Powering Strong Communities

Long-term storage gets a closer look with the growth of renewables, decarbonization push

Energy storage in recent years has been touted as a potential holy grail for the power sector and the technology continues to see impressive growth in the U.S. in terms of deployments.

With continued growth in wind and solar power, long duration energy storage is seen by some as a key way in which to help smooth the country’s transition to a future where renewable energy plays a central role in the overall power supply mix and the push for decarbonization continues apace.

Long-duration storage is still in the early stage of the product maturity curve and there are many economic and operational challenges that must be addressed if it is to play a key role in supporting the grid.

Why long duration energy storage?

The increased interest in long-duration storage “stems from a growing appreciation and acknowledgement of the need for ‘firm’ low-carbon energy resources to complement variable renewable generators like wind and solar,” noted Dr. Scott Litzeleman, Program Director at the Department of Energy’s (DOE) Advanced Research Projects Agency-Energy (ARPA-E), and Max Tuttman, a Technology-to-Market Advisor at ARPA-E, in an April 2020 blog.

Longer durations “will be needed to displace more capital-intensive baseload and load-following plants (which run at some level of output for most hours). If this can be achieved at a price point where the capital needed to build and operate” a long duration storage system is less than the savings from displacing infrastructure like a load-following power plant, then the opportunities for long duration storage “will begin to flourish.”

While the current generation of lithium-ion batteries “can thrive at shorter durations, where the value that they generate exceeds their cost,” cost increases more rapidly with duration than long duration storage technologies.

Conversely, long duration storage, “due to its more expensive power components, may struggle to be profitable at shorter durations, but its more gradual cost curve enables deployment in scenarios where there are jumps in value” caused by the deferment or displacement assets needed for reliability.

Steps taken in California tied to long duration storage

In California, a significant development related came in October 2020 when eight community choice aggregators (CCAs) launched a joint request for offers (RFO) to procure up to 500 megawatts of long-duration storage.

The RFO is seeking a minimum 10-year contract for grid-charged technologies.

Central Coast Community Energy, CleanPowerSF, Marin Clean Energy, Peninsula Clean Energy, Redwood Coast Energy Authority, San José Clean Energy, Silicon Valley Clean Energy (SVCE) and Sonoma Clean Power are seeking one or more projects to come online by or before 2026 with a minimum discharge period of eight hours.

The CCAs said that long-duration storage provides grid resiliency to support higher concentrations of renewable energy on the grid. “Similar to battery storage today, which helps provide energy during a few evening hours when solar stops producing, long-duration storage will be able to charge from the grid when renewable resources are at their peak, and discharge for periods of 8-16 hours when renewable production is lower,” a news release related to the RFO noted.

A fact sheet produced by the CCAs said that long-duration storage can be a variety of technology solutions that can go beyond four hours and does not have to be paired with a renewable resource such as solar but can be charged by the transmission grid. They said that long-duration is currently undefined by the California Public Utilities Commission.

The expected value of the proposed resource is a primary concern for ranking offers, the CCAs said in the RFO. “Offers will be scored based on the competitiveness of their total cost relative to the value of the project. The value of the project will be derived from stochastic modeling conducted by the joint CCAs along with stress testing under various market and/or regulatory scenarios.”

The deadline to submit proposals in response to the RFO was Dec. 1 and a shortlist was scheduled for completion on March 2.

 In response to a question from Public Power Current, Pamela Leonard, Communications Manager at SVCE, said that given the CCAs “are still in the evaluation stage for the RFO, all that we are able to share for now is that we received bids for 18 different types of long-duration technologies.”

“SVCE is governed by local elected officials who are committed to meeting and exceeding California’s climate and renewable power goals,” SVCE CEO Girish Balachandran. “We have a strong preference to allow each load serving entity the flexibility to choose the means by which they meet these goals,” he said.

“SVCE has proactively procured energy storage far in exceedance of any state mandates because we recognize that storage can increase the value of solar PV resources and help with California’s overall GHG reduction goals and grid reliability.”

A Feb. 24 webinar hosted by the group Our Energy Policy examined a number of topics related to long duration energy storage including the CCA RFO.

Two of the webinar participants, Erik Kim, Power Resources Planner at SVCE, and Jan Pepper, CEO of Peninsula Clean Energy, offered additional details on the RFO process.

Pepper said that 51 entities submitted 314 unique pricing offers in response to the long duration energy storage RFO.

Kim noted that a request for information (RFI) released prior to the issuance of the RFO “provided us with a lot of good information.” The RFI was issued in June 2020.

The robust response to the RFO shows “that the market is ready and that others who are willing to participate in a similar type of” RFO or request for proposals “will see a large amount of choices,” he said.

When discussing policy support to help advance long duration storage, Kim said that “storage is no longer a one-sided thing. It’s a collaborative effort by the grid operators, the regulators” and buyers and developers.

He noted that the CCAs involved in the long duration storage solicitation effort “shopped this around” to the Department of Energy (DOE), as well as the California Public Utilities Commission, California Energy Commission and the California Independent System Operator.

“It’s giving them the exposure that, look, these technologies are coming in,” Kim said. “We have a whole host of technologies with these various durations. You have to be aware of this – that it’s no longer a four-hour game, it’s no longer just a lithium ion game.”

Kim emphasized the need for regulatory certainty. As a load-serving entity, “when we think about capacity, we can’t procure based off of a potential of a mandate to come in place. Because if we go ahead and sign a 10, 15, 20-year contract, and we’re stuck with a construct where it’s still a four hour storage requirement we’ve put in a lot of risk there,” he said.

Public power opposes mandating procurement of expensive long duration bulk storage

Public power groups in California have voiced opposition to mandating the procurement of expensive long duration bulk storage in the state.

An example of this can be found with the proposed Eagle Mountain pumped hydro project near the Joshua Tree National Park in California. In August 2020, investor-owned NextEra Energy Resources said that it “stands ready” to construct Eagle Mountain, a 1,300-MW pumped storage project.

In a guest commentary for CalMatters in August 2020, Michael Webster, executive director of the Southern California Public Power Authority (SCPPA), noted that California’s utilities “have made tremendous progress in meeting aggressive clean energy goals in an affordable manner – and on an international stage.”

Webster said that publicly-owned utilities, which serve about 27% of the state’s electricity needs, are currently procuring more than a third of their electricity from eligible renewable resources and were on track to meet the state’s 2030 and 2045 mandates. 

“Foundational to this success story is the ability of local leaders to decide what is the right combination of energy resources for their communities. With the ongoing COVID-19 crisis poised to exacerbate an already extreme affordability crisis, it is incumbent upon the California Legislature to protect communities from new, unnecessary procurement mandates,” he wrote.

“This includes relentless efforts by Florida-based NextEra to force California’s ratepayers to buy into their multibillion-dollar Eagle Mountain pumped hydropower storage project in Southern California’s desert,” Webster said. 

Webster called for the rejection of Assembly Bill 1720 last year, which he said would “create an unprecedented state-run procurement process for energy storage, effectively usurping local decision-making that has worked so well for ratepayers.” 

Publicly-owned utilities are well-positioned to meet California’s clean energy goals, the SCPPA executive director said. “Our diverse and balanced portfolios already account for storage needs, in part because of our commitment to adopt long-duration energy storage technologies in a manner that appropriately meets the needs of our communities -- not those of out-of-state special interests,” he wrote.

Sarah Taheri, State Government Relations and External Affairs Manager at the Northern California Power Agency (NCPA), said, “Our members are undergoing planning efforts and making investments in clean resources for the future. Any policies that change that trajectory could be costly to implement and yet may not provide additional reliability benefits for publicly owned utility customers.”

Recognizing that emerging technologies “sometimes need support to pencil out for the industry, NCPA has historically advocated for policies that incentivize technologies that need assistance, rather than procurement mandates,” she noted.

Group says state will need to deploy up to 55 GW of long duration energy storage

By 2045, California will need to deploy up to 55 gigawatts (GW) of long duration energy storage to support the state’s 100% clean electricity goals, the California Energy Storage Alliance said in December 2020.

The alliance said that by 2030, the state will need 2-11 GW of new operational long duration energy storage.

These findings were the result of a modelling study released today by the group.

The study, “Long Duration Energy Storage for California's Clean, Reliable Grid,” conducted by Strategen, modeled that California’s future grid will be heavily reliant on intermittent and variable solar generation.

“That dependance underscores the need for dependable, abundant, and long duration energy shifting resources that can provide more than four hours of power, currently the market standard in the state,” the California Energy Storage Alliance said.

The study focuses on long duration energy storage assets, modeled as assets with minimum dispatch durations of 5-, 10-, and 100 hours.

The alliance noted that the California Public Utilities Commission in early 2020 called for 1 GW of new long duration energy storage capacity by 2026.

California Energy Commission looks to fund research projects

Meanwhile, the California Energy Commission (CEC) has taken steps to support the development of long duration storage through grants.

One recipient of those grants is Indian Energy, a privately held microgrid developer and systems integrator, specializing in developing large-scale advanced energy resiliency solutions for the Department of Defense, CCAs and Tribal Utility Authorities. Indian Energy is 100 percent Native American Indian-owned and operated.

In August 2020, Indian Energy said that it was awarded $1.2 million by the CEC to demonstrate a non-lithium ion, long-duration energy storage solution.

Utilizing the grant funds; Indian Energy, along with strategic partners Webcor and KE Storage Corporation (KESC), will develop an energy storage integration and certification nit (VICU), located on the Viejas Band of Kumeyaay lands. The VICU will demonstrate the long duration energy storage capabilities of KESC NextGen flywheel technology. The project will also incorporate 150 kilowatts of Solar PV and provide grid support and resiliency to the Tribe’s emergency medical services facility, Indian Energy said.

More recently, Indian Energy in January 2021 said that it had accepted a grant of more than $5 million from the CEC to develop and demonstrate long-duration, non-lithium ion based energy storage technologies. 


During the Our Energy Policy webinar, Noel Bakhtian, Executive Director at the Berkeley Lab Energy Storage Center, said that “We know that there’s a number of existing technologies that are claiming to be long duration,” mentioning compressed air, pumped hydro and gravity storage.

“But we also have research in the works for innovative new technologies,” said Bakhtian, who served as moderator for the webinar.

She asked webinar participants to weigh in on “various options available and where you might see the most potential.”

“I think there’s a lot of different use cases,” Pepper said. “All of these different technologies solve for different types of issues that we’re trying to solve. They all have different efficiencies,” she said. “They use different types of materials. They have different environmental impacts, so there’s a lot of different things to take into account here.”

She believes that “some are more likely to be able to be used in certain geographies than others, so having a mix is really a good thing.”

Mateo Jaramillo, CEO and Co-Founder of long duration energy storage firm Form Energy, said on the webinar that “the market will want multiple solutions that have different combinations of specifications because that’s how you get to a lowest cost.”

Lithium ion “is the fixture on the grid right now. It will only continue to be deployed at great volumes and so in many ways, the consideration for what else is going to show up on the grid should be, well, what compliments lithium ion?”

In California, NCPA and the Los Angeles Department of Water and Power are evaluating the potential use of green hydrogen for meeting their long-duration needs.

Utilizing green hydrogen in existing natural gas plants has multiple benefits. It will facilitate the transition of existing resources and infrastructure as part of the state’s decarbonization strategy and will continue to provide flexible capacity that is needed to support the integration of intermittent renewables as state RPS policy advances.

Report looks at the role of long duration energy storage in deep decarbonization

The World Resources Institute (WRI) in September 2020 released an issue brief aimed at informing policymakers about the state of storage technologies and how utility-scale storage, including long-duration storage, can support a decarbonized grid.

The issue brief, “The Role of Long-Duration Energy Storage in Deep Decarbonization: Policy Considerations,” said that long duration storage has the potential to support deep decarbonization of the U.S. power sector.

“Storage could play an expanded role in providing sufficient capacity and energy to meet demand at all hours as more variable renewable energy sources come online. Modeling studies of 100 percent clean energy and deep-decarbonization scenarios suggest that long-duration storage technologies could help address future grid needs when storm events reduce renewable generation for days and when seasonal variability of renewable supply extends for weeks,” WRI said.

“However, many studies show a greater need to address these issues when wind and solar exceed 50–60 percent of generation and that shorter-duration storage (four-hour batteries) could address near-term grid need,” the issue brief noted.

Long duration storage “will need to compete economically with alternative technologies and operational strategies, and the ability to increase long-duration storage capacity will depend on achieving significant cost reductions,” WRI went on to say in the issue brief.

“Studies show that seasonal storage technologies would have to decrease substantially in cost—potentially by several orders of magnitude—to compete with alternative solutions such as dispatchable clean energy generation, load shifting, excess renewables capacity, conventional generating capacity with carbon capture, and transmission,” the issue brief said.

The issue brief offered the following recommendations for policymakers:

  • Encourage further development of long-duration storage to widen the range of options available to address grid needs in coming years;
  • Drive improved understanding of regional grid needs and how storage could contribute to deep decarbonization;
  • Support and encourage innovation in storage technology for future grid applications; and
  • Develop new financing and procurement models that better match the needs of long-duration storage assets

In a section of the report that addresses current policy, market and regulatory drivers of utility-scale storage, WRI said that the degree of state involvement in demonstration projects varies greatly.

It noted, for example, that the New York Power Authority (NYPA) took a strong role by hosting an “innovation challenge” that led to a demonstration of zinc-air technology for providing long-duration storage and facilitating renewable integration.

In January 2020, NYPA announced a collaboration with an energy storage company to develop a demonstration energy storage system, using new zinc-air energy storage technology, in New York State.

The project, selected as a winner through the NYPA Innovation Challenge, will have the ability to provide back-up power, help level grid demand, and move the state further toward a carbon-free electric grid supported by renewable energy resources, NYPA noted.

NYPA connected with Zinc8 Energy Solutions Inc., a Vancouver, B.C. developer and manufacturer of long-duration, low-cost zinc-air energy storage solutions, through its NYPA Innovation Challenge, which was launched in May of 2019 in collaboration with the New York University Tandon School of Engineering’s Urban Future Lab (UFL).

NYPA said it selected Zinc8 Energy Solutions’ zinc-air energy storage technology to demonstrate energy storage and demand management that can help build longer duration flexibility into the grid and optimize the role storage resources play.

National Renewable Energy Laboratory

Meanwhile, at the federal level, the DOE’s National Renewable Energy Laboratory (NREL) in January 2020 launched the multiyear storage futures study.

The study explores how energy storage technology advancement could impact the deployment of utility-scale storage and adoption of distributed storage, as well as future power system infrastructure investment and operations.

In the first report in the series, The Four Phases of Storage Deployment: A Framework for the Expanding Role of Storage in the U.S. Power System, a framework is outlined for the possible evolution of the stationary energy storage industry and the power system as a whole. The framework presents a value proposition of cost-competitive storage deployment in four phases, potentially resulting in hundreds of gigawatts of installed capacity and a significant shift in our electric grid, NREL said.

Phase four is considered by NREL as the most uncertain of the phases.

It characterizes a possible future in which storage with durations from days to months is used to achieve very high levels of renewable energy in the power sector, or as part of multisector decarbonization.

Technologies options in this space include production of liquid and gas fuels, which can be stored in large underground formations that enable extremely long-duration storage with very low loss rates. This low loss rate allows for seasonal shifting of renewable energy supply, and generation of a carbon-free fuel for industrial processes and feedstocks.

Phase four technologies “are generally characterized by high power-related costs associated with fuel production and use but with very low duration-related costs”. Thus, traditional metrics such as cost per kilowatt-hour of storage capacity are less useful, and when combined with the potential use of fuels for non-electric sector applications, makes comparison of phase four technologies with other storage technologies more difficult, the study said.

The potential opportunities for phase four technologies measure in the hundreds of gigawatts in the United States, and these technologies could potentially address the residual demand that is very difficult or expensive to meet with renewable energy resources and storage deployed in the first three phases.

“Our four phases framework is intended to describe a plausible evolution of cost-competitive storage technologies, but more importantly, it identifies key elements needed for stakeholders to evaluate alternative pathways for both storage and other sources of system flexibility,” the study said.

Specifically, an improved characterization of various grid services needed, including capacity and duration, could help provide a deeper understanding of the tradeoffs between various technologies, and non-storage resources such as responsive demand. Such a characterization would help ensure the mix of flexibility technologies deployed is robust to an evolving a grid, which will ultimately determine the amount of storage and flexibility the power system will need, NREL said.

Details on the first three phases are available here.


ARPA-E is focused on long duration energy storage development through its DAYS (Duration Addition to electricitY Storage) program.

The projects that comprise ARPA-E’s DAYS program “will develop energy storage systems that provide power to the electric grid for durations of 10 to approximately 100 hours, opening significant new opportunities to increase grid resilience and performance,” ARPA-E notes on its website.

The extended discharge times of DAYS projects “will enable a new set of applications including long-lasting backup power and even greater integration of domestic, renewable energy resources.”

Current DAYS projects include:

Brayton Energy (Location: Hampton, N.H.): The Brayton Energy team will develop a key component to enable a cost-competitive Laughlin-Brayton battery energy storage system that combines thermal storage and innovative turbomachinery to generate power. When the system is charging, an electrically driven heat pump will accumulate thermal energy in a high temperature thermal energy storage medium. During discharge, electricity is produced by heating a gas using the stored thermal energy and sending it through the generation turbine that drives an electric generator;

Form Energy (Location: Somerville, Mass.): Form Energy will develop a long-duration energy storage system that takes advantage of the low cost and high abundance of sulfur in a water-based solution. Previous MIT research demonstrated that aqueous sulfur flow batteries represent the lowest chemical cost among rechargeable batteries. However, these systems have relatively low efficiency. Conversely, numerous rechargeable battery chemistries with higher efficiency have high chemical costs. The solution requires low chemical cost, high efficiency, and streamlined architecture. The team will pursue several competing strategies and ultimately select a single approach to develop a prototype system. Focus areas include developing anode and cathode formulations, membranes, and physical system designs; and

University of Tennessee (Location: Knoxville, Tenn.): The University of Tennessee, Knoxville team will develop an energy storage system based on an innovative electrolyzer/fuel cell combination. Typically, fuel cells produce water from hydrogen and oxygen. The Tennessee team will instead use the fuel cell to produce hydrogen peroxide, a liquid that can be stored. When extra power is needed on the grid, the fuel cell will produce peroxide and electricity. Available electricity then can be used to convert the peroxide back to hydrogen and oxygen during the charging cycle, which can be stored for future use. The benefit of using peroxide rather than water is higher efficiency in both charging and discharging the system.

DOE launches design and construction of grid energy storage research facility

The DOE on March 10 announced the beginning of design and construction of the Grid Storage Launchpad, a $75 million facility located at Pacific Northwest National Laboratory (PNNL) in Richland, Wash.

The DOE said that the Grid Storage Launchpad “will boost clean energy adaptation and accelerate the development and deployment of long-duration, low-cost grid energy storage.”


The American Public Power Association (APPA) supported legislation to accelerate the development of next-generation energy storage that was signed into law in late 2020 as part of a major energy bill that was included in the year-end spending package.

The Better Energy Storage Technology (BEST) Act, authored by U.S. Senators Susan Collins (R-ME), Martin Heinrich (D-NM) and Tina Smith (D-MN), will support grid-scale energy storage research and development and improve the efficiency of the nation’s electric grid, while helping to align research efforts on energy storage technologies, Collins office noted.

  • Demonstration Projects: Requires DOE to undertake three energy storage system demonstration projects, including a minimum of one project designed to address seasonal variations in supply and demand;
  • Technical and Planning Assistance:  Establishes a program at DOE to assist electric utilities with identifying, evaluating, planning, designing, and developing processes to procure energy storage systems;
  • Research and Development:  Requires the DOE to establish a cross-cutting energy storage system research and development program with the goal of reducing the cost and extending the duration of energy storage systems; and 
  • Joint Long-Duration Demonstration Initiative:  Establishes a joint program between DOE and the Department of Defense to demonstrate long-duration storage technologies

APPA  Legislative & Resolutions Committee approves energy storage resolution

APPA’s Legislative & Resolutions Committee in March approved seven policy resolutions during the association’s 2021 virtual Legislative Rally including one related to energy storage.

APPA supports policies that bolster research and development of energy storage technology and urges Congress and federal agencies to support this technology in a manner that recognizes state and local authority, increases reliability, and keeps costs affordable for consumers.

APPA energy storage tracker

APPA’s Public Power Energy Storage Tracker is a resource for association members that summarizes energy storage projects undertaken by members that are currently online. 

Click here for additional details on the tracker.