charging (day) and discharging (night). yield, which grew by 22% compared to a traditional greenhouse. Throughout the night, the recommended technology raised the temperature in the greenhouse by 3 \({}^{\circ}\)C above that of a conventional greenhouse and 4.7 \({}^{\circ}\)C over that of the outside. Additionally, the suggested remedy lowered the experimental greenhouse's air temperature by 3 \({}^{\circ}\)C outside and 1.9 \({}^{\circ}\)C within the traditional greenhouse. The schematics of the proposed system by [PERSON] et al. [52] are demonstrated in Figure 32.  
[PERSON] et al. [53] investigated and addressed the performance of combining two systems--a water-filled passive solar system and a rock bed TES system--to heat a Canarian greenhouse. In the Mediterranean region, thermal solar energy storage and reuse is crucial for greenhouse heating throughout the winter. The extra thermal energy in the greenhouse was kept for use during the colder months by storing it in the water and the rock bed. Two Canarian-style greenhouses were used for the experiment; one had a combined heating system (which included water storage and a rock bed as SHTES devices), while the other did not. The aforementioned greenhouses were located in the southern Moroccan province of Souss-Massa. The findings illustrate that utilizing the proposed combined heating system can augment the indoor air temperature during nighttime by 3-5 \({}^{\circ}\)C on clear days and 2-3 \({}^{\circ}\)C on cloudy or rainy days, with consistent effects (lower fluctuations) throughout the winter season. Moreover, overnight, the relative humidity of the air in the heated greenhouse decreased by 10-15%. Moreover, on clear days, this heating system raised the substrate temperature by 4 \({}^{\circ}\)C, on cloudy or rainy days, it raised it by 3 \({}^{\circ}\)C at night. Finally, the greenhouse with the proposed heating experienced exceptionally robust plant growth, resulting in a substantial 49% increase in tomato yield. In other words, this system's thermal energy restoration meets a considerable portion of the greenhouse heating requirements. Additionally, implementing this heating system decreased the Tuta absoluta (serious pest of tomato crops) population growth within the heated greenhouse. Based on the presented economic evaluation, this approach proves highly advantageous and holds the potential to generate income for farmers. The schematics of the proposed system by [PERSON] et al. [53] are demonstrated in Figure 33.  
In another work, [PERSON] et al. [54] employed a solar heating cooling system (SHCS) using quartzitic sandstone as the thermal storage material to store and utilize the surplus air thermal energy (SATE) in greenhouse production. They tested the system's heating and cooling capabilities during the winter. The difference between this work and their previous work [53] is that the new effort did not employ water tanks as a passive heating/cooling system in contrast to the earlier work [53]. Like their previous work, the system was located within the Souss-Massa region of Morocco.