How Long Term Energy Storage Will Impact The Future Of Renewables
- Sarah Lozanova
- 2 days ago
- 11 min read
As the world transitions to renewable energy sources, the issue of intermittency must be overcome. If renewable electricity sources, including wind and solar power, can completely phase out the use of coal and natural gas, we will need to have energy around the clock. Sometimes, wind and solar farms produce surplus power when demand is low, resulting in waste. Therefore, long term energy storage is essential for slowing climate change and ensuring a stable energy supply.
Although lithium-ion batteries in utility-scale battery storage systems are great for short-term energy storage, they are not currently cost-effective for long periods of time, and they can experience issues with thermal runaway. Advancing long-duration energy storage (LDES) technologies is critical to the decarbonization of energy by providing system flexibility and managing fluctuations in energy supply and demand. Let’s explore this topic to gain a greater understanding of how long term energy storage can help decarbonize energy in a reliable and cost-effective manner.
What Is Long Term Energy Storage?
Long term energy storage (LTES) refers to technologies capable of storing energy for extended durations—typically 10 hours or more—allowing electricity generated from renewable sources to be used when production is low. The U.S. Department of Energy defines long duration energy storage as systems that can discharge electricity for 10+ hours at rated power, a critical capability for supporting grid stability and decarbonization.
LDES technologies span mechanical, thermal, electrochemical, and chemical systems. These solutions aim to be low-cost, scalable, and composed of abundant materials while offering high energy densities. While there’s no dominant long term battery storage technology yet, several options are gaining traction in pilot and demonstration phases.
To accelerate deployment, the Bipartisan Infrastructure Law appropriated $505 million to support LDES demonstrations and help communities integrate grid-scale storage. According to Greentech Media, the five most promising long term energy storage technologies are:
This is the most established form of long term energy storage, accounting for over 90% of grid-scale energy storage worldwide. This system operates by pumping water from a lower reservoir to an upper reservoir when excess electricity is available—usually from renewable sources like solar or wind. When demand rises, the stored water is released through turbines to generate electricity, providing reliable and flexible power.
PSH systems can store energy for hours or even days, making them a proven form of long duration energy storage. Once constructed, they offer low operational costs and long lifespans—many facilities operate effectively for 50 years or more. However, PSH projects require specific topography and large-scale infrastructure, often costing billions of dollars and facing environmental and regulatory challenges. These systems can impact aquatic ecosystems, disrupt river flows, and require extensive permitting and community engagement.
The first uses of PSH date back to the 1890s in Switzerland and Italy, with the United States adopting the technology in the 1930s. As of 2024, the U.S. has 43 operational PSH facilities providing over 22 gigawatts (GW) of capacity. According to the U.S. Department of Energy, there is the potential to double pumped storage capacity, adding up to 40-50 GW to support the growing need for long term battery storage alternatives.
New approaches, like closed-loop PSH systems that do not rely on natural bodies of water, are being explored to reduce environmental impact and expand feasible locations. As the grid transitions to high levels of renewable penetration, modernizing and expanding pumped storage hydropower will play a critical role in balancing supply and demand over longer durations.
Stacked Blocks
Stacked block systems offer a gravity-based approach to long term energy storage that mimics the principles of pumped hydro but with fewer site limitations. Instead of water, these systems store energy by lifting and lowering massive blocks, using cranes to convert excess electricity into potential energy.
The Swiss company Energy Vault is a leader in this emerging space, having developed a modular tower system that uses custom-designed composite blocks. During periods of low demand and surplus electricity—typically from renewable sources like wind or solar—electric motors power cranes to lift the blocks into a stacked formation. When electricity is needed, the process is reversed: the blocks are lowered, and the motors function as generators, converting the potential energy back into electricity.
These systems boast a round-trip efficiency of up to 85%, rivaling that of lithium-ion batteries but without the associated chemical degradation or fire risk. Importantly, stacked block energy storage is scalable, relatively easy to deploy, and has a long operational life, making it a compelling option for long duration energy storage.
In a significant milestone for the industry, Energy Vault was selected to build a 440-megawatt-hour long term energy storage system in Nevada. Unlike pumped hydro, stacked block systems do not require specific topographical features and can be built near industrial or utility sites, offering more flexibility in siting.
As utilities and grid operators seek alternatives to conventional long term battery storage, gravity-based technologies like Energy Vault’s stacked blocks provide a mechanically simple, durable, and potentially lower-cost solution for storing energy at scale.
Liquid Air Energy Storage (LAES)
This innovative long term energy storage technology that converts surplus electricity into stored energy by liquefying air or nitrogen at extremely low temperatures—typically below -150°C. The process begins when off-peak or excess renewable energy powers a liquefaction unit, cooling and compressing ambient air into a liquid state. This liquid air is then stored in low-pressure, insulated cryogenic tanks.
When electricity demand rises, the system reverses: the liquid air is exposed to ambient or waste heat, causing it to rapidly expand back into a gas. This expansion drives a turbine, generating electricity. Since air is freely available and LAES systems can be built anywhere with access to electricity and adequate space, this long term battery storage alternative has none of the geographical constraints associated with pumped storage hydropower or other gravity-based systems.
LAES uses mature technologies from the industrial gas and power generation sectors, making it highly scalable and relatively low-risk. It also offers advantages such as long asset life (over 30 years), no degradation in capacity over time, and the ability to utilize waste heat or cold from industrial processes, which can significantly boost system efficiency.
Highview Power, a leader in long duration energy storage, has made significant strides in commercializing LAES. The company has successfully operated pilot plants in the UK, including a 5 MW/15 MWh facility near Manchester. In 2023, it broke ground on one of the world’s largest LAES facilities in Carrington, Greater Manchester—a 50 MW / 300 MWh project expected to provide grid-balancing services and support renewable integration. Highview also has additional projects under development in the U.S. and Europe, with plans to scale up to gigawatt-hour capacities.
As the global push for decarbonization intensifies, LAES is emerging as a viable long term energy storage solution for utilities, especially where chemical battery storage may pose safety, sustainability, or cost challenges. Its flexibility, scalability, and reliance on abundant resources make it an increasingly attractive option in the growing ecosystem of long duration energy storage technologies.
Underground Compressed Air Energy Storage (CAES)
This is a proven and increasingly refined long term energy storage solution that stores surplus electricity in the form of high-pressure air. During times of excess power generation—typically from renewable sources like solar or wind—electricity is used to run industrial compressors that inject air into underground caverns, aquifers, or depleted mines. When demand rises, the compressed air is released, heated (often using natural gas or recovered thermal energy), and passed through a turbine to generate electricity.
CAES systems are typically built using natural geological formations like salt caverns, but newer approaches are expanding site possibilities. Traditional systems, such as those in Huntorf, Germany (1978) and McIntosh, Alabama (1991), have demonstrated long-duration capability, with storage cycles ranging from 8 to over 24 hours. However, they require specific geologic conditions and supplementary fossil fuels, which have limited widespread deployment.
To address these limitations and modernize the technology for net-zero goals, Canadian energy company Hydrostor is leading the development of advanced-adiabatic CAES systems, sometimes referred to as A-CAES. These systems capture and store the heat generated during air compression and reuse it during expansion, eliminating the need for natural gas and making them a truly clean long duration energy storage option.
Hydrostor’s innovation also includes engineered storage caverns, allowing deployment even in regions without ideal geologic formations. These purpose-built shafts or repurposed mine sites make CAES more accessible and cost-competitive, with an expected lifespan of 50+ years and minimal environmental impact.
Williston Lake Project (California) – A proposed 500 MW / 4,000 MWh facility in partnership with California’s Central Coast power providers, designed to deliver up to 8 hours of dispatchable clean power daily.
Silver City Project (Australia) – A 200 MW / 1,500 MWh system near Broken Hill, expected to support remote mining operations and enhance regional grid stability.
Goderich A-CAES Facility (Ontario, Canada) – Hydrostor’s flagship demonstration plant has been successfully operating since 2019 and continues to validate the commercial viability of advanced CAES technology.
These systems offer high round-trip efficiency (up to 70%), low operating costs, and excellent scalability, positioning underground compressed air as a key contender in the long term battery storage market. CAES can deliver grid services such as peak shaving, frequency regulation, and renewable load shifting, making it a valuable complement to intermittent energy sources.
Flow Batteries (Redox Flow Batteries)
Flow batteries—also known as redox flow batteries—are a versatile class of long term battery storage technology that store energy in externally circulated liquid electrolytes. These electrolytes contain active chemical species dissolved in solution and are stored in separate tanks. During charging and discharging cycles, the liquids are pumped through a central electrochemical cell, where ions are exchanged across a membrane, creating an electrical current.
Unlike lithium-ion batteries, where energy storage capacity is tied to the volume of the battery cell, flow batteries decouple power (determined by the size of the stack) from energy capacity (determined by the size of the tanks). This modular design makes them ideal for long term energy storage, particularly in grid applications that require daily or multi-day energy discharge over 10+ hours.
The most common flow battery chemistries include:
Vanadium Redox Flow Batteries (VRFB) – Use vanadium ions in different oxidation states for both electrolytes, reducing cross-contamination and improving cycle life.
Iron Flow Batteries – Use iron and saltwater-based electrolytes for non-toxic, cost-effective performance, suitable for long-duration applications.
Zinc-Bromine and All-Organic Systems – Emerging chemistries focused on increasing energy density, lowering cost, and improving environmental safety.
ESS Inc., a U.S.-based company headquartered in Oregon, is a leading manufacturer of iron flow batteries, known for using Earth-abundant, non-flammable, and fully recyclable electrolytes. Their iron flow battery design offers a 25-year operating life with no capacity degradation, making it highly attractive for utilities and industrial users seeking long term energy storage solutions.
Recent flow battery projects include:
Sacramento Municipal Utility District (SMUD), California: ESS signed a landmark agreement to deliver up to 200 MW / 2 GWh of iron flow battery systems to SMUD, aimed at supporting the utility’s goal to achieve zero carbon emissions by 2030. The project will be one of the largest flow battery installations globally.
ESS Energy Center, Oregon: The company recently expanded its manufacturing capacity to meet growing demand for U.S.-made, IRA-compliant long duration energy storage systems.
San Diego Gas & Electric (SDG&E): ESS is also deploying smaller pilot projects in California to support wildfire mitigation and microgrid resilience.
Flow batteries typically offer lower energy density than lithium-ion systems but compensate with long cycle life, enhanced safety, and the ability to withstand deep discharges without performance loss. These features make them well-suited for daily cycling, renewables smoothing, and time-shifting solar or wind generation.
As utilities and grid operators seek alternatives to lithium-ion for durations exceeding 10 hours, flow batteries are gaining ground as a reliable, scalable, and environmentally friendly long term energy storage solution.
Why Long Term Energy Storage is Critical
As the world moves toward renewable energy, long term storage solutions are increasingly vital to ensure a stable and reliable power supply.
🔋 Increasing Demand for Storage: The shift towards renewable energy sources amplifies the need for long-duration energy storage to balance energy production and consumption.
🔋 Challenges of Intermittency: Renewable sources like solar and wind are intermittent, leading to periods of excess generation and shortfalls. Solar energy is unavailable at night, and wind energy can fluctuate, complicating grid stability.
🔋 Grid Stabilization: Long term energy storage solutions can store excess energy during peak production times and release it during low generation periods, ensuring consistent energy availability. This capability helps stabilize the grid and mitigates the risks associated with renewable energy intermittency.
🔋 Support for Renewable Transition: Effective energy storage enhances the reliability of renewable energy systems, reducing dependence on fossil fuels. It facilitates the integration of renewable energy into the grid, promoting a cleaner, more sustainable energy future.
🔋 Power Grid Services: Long term storage can provide essential grid services, including voltage and frequency regulation, necessary for maintaining overall grid stability.
🔋 Cost Efficiency: Long term energy storage can lower overall energy costs by optimizing energy availability and reducing the need for backup fossil fuel generation.
Benefits Of Long Term Energy Storage
There are many benefits of being able to store energy for long durations.
✅ Grid Stability and Reliability: Long term energy storage helps balance supply and demand, reducing the risk of blackouts and ensuring a steady energy supply even during peak usage times.
✅ Renewable Energy Integration: It allows for the effective integration of intermittent renewable sources like solar and wind, storing excess energy generated during peak production times for use when production is low.
✅ Environmental Benefits: By enabling greater use of renewable energy and reducing reliance on fossil fuels, long term storage helps lower greenhouse gas emissions and mitigate climate change.
✅ Economic Savings: It can lower energy costs by storing cheap, off-peak energy and releasing it during expensive peak periods, as well as reducing the need for expensive grid upgrades.
✅ Energy Security: Enhances energy independence and security by reducing the need for imported fuels and providing a reliable backup during emergencies or natural disasters.
Challenges of Long Term Energy Storage
Long term energy storage faces several significant challenges encompassing technological, economic, regulatory, and environmental factors. Here’s a deeper look at these challenges:
Technological Challenges
Many storage systems, such as advanced batteries (e.g., lithium-ion, solid-state) and hydrogen storage, are still in the developmental stages. Key issues include:
Efficiency: The round-trip efficiency of many storage technologies remains low. For example, traditional lithium-ion batteries can have efficiencies of around 80-90%, while some long-duration technologies like pumped hydro can be lower, affecting overall energy retention.
Energy Density: Many current technologies do not provide adequate energy density for long-term storage, making them less viable for widespread use. Hydrogen, while promising, requires significant infrastructure for storage and distribution.
Lifespan: Over time, the degradation of energy storage systems poses a significant hurdle. For instance, while lithium-ion batteries may last 10-15 years, alternative technologies like flow batteries need to prove their longevity and reliability over similar or longer periods.
Economic Hurdles
The economic landscape for long term energy storage technologies is challenging due to the following:
High Initial Costs: The upfront capital required for deploying advanced energy storage systems can be substantial, often deterring investment. Technologies like pumped hydro and compressed air energy storage require significant infrastructure investments.
Uncertainty of Returns: The financial viability of these projects often depends on energy market dynamics and regulatory incentives, which can vary significantly over time, leading to uncertainty regarding long-term financial returns.
Regulatory Issues
Regulatory frameworks often lag behind technological advancements, leading to:
Lack of Clear Guidelines: Many regions lack comprehensive policies that specifically address integrating LTES systems into existing energy grids, creating barriers to deployment.
Incentives: Without appropriate incentives and support mechanisms, utilities and private investors may hesitate to commit to long term energy storage projects, despite their potential benefits.
Environmental and Safety Concerns
Long term energy storage technologies must also navigate environmental and safety challenges, which include:
Environmental Impact: The production and disposal of certain storage technologies can have significant environmental consequences, necessitating rigorous assessments and sustainable practices.
Safety Risks: Technologies such as lithium-ion batteries pose safety risks, including fire hazards and chemical leaks. Hydrogen storage also presents safety challenges related to flammability and high-pressure storage requirements.
The LDES Council
The LDES Council is a nonprofit, executive-led organization with over 60 members in 19 countries. It is dedicated to accelerating long term energy storage technologies and applications. The council provides guidance on LDES systems to governments, utility providers, and large electricity users, and its members include technology innovators, investors, and energy users.
The LDES Council is dedicated to the wide-scale adoption of long-duration energy storage to accelerate the use of clean energy, replace fossil fuels, and achieve carbon neutrality. It provides member-driven, fact-based guidance and research to help achieve net zero for energy grids by 2040.
Long Term Energy Storage Puts Climate Goals Within Reach
About 20% of the electricity produced in the United States in 2021 was from renewable sources, primarily wind, hydropower, and solar, according to the Energy Information Administration. However, to slow climate change, it is critical to phase out the use of fossil fuels as quickly as possible. The advancement of LDES is essential for curtailing greenhouse gas emissions while ensuring a reliable and cost-effective power supply.
Several companies are constructing long term energy storage systems, including Energy Vault, Highview Power, Hydrostor, and ESS, and the Bipartisan Infrastructure Law is allocated $505 million for LDES demonstrations. As more LDES projects are constructed, it will be easier to evaluate which technologies are the most promising for large-scale deployment for the power sector.
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