The present experimental investigation covers the construction of a latent heat thermal energy storage system (LHTES), which uses sodium nitrate (NaNO3) as phase change material (PCM). The storage unit is filled with 300 kg of the PCM. For the heat transfer a vertically arranged bimetallic mono tube with longitudinal fins is used. The fins increase the heat flux into/from the PCM. Thermal oil is used as a heat transfer medium, as it allows working temperatures up to 400°C. This thermal energy storage is able to store 60 kWh of thermal energy and can be loaded with a power up to 200 kW. One part of the investigation results presented in this paper was the determination of the storable energy and the comparison with data from literature and calculations. Additionally, the melting behavior of the PCM was measured with temperature sensors located at different positions over the height of the storage unit. Finally, the entrance of the heat transfer medium was changed from the top to the bottom of the thermal energy storage unit and a different melting behavior could be detected.

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