their development. Automotive-oriented technologies rely on solid electrodes, which feature a high energy density but require an expensive manufacturing process. Liquid electrodes represent a cheaper and less dense alternative as they do not need any processing. Molten-salt/liquid-metal batteries These batteries are composed of two molten metal alloys separated by an electrolyte. They are simple to manufacture but require a temperature of several hundred degree Celsius to keep the alloys in a liquid state. This technology includes ZEBRA, sodium-sulfur batteries and liquid metal. Sodium sulphur batteries are being used for grid storage in Japan and in the United States. The electrolyte is composed of solid beta alumina. The liquid metal battery, developed by the group of Pr. Donald Sadoway, uses molten alloys of magnesium and antimony separated by an electrically insulating molten salt. It is being brought to market by MIT spinoff company Ambri, which is currently contracted to install a first 250MWh system for TerraScale data centre company near Reno, Nevada. Flow batteries In rechargeable flow batteries, the liquid electrodes are composed of transition metals in water at room temperature. They can be used as a rapid-response storage medium. Vanadium redox batteries are a type of flow battery. Various flow batteries are installed at different sites including; Huxley Hill wind farm (Australia), Tomari Wind Hills at Hokkaidō (Japan), as well as in non-wind farm applications. A 12 MW·h flow battery was to be installed at the Sorne Hill wind farm (Ireland). These storage systems are designed to smooth out transient wind fluctuations. Hydrogen Bromide has been proposed for use in a utility-scale flow-type battery. Examples In Puerto Rico a system with a capacity of 20 megawatts for 15 minutes (5 megawatt hour) stabilizes the frequency of electric power produced on the island. A 27 megawatt 15-minute (6.75 megawatt hour) nickel-cadmium battery bank was installed at Fairbanks Alaska in 2003 to stabilize voltage at the end of a long transmission line. In 2014, the Tehachapi Energy Storage Project was commissioned by Southern California Edison. In 2016, a zinc-ion battery was proposed for use in grid storage applications. In 2017, the California Public Utilities Commission installed 396 refrigerator-sized stacks of Tesla batteries at the Mira Loma substation in Ontario, California. The stacks are deployed in two modules of 10 MW each (20 MW in total), each capable of running for 4 hours, thus adding up to 80 MWh of storage. The array