In for the long haul: Charting the rise of long duration energy storage

ESS energy storage container
ESS is continuing to scale production to meet global demand, with a current production capacity of 80 MW / 800 MWh per year at the company’s Oregon factory. The ESS battery relies on iron flow technology.

The tech march of long duration energy storage (LDES) has successfully pushed the temporal envelope for usage into the double-digit hours range, securing LDES as an integral element of renewable energy system design.

The challenge that remains is for LDES researchers and manufacturers to crunch costs enough that the technology will be more broadly adopted by both commercial and industrial customers.

The myriad solutions for LDES complicate the notion of cooperative cost reduction efforts across the industry. “LDES includes electrochemical energy storage such as static batteries, flow batteries, metal (iron) air batteries, and other battery chemistries,” says the LDES Council. “There are metal-air batteries based on iron and zinc; nickel-hydrogen, redox flow chemistries like Vanadium and zinc-bromine.”

Beyond such chemistries, players including the U.S. Department of Energy, grid operators and utilities are helping to commercialize compressed air, pumped heat, advanced pumped hydro, flywheels, thermal, gravitational and hydrogen LDES solutions, the council explains.

While LDES is more widely utilized in utility-scale applications thus far, some technologies are competitive at the C&I scale.

“C&I microgrids can certainly benefit from LDES technologies,” says Chad Spring, associate director of business development at EnerVenue, which relies on a nickel-hydrogen technology that has been tested for decades on the International Space Station and Hubble Space Telescope. “One example is storing energy from the sun via an onsite PV array during the day, and then dispatching that stored energy at night over a 10 to 12-hour period as a way to ensure 24/7 electricity,”

In one example of a C&I-scale adoption, Coldwell Solar selected LDES from ESS Inc. for microgrids to power California wineries located in wildfire prone areas. The ESS battery relies on iron flow technology.

“The systems will help guard the wineries against the impacts of Public Safety Power Shutoff (PSPS) events and other grid interruptions, while lowering their carbon footprint and supporting the stability of the local grid,” notes an ESS spokesperson. 

Federal Support

Strong support in the LDES cost reduction effort is coming from the federal government, both in terms of tech development via DOE programs, and in terms of tax incentives under the Inflation Reduction Act (IRA).

DOE established its LDES Earthshot in 2021. “Long duration energy storage systems – defined as technologies that can store energy for more than 10 hours at a time – are a critical component of a low-cost, reliable, carbon-free electric grid. In alignment with DOE’s Energy Earthshot Initiative, the Long Duration Storage Shot sets a bold target to reduce the cost of grid-scale energy storage by 90% within the decade,” DOE announced in 2021.

Potentially faster results soon will begin accruing from the IRA’s domestic content requirement for a “bonus” tax incentive, which is inspiring a growing wave of new investment in U.S.-based storage manufacturing.

Lengthening duration, lowering cost

Energy storage technologies typically fall into three duration categories: short duration, which offers fewer than four hours; intraday long-duration with 4 to 12 hours of storage; and ultra long-duration, which is anything over 12, according to an ESS spokesperson. To date, most grid-scale storage projects have been short duration, or under four hours.

LDES has had a variety of definitions in the industry. The National Renewable Energy Laboratory (NREL) “found in a literature review that LDES can refer to duration ranging from 4 hours to multiple days, with 10-plus hours being cited most frequently (consistent with ARPA-E’s definition),” the lab reports.

However, NREL projects that average duration of installed grid storage capacity will only need to be about 6.5 hours to achieve a zero-carbon grid, the ESS spokesperson points out.  

Because of the different chemistries and techniques that comprise LDES, it serves as a complement to, rather than a replacement for short-duration batteries.

“The majority of LDES technologies are not ideal for frequency and voltage regulation or fast frequency response use cases due to response times, ramp rates, etc.  These use cases require faster cycling with higher power over short periods of time,” says Spring.

Given these performance demands, lithium-ion battery chemistry now commands the short duration market. However, that may not always be the case: “All LDES technologies are challenging the lithium incumbent. Salt, iron, zinc, sodium, and vanadium are all chemistries in the LDES space ramping up to take market share away from LFP and NMC [lithium-ion] chemistries,” observes Spring. “Here at EnerVenue, we are actively scaling up our nickel-hydrogen battery technology, which is ideally suited for 2-12 hour use cases.”

Learn more about the EnerVenue technology in this episode from The Pitch from our archives:

Cost driven by discharges

The end-user demand for discharge cycling frequency and duration is key to determining cost for LDES.

“Essentially, three parameters determine the economic competitiveness of a storage asset: 1) power-specific cost, i.e., how much the storage costs per unit of power ($/kW), 2) energy-specific cost, i.e., how much the storage costs per unit of energy ($/kWh), and 3) round-trip efficiency, i.e., how much energy is lost per charge-discharge cycle,” explains Miikka Jokinen, lead, exploration and scouting for Wärtsilä’s Next Business Lab.

As discharge periods lengthen, LDES costs go down compared with lithium. “The longer the duration of the storage asset, the fewer full charge-discharge cycles it is going to make, and the impact of the lower [LDES] efficiency [compared with short duration batteries] is smaller,” Jokinen explains. “Typically, [LDES is] not competitive in similar power and energy requirements compared with lithium-ion and other short-duration storage technologies. But in long-duration applications (8 hours or more) short-duration storage prices escalate more than LDES prices do.”

LDES tech therefore often benefits projects in the 100 MW/1000-1500 MWh range or 10- to 15-hour duration.

“This is driven by the lower energy-specific cost of these technologies, meaning that the medium for energy storage is more affordable than in Li-ion batteries,” Jokinen suggests.

At times, both frequent cycling and long duration are required in an LDES system. Applications that require both frequent cycling and long-duration storage is where ESS Inc. says its iron flow technology shines as a “cost-effective energy storage technology over a system’s 25-year design life.”

“Today, ESS technology offers at least a 15% improvement in capital efficiency compared with lithium-ion; that is bankable thanks to our industry-leading guarantee from Munich RE,” the ESS team tells us.

Domestic content demands

One factor driving LDES economics is the new trend for U.S.-based manufacturing. One example of new U.S. investment in LDES is EnerVenue, which is investing in U.S. manufacturing to cover IRA content requirements, recently announcing a 1 million sq ft gigafactory in Shelby County, Ken.

“When it comes to short-duration lithium-based technologies, it is certainly more difficult to have a high level of U.S.-based content,” Spring says. “With over 80% of lithium coming from China — and with the vast majority of that content being allocated to the electric vehicle industry — it is imperative that non-lithium chemistries fast-track their commercial and manufacturing readiness to accelerate the clean energy and energy storage revolution.”

Similarly, ESS is continuing to scale production to meet global demand, with a current production capacity of 80 MW / 800 MWh per year at the company’s Oregon factory.

European demand for LDES may help spur more U.S. investment in manufacturing. Germany’s LEAG and ESS recently joined the Energy Resilience Leadership Group (ERLG), a multi-stakeholder initiative led by Breakthrough Energy and Siemens Energy that brings together corporate CEOs, political leaders, financial institutions, and startups at the technology frontier, LEAG notes. The group was launched at the 2023 Munich Security Conference with the goal to enhance Europe’s energy resilience by rapidly bringing emerging climate technologies to scale.

Still, wider domestic sourcing for LDES will remain a challenge for years to come Jokinen believes: “Some LDES companies are in line with IRA expectations, others are partly complying, and this seems to be technology dependent. Currently, it is perhaps too bold to say that LDES would have broader supply chains simply because the industry is still in its infancy.”


Charles W. Thurston is a contributor to Solar Builder.

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