Concentrated solar technologies have been successfully used to collect solar irradiance and transform it into useful heat for electricity generation. A problem in these systems is often that a mismatch between input and output is present due to variable solar irradiance and energy demand. To compensate for this mismatch storage is utilized to store heat during times when excess heat is present, which is subsequently released when the energy demand exceeds the
solar irradiance input. Phase change materials are a novel concept used to store heat by utilizing the energy required for a phase change and can be added to a heat transfer fluid tocreate a slurry with enhanced heat storage capabilities.\

A study has been conducted to identify characteristics of materials that are suitable for heat storage in a phase change material slurry and selected materials accordingly. This has been done for the specific operating temperature range between 200 ∘C to 300 ∘C. Using these materials a numerical model of a phase change material slurry has been developed to determine which parameters influence the performance of such a system and to establish a system that shows optimal thermal performance. To check if such a system is a good option for heat storage a comparison is made with a heat storage system where the phase change material is stored in a shell and tube packed bed.

A numerical model has been developed using the apparent heat capacity method to model the phase change. An analysis is performed to find the optimal sizing of the phase change slurry system. With use of a test case, a day with variable solar irradiance input and a fixed energy demand, the transient behaviour of the systems has been tested. A second comparison has been made for scaled up systems to limit the costs of the systems.

LiNO3 has been selected for the phase change material, encapsulated with engraved natural graphite, suspended in MarloTherm A. For the test case 91 643 units, a combination of a collector and heat exchanger to the organic Rankine cycle, are required when these are
designed for optimal thermal performance. The total mass of phase change material required equals 6575 kg, including storage. When applying the same sizing to the shell and tube packed
bed model it has been found that it can not meet the energy demand at all times throughout the day. Scaling up this system to more practical dimensions results in less units, 145, but the phase change material mass that is required increases to 99 061 kg.

With the parameters from the test case the transient behaviour of both systems has been analyzed. It was found that a smaller mass of phase change material is required for the phase change slurry system due to the possibility to cycle the phase change material faster between solid and liquid phase. Next to that the heat transfer fluid in the shell and tube packed bed system only contains sensible heat. Therefore less energy can be transferred when the heat
transfer fluid is at the same temperature as the phase change slurry model.