Non-lithium long-duration storage technologies have attracted more than $6bn in funding over the past decade. Yet outside China, the operational capacity of emerging alternative technologies remains below a gigawatt-hour. Several early developers have stalled, exited, or pivoted toward lithium-ion-based projects to remain bankable.

Recent policy interventions have brought LDES technologies back into focus. Italy's MACSE tender, GB's LDES Cap and Floor, and Germany's planned long-duration procurement all target longer durations. These go beyond what merchant markets currently reward.

Similar mechanisms are emerging globally. New South Wales' LTESA targets 8+ hour storage with the latest tender round awarding all contracts to lithium-ion projects. In the US, New York's Index Storage Credit provides targeted support for longer-duration assets. California has also moved forward with dedicated LDES procurement, requiring utilities to contract for storage with durations of 8 hours or longer.

With dedicated LDES tenders now launching across Europe and the US, the question is which technologies are ready to compete.

This research examines:

• Which long-duration storage technologies exist today, and how mature are they
• How they compare economically with lithium-ion
• Where alternative LDES technologies offer value
• What real-world power markets actually require in terms of storage duration

For any further information on this topic, reach out to the author - timothee@modoenergy.com.

Alternative LDES remain pre-commercial despite $6bn in funding

​Multiple technologies are racing to deliver cost-competitive storage. They target durations that lithium-ion cannot economically serve. Rising renewable penetration exposes multi-day gaps when wind and solar generation are low. These technologies aim to fill that window.

​These alternative LDES technologies fall into four families:

• Electrochemical systems (flow batteries, zinc hybrid, metal-air)
• Mechanical systems (adiabatic compressed air, liquid air, gravity-based storage, novel pumped hydro)
• Thermal storage (latent and sensible heat)
• Chemical storage/Hydrogen

​Despite significant investment, commercial progress remains uneven.

​Some technologies are advancing. Highview Power's 50 MW liquid-air project at Carrington reached financial close in 2024. Energy Dome has deployed its first commercial CO₂ battery in Sardinia. Form Energy opened its first large-scale iron-air manufacturing facility in West Virginia. Invinity has delivered multiple vanadium flow battery projects totalling over 50 MWh. Hydrostor secured an LTESA for its Silver City compressed air project in New South Wales.

​Others have stalled. NGK Insulators shut down its sodium-sulfur battery production. Ambri restructured after failing to commercialise its liquid metal battery. Corre Energy was liquidated in November.

Overall, this mixed outcome reflects the difficulty of competing with lithium-ion's established supply chain and operating track record.

​These technologies also target very different durations. Flow batteries and zinc hybrids aim for 6-12 hours, where lithium-ion already operates but faces degradation concerns at high cycling.

Compressed air, liquid air and some thermal systems aim for 12-24 hours, seeking a window where lithium-ion economics become less certain. Meanwhile, Iron-air batteries target multi-day discharge and aim for an extremely low cost per MWh stored.

These duration claims remain largely declarative. Most technologies lack sufficient commercial trading operations backlog to validate performance at scale or prove their cost assumptions in real-world deployments.

Alternative LDES face unfavourable cost trajectories against falling lithium-ion prices

Cost data for alternative LDES remains sparse and often modelled rather than observed. Company disclosures typically rely on projected learning curves rather than realised performance. Nevertheless, comparing technologies across discharge duration and cycling patterns allows us to confront stated ambition with economic reality.

​Pumped hydro remains dominant globally, with more than 160 GW installed. It offers proven reliability and low operating costs where topography allows. However, in mature markets, most suitable sites have been developed. Greenfield projects face high CAPEX and long development timelines.

Lithium-ion offers a cost advantage for durations up to 8-10 hours. Around 10 hours, the cost advantage of lithium-ion over alternative LDES narrows.

Liquid-air storage and CO₂ batteries show promising results at longer durations. Form Energy's iron-air battery quotes attractive costs for multi-day storage, but deployment history remains limited.

Vanadium flow batteries have demonstrated deployment in fire-sensitive environments and high-cycle applications. However, electrolyte costs remain high. Learning curves have been too shallow to compete with lithium-ion at scale. Beyond 10-12 hours, their degradation advantage becomes less relevant as cycling intensity declines.

Non-cost factors create niches for alternative LDES

Cost dominates most storage investment decisions. But in specific contexts, safety requirements, grid constraints, asset lifetime, and supply chain considerations shift the balance toward alternative technologies despite higher upfront costs.

Typical niches where lithium-ion is at a disadvantage:

• Fire-sensitive environments favour non-flammable technologies. Dense urban areas and critical infrastructure increasingly block lithium-ion batteries due to safety and insurability grounds. Flow batteries, thermal storage and iron-air face fewer permitting hurdles.
• Isolated grids reward long asset life. Islands and remote sites cannot easily replace storage. Alternative LDES designed for 30-40 year lifetimes hold advantages over lithium-ion's 15-20 year cycle. But these locations also demand proven reliability and minimal maintenance. Unproven technologies face higher deployment barriers in isolated systems.
• ​Backup and resilience applications prioritise calendar lifetime over cycling, favouring technologies that retain capacity over long idle periods.
• Supply chain and sovereignty constraints increasingly shape procurement. American IRA and European Critical Raw Materials Act favour bulk materials and domestic manufacturing over lithium-ion's dependence on Asian production and critical minerals.
• Industrial heat creates a distinct market. Thermal technologies like Antora’s primarily decarbonise industrial process heat. Electrical storage via turbine is a logical expansion, placing them in a complementary arena to grid-focused LDES.

​Alternative LDES developers are increasingly diversifying. Many now pair lithium-ion for near-term competitiveness with their own technology to capture longer-duration procurement

Alternative LDES developers are increasingly diversifying their project configurations. Many now pair lithium-ion for near-term competitiveness with their own LDES technology for expected procurement for longer durations.

Energy Vault, for instance, has delivered a lithium-ion-hydrogen hybrid project. Highview Power is pairing liquid air storage with lithium-ion.

This hybrid approach captures merchant revenues in the near term while positioning for contracted support from network operators targeting long-duration capacity.

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Storage demand splits into daily cycling, multi-day gaps and seasonal needs

The economics of long-duration storage remain uncertain in merchant markets. Many LDES projects will depend on contracted support from network operators or regulators targeting specific system needs.

Three distinct timescales dominate today's use cases.