Abstract: In various embodiments, phase change and heat exchange methods between heat collection, heat transfer, heat exchange, heat storage, and heat utility systems are described. In certain embodiments, the heat transfer fluids/heat exchange fluids, heat storage media, and working media in the system are all phase change materials with transition temperatures close to each other and in decreasing order and perform their respective function through phase changes within a relatively narrow temperature range. Methods to control heat transfer rate, heat exchange and/or heat charging/discharging rate between heat collection, thermal energy storage and heat utility apparatus at will are provided. Methods of controlling such systems are also provided.