If we look at the list of the largest energy storage devices in Wikipedia, it turns out that if we take into account the amount of energy stored in a single installation – then, after pumped storage hydroelectric plants and after installations using compressed air, the third place is taken by devices storing energy in molten salts heated to high temperatures. We already talked about this method in Chapter 7 (see Section 7.3.1) when discussing concentrated solar power (CSP) plants. Solar power is not converted in them directly into electricity, as in photovoltaic (PV) panels, but into thermal energy, which in turn is converted into electricity by a heat engine. The advantage of such a scenario is that the conversion to electricity doesn’t need to happen right away – as in PV facilities – but some part of the thermal energy collected may be stored and used later, which allows the CSP plants to provide electric power for several hours after the sunset.
The molten salt technology has been developed in the late 1990-s in Sandia National Laboratory. Soon afterwards, it began to be used successfully in CSP power plants. However, it has only recently been realized that this technology can also be used to store energy from other sources – for example, power surpluses generated on a windy day by wind turbines. And secondly, that the medium in which thermal energy is deposited does not necessarily have to be molten salt. In this context, two exciting recent news come from Australia, Germany and the United Kingdom.