The Case for Long-Duration Energy Storage (LDES)
Why Long-Duration Storage Matters Now
Four-hour lithium-ion batteries dominate today's storage market. However, they cannot bridge multi-day renewable energy gaps, replace gas peaker plants that run for 12–16 hours at a stretch, or provide seasonal balancing in northern locations. LDES systems are designed to close that gap, and can discharge for eight hours or longer (up to days or weeks).
The LDES market is small but accelerating. Two technologies (iron-air flow batteries and compressed air) have crossed from demonstration into commercial scale, state utility commissions are approving LDES into the rate base, and corporate offtakers are signing long-term contracts.
What's Inside
- Where LDES works best today. Industrial process heat currently offers the strongest economics. Multi-day reliability for uptime-sensitive buyers like data centers, diesel displacement at off-grid sites, and renewable curtailment capture are also viable now.
- Where lithium-ion stops being economical. Lithium-ion batteries excel at short durations, but after about 12 to 24 hours, they stop being economical. That's where LDES comes in.
- What LDES needs to scale. Four conditions must converge for LDES to reach gigawatt levels: capital costs falling toward US$20 per kWh, markets willing to pay for long-duration, sustained competitiveness against improving lithium-ion cost and performance, and policy that encourages decarbonization.
- How PJM, ERCOT, and CAISO compare. Relae modeled LDES deployment under deep decarbonization and high load growth. If clean, firm alternatives stay expensive, PJM alone could need between 31–177 GW of LDES. If clean, firm power becomes more affordable, PJM's needs fall to 11 GW at most.
Frequently Asked Questions
LDES systems can discharge electricity for eight hours or longer, sometimes for days or even weeks at a time. There are four types of LDES technologies: mechanical, chemical, electrochemical, and thermal.
In situations that require power for longer than a four-hour battery can provide, like steady heat at an industrial site or continuous operations at a data center.
The cost of clean, firm power (like geothermal and small modular reactors) could change how much LDES gets built on US grids by as much as sixteen-fold. Without deep decarbonization, LDES deployment will be negligible in PJM, ERCOT, and CAISO.
Relae is the trusted advisor in energy and climate, delivering scientifically rigorous, technically advanced, and commercially grounded solutions. Our scientists, engineers, and policy experts pair systems-level knowledge with project-level understanding to help clients achieve their energy and climate goals.
For this paper, Relae conducted an independent assessment of where LDES technologies stand today, backed by our own capacity expansion modeling across PJM, ERCOT, and CAISO.
Douglas Bryan
Douglas Bryan
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Douglas Bryan is an energy economist with a decade of experience across global energy markets, including the US, Canada, Europe and Australia. He specializes in evaluating the impacts of policy and investment decisions through advanced energy system modeling.
Douglas has led a diverse range of analyses on utility integrated resource planning, electricity decarbonization policy, and market advisory due diligence. He has extensive experience evaluating the business case for power sector investments, including battery and long-duration energy storage, and advising utilities on the greenhouse gas implications of load and resource planning scenarios. He also leads Relae’s battery storage modeling Beyond electricity, he has simulated deployment of Carbon Dioxide Removal technologies, including Direct Air Capture, BECCS and Ocean Alkalinity Enhancement, via energy-economy modeling.
A trusted expert in energy system and economic analysis, Douglas previously served as a Senior Project Manager at Navius Research, where he presented at regulatory tribunals and led technical workshops. At Relae, he leverages this background to help clients navigate complex decarbonization efforts. He provides the rigorous analysis needed to quantify the carbon impact of operations and identifies the most effective strategies for integrating low-carbon energy solutions into power portfolios.
Julia Millot
Julia Millot
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Julia Millot is a Senior Power Decarbonization Manager at Relae, working directly with clients on measuring and reducing electricity-related GHG emissions and optimizing power portfolios. Julia has over a decade of experience working with clients in the energy, tech, retail, financial, and manufacturing sectors on growth and climate strategies. Prior to Relae, she led US Climate Advisory at Position Green and ran her own consultancy, Green Opal Advisors, focusing on corporate decarbonization.
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