Abstract
Solar collectors have been rigorously modified over the years to better serve the thermal needs of the era. Various design innovations have paved their way to invent new ways of gaining more solar energy in the form of useful heat. Few of these approaches have been commercialized and others have taught lessons. New technological advancements, like phase change materials (PCM), and their integration with solar collectors produced better results in recent years. Hence, various methods of integrating PCM inside the collector cavity were investigated. This review studies innovative concepts of integrating PCMs in flat plate (water/air), evacuated tube, and photovoltaic/thermal solar collectors. Flat plate collectors for water and air heating have been extensively studied. Uses of nano-composite PCM in solar collectors are also compiled. It was observed that maximizing the contact surface area between the PCM and the absorber plate significantly enhances the outlet temperatures. General trends, proportionalities and noteworthy observations are also discussed for each type.