Large rock caverns for heat storage in district heating networks – A comparative study for the city of Salzburg

Large heat storages play a key role for the implementation of renewable energy and industrial waste heat in heat distribution networks. Currently, insulated steel tanks are used as daily buffer storage. However, storage volumes are limited, energy losses are high, especially in winter season and the construction costs are also comparable high. Hence, alternatives are necessary. One option is to use underground space for large heat storages. This is possible in regions with mountains in or close by the urban areas such as often the case in Alpine regions. In this paper a case study for large underground heat storages in the heat distribution network of Salzburg is presented. Possible locations for large underground heat storages along the existing heat distribution network were identified, also based on the geological conditions. Two locations were selected and the temperature distribution in the underground around the heat storage cavern was numerically simulated using COMSOL with the aim to determine the energy losses and the temperature change at the ground surface. The results showed that the energy losses can be reduced considerably by >70% compared to insulated steel tank storages and that the surface temperatures are not much influenced by the heat storage below.