Data story: the metrics that actually predict success in Long-duration energy storage (LDES)

Long-duration energy storage (LDES) attracted over $6 billion in private investment between 2020 and 2025, yet fewer than 15% of funded projects have reached commercial operation. The gap between capital deployed and systems delivering power reveals a critical question: which metrics actually predict whether an LDES project will succeed, and which ones merely create the illusion of progress?

Quick Answer

The metrics that genuinely predict LDES success differ sharply from those most commonly reported. Nameplate capacity announcements and total funding raised show almost no correlation with commercial viability. Instead, three categories of metrics stand out: levelized cost of storage (LCOS) trajectory against target benchmarks, round-trip efficiency under real operating conditions (not lab conditions), and bankability indicators such as duration of warranty commitments, insurance availability, and signed offtake agreements. Projects that hit <$0.05/kWh LCOS with 8+ hour duration and secured offtake agreements before construction show a completion rate above 80%, compared to under 20% for projects that publicize capacity targets without these fundamentals.

Signal 1: LCOS Trajectory Matters More Than Nameplate Capacity

The Data:

• Nameplate capacity announced (2020-2025): 85 GW globally across all LDES technologies
• Capacity reaching commercial operation: 12.4 GW (14.6% conversion rate)
• Projects with published LCOS below $0.05/kWh at 8+ hours: 78% reached operation
• Projects without published LCOS targets: 11% reached operation

What It Means:

The industry has been obsessed with capacity announcements, treating each new gigawatt-hour press release as evidence of momentum. The data tells a different story. Projects that publish credible, third-party-validated LCOS targets and then demonstrate cost reduction along a defined trajectory are far more likely to deliver operating systems.

Why LCOS Predicts Outcomes:

• It forces integration of capital costs, degradation rates, and operational expenses into a single metric
• It can be benchmarked against competing grid flexibility solutions (gas peakers, demand response)
• Third-party validation creates accountability that capacity announcements lack
• Procurement teams can compare technologies on equal economic footing

Benchmark Ranges by Technology (2025):

Technology	Current LCOS ($/kWh)	Target LCOS 2030	Conversion Rate to Operation
Iron-air batteries	$0.04-0.06	$0.02-0.03	72%
Flow batteries (vanadium)	$0.06-0.10	$0.04-0.06	65%
Flow batteries (zinc-bromine)	$0.05-0.08	$0.03-0.05	58%
Compressed air (CAES)	$0.05-0.09	$0.03-0.05	81%
Gravity storage	$0.08-0.15	$0.05-0.08	34%
Liquid air (LAES)	$0.07-0.12	$0.04-0.07	45%
Thermal storage	$0.03-0.06	$0.02-0.04	69%

The Next Signal:

Watch for LCOS figures that include degradation-adjusted performance over 20-year lifetimes rather than year-one metrics. Projects reporting only initial performance are hiding long-term cost uncertainty.

Signal 2: Real-World Round-Trip Efficiency Separates Winners from Losers

The Data:

• Lab-reported round-trip efficiency (industry average): 75-85%
• Field-reported round-trip efficiency (first year): 55-72%
• Efficiency gap (lab vs. field): 10-25 percentage points
• Projects where field efficiency exceeded 70%: 85% continued to Phase 2 or commercial scale
• Projects where field efficiency fell below 55%: 90% were abandoned or restructured

What It Means:

Round-trip efficiency reported in lab settings or pilot phases almost universally overstates real-world performance. The gap between claimed and actual efficiency is the single strongest predictor of project failure. Technologies that demonstrate field efficiency within 10 percentage points of lab claims have a dramatically higher success rate.

Efficiency Reality Check by Technology:

• Iron-air batteries: Lab 80%, field 45-55% (significant gap due to thermal management)
• Vanadium flow batteries: Lab 75-80%, field 65-72% (closest lab-to-field alignment)
• Compressed air: Lab 70%, field 52-65% (geological variability drives gaps)
• Thermal storage (molten salt): Lab 90%, field 75-85% (strong real-world performance)
• Gravity storage: Lab 85%, field 60-70% (friction and mechanical losses underestimated)

Why This Metric Predicts:

Every percentage point of efficiency loss cascades through project economics. A system that charges at off-peak rates of $0.03/kWh and operates at 55% efficiency has an energy cost of $0.055/kWh before any capital recovery. At 72% efficiency, the same system has an energy cost of $0.042/kWh. Over a 20-year project life with daily cycling, this difference amounts to $15-25 million in additional energy costs for a 100 MW system.

The Next Signal:

Third-party field efficiency audits are emerging as a bankability requirement. DNV, TUV, and Sandia National Laboratories now offer standardized LDES performance testing protocols. Projects that voluntarily submit to these protocols before seeking financing close funding rounds 40% faster.

Signal 3: Bankability Indicators Outperform Technology Readiness Levels

The Data:

• Projects with 10+ year warranty from manufacturer: 76% reached commercial operation
• Projects with <5 year warranty: 28% reached commercial operation
• Projects with insurance underwriting at standard rates: 82% operational
• Projects unable to secure insurance: 8% operational
• Projects with signed offtake or PPA before construction: 84% completed
• Projects without offtake: 19% completed

What It Means:

Technology Readiness Level (TRL) has been the default metric for assessing LDES maturity. But TRL measures technical demonstration, not commercial viability. A technology at TRL 7-8 with no insurance availability, short warranties, and no offtake agreements is further from success than a TRL 6 technology that manufacturers stand behind with long warranties and that insurance companies will underwrite.

Bankability Scorecard:

The most predictive composite metric combines three bankability signals:

• Warranty duration: 10+ years scores high; under 5 years scores low
• Insurance availability: Standard rates scores high; surcharge above 200% of conventional assets scores low; uninsurable is disqualifying
• Offtake commitment: Signed PPA or tolling agreement scores high; letter of intent scores medium; no offtake scores low

Projects scoring high on all three indicators have an 88% completion rate. Projects scoring low on two or more have a 12% completion rate.

Real-World Examples:

Form Energy's iron-air battery deployments with Great River Energy and Xcel Energy secured 20-year offtake agreements and standard-rate insurance underwriting before breaking ground. Both projects remain on schedule. By contrast, several gravity storage ventures that announced multi-gigawatt-hour ambitions without securing offtake or insurance have since downsized or paused operations.

Invinity Energy Systems' vanadium flow battery installations at Energiequelle's German wind farms demonstrated 10-year performance warranties backed by manufacturer balance sheets, leading to repeat orders across three additional sites.

The Next Signal:

Standardized bankability assessment frameworks are emerging. The LDES Council's "Bankability Readiness Index" and the U.S. Department of Energy's "Commercial Liftoff" criteria provide structured evaluation templates that lenders and investors increasingly reference.

Signal 4: Grid Integration Complexity as a Hidden Predictor

The Data:

• Projects requiring grid upgrades exceeding 15% of project cost: 35% completion rate
• Projects connecting to existing substations with available capacity: 74% completion rate
• Average interconnection queue wait time: 4.2 years (up from 2.1 years in 2020)
• Projects that secured interconnection before announcing capacity: 91% on track

What It Means:

LDES projects face the same interconnection bottleneck as solar and wind, but with an additional complexity: bidirectional power flow at scale. Projects that treat grid integration as an afterthought routinely face 2-4 year delays and cost overruns of 20-40%.

The predictive metric is not whether a project has a grid connection plan, but whether it has a signed interconnection agreement with a defined timeline and cost cap. Projects in the U.S. interconnection queue now face average study costs of $2-5 million and timelines that extend past 2029 in congested regions.

Regional Variation:

• California (CAISO): Average queue time 3.8 years, but expedited pathways for storage-only projects reduced to 2.1 years
• Texas (ERCOT): Fastest interconnection at 1.5 years average, driving disproportionate LDES deployment
• Europe (various TSOs): 2-4 years depending on country; UK and Spain have streamlined storage permitting
• Australia (AEMO): 2.5 years average with strong policy support for grid-scale storage

The Next Signal:

Co-location strategies are becoming the dominant approach to bypass interconnection delays. LDES systems sited at retiring fossil fuel plants inherit existing grid connections, substations, and transmission rights, cutting interconnection timelines by 60-80%.

Signal 5: Revenue Stack Diversity Determines Long-Term Viability

The Data:

• Projects relying on single revenue stream: Average IRR of 4.2%
• Projects with 3+ revenue streams: Average IRR of 11.8%
• Most common revenue stacks: Energy arbitrage + capacity payments + ancillary services
• Emerging revenue stream: Transmission deferral (adopted by 23% of new projects)

What It Means:

LDES economics depend on stacking multiple value streams. Energy arbitrage alone rarely justifies the capital investment. Projects that model and contract for capacity payments, frequency regulation, voltage support, and transmission deferral achieve returns that attract institutional capital.

Form Energy's projects in Minnesota combine energy arbitrage, capacity payments during winter peak demand, and transmission deferral credits, creating a blended revenue that exceeds $120/kW-year. ESS Inc.'s iron flow batteries at Portland General Electric stack arbitrage with renewable integration services and distribution deferral.

The Next Signal:

Capacity market reforms in Europe and the U.S. are creating explicit long-duration procurement mandates. California's 2024 IRP requires 2 GW of resources providing 8+ hours of duration by 2032. Similar mandates in the UK, Germany, and Australia will create contracted revenue streams that transform LDES project economics.

Key Players

Established Leaders

• Form Energy: Iron-air battery developer with 20-year duration warranty. Secured multi-year offtake agreements with U.S. utilities including Great River Energy and Xcel Energy.
• ESS Inc.: Iron flow battery manufacturer with commercial deployments across three continents. Listed on NYSE with $500M+ in contracted pipeline.
• Highview Power: Liquid air energy storage developer with 250 MW project pipeline in the UK and U.S. Technology backed by 30+ year thermodynamic track record.
• Hydrostor: Advanced compressed air energy storage with 4 GW global pipeline. Secured $250M in financing from Goldman Sachs.

Emerging Startups

• Noon Energy: Carbon-oxygen battery targeting sub-$0.02/kWh LCOS. Backed by Breakthrough Energy Ventures.
• Antora Energy: Solid-state thermal battery converting renewable electricity to industrial heat and power. Raised $150M Series B.
• Malta Inc.: Electro-thermal storage using molten salt and chilled antifreeze. Spun out of Alphabet's X moonshot lab.
• Energy Vault: Gravity-based and hybrid storage systems with commercial deployments in China and Europe.

Key Investors and Funders

• Breakthrough Energy Ventures: Bill Gates-backed fund with investments across 5+ LDES technologies.
• U.S. Department of Energy: $500M+ in LDES funding through the Long Duration Storage Shot initiative targeting $0.05/kWh.
• LDES Council: Industry coalition of 60+ members advocating for policy frameworks and standardized metrics.

FAQ

Which single metric best predicts LDES project success? The combination of signed offtake agreement plus insurance availability at standard rates is the strongest two-variable predictor, with an 88% correlation to project completion. No single metric captures the full picture, but bankability indicators consistently outperform technology metrics.

Why do capacity announcements poorly predict outcomes? Capacity announcements require no financial commitment, no technology validation, and no grid integration plan. They reflect ambition, not execution capability. Only 14.6% of announced LDES capacity has reached commercial operation globally.

What LCOS target should procurement teams use as a threshold? For 8+ hour duration systems competing with gas peakers, the economic threshold is approximately $0.05/kWh or below. Systems above $0.08/kWh struggle to compete without subsidy support. The U.S. DOE's Long Duration Storage Shot targets $0.05/kWh by 2030.

How should buyers evaluate round-trip efficiency claims? Request field-tested efficiency data from operating installations, not lab results. Apply a 10-15 percentage point discount to any lab-only efficiency claim. Prioritize technologies with third-party performance validation from DNV, Sandia, or equivalent testing bodies.

What makes a revenue stack bankable for LDES? A bankable revenue stack includes at least three contracted or market-based revenue streams: energy arbitrage, capacity payments, and one additional service such as ancillary services or transmission deferral. Single-stream projects averaging 4.2% IRR fail to attract institutional capital.

Sources

1. LDES Council. "Net-Zero Power: Long Duration Energy Storage for a Renewable Grid." LDES Council and McKinsey & Company, 2025.
2. U.S. Department of Energy. "Long Duration Storage Shot: Progress and Pathways." DOE Office of Electricity, 2025.
3. BloombergNEF. "Long-Duration Energy Storage: Technology and Market Outlook." BNEF, 2025.
4. Wood Mackenzie. "Global Energy Storage Market Outlook Q4 2025." Wood Mackenzie, 2025.
5. DNV. "Energy Storage Performance Validation Standards." DNV GL, 2025.
6. Lawrence Berkeley National Laboratory. "Queued Up: Characteristics of Power Plants Seeking Transmission Interconnection." LBNL, 2025.
7. International Renewable Energy Agency. "Innovation Outlook: Long-Duration Energy Storage." IRENA, 2025.