Project types are categorized according to the storage technology in use. There are six top-level categorizations of storage type: thermal, thermochemical, mechanical, electrochemical, electrical and chemical. It is important to note that these categories are preliminary, and new terms can easily be added (when categorizing a new project, for instance).
- Thermal storage types are further divided into low and high temperature applications. Low temperature storage types include liquid air (LAES) and ice thermal storage. Tertiary categories for high temperature thermal storage are not yet defined.
- There are not yet any secondary or tertiary storage types listed under thermochemical.
- Mechanical storage types include compressed air storage (CAES), flywheels (FES), and pumped hydro storage (PHS). Compressed air storage is further divided into diabatic, adiabatic, and isothermal tertiary storage types.
- Electrochemical storage has two main subcategories: flow batteries and secondary batteries. Flow batteries include iron-chromium, zinc-iron, zinc-bromine, polysulfide bromine, and vanadium redox. Secondary batteries include molten-salt, sodium-sulphur, zinc-air, lead-acid, lithium-ion, and nickel-cadmium batteries.
- Electrical storage include supercapacitors, superconducting magnetic storage, and capacitors. There are no tertiary levels.
- Chemical storage includes hydrogen fuel cells, biofuels, and power-to-gas applications.