We are building the greatest power plants in human history—and then throwing away the electricity.
In 2025, U.S. grid operators shattered their own curtailment records from just the year before. Texas is dumping over 8 TWh of wind and solar per year into the void. PJM's curtailment jumped sixfold in 2024; 2025 surpassed that.
The IEA confirms the picture is global and accelerating: curtailment volumes rose roughly 55% in 2024 alone, with negative-price hours surging across China, Germany, Brazil, Chile, the UK, and Ireland. Annual U.S. curtailments now total roughly 20 million MWh, enough wasted clean energy to power every home in Los Angeles for a year.
The diagnosis is simple. We have built an abundance of cheap, clean generation. What we have not built is the ability to move it through time. A four-hour lithium-ion battery can shave the evening peak. But it cannot bridge a three-day windless cold snap in February.
Enter Long-Duration Energy Storage (LDES), systems designed to store electricity for ten hours to ten days. The LDES Council and McKinsey estimate the world may need 85 to 140 terawatt-hours of long-duration storage by 2040 to keep the lights on in a decarbonized power system. Installed capacity today sits at roughly 247 gigawatt-hours (1 terawatt = 1000 gigawatts). The gap is staggering.
This report highlights the top energy storage stocks to watch, grouped by technology.
Grid-Scale Integrators
These companies deploy grid-scale storage at volume. Rather than inventing new chemistries, they are building, financing, and operating battery plants as infrastructure assets.
- Fluence Energy (NASDAQ: FLNC) is the global leader in grid-scale battery storage, born from a Siemens/AES joint venture and now independent. Fluence posted $2.3 billion in FY2025 revenue and is guiding $3.2–$3.6 billion for FY2026, with roughly 85% already in backlog. Its $30 billion pipeline is growing 30% per quarter. Fluence deploys lithium-ion systems, but its real moat is software: an AI-powered bidding platform that optimizes storage assets across nearly 50 markets. The institutional pick for the current grid storage buildout.
- Energy Vault (NYSE: NRGV) began life as a gravity-storage curiosity, stacking concrete blocks with cranes, but has reinvented itself into a storage integrator and asset owner. FY2025 revenue hit $203.7 million, up over 340% year-over-year, with a $1.3 billion backlog. The shift to watch is its "own-and-operate" model: instead of just building storage for clients, Energy Vault is owning the assets and selling the electrons, creating recurring revenue. It has also moved into AI data center infrastructure with Crusoe. Still unprofitable, but contracted capacity jumped from 65 MW to 540 MW in twelve months.
Electrochemical LDES Beyond Lithium
Lithium-ion dominates 4-hour storage. But lithium is expensive, degrades with time, and carries fire risk, all of which worsen the longer you try to stretch the discharge window. The companies below are commercializing alternative chemistries for 8-to-100+ hour durations.
- Eos Energy Enterprises (NASDAQ: EOSE) makes zinc-based batteries—aqueous, non-flammable, manufactured entirely in the U.S.—for 3-to-12+ hour grid applications. FY2025 revenue hit $114.2 million, more than 7x the prior year, and management is guiding $300–$400 million for 2026. But Eos remains deeply unprofitable despite the topline growth. The company's survival hinges on IRA manufacturing tax credits and whether it can convert a $19 billion pipeline before cash runs out.
- ESS Tech (NYSE: GWH) builds iron flow batteries using iron and saltwater, possibly the cheapest, safest chemistry in LDES. But ESS is in survival mode: FY2025 revenue collapsed to $1.6 million as it wound down legacy contracts to pivot toward a new gigawatt-scale platform. Strategic lifelines include an IP acquisition of VoltStorage, a $9.9 million U.S. Air Force contract for batteries in Alaska, and Google's participation in a pilot project with Salt River Project. A deep-value bet on whether iron flow can ever reach commercial scale.
- Form Energy (private, valued above $1 billion) is the most consequential company on this list. Its iron-air battery stores electricity by rusting iron pellets and discharges by un-rusting them. The result is 100-hour duration, at a projected cost below one-tenth of lithium-ion. Form launched commercial production at its Weirton, West Virginia factory and in rapid succession announced a 30 GWh project with Xcel Energy and Google (the largest battery by energy capacity ever announced), a 12 GWh agreement with Crusoe for AI data centers, and its first international deployment in Ireland. Pipeline: 75+ GWh. Watch for an IPO.
- Invinity Energy Systems (AIM: IES) manufactures vanadium flow batteries, a chemistry prized for near-zero degradation over decades. Its largest project, a 20.7 MWh system in southeast England partially funded by the UK government, is expected online in 2026. Vanadium flow occupies a sweet spot for high-cycle, 6-to-12-hour applications where calendar life matters more than energy density. The risk: vanadium price volatility and Invinity's small scale.
Thermomechanical LDES
These companies store energy not as chemistry but as physics, via liquid air, pressurized CO₂, or superheated carbon. The working medium is cheap and doesn't degrade. The challenge: first-of-a-kind project risk.
- Highview Power (private, £300 million raised) stores energy as liquid air cooled to −196°C, shrunk to 1/700th its volume, held in insulated tanks, and then re-expanded through turbines to generate power. Highview broke ground in late 2025 on a 50 MW/300 MWh facility in Carrington, Manchester, backed by the UK Infrastructure Bank, Centrica, Rio Tinto, Goldman Sachs, and the Lego family's KIRKBI. Operation is targeted for late 2026. Two additional 3.2 GWh projects have been deemed eligible for Ofgem's cap-and-floor support scheme. If all three proceed, Highview would deliver over 7 GWh of dispatchable storage to the UK grid.
- Energy Dome (private, backed by Google and Ørsted) stores energy by compressing CO₂ in a closed-loop cycle with no emissions or rare materials—just water, steel, and carbon dioxide under an inflatable dome. Its 20 MW/200 MWh facility in Sardinia came online in mid-2025. Replication is now underway: India's NTPC is building one, Alliant Energy has approval to begin construction in Wisconsin, and Google has formed a global partnership to deploy CO₂ Batteries at data centers across three continents. Each unit: 5 acres of flat land, off-the-shelf components, 75%+ round-trip efficiency, no degradation over 30+ years. The closest thing to plug-and-play LDES.
- Antora Energy (private, $309 million raised) heats blocks of solid carbon with excess renewable electricity until they glow white-hot, then converts the heat back to electricity. Antora is targeting industrial decarbonization, rather than the grid, with a zero-carbon process heat for steel, cement, and chemicals. If it works, it represents a parallel market for renewable overcapacity.
Private Bellwethers
These are pre-revenue or early-revenue companies whose technologies, if proven, could reshape the cost curve. Watch as IPO candidates, acquisition targets, or cautionary tales.
- Noon Energy ($28 million Series A, backed by Aramco Ventures and Emerson Collective) has built a carbon-oxygen battery that charges by splitting CO₂ and discharges by recombining it, using a reversible fuel cell. In January 2026, Noon demonstrated 100+ hours of continuous discharge from a containerized system in California. Like a flow battery, you can scale storage capacity independently of power output, the critical feature for multi-day applications.
- Malta Inc. (Alphabet X spinout, $50 million Series B, backed by Breakthrough Energy Ventures) stores electricity as heat in molten salt and cold in antifreeze, then reconverts it to power using a heat engine. Malta's pitch is utility-scale systems built from industrial-grade components with no exotic materials. Pre-commercial, but presenting deployment economics to the DOE.
- e-Zinc ($25 million Series A, backed by Toyota Ventures, Mitsubishi Heavy Industries, Eni Next) is building a zinc-air battery in Toronto for the 10-to-100+ hour window. Like Noon, its architecture decouples power from energy capacity. The near-term play is displacing diesel generators for multi-day backup, a market with immediate demand and less regulatory friction than grid-scale interconnection.
Signals to Watch
For those tracking long-duration energy storage stocks, here are the near-term signals that matter:
- Curtailment as a demand signal. Every megawatt-hour of wasted renewable energy is a megawatt-hour that a storage asset could have captured and sold at peak prices. As curtailment accelerates, the economic case for LDES writes itself.
- The data center catalyst. Form Energy's Crusoe and Google deals signal a new buyer class. AI data centers need 24/7 firm power, and clean-energy commitments require it to be clean. LDES paired with renewables is emerging as a pragmatic path: cheaper than small modular reactors (which remain years from deployment), more scalable than geothermal, and more bankable than green hydrogen.
- The UK cap-and-floor regime. Ofgem's LDES support scheme guarantees a minimum revenue floor for qualifying projects. Final awards are expected summer 2026. If this unlocks pension and sovereign-fund capital, other governments will imitate it.
- U.S. tax credits. IRA manufacturing credits and investment tax credits are keeping several of these companies alive. Any legislative threat, or expansion, will move the entire sector.
- Form Energy's IPO. 75+ GWh under agreement, a factory in production, marquee customers. The most obvious LDES IPO candidate. Its timing and valuation will set the tone for the sector's access to public-market capital.
The grid has enough generation. It badly needs a vault. And while the physics of each company’s approach differs, the thesis is the same: the sun and wind produce more energy than we can use in real time; whoever can bank the surplus will own the most valuable infrastructure of the clean-energy era.