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Flow batteries for grid-scale energy storage

One challenge in decarbonizing the power grid is developing a device that can store energy from intermittent clean energy sources such as solar and wind generators. Investigators worldwide are exploring a variety of other less-expensive, more-abundant options.

by Nancy W. Stauffer | MIT Energy Initiative

As the world moves towards renewable energy sources like solar and wind, the need for reliable energy storage becomes increasingly important. One promising solution is using flow batteries, which can store large amounts of energy for long periods, offering cost and longevity advantages. However, while flow batteries offer flexibility in adjusting capacity and power separately, they also pose challenges related to electrolyte degradation, crossover, and high capital costs.

Design and operation of a flow battery. Negative and positive electrolytes in large tanks contain atoms or molecules that can electrochemically react to release or store electrons. Pumps send the electrolytes through separate loops to porous electrodes that are separated by a membrane. When the battery is delivering power, electrons liberated by reactions on one side travel to the other side, passing along an external circuit and powering devices on the grid. That movement forces other charged species called ions to pass through the membrane from one electrolyte to the other to keep the system electrically neutral. During charging, the opposite set of flows and reactions occurs as the battery stores power. Credit: Dorothy Loudermilk, SCS Graphic Services, University of Illinois Urbana-Champaign

The most popular flow battery design features vanadium in different oxidation states on each side of the battery. Vanadium is attractive due to its ability to withstand degradation and prevent cross-contamination of the electrolytes. However, the supply chain for vanadium is unreliable, leading to high and volatile prices that hinder widespread deployment.

Researchers are exploring alternative chemistries for flow batteries that use materials that are more abundant and less expensive than vanadium, such as organic molecules or other metals like iron or manganese. However, finding alternatives is not easy, as other chemistries may offer lower initial capital costs but may be more expensive to operate over time, requiring periodic servicing to rejuvenate or replace electrolytes.

To evaluate the feasibility of new energy technologies like flow batteries, researchers have developed a framework for assessing the levelized cost of storage over the system’s lifetime. The framework considers the capital and operating costs and provides general guidance for pursuing different options. However, comparing the economics of different options remains challenging due to the complexity of the electrochemical system, where adjusting one component can affect others.

Researchers emphasize the importance of finding grid-scale, long-duration energy storage solutions to combat climate change. They suggest that there are several chemistries currently being researched, but there is a need to focus on solutions that can compete with vanadium and be deployed and operated long-term. Advances in one type of flow battery chemistry can be applied to others, helping to prepare the technology for grid-scale storage in the future.

Flow batteries offer promising energy storage solutions for renewable energy sources like solar and wind. However, challenges related to electrolyte degradation, crossover, and high capital costs must be addressed to enable widespread deployment. Research into alternative chemistries, techno-economic modelling, and long-term operation and remediation is crucial to determine where to focus research and development investments. Finding grid-scale, long-duration energy storage solutions is essential to combat climate change and transition towards a sustainable future.

This article appears in the Winter 2023 issue of Energy Futures, the magazine of the MIT Energy Initiative.