This study investigates innovative solutions for balancing energy supply and demand using long-term thermal energy storage (TES) systems, with a focus on tank thermal energy storage (TTES) for European buildings, which account for approximately 40% of energy consumption in the European Union. Research conducted at the Technical University of Košice explores the potential of TTES systems for efficient and long-term energy storage. The accumulation is carried out in three existing underground tanks of different volumes. Among various outputs, we present the cooling process resulting from covering the water surface and the effect of tank size on cooling. The findings indicate that covering the water surface in the tanks can effectively double the energy retention time, thereby extending the cooling period. A tank with a larger volume cools slower and better ensures the formation of temperature layers. Temperature layering allows for better utilization of the tanks’ potential in terms of energy. The overall result is a significant reduction in heat losses and CO₂ emissions. These results demonstrate the critical role of TTES in stabilizing renewable energy sources, especially solar energy, to support sustainable energy solutions in buildings by providing reliable and long-term energy storage.

Utilization of Thermal Tank Energy Storage Systems (TTES) for efficient storage and release of thermal energy. TTES systems are an integral part of energy infrastructures that enable the storage of surplus energy in the form of heat and its subsequent use as required. We focus on the study of the benefits and challenges associated with the implementation of TTES systems and analyze their impact on temperature stabilization, minimization of heat losses, and overall efficiency. We also discuss the flexible control of tank charging and discharging in TTES systems. Finally, we conclude by reviewing further research aimed at optimizing TTES systems to achieve sustainable and efficient use of thermal energy in the future.

Accumulation of thermal energy in an underground reinforced concrete thermal energy tank with a volume of 24m³ of water, for 2 years. In these 2 years, 4 cycles are measured, namely 2 times charging and 2 times discharging. The measured data in these cycles indicate the charging and discharging time. By evaluating the data, we point out the losses of accumulated energy. Solar hot water collectors, which heat the medium in the thermal energy tank, serve as a source for recharging. The thermal energy tank has the potential to reduce the energy demand of buildings.