In a world increasingly fuelled by renewable energy, long duration energy storage becomes more important by the day. Wind and solar power are essential for decarbonisation, but their natural variation means we need a way to balance energy supply and demand.
The UK government is running a cap-and-floor scheme to incentivise investment in LDES which we will discuss later in this article. In this context, LDES refers specifically to long-duration electricity storage rather than the broader category of long-duration energy storage.
The term ‘long duration’ in LDES refers to energy storage systems capable of discharging stored energy for extended periods. For context, the most common form of energy storage in the UK is battery energy storage systems (BESS), which typically store energy for 1-4 hour durations. In contrast LDES can store energy for up to months at a time!
There are multiple LDES solutions, each storing energy in different ways. Key technologies include compressed air, thermal, electrochemical, mechanical, and chemical storage. In this article, we’ll explore these different approaches and how they support a more resilient, low-carbon energy system.
Types Of Long Duration Energy Storage Solutions
A reliable and flexible energy system requires multiple storage technologies working in synergy.
Mechanical Storage
Mechanical storage systems use kinetic or potential energy to store and release electricity.
Pumped Hydro Storage (PHS)
Water is pumped to a higher elevation when surplus renewable energy is available and releases it through turbines to generate electricity during peak demand.
Liquid Air Energy Storage (LAES)
Air is cooled to a liquid state for storage, then reheats it for expansion, driving a turbine to generate power.
Flywheels
Energy is stored in a spinning rotor, allowing for rapid charge and discharge cycles.
Gravity-Based Systems
Heavy weights (such as concrete blocks) are lifted and lowered to store and release energy efficiently.
Compressed Air Energy Storage (CAES)
CAES works by storing surplus electricity as compressed air in underground caverns. When renewables generate more power than we need, the excess energy is used to compress air and pump it into massive underground caverns. When electricity demand increases, the stored air is released, expanded, and driven through turbines to generate power.
This method provides a cost-effective and sustainable way to support grid stability and maximise renewable energy utilisation.
Advantages of CAES:
Very long duration: Unlike many other storage technologies, CAES can provide energy storage over days, weeks or even months. This means CAES can offer seasonal storage, balancing the fluctuations in renewable generation throughout the year.
Minimal degradation: Underground caverns used for storage experience negligible wear over time, ensuring long-term reliability.
Integration with green hydrogen production and storage: By using hydrogen in place of compressed air, efficiency improves, as hydrogen has a higher energy density, enabling more energy to be stored in the same space. At Storelectric, our CAES model integrates hydrogen storage with green hydrogen production.
Cost-effectiveness: CAES can utilise existing geological formations, reducing infrastructure costs.
Preservation of green spaces: CAES requires minimal surface infrastructure, allowing for the preservation of natural landscapes.
Thermal Energy Storage (TES)
TES captures and retains heat or cold for later use, balancing energy demand over time.
Sensible Heat: Uses materials like molten salt or water to store energy by heating them up and releasing that heat when needed.
Latent Heat: Uses phase-change materials (PCMs), such as paraffin wax, which absorb or release heat when they change from solid to liquid and vice versa.
Thermochemical Storage: Uses reversible chemical reactions, like salt hydrates, to store and release energy efficiently.
Benefits of Thermal Energy Storage:
- Cost Effective: TES systems are generally more affordable than other storage technologies due to the materials use. The most commonly used TES storage mediums (like water, molten salts and concrete) are widely available and lost cost.
- Scalability: TES can meet diverse energy requirements, from residential heating to large industrial facilities. Often TES systems use modular designs which means expansion and customisation is a simple process.
This method allows surplus renewable electricity to be converted into heat, which can then be used for industrial processes or even domestic heating, reducing dependence on fossil fuels.
Electrochemical Storage
Electrochemical storage systems, such as batteries, store electricity in chemical form and convert it back into electrical energy when needed.
Static Batteries: Lithium-ion and sodium-sulfur batteries provide high energy density and efficiency, making them ideal for shorter-term grid balancing.
Flow Batteries: Vanadium redox and zinc-bromine batteries store energy in liquid electrolytes, allowing for scalable and long-lasting storage.
Metal-Air Batteries: Technologies like iron-air batteries use oxygen from the air to generate electricity, offering a cost-effective and durable storage option.
Benefits of Electrochemical Storage:
- High Energy Density: Batteries can store significant amounts of energy in a compact space, making them suitable for various applications, from portable electronics to grid-scale storage.
- Rapid Response Times: Electrochemical storage systems can quickly discharge energy, providing immediate power during peak demand or emergencies.
- Modular Scalability: Battery systems scale up or down easily to match specific energy storage requirements, offering flexibility in deployment.
Batteries are well-suited for short-to-medium-duration applications but are often less practical for very long-duration storage due to cost and degradation over time. Additionally, their environmental impact is a growing concern, as lithium mining and resource scarcity pose sustainability challenges.
The extraction of lithium, cobalt, and nickel is energy-intensive, contributes to habitat destruction, and raises ethical issues related to mining practices. Furthermore, battery disposal and recycling remain complex, with limited infrastructure to recover and reuse critical materials efficiently.
Chemical Storage
Chemical storage involves converting electricity into storable fuels, such as hydrogen or ammonia, which can later be used to generate power.
Hydrogen Storage: Uses renewable electricity to power electrolysis, producing green hydrogen. This hydrogen is stored as compressed gas or in carriers like ammonia and later used in fuel cells or combustion processes to generate electricity.
Benefits of Chemical Storage:
- High Energy Density: Chemical fuels like hydrogen have a high energy content per unit mass, making them efficient for decarbonising heavy industries, transport, and power generation.
- Versatility: Stored chemical energy has a wide applicability, meaning it can be utilised across various sectors, including transportation, industrial processes, and electricity generation.
The UK’s Commitment to Long Duration Energy Storage
The UK government is actively encouraging the development and deployment of long-duration energy storage to help support the journey to net zero. They are doing this through:
Cap and Floor Scheme: This scheme provides financial certainty for investors in large-scale energy storage projects by setting both a minimum (floor) and maximum (cap) revenue level. If a project’s revenue falls below the floor, the government provides top-up payments to ensure a stable return on investment. On the other hand, if revenues exceed the cap, the excess is returned to consumers or the government. This balance encourages investment in vital storage infrastructure while protecting consumers from excessive costs.
GB Energy: Labour’s publicly owned energy company has been established to support their clean power mission. The Great British Energy Bill, the legal document which created up GBE, outlines their purpose stating:
“GBE would participate in: the production, distribution, storage and supply of clean energy; the reduction of greenhouse gas emissions; improvements in energy efficiency; and measures to ensure the security of the UK’s energy supply”
As above, energy storage will play a key role in achieving GB Energy’s goals and is set to feature in their investment portfolio.
Infrastructure Upgrades: The new Planning and Infrastructure Bill aims to streamline grid connection queues. As a result, clean energy technologies will come online more quickly.
The future of Long Duration Energy Storage
Long Duration Energy Storage technologies enable the full utilisation of renewable power, revolutionising the energy transition. As nations progress toward decarbonisation, continued investment in LDES will be crucial for ensuring a stable, low-carbon energy future. The next phase of energy storage lies in developing a holistic green energy system. A diverse range of energy generation and storage technologies will work in tandem to create a resilient, adaptable grid.
Ideally, different technologies will cater to varying energy demands across the nation, ensuring reliability at all scales, from grid-level seasonal storage to domestic solutions like solar panels and batteries.
Investing in and deploying the right infrastructure will be key to accelerating the energy transition, enabling a future where clean power is accessible, efficient, and seamlessly integrated.
