When it comes to energy storage, most people are quite familiar with lithium-ion (Li-ion) batteries. They are, of course, commonly used to power cell phones, electric vehicles (EVs), power tools, and many other devices. They have also been one of the leading forms of battery energy storage used in power grid applications.
Yet, meeting all of the projected energy storage needs with Li-ion batteries could be challenging. The American Clean Power Association (ACP) and Wood Mackenzie Power & Renewables provide a quarterly update on U.S. energy storage markets, deployments, policies, regulations, and financing. In their most recent report, released on Sept. 25, researchers estimate that almost 66 GW of new energy storage power capacity will be installed in the U.S. between 2023 and 2027.
But the U.S. is not the only country adding energy storage. Earlier this year, BloombergNEF issued a market outlook in which its experts projected global cumulative energy storage capacity will skyrocket to 508 GW/1,432 GWh by 2030. The report says annual additions worldwide will reach 88 GW/278 GWh by then, with China being the largest energy storage market.
Notably, the projections above don’t factor in Li-ion battery demand from the electric vehicle (EV) market. Last year, the World Economic Forum questioned whether there was enough lithium available to make all the batteries needed for EVs. It suggested the world could face lithium shortages as soon as 2025. While Li-ion batteries will certainly be a large part of the energy storage mix in the future, other forms of storage will also be necessary.
Redox Flow Batteries
Reduction-oxidation (redox) flow batteries, or RFBs, are a class of batteries well-suited to the demands of grid-scale energy storage. RFBs flow redox-active electrolytes from large storage tanks through an electrochemical cell where power is generated. The electrolytes are specifically designed such that they can be electrochemically reduced (accept electrons) or oxidized (provide electrons). One tank of the flow battery houses the cathode (catholyte or posolyte), while the other tank houses the anode (anolyte or negolyte). The larger the electrolyte supply tanks, the more energy the RFB can store.
Several different chemistries can be used in RFBs including vanadium, iron, zinc-bromine, and others. Sumitomo Electric, maker of a vanadium RFB system, touts the following three features as top selling points:
■ Long Life. In principle, the number of charge-discharge cycles is not a factor in degradation, and therefore, the system has a durability (design life) of more than 20 years. In addition, the electrolyte does not deteriorate and can be reused semi-permanently.
■ High Safety. It can be operated at normal ambient temperature (without air conditioning) and is made of noncombustible and flame-retardant materials, making it extremely safe with little risk of fire. In addition, since the state of charge can be accurately monitored, stable continuous operation over a long period of time is possible regardless of charging/discharging patterns.
■ Flexible Design and Operation. The number of cell stacks determines the output (kW) and the amount of electrolyte determines the discharge time capacity (kWh) separately, allowing for flexible system design and operation with independent output and discharge time capacity.
Conrad Nichols, technology analyst at IDTechEx, notes in a report released Sept. 29 that RFB deployments for storage applications over the last decade have been “sporadic and few” compared to Li-ion battery deployments. However, Nichols expects energy storage technologies that can provide longer durations of storage, such as RFBs, will be needed as renewable energy penetration expands. Therefore, he predicts the RFB market will be valued at $2.8 billion in 2034.
Flow Battery Projects Gain Momentum
Multiple suppliers have announced RFB projects in recent months. For example, Sumitomo said it received an order from Vecco Group Pty. Ltd., an integrated mining business in Australia, for a 250-kW/750-kWh system. The project will be Sumitomo’s first vanadium RFB installation in Australia. Also, in Australia, Energy Storage Industries (ESI), the Asia-Pacific license holder of ESS Inc.’s iron flow battery technology, delivered a 1-MW/10-MWh long-duration energy storage (LDES) system for the Stanwell Clean Energy Hub in Queensland. ESS said the eight- to 12-hour storage duration makes the batteries ideal for supporting and firming the electricity network. This was the first iron flow battery project in Australia and the largest in the world.
In California, Redflow announced it will provide zinc-bromine flow batteries for a 34.4-MWh LDES project to support Valley Children’s Hospital in Madera. The project is one of 15 that were announced by the U.S. Department of Energy, which is providing up to $325 million to help accelerate the development of LDES technologies. The Valley Children’s Hospital project is being sponsored and potentially co-funded by the California Energy Commission.
Meanwhile, Stryten Energy and Snapping Shoals EMC, a consumer-owned non-profit cooperative serving customers in the ever-expanding Atlanta metro region, celebrated the installation of Georgia’s first vanadium RFB system. “We’ve kind of run to our extreme limit as to where we can go with conventional batteries so this is truly a new frontier for energy storage to be able to get to multiple hours—multiple potentially days—and really being able to see it connected to a physical grid and a real community with real customers is exciting,” Rich Simmons, director of Research & Studies at Georgia Tech, said in a video produced in conjunction with the celebration.
—Aaron Larson is POWER’s executive editor.