Trend watch: Long-duration energy storage (LDES) in 2026 — signals, winners, and red flags

Global long-duration energy storage deployments reached approximately 2.4 GW of new capacity in 2025, and cumulative investment in LDES technologies surpassed $8 billion between 2020 and 2025 according to the Long Duration Energy Storage Council. For grid operators, utilities, and energy investors, 2026 marks the year when LDES transitions from pilot curiosity to procurement necessity. Renewable penetration levels above 50% in multiple markets are exposing the limits of four-hour lithium-ion batteries, and the technologies capable of storing energy for 10 to 100+ hours are entering their first wave of commercial-scale deployment.

Why It Matters

The physics of grid decarbonization creates an unavoidable storage gap. Solar generation peaks at midday and drops to zero at sunset. Wind output fluctuates across hours and days. Lithium-ion batteries, which dominate the current storage market, are economically optimized for durations of two to four hours. They can shift solar energy from afternoon to evening, but they cannot bridge multi-day wind droughts, seasonal demand swings, or week-long weather events that suppress renewable output across entire regions.

The International Energy Agency estimates that achieving net-zero electricity systems globally will require 1.5 to 2.5 TWh of long-duration storage capacity by 2040. That represents a roughly 100-fold increase from today's installed base. The investment required is measured in hundreds of billions of dollars, and the procurement decisions made in 2026 and 2027 will determine which technologies, companies, and supply chains capture this market.

The economic case is also sharpening. As grids add more renewables, wholesale electricity prices during periods of high solar or wind output are collapsing toward zero or going negative. Storage systems that can absorb cheap energy during these surplus windows and discharge it 12 to 72 hours later capture significant arbitrage value. Simultaneously, capacity markets and reliability mandates increasingly require grid operators to procure firm, dispatchable resources that can deliver power for durations that lithium-ion cannot serve economically. LDES fills precisely this gap.

For regions still dependent on natural gas peaker plants for reliability, LDES represents the pathway to retiring those assets without compromising grid stability. California's 2025 grid emergencies during extended heat waves underscored the risk of relying solely on short-duration batteries when demand peaks persist for multiple consecutive days.

Signals to Watch

Iron-Air Batteries Reach Commercial Deployment

Form Energy began construction of its first commercial iron-air battery manufacturing facility in Weirton, West Virginia in 2023, with production capacity targeting GWh-scale output by 2026. The company's 100-hour iron-air battery system uses iron, water, and air as its primary inputs, materials so abundant and inexpensive that system costs are projected to fall below $20 per kilowatt-hour of storage capacity at scale. Georgia Power, Xcel Energy, and Great River Energy have signed offtake agreements for early deployments ranging from 10 MW to 85 MW. The critical signal to track in 2026 is whether Form Energy's Weirton facility achieves nameplate production rates and whether the first utility installations demonstrate projected round-trip efficiency of approximately 45% under real operating conditions. Low round-trip efficiency is inherent to iron-air chemistry and acceptable for multi-day applications, but it must be validated at scale to maintain investor confidence.

Flow Batteries Scale Beyond Demonstration

Vanadium redox flow batteries (VRFBs) and zinc-bromine flow systems are moving from demonstration to repeated commercial procurement. China deployed over 600 MWh of vanadium flow battery capacity in 2024 alone, anchored by the 100 MW/400 MWh Dalian installation, the world's largest flow battery project. In the West, Invinity Energy Systems secured orders for multiple 10 to 50 MWh projects across the United States and United Kingdom. ESS Inc. shipped its iron flow battery systems to customers in six countries. The signal to watch is whether flow battery manufacturers can reduce installed costs below $300 per kilowatt-hour, the threshold at which they become competitive with lithium-ion for eight-hour-plus applications. Vanadium price volatility remains a concern, but leasing models and vanadium recycling programs are emerging to mitigate this risk.

Compressed Air and Gravity Storage Enter Procurement Pipelines

Mechanical storage technologies are attracting utility-scale contracts. Hydrostor, a Canadian company developing advanced compressed air energy storage (A-CAES), secured a 500 MW project in California and a 200 MW project in Australia, both targeting commercial operation before 2028. Energy Vault deployed its first gravity-based energy storage system in China, using a crane system to stack and lower composite blocks to store and release energy. These mechanical approaches offer 30 to 50 year asset lifetimes, significantly longer than electrochemical systems. Watch for construction milestones and financing closings as leading indicators that utilities are willing to commit capital to these technologies at scale.

Policy Mandates Create Guaranteed Demand

The U.S. Department of Energy's Long Duration Energy Storage Shot initiative targets a 90% cost reduction for systems delivering 10+ hours of duration. California's Senate Bill 1314, enacted in 2025, directs the California Public Utilities Commission to procure at least 1,000 MW of long-duration storage by 2032. The EU's revised Electricity Market Design includes provisions that favor long-duration flexibility resources in capacity mechanisms. India announced targets for 40 GWh of LDES procurement as part of its renewable integration strategy. These policy signals reduce demand risk for manufacturers and project developers, enabling larger capital commitments and faster scale-up.

Winners and Red Flags

Winners

Iron-air technology developers with utility offtake agreements are positioned to capture the multi-day storage market that no other technology can serve economically. Form Energy's partnerships with major U.S. utilities and its domestic manufacturing strategy align with both market demand and Inflation Reduction Act incentives. The company's use of abundant, non-toxic materials eliminates the supply chain bottlenecks that constrain lithium-ion and vanadium flow batteries.

Flow battery manufacturers with cost reduction roadmaps and operating track records will capture the 8 to 24 hour duration segment where lithium-ion economics break down. Companies like Invinity Energy Systems, ESS Inc., and China's Rongke Power benefit from the inherent advantage of flow batteries: decoupled power and energy sizing allows operators to increase storage duration by simply adding more electrolyte, without replacing the entire system.

Utilities and grid operators that procure LDES proactively will avoid the reliability crises and peaker plant dependencies that increasingly constrain grids with high renewable penetration. Early procurement also locks in pricing before demand-driven cost increases materialize as multiple markets compete for limited initial manufacturing capacity.

Red Flags

LDES startups without utility contracts or credible manufacturing partners face a capital-intensive path to commercialization. The gap between laboratory prototypes and grid-scale deployment requires hundreds of millions of dollars in factory investment, years of permitting, and utility customers willing to accept first-of-a-kind technology risk. Companies relying solely on venture capital without strategic utility or industrial partners should be assessed skeptically.

Technologies with unproven round-trip efficiency at scale risk disappointing investors and customers. Several LDES approaches demonstrate attractive economics on paper but have not operated continuously at grid scale through full seasonal cycles. Executives should demand independently verified performance data from operational installations before committing procurement budgets.

Regions without LDES procurement mandates or incentive frameworks will fall behind in grid reliability as renewable penetration increases. Markets that continue to rely exclusively on lithium-ion for all storage needs will face growing curtailment costs, reliability gaps during extended weather events, and escalating dependence on gas peaker plants.

Sector-Specific KPI Benchmarks

Sector	KPI	Laggard	Average	Leader	Notes
Grid Storage	Levelized cost of storage, 10+ hr ($/MWh)	>$250	$150-200	<$100	Iron-air targeting lowest tier
Grid Storage	Duration capability (hours)	<8	10-24	>100	Multi-day systems emerging
Grid Storage	Round-trip efficiency (%)	<40%	50-70%	>75%	Flow batteries lead on efficiency
Grid Storage	Cycle life (cycles to 80% capacity)	<3,000	5,000-10,000	>20,000	Flow batteries inherently durable
Manufacturing	Annual production capacity (MWh)	<100	500-2,000	>5,000	Scale-up phase in 2026
Project Dev	Permitting to operation timeline (months)	>48	24-36	<18	Regulatory frameworks maturing

What's Working

Iron-air battery development is progressing on schedule. Form Energy's Weirton facility represents a $760 million investment supported by $290 million in DOE grants and $150 million in IRA manufacturing tax credits. The company's partnership with ArcelorMittal to source iron from domestic steel production creates a uniquely resilient supply chain. Multiple utility partners have committed to initial deployments that will generate the operational data needed to accelerate subsequent procurement.

Vanadium flow batteries are proving bankable for 4 to 12 hour applications. The Dalian VRFB project in China has operated since 2022, providing grid regulators with multi-year performance data that validates the technology's durability and reliability. Invinity Energy Systems' installations across the UK and U.S. have demonstrated capacity retention above 99% after thousands of cycles, a characteristic that lithium-ion systems cannot match over equivalent timeframes.

Hybrid storage architectures combining lithium-ion with LDES are emerging as the practical optimum. Several utilities are deploying lithium-ion for fast response and short-duration shifting alongside flow or iron-air batteries for extended duration needs. This hybrid approach captures the strengths of each technology while avoiding over-reliance on a single chemistry. Portland General Electric's Clean Energy Plan explicitly calls for a mixed portfolio of two-hour, eight-hour, and 100-hour storage resources.

What Isn't Working

Round-trip efficiency remains a commercial liability for some technologies. Iron-air batteries operate at approximately 45% round-trip efficiency, meaning more than half the energy used to charge the system is lost as heat. While this is acceptable for multi-day storage where the alternative is curtailment or gas peaking, it limits the technology's competitiveness for shorter-duration applications where lithium-ion achieves 85% to 92% efficiency. Hydrogen-based storage systems face even larger efficiency penalties, typically 30% to 40% round-trip.

Vanadium supply concentration creates pricing risk. Approximately 65% of global vanadium production originates from China and Russia. Vanadium pentoxide prices spiked above $35 per kilogram in 2024 before retreating, introducing cost uncertainty that complicates long-term project economics. Vanadium leasing models and electrolyte recycling mitigate this exposure, but the fundamental supply concentration remains a strategic vulnerability.

Permitting and interconnection timelines are delaying projects. LDES installations face the same interconnection queue backlogs plaguing all grid-connected resources in the United States, where average wait times exceeded 5 years in 2025 according to Lawrence Berkeley National Laboratory. Novel technologies also face additional scrutiny from permitting authorities unfamiliar with their safety and environmental profiles.

Key Players

Established Leaders

• Form Energy is developing iron-air batteries targeting 100-hour storage at system costs below $20/kWh. Its Weirton, WV manufacturing facility is the first commercial-scale iron-air factory globally.
• Invinity Energy Systems manufactures vanadium flow batteries with installations across the U.S., UK, and Australia, and reported a 300% increase in contracted pipeline from 2024 to 2025.
• ESS Inc. produces iron flow batteries for commercial and utility-scale applications, with deployments across North America, Europe, and Asia-Pacific.
• Hydrostor is developing advanced compressed air energy storage projects totaling over 4 GW globally, with flagship projects in California and Australia.

Emerging Challengers

• Energy Vault commercialized gravity-based energy storage and is expanding into hybrid battery-plus-gravity systems for utility customers.
• Ambri is scaling liquid metal battery technology using calcium and antimony electrodes, targeting 12+ hour grid storage at low cost.
• EnerVenue manufactures nickel-hydrogen batteries originally developed for satellites, now adapted for grid storage with 30,000+ cycle durability.
• Noon Energy is developing carbon-oxygen batteries targeting 100-hour duration with higher round-trip efficiency than iron-air alternatives.

Key Investors and Funders

• U.S. Department of Energy has committed over $1 billion in grants, loans, and tax credits specifically for LDES manufacturing and deployment through the IRA and Bipartisan Infrastructure Law.
• Breakthrough Energy Ventures has invested in Form Energy, Ambri, and other LDES startups as part of its grid decarbonization thesis.
• Temasek, Saudi Aramco Energy Ventures, and strategic corporate investors are backing LDES companies as complements to their renewable energy portfolios.

Action Checklist

• Assess your grid or facility's storage duration requirements by modeling renewable intermittency scenarios including multi-day wind droughts, extended cloud cover, and seasonal demand variation to determine whether four-hour lithium-ion adequately addresses reliability needs
• Issue a request for information to at least three LDES technology providers (flow battery, iron-air, compressed air, or mechanical) to establish baseline cost, timeline, and performance expectations for 10+ hour applications
• Evaluate hybrid storage architectures that pair existing or planned lithium-ion capacity with longer-duration LDES systems to optimize across fast-response and multi-day reliability requirements
• Engage interconnection and permitting processes early, as LDES projects face the same queue backlogs as other grid-scale resources but may also require additional review for novel technologies
• Monitor policy developments including state-level LDES procurement mandates, IRA manufacturing credits, and capacity market rule changes that create or remove economic incentives for long-duration storage
• Negotiate vanadium or other critical material supply agreements or leasing arrangements if pursuing flow battery technology, to mitigate commodity price volatility
• Require independently verified performance data from operational installations before finalizing procurement commitments, particularly for first-of-a-kind deployments

FAQ

Q: How does LDES differ from standard lithium-ion grid storage? A: Standard lithium-ion batteries are optimized for two to four hours of discharge duration. LDES technologies are designed for 10 to 100+ hours, addressing multi-day renewable intermittency, seasonal shifts, and extended weather events that short-duration batteries cannot cover. LDES systems typically use different chemistries (iron-air, vanadium flow, zinc-bromine) or mechanical approaches (compressed air, gravity) that sacrifice some round-trip efficiency for dramatically lower cost per unit of stored energy at long durations.

Q: What is the expected cost trajectory for LDES technologies? A: The DOE's Long Duration Energy Storage Shot targets a 90% cost reduction for 10+ hour systems relative to 2020 baselines, aiming for storage costs below $0.05 per kilowatt-hour of delivered energy. Iron-air batteries are targeting system costs below $20/kWh of capacity, roughly one-fifth the cost of lithium-ion systems at equivalent durations. Flow batteries are projected to reach $150 to $200/kWh installed cost by 2028 as manufacturing scales. Compressed air and gravity systems offer the lowest marginal cost of additional duration, since extending storage requires only larger caverns or taller structures.

Q: Which LDES technology is most commercially ready? A: Vanadium redox flow batteries are the most commercially mature LDES technology, with multi-year operational track records at utility scale (notably the 100 MW/400 MWh Dalian project). Iron-air batteries are the most promising for multi-day (100+ hour) applications but are still in the early stages of commercial manufacturing. Compressed air energy storage has decades of operational history at two legacy facilities but is only now scaling through next-generation adiabatic designs from companies like Hydrostor.

Q: How should organizations evaluate round-trip efficiency for LDES? A: Round-trip efficiency matters less for LDES than for short-duration storage because the alternative to LDES is typically curtailment (wasting renewable energy entirely) or running gas peaker plants. A system with 45% round-trip efficiency that stores otherwise curtailed solar energy still delivers value that a 90% efficient lithium-ion battery cannot, because the lithium-ion system would be prohibitively expensive at 100-hour duration. Evaluate LDES efficiency in the context of avoided curtailment value and avoided fossil fuel costs, not in direct comparison to lithium-ion metrics.

Sources

• Long Duration Energy Storage Council. (2025). "LDES Global Market Report 2025." https://www.ldescouncil.com/reports
• International Energy Agency. (2025). "Energy Storage Outlook: Technologies and Deployment Pathways to 2040." https://www.iea.org/reports/energy-storage
• Form Energy. (2025). "Form Energy Announces Progress on Weirton Manufacturing Facility." https://www.formenergy.com
• U.S. Department of Energy. (2025). "Long Duration Energy Storage Shot Fact Sheet." https://www.energy.gov/eere/long-duration-storage
• Lawrence Berkeley National Laboratory. (2025). "Queued Up: Characteristics of Power Plants Seeking Transmission Interconnection." https://emp.lbl.gov/queues
• BloombergNEF. (2025). "Long-Duration Energy Storage: State of the Industry 2025." Bloomberg New Energy Finance.
• Invinity Energy Systems. (2025). "Annual Report and Operational Update." https://www.invinity.com
• Wood Mackenzie. (2025). "Flow Battery Market Outlook and Vanadium Supply Analysis." https://www.woodmac.com