There are a variety of factors that need to be taken into account when choosing a suitable storage technology. Some of the most important are described below:

Volume Specific Thermal Capacity

Thermal capacity is the key issue in the design of a thermal energy storage system as it dictates the amount of volume required for storing thermal energy.

Technologies that have high energy density are relatively expensive, except for concrete, however concrete might not be suitable for most industrial applications as it operates at high temperatures. For the case of pressurised water, it has a low thermal capacity (20-30 kWh/m³) which means that large volumes of storage is required to meet demand. The thermal capacity for pressurised water is given as a range because the injector capacity reduces as the pressure in the vessel increases ^[10].

Efficiency

Efficiency of a thermal storage system is lost due to heat dissipation during heat transfer via piping, heat exchangers, storage tanks and leakages. Using direct storage system has the advantage of eliminating losses due to elimination of a heat exchanger, as the working fluid (steam) is stored directly into an accumulator. Latent heat and chemical heat storage systems have the advantage of being able to store heat for long periods of time but they are immature and case specific technologies ^[11].