## 2 Literature Review
### LHTES Systems in Greenhouses
#### 2.1.2 LHTES in Greenhouse-Solar Collector Hybrid System
Dry fresh banana and pineapple slices were used to assess the drying performance of both configurations. Using PCM thermal storage resulted in a 75% increase in drying efficiency. The PCM-based dryer's simple payback period was 1.6 years, less than its 25-year estimated life duration. All sides of the greenhouse were coated with polycarbonate sheets, allowing short-wave light from the sun while blocking out reflected long-wave radiation, creating a regulated atmosphere. Trays were utilized within the greenhouse chamber to store food goods. Two exhaust fans were attached at the top of the greenhouse to remove the majority of the air. This allowed for improved air circulation throughout the whole system. Paraffin wax was kept in cylindrical tubes with both ends shut to prevent outflow when melted. At the bottom of the greenhouse, a tight arrangement of parallel-oriented PCM-filled tubes was present. Solar air collectors absorb solar energy during the day, which causes the air inside them to warm up. The connecting pipes then transfer the heated air to the greenhouse. As a result, some of the heat is retained in the PCM while the other portion is transferred to the greenhouse. Along with the heat provided by the air collector, heat is also produced within the greenhouse during the daytime by solar radiation that is directly absorbed. Together, they dry the food items that are stored in the greenhouse. The PCM is utilized for prolonged drying times with continuous and uniform drying. It becomes heated during the hours of maximum sunlight and releases during the hours of minimum sunlight. The average thermal efficiency attained by the dryer with and without PCM is 30.34% and 23.25% for drying banana and 30.28% and 4.26% for drying pineapple, respectively. With the inclusion of PCM thermal storage, the drying efficacy is increased by 75%. A similar tendency may be seen in the temperature changes and drying rate, indicating that the PCM performs better. The use of a PCM ensures consistent drying and minimizes temperature swings. The payback period was discovered to be roughly 1.6 years, which is appealing given the predicted lifetime of 25 years. [PERSON] et al. [36] provided an experimental study on a new mixed-mode solar greenhouse drying system employing a PCM. The goal was to examine how well red pepper dries when using paraffin wax as the PCM. The drying system comprised two solar greenhouses, a storage container, and two similar solar air heaters. According to the testing findings, the air temperature inside a solar greenhouse with a PCM was approximately 7.5 \({}^{\circ}\)C greater than other driers during the whole night. After sunset, the relative humidity in the drying room with a PCM was roughly 18.6% lower than the surrounding air. It was presented that using a PCM in solar greenhouse dryers is a potential solution to improve the effectiveness of the drying process. The system's schematics and pictures suggested by [PERSON] et al. [36] are displayed in Figure 18.  
Figure 13.0 The suggested system’s schematics by [PERSON] et al. [34]: (**a**) the heated hydroponic greenhouse (HG) used for research and (**b**) the employed solar air heater with latent storage energy (SAHL).