The basic principle is the same in all TES applications. Energy is supplied to a storage system for removal and use at a later time. What mainly varies is the scale of the storage and the storage method used. The process of storing thermal energy can be described in three steps, referred to as a cycle.
Thermal Energy Storage in district heating and cooling systems serves as a reserve of thermal energy, which can be used to supply heat or cooling load in times of peak demand or in times of high electricity prices – when heat is produced through electric heaters or heat pumps.
The energy, in the form of hot or chilled water, can then be distributed to buildings via a pipe network for immediate use or be stored in thermal storages for later use. The thermal energy can be stored for a few hours or days, for example in heat storage tanks, or for several months in large pits or other storage facilities.
The process of storing thermal energy can be described in three steps, referred to as a cycle. These steps are charging, storing and discharging. The storage cycle applies to sensible, latent and chemical storage; the differences between these methods are the material, the temperature of operation and a few other parameters.
The IRENA and ETSAP organizations described in their report “Thermal Energy Storage – Technology brief the potential of implementation of TES systems (IEA-ETSAP and IRENA, 2013). One of the most common technologies installed today is domestic hot water tanks.
There are three methods used and still being investigated in order to store thermal energy. The most direct way is the storage of sensible heat. Sensible heat storage is based on raising the temperature of a liquid or solid to store heat and releasing it with the decrease of temperature when it is required.