Solar energy is widely acknowledged as a renewable and environmentally friendly energy source. Efficient storage of heat energy is a crucial challenge in solar thermal applications. Phase change materials (PCMs) have gained prominence due to their unique ability to store and release thermal energy through phase transition. The advantageous characteristic of PCMs is their low melting point, facilitating efficient heat storage and retrieval through latent heat of vaporization. This comprehensive review focuses on selecting suitable PCMs for diverse applications, considering their melting point and thermal properties. PCMs with high heat capacity and excellent solar radiation absorption are favored in solar applications, especially for systems requiring large thermal energy storage capacities. This review article underscores the importance of PCMs in low-temperature (0-120 °C) solar thermal applications such as solar desalination, solar water heaters, solar cookers, solar dryers, solar air heaters, and solar chimneys, emphasizing their role in practical heat storage and release. By carefully selecting PCMs based on melting point and thermal properties, the performance and efficiency of solar thermal systems can be optimized, contributing to a greener and more sustainable future.
The traditional approach of open-sun drying is facing contemporary challenges arising from the widespread adoption of energy-intensive methods and the quality of drying. In response, solar dryers have emerged as a sustainable alternative, utilizing solar thermal energy to effectively dehydrate vegetables. This study investigates the performance of a single-basin, double-slope solar dryer utilizing natural convection for drying bottle gourds and tomatoes, presenting a sustainable alternative to traditional open-sun drying. The solar dryer exhibited superior moisture removal efficiency, achieving a 94.42% reduction in tomatoes and 83.87% in bottle gourds, compared to open-sun drying. Drying rates were significantly enhanced, with maximum air and plate temperatures reaching 54.42 °C and 63.38 °C, respectively, accelerating the dehydration process. Moisture diffusivity analysis revealed a marked improvement in drying behavior under solar drying, with values ranging from 3.12 × 10-11 to 4.31 × 10-11 m2/s for bottle gourds, and 4.65 × 10-11 to 2.31 × 10-11 m2/s for tomatoes. Energy efficiency assessments highlighted the solar dryer's advantage, with exergy efficiency peaking at 61.78% for bottle gourds and 68.5% for tomatoes. Furthermore, the activation energy required for drying was significantly lower in the solar dryer (29.14-46.41 kJ/mol for bottle gourds and 27.16-55.42 kJ/mol for tomatoes) compared to open-sun drying, enhancing energy conservation. Visual inspections confirmed the superior quality of the solar-dried vegetables, free from dust and impurities. An economic analysis underscored the system's viability, with payback periods of 2 years for bottle gourds and 1.6 years for tomatoes. Overall, this study demonstrates the efficacy of solar dryers in optimizing vegetable preservation while promoting energy efficiency, aligning with global sustainability goals by reducing post-harvest losses and supporting eco-friendly practices.