1. Stationary electricity storage technologies

Electricity storage technologies can be grouped into three main temporal categories (short-term, long-term and distributed battery storage) according to the types of services they provide. These systems include a number of technologies at various stages of development. Generally speaking, pumped-storage systems, also known as pumped-storage energy transfer stations (PETS), compressed-air energy storage systems (CAES) and certain battery technologies are the most mature, while flow batteries, superconducting magnetic energy storage systems (SMES), supercapacitors and other advanced battery technologies are still at much earlier stages of development.