Advanced high temperature latent heat storage system - design and test results

Abstract

Processes with a two-phase heat transfer fluid (e.g. water/steam) require isothermal energy storage. Latent heat storage systems are an option to fulfil this demand. For high temperature applications nitrate salts are suitable materials for phase change storage. The main drawback of these materials is the low thermal conductivity, limiting the power density during the charging/discharging process. At DLR the so called sandwich-concept has been developed to realize latent heat storage with high power densities for applications in solar thermal power plants and process industry. This concept has already been demonstrated successfully for three different storage units ranging from 2-100 kW at melting temperatures of 142 °C and 222 °C. In 2008, a test storage using sodium nitrate as phase change material (PCM) with a melting temperature of 306 °C was operated in a 5 kW laboratory loop. The designed heat transfer rate was achieved and after 172 cycles no degradation was observed.