Energy Storage via Thermal Technologies

Production and Distribution of Electricity and Heat

Renewable energy sources such as wind and solar energy are not always available (dispatchable). Therefore, renewable electricity and heat need to be stored to meet the end-user demand. Energy storage is currently a key technology cluster because enables electricity and heat to be stored (electricity storage and heat storage, respectively) and made available on demand. However, electricity cannot be stored as it is and needs to be transformed in another form of energy to be stored. Accordingly, energy (electricity) storage systems (ESS) are usually referred to as to the form in which energy is stored (chemical, electrochemical, mechanical, thermal storage). A wide range of energy storage technologies exists, but no technology is suitable for all applications. ESS range from large-size, long-term storage (e.g., pumped-hydro storage, compressed-air or gas storage) to small-size, short-term storage (e.g. flywheels, electrochemical capacitors). With the sole exception of pumped hydro storage, all ESS technologies still have modest deployment and require additional R&D to reduce costs and exploit their full potential. Nevertheless, ESS are set to play a growing role in the transition to a sustainable energy systems as they allow renewable electricity and heat to meet the variable end-use demand, add flexibility to the energy system, facilitate the integration of distributed generation and electro-mobility in the electrical grids, and support regulation and reserve capacity; not least, they may be used in combined devices (e.g. heat pumps with heat storage for residential service). In Italy, investors and consumers interest in small-size ESS is constantly increasing while large-size ESS (i.e., a significant pumped hydro power capacity) is traditionally used for power grid regulation. Key parameters for ESS are energy storage capacity (size) and energy density, charge and discharge power and time, allowable storage time, energy losses during charging, storage and discharging phased (storage cycle efficiency), life span (allowable number of charge/discharge cycles), and costs (investment and operation costs). For instance, ESS with high storage loss (parasitic loss) are suitable to short-term storage, while ESS with low parasitic loss are suitable to long-term storage. This paper deals with energy storage via thermal ESS also reffered to as TES (thermal energy storage). They include sensible heat storage, latent (phase-change) heat storage, and thermo-chemical heat storage. High-temperature sensible heat storage via oil and molten salt is also used in Concentrating Solar Power (CSP) plants to store solar heat for electricity production. In Italy, however, thermal ESS or TES still have very small commercial penetration.

27-07-2022

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