They will allow the grid-scale storage of renewable energy
Until recently it has been necessary for electrical generation and demand to match exactly in order to operate electrical networks in a stable way. To ensure that this balance is met at all times, complex control systems keep generation equal to the demand. The focus of balance is often put on controllable generation, which means that enough spinning reserve is necessary to guarantee the stability. However, this practice increases the operational price of the electrical system. Such fine balancing was necessary because large scale and efficient electrical storage was not readily available. This is no longer the case, with lithium-ion batteries recently proving their growing capacity to store energy in a cost-competitive way and with a longer lifespan than previous alternatives. However, this kind of storage has its limitations, such as the speed to deliver energy and its wear; so, the possibility to use them as support of electrical networks remains limited. The search for more effective large-scale and efficient energy storage systems is still on going and has been spurred on by the proliferation of renewable energy sources, as their generation is intermittent and not easily controllable, with supply rarely able to match demand.
Scientist at the MIT, headed by Donald Sadoway, research electrical storage technologies in the search for an effective solution to grid balancing. Around a decade ago, they presented a battery of molten metals whose promising properties make it a top-class battery to be studied and financed. Contrary to lithium-ion batteries, in molten metal batteries all of the main elements are in liquid form; not only the electrolytic materials —made up of molten salt—, but also the electrodes —made up of molten metals—. According to the researchers, these batteries can store and discharge high levels of energy, they use materials abundantly present in nature, they are cheap, and they endure numerous total discharge cycles without losing capacity. Scientists have proved that the chosen molten metals and electrolyte influence the temperature at which the battery must operate to keep the elements in liquid form and they were able to reduce such temperature to just over 430ºC —from the 700ºC of the first materials that were tested—. There are still challenges to overcome to take this technology to the commercial stage; such as finding a way to seal the steel cells in a lasting way or reducing the manufacture costs.
There is no doubt, storage will play a main role in the future electrical grid. It will allow the increment of the penetration of renewable energies in the energy mix. If everything is on course, molten metal batteries will be key players in the new energy system.
Inmaculada Saboya Bautista
Inmaculada holds a PhD in Electrical Energy from Universidad Pontificia de Comillas and forms part of Norvento’s microgrid and grid studies team. Contact Inmaculada.