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?
LDES technologies include mechanical, thermal, electrochemical, and chemical storage systems that can store energy economically for days or even weeks. Ideally, these technologies will use low-cost and readily available raw materials and have high energy densities. However, there is currently no clear leader among long-duration energy storage technologies, but there are several promising options.
The United States Department of Energy defines LDES as energy storage systems capable of providing electricity for durations of 10 hours or more. The Bipartisan Infrastructure Law appropriates $505 million to develop LDES demonstrations “to validate new technologies and enhance the capabilities of customers and communities to integrate grid storage more effectively.”
According to Greentech Media, the five most promising long term energy storage technologies are:
This involves pumping water from a low to a high reservoir. When electricity is needed, water is released and generates electricity at hydroelectric power plants. Once built, these long term energy storage projects are inexpensive to operate. However, few sites are suitable for this application, because they disrupt ecosystems, and projects can cost billions of dollars.
The first use of PSH dates back to the 1890s in Switzerland and Italy, and it was first used in the United States in the 1930s. There are currently 43 PSH plants in the United States, and there is the potential to double the pumped storage hydropower capacity for long term energy storage.
Stacked Blocks
Like pumped hydro, this technology involves converting electricity into potential energy through the use of heavy blocks. However, it doesn’t have many of the same challenges and can be deployed in a wider range of locations.
The Swiss company Energy Vault creates stacked block energy storage systems that power crane motors to move concrete blocks up a tower. Then, the crane motors can go in reverse when lowering blocks, creating electricity in a process that is about 85% efficient. Energy Vault was recently selected for a 440-mWh long term energy storage system in Nevada.
Liquid Air Energy Storage (LAES)
This long term energy storage technology involves storing electricity in the form of liquid air or Nitrogen at temperatures below -150 degrees Celsius. A charging device uses off-peak electricity to power a liquefier, which produces liquid air held in an insulated tank at low pressure. A power recovery unit re-gasifies liquid air to power a turbine to generate electricity. Unlike pumped hydro, there aren’t geographical constraints for this long term energy storage technology, and it uses components in other commercial applications.
Highview Power specializes in cryogenic energy storage and is based in the United Kingdom and the United States. It has numerous projects in various stages of development that utilize LAES technology, including two existing pilot projects.
Underground Compressed Air
This concept uses excess electricity to pump compressed air into a cavern. Releasing the compressed air powers a generator to produce electricity as needed.
Although this approach to long term energy storage has geologic constraints, the Canadian company Hydrostor is trying to overcome this by using purpose-built caves or mine shafts. It has a variety of projects in development or operation in the United States, Canada, Chile, and Australia.
Flow Batteries (Redox Flow Batteries)
This electrochemical cell provides chemical energy from two chemical components dissolved in liquids pumped through the system on separate sides of a membrane between two electrodes. Most batteries contain two tanks of liquids that circulate in their own respective spaces.
ESS is a publicly traded company based in the United States that produces flow batteries with a liquid electrolyte containing dissolved iron. It has a deal with the Sacramento Municipal Utility District in California to provide 200 MW of its products for long term energy storage.
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 allocating $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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