Powering Strong Communities

Technologies Offer Increasing Array of Long Duration Energy Storage Options

While lithium-ion technology has been king of the hill when it comes to energy storage options for utilities, this year could prove to be a key inflection point for the emergence of alternative energy storage technologies in the U.S. if recent developments are any indication.

For several years, lithium-ion batteries have dominated the energy storage landscape for electric utilities, but one of the limitations of lithium-ion batteries is the limited amount of storage hours they can provide. And there have also been safety concerns raised about fires occurring at lithium-ion facilities.

There is a wide array of storage technologies that differentiate themselves from lithium ion by offering longer storage durations, which is becoming increasingly important as intermittent renewable energy sources continue to expand across the U.S. power grid.

“The value of long-duration energy storage, which helps address variability in renewable energy supply across days and seasons, is poised to grow significantly as power systems shift to larger shares of variable generation such as wind and solar,” a report posted on the National Renewable Energy Laboratory notes.


One of the companies making a splash in the iron flow battery space in recent months is ESS Inc. Two California public power utilities, SMUD and Burbank Water and Power, in 2022 announced agreements with ESS.

SMUD and ESS on Sept. 20, 2022 announced an agreement to provide up to 200 megawatts (MW)/2 gigawatt-hours (GWh) of long duration energy storage that will be provided by ESS. The agreement calls for ESS to deliver a mix of its long-duration energy storage technology for integration with the SMUD electric grid beginning in 2023.

In November, ESS and Burbank Water and Power entered into an agreement for ESS to deliver BWP’s first utility-scale battery storage project. Under the agreement, a 75 kilowatt (kW)/500 kilowatt hour kWh ESS “Energy Warehouse” will be installed and connected to a 265 kW solar array on BWP’s EcoCampus.

The iron flow battery will support the increased use of renewable power and allow excess renewable energy to be stored and used as baseload energy for Burbank, improving the resilience and reliability of the grid.


In late January, Form Energy announced that it had entered into definitive agreements with investor-owned Xcel Energy to deploy Form Energy’s iron-air battery systems at two of Xcel Energy's retiring coal plant sites.

Xcel Energy–Minnesota will deploy a 10 MW/1,000 MWh multi-day storage system at the Sherburne County Generating Station in Becker, Minnesota. Xcel Energy–Colorado will deploy a 10 MW/1,000 MWh multi-day storage system at the Comanche Generating Station in Pueblo, Colorado. Both projects are expected to come online as early as 2025 and are subject to regulatory approvals in their respective states.

In December, West Virginia Gov. Jim Justice announced that Form Energy will partner with the state of West Virginia to build its first iron-air battery manufacturing facility on 55 acres of property in the northern panhandle of West Virginia, along the Ohio River.

Meanwhile, California community choice aggregator Central Coast Community Energy in January said that it signed a 25-year power purchase agreement for a compressed air energy storage project with Hydrostor.

The nearly $1 billion power purchase agreement calls for the delivery of 200 megawatts, 1,600-megawatt hours of energy storage to 3CE from Hydrostor’s planned Willow Rock Energy Storage Center that will use the company’s Advanced Compressed Air Energy Storage technology. Hydrostor says the project, when completed, will abate up to 28 million metric tons of carbon dioxide over its lifetime.

Hydrodstor’s technology combines elements of a compressed air storage system with a pumped hydro system. The process stores energy as compressed air but captures and stores the heat of compression for future use. The compressed air is stored in a purpose-built underground cavern that uses a water reservoir to maintain constant pressure. The facility discharges energy by reversing the process, using the stored heat and pressure to power a conventional turbine generator. The system has no performance degradation over its 50-year plus expected lifetime, Hydrostor said.

Hydrostor said its technology offers the same services as a natural gas plant while having zero emissions because it uses surplus electricity as fuel. The company is targeting high value grid applications such as transmission deferral and fossil fuel generation replacement.


In early January, Energy Vault Holdings, Inc. and California investor-owned utility Pacific Gas and Electric announced the companies are partnering to deploy and operate a utility-scale battery plus green hydrogen long-duration energy storage system with a minimum of 293 megawatt-hours of dispatchable energy.

The system is designed to power downtown and the surrounding area of the City of Calistoga, Calif, for a minimum of 48 hours during planned outages and potential Public Safety Power Shutoffs, which is when the powerlines serving the surrounding area must be turned off for safety due to high wildfire risk.

PG&E submitted the project contract for review and approval to the California Public Utilities Commission on December 30, 2022, with a request for the issuance of a final resolution approving the project by May 15, 2023.

The energy storage system will be owned, operated and maintained by Energy Vault while providing dispatchable power under a long-term tolling agreement with PG&E.

The system’s capacity may be expanded to 700 MWh, which would allow it to operate for longer without refueling, enabling further flexibility for PG&E and the City of Calistoga.

Energy Vault’s system will replace the typical, mobile diesel generators used to energize PG&E’s Calistoga microgrid during broader grid outages.

Construction is anticipated to begin in the fourth quarter of 2023 with commercial operation expected by the end of second quarter of 2024.

Upon completion, this project is expected to be the first-of-its-kind and the largest utility-scale green hydrogen project in the United States.

Los Angeles Department of Water and Power

The Los Angeles Department of Water and Power told Public Power Current that it recognizes the benefits of green hydrogen as a “power-to-gas” long-duration energy storage solution, through the use of electrolyzers, a system that uses electricity to break water into hydrogen and oxygen in a process called electrolysis.

LADWP was asked to provide additional details on where things currently stand in terms of LADWP’s possible pursuit of green hydrogen for storage.

As a purchaser of power produced by the Intermountain Power Project (IPP), LADWP is involved in installing two, 420 MW each, combined cycle generating units at IPP that will be capable of using hydrogen fuel (blended with natural gas) when placed in service in July 2025. The hydrogen will be produced using renewable energy and electrolyzers, and then stored in salt caverns for long-duration energy storage that can store and provide a seasonal supply of hydrogen, LADWP officials noted.

LADWP does not plan to be directly involved in the production of green hydrogen in the Los Angeles area at this time, but it will work with energy developers to implement green hydrogen projects to provide grid reliability and a zero carbon energy source.

LADWP officials said that its strategic long-term resource plan includes options for eventually purchasing green hydrogen from the market to spur development of green hydrogen capacity in the Los Angeles area.

The utility believes this technology is necessary to ensure the power system remains resilient during emergency events, such as an earthquake, wildfire, or other situations when clean dispatchable generation capacity may be necessary to maintain grid reliability and resiliency as it transitions to 100% clean energy.

LADWP officials said the utility is looking at a variety of energy storage technologies as well as green hydrogen as its transition to a 100% clean energy future.

The officials said the utility will need energy storage to mitigate the intermittent generation challenge posed by renewable resources (variable wind and solar) and to provide resources for periods of low renewable generation, high energy demand periods, and loss of generation and/or transmission lines to maintain grid reliability and resiliency.

LADWP officials point out that there are trade-offs with different technologies: Batteries are limited in their ability to store large quantities of energy economically and shift the energy beyond the daily or hourly timeframe. Pumped hydro is limited by location (it is challenging to find new sites for large hydroelectric plants) and is constrained by water availability, the officials noted.

Green hydrogen offers the potential for long-duration energy storage that uses excess renewables available in the spring when electricity demand is low to produce hydrogen for use in the summer when electricity demand is high -- referred to as seasonal storage, they said. Another benefit is that, in some cases, the existing power generating units can be modified to use green hydrogen.

As the green hydrogen economy scales up, LADPW expects that it will become a viable, low-cost solution for seasonal energy storage that offers the flexibility to decarbonize the electric grid and other sectors of the economy.

Orlando Utilities Commission Explores Deployment of Long-Duration Energy Storage Facility

In early January, Florida public power utility Orlando Utilities Commission said it will explore deployment of a long-duration energy storage facility as a way in which to help achieve the utility’s net-zero carbon emission goals.

The facility will be provided by Malta Inc. Malta’s storage technology converts excess electricity into thermal energy that is stored in salt and coolant. When needed, the plant regenerates gigawatt hours of electricity for residential and commercial use.

The Malta facility would be situated at OUC’s Indian River Plant in Brevard County on Florida’s East Coast.

Malta’s more than 100-megawatt utility-scale system provides more hours of energy storage than lithium-ion batteries and could provide energy storage diversity for OUC. The increased duration facility has the potential to help OUC ensure grid reliability despite the variable nature of clean and renewable energy resources like solar.

NYPA Signs Agreement for Planned Deployment of Zinc-Air Storage System

Another public power utility pursuing long-duration energy storage technology is the New York Power Authority.

In April 2021, NYPA signed an agreement with Zinc8 Energy Solutions Inc. and the University at Buffalo for the planned deployment of Zinc8’s zinc-air energy storage system, marking a first demonstration of a long-duration use in New York State and a development that could support further integration of renewable power sources into the electric grid.

In January 2022, New York Gov. Kathy Hochul announced that Zinc8 will relocate its $68 million manufacturing facility and U.S. headquarters to Kingston, N.Y.

Zinc8's technology has been developed around the utilization of zinc as the anode fuel, which is expected to offer advantages over other metals due to its high energy density, abundant availability, low cost, and ease of storage and handling.

When the system is delivering power, the zinc particles are combined with oxygen drawn from the surrounding air. When the system is recharging, zinc particles are regenerated, and oxygen is returned to the surrounding air. The regenerative system does not require fuel replacement and offers scalable energy capacity through the simple introduction of additional fuel tanks.

Wisconsin Utility Pilot Project Tests New Form of Long-Duration Energy Storage

In early February, WEC Energy Group, a Wisconsin-based investor-owned utility, announced that the company will lead a pilot project at its Valley Power Plant in Milwaukee to test a new form of long-duration energy storage.

WEC Energy Group is collaborating with the Electric Power Research Institute and CMBlu Energy, the developer and manufacturer of the long-duration battery based in California and Germany.

This 1-to-2-megawatt-hour pilot project will be one of the first to test this type of energy storage system on the U.S. electric grid, WEC Energy Group said.

The CMBlu Organic SolidFlow energy storage system uses a proprietary flow battery technology with components from recyclable materials.

The project will test the performance of the battery system, including discharge durations of five to 10 hours — up to twice as long as the typical lithium-ion batteries in use today.

The pilot project is planned for testing in the fourth quarter of this year.

Findings will be shared with the utility industry. EPRI will share a complete analysis of the project in early 2024.

APPA Storage Tracker

The American Public Power Association’s Public Power Energy Tracker is a resource for association members that summarizes public power energy storage projects that are currently online. The tracker is available here.

APPA Energy Storage Working Group

APPA’s Energy Storage Working Group (ESWG) is part of a cooperative agreement between APPA and the Department of Energy (DOE) Office of Fossil Energy and Carbon Management to lower barriers to integrating battery storage with the operation of fossil fuel generation assets.

In 2022, the ESWG developed a report on energy storage challenges, solutions, and opportunities for public power.

APPA is continuing to convene members to get feedback, advice, and other input on the energy storage challenges and opportunities for integrating energy storage. The next ESWG virtual meeting is scheduled for February 23, 2023, from 2 – 3:30 PM ET. The main goal for the meeting will be to discuss the baselines for an energy storage maturity model framework.

If you are interested in joining or learning more about the Energy Storage Working Group, please contact [email protected].