This work provides an overview of state-of-the-art seasonal thermal energy storage with the focus on tank and pit TES construction. Aspects of TES modelling are discussed. Based on modelled and measured data the effects of construction type, system configuration and boundary conditions on thermal losses of large-scale TES are identified. It is found that available coarse-structure TES models simplify the real processes such that a detailed analysis with the objective to enhance TES design is not possible.