The Role of Energy Density for Grid-Scale Batteries

Abstract

For grid-scale battery energy storage systems it is often presumed that cell level energy density is not too important. Yet, countless publications highlight low energy density as the key limitation of technologies such as redox flow batteries or aqueous alkali-ion batteries that are inherently developed for stationary applications.Here, we resolve this apparent conflict by quantifying the areal energy density, expressed in kWh m-2, of over forty MWh-scale battery energy storage systems deployed around the world.[1] Via satellite imagery we compare lithium-ion, sodium-sulfur, and flow battery projects and show that the amount of energy that is stored per land area is often comparable between these technologies, even though the energy density on cell level varies by an order of magnitude. We highlight excellent safety and vertical scalability as key untapped advantages of aqueous batteries and provide examples of where they can excel, besides simply competing with state-of-the-art lithium-ion batteries. We show, for example, that MWh-scale aqueous flow batteries can safely be deployed underground and within buildings, feats that due to safety constraints are not possible with current lithium-ion batteries at this scale.Seeing satellite images of battery installations near solar farms is a humbling experience that every researcher working in the field should come across and we provide the locations of all the examined battery installations in a Google Earth file. Grasping the fantastical scale at which renewables are, and must continue to be, deployed certainly provides some perspective regarding energy density of individual battery cells. [1] Reber, D., Jarvis, S.R., Marshak, M.P., The role of energy density for grid-scale batteries, ChemRxiv, 2022, doi: 10.26434/chemrxiv-2022-5ddhs