A Practical Phase Change Thermal Energy Storage for Concentrating Solar Power Plants
Abstract
Thermal energy, collected in concentrating solar collectors such as power tower or parabolic trough, can be stored cost effectively and efficiently in phase change materials (PCM) such as inorganic salt mixtures. Storing heat as latent heat in PCM, compared with the more conventional sensible heat method, reduces the amount of molten salt used by 30% and the container size by 60%. However, a major issue that is preventing the commercial use of PCM for thermal storage is that it is expensive to discharge the latent heat stored in the PCM melt. The reason being that when salt solidifes around heat transfer tubes, heat transfer coefficient decreases significantly and requires expensive heat exchangers. Terrafore’s innovative approach uses a coated shell and tube heat exchanger and a specific compostion of the salt mixtures called a dilute eutectic. The combination of using a dilute eutectic composition of salt mixture with anti-stick coatings on heat exchanger tubes, and mixing a nucleating agent to the salt mixture allows the salt to freeze as a slurry which can be pumped to an external heat exchanger thereby increasing heat transfer coefficient by forced convection. This paper presents the preliminary results of the on-going research at Terrafore funded by the United States Department of Energy and discusses the benefits of using PCM-TES in solar plants.