## 2 Literature Review
### LHTES Systems in Greenhouses
#### 2.1.2 LHTES in Greenhouse-Solar Collector Hybrid System
Furthermore, the shutter was only employed at night. Thermal energy analysis assessed the distribution of absorbed, utilized, stored, and lost energy in the greenhouse, with or without a nighttime shutter. The experimental results showed that the temperature variations overnight in both greenhouses exceeded 2 \({}^{\circ}\)C between the first (which had a shutter) and the second (which did not). In addition, the greenhouse's solar-heated nighttime temperature was maintained at 15 \({}^{\circ}\)C even when the outside temperature dropped to 8 \({}^{\circ}\)C. At night, the radiation heat loss rate was predicted to be 24% of total heat losses in the greenhouse with a shutter and 61% without a shutter. To summarize, during the cold season in Tunisia in December, the solar system's quantity of nighttime recovered heat was around 440 W (per volume of collector); that was 62 W (per area of collector) during the entire night inside the greenhouse with a shutter. The experimental setup's schematic and pictures suggested by [PERSON] et al. (2018) and [PERSON] et al. (2018) are demonstrated in Figures 15a and 15b, respectively. Figure 14: The suggested experimental setup’s schematic by [PERSON] and [PERSON] (2018). Figure 15: _Cont._  
There are various typical forms of building solar greenhouses. A distinctive thin cover is installed on a unique structure's curving glass roof. In this instance, the cover adjusts the solar light's spectral characteristics for multifunctional greenhouse purposes. It reflects the unneeded wavelengths onto a tube collector mounted in the focal line of the curving roof. The fundamental concept of the unique greenhouse stated above was strengthened by [PERSON] and [PERSON] [33]. The effectiveness of the collectors utilized for the roof of the single solar greenhouse system was surveyed. A genetic algorithm optimized the collector tube radius versus the PCM volume. According to the simulation findings, using this solar greenhouse with an improved system has a tremendous impact on both the energy budget and the economy. The system's schematics suggested by [PERSON] and [PERSON] [33] are shown in Figure 16.  
Figure 16: The suggested system’s schematics by [PERSON] and [PERSON] [33]. (**a**) considered greenhouse with a curved roof and selective cover and (**b**) cross-section of collector tube with PCM. Figure 15: The suggested experimental setup’s schematic and pictures by (**a**) [PERSON] et al. [31] and (**b**) [PERSON] et al. [32]. Hydrooponic greenhouses promise superior quality, more nutrients, a more significant production, and more effective water and fertilizer usage than traditional greenhouses, but they also need more electricity. [PERSON] et al. [34] focused on a new hydroponic greenhouse in Tunisia, installed at the Research and Technology Center of Energy. Considering the application's thermal loads, a solar air heater with latent thermal storage employing a PCM was also developed for hydroponic greenhouse heating. With the proposed solar air heater with PCM heating, the hydroponic greenhouse's overnight temperature increased by 6 \({}^{\circ}\)C, and the nocturnal temperature was often over 15 \({}^{\circ}\)C. The heated hydroponic greenhouse typically had a daily temperature of over 32 \({}^{\circ}\)C. Compared to conventional solar heating, the two densely packed beds of latent storage energy improved the greenhouse environment, especially at right and in the cold. The heated hydroponic greenhouse (HG) used for the research and the employed solar air heater with latent storage energy (SAHL) suggested by [PERSON] et al. [34] are illustrated in Figures 17a and 17b, respectively. Solar drying technology has been modified as a superior food preservation method, since direct sunlight has a dangerous risk of microbial assault and a probability of air contamination. [PERSON] et al. [35] examined a mixed-mode solar dryer for this investigation. The dryer was tested with and without PCM thermal storage.