Energy storage technologies may be electrical or thermal. Electrical energy stores have an electrical input and output to connect them to the system of which they form part, while thermal stores have a thermal input and output. The principal electrical energy storage technologies described are electrochemical systems (batteries and flow cells), kinetic energy storage (flywheels) and potential energy storage, in the form of pumped hydro and compresse. Energy storage technologies may be electrical or thermal. Electrical energy stores have an electrical input and output to connect them to the system of which they form part, while thermal stores have a thermal input and output. The principal electrical energy storage technologies described are electrochemical systems (batteries and flow cells), kinetic energy storage (flywheels) and potential energy storage, in the form of pumped hydro and compressed air. Complementary thermal storage technologies include those based on the sensible and latent heat capacity of materials, which include bulk and smaller-capacity hot and cold water storage systems, ice storage, phase change materials and specific bespoke thermal storage media.For the majority of the storage technologies considered here, the potential for fundamental step changes in performance is limited. For electrochemical systems, basic chemistry suggests that lithium-based technologies represent the pinnacle of cell development. This means that the greatest potential for technological advances probably lies in the incremental development of existing technologies, facilitated by advances in materials science, engineering, processing and fabrication. These considerations are applicable to both electrical and thermal storage. Such incremental developments in the core storage technologies are likely to be complemented and supported by advanc. Energy storage embraces a wide range of energies, technologies, scales and applications. Energy may be converted to stored form in chemical, electrical, kinetic, potential or thermal media. It can be converted for final use directly, for example when heat is taken from a thermal energy store, or indirectly via an energy conversion system, for example when electricity is generated via the turbine generator of a pumped hydro storage system.Energy storage systems are generally described as either electrical or thermal. Electrical energy storage embraces all the technologies and systems where the external interface is electrical. The energy storage medium itself may use one of a number of technologies, including electrochemical systems, kinetic energy storage and potential energy storage.The electrical interface is an essential element of electrical energy storage systems and is provided by a power conversion system (PCS). The PCS can represent more than 25% of the overall cost of a complete electrical energy storage system.In contrast, thermal energy storage systems utilise either the sensible or latent heat capacity of materials to provide a heating or cooling resource, which can. Electrical energy storage embraces a broad range of technologies, which either directly or indirectly provide electrical energy storage via an electrical input and output. The principal technologies of interest within the context of the present paper are:••electrochemical systems (embracing batteries and flow cells),••kinetic energy storage systems, more commonly referred to as flywheel energy storage,••potential energy storage in the form of either pumped hydro or compressed air storage.Further developments are in hand in relation to hydrogen storage systems in. Thermal energy storage technologies are based on either the sensible or latent heat capacity of materials or, alternatively, upon reversible thermochemical reactions. The time constant associated with thermal energy storage is usually measured in hours, days or even months, so that they can provide for seasonal storage capacity. Such large-scale installations are often deployed in conjunction with renewable energy sources in Germany and Scandinavia.Systems based on the sensible heat capacity of materials include hot and cold water tanks, underground thermal energy storage (UTES) or specific bespoke materials and structures.The storage of either hot or chilled water is a well-established technique and is practised over a full spectrum of capacities. It ranges in scale from the simple domestic hot water cylinder, the bulk hot water storage associated with combined heat and power and district heating schemes and through to the bulk storage of chilled water, to reduce the peak loads on air-conditioning systems. Design considerations for such tanked water schemes include the anticipated levels of stratification in the storage vessels, the trade-off between storage temperature and heat losses and gains and the insulation levels employed.UTES. The essential performance characteristics of any energy storage medium, whether electrical or thermal, may be described in terms of such factors as:••energy density (Wh/kg),••power density (W/kg),••cycle efficiency (%),••self-discharge characteristics,••.
