As the world moves toward cleaner energy sources, a major challenge remains: how do we store renewable energy for when we need it most?
Current battery energy storage technologies are relatively expensive to build and have traditionally struggled to store enough energy to meet the demand when the sun isn't shining or the wind isn't blowing.
But new alternatives, known as long-duration energy storage (LDES) batteries, which have large energy capacities, are now offering a promising solution. These technologies may soon allow us to store electricity created by solar panels and wind turbines for extended periods, to ensure there is a steady and constant supply of power on demand.
In addition LDES batteries can provide backup power options in critical situations, such as for hospitals or during natural disasters.
Associate Professor Chris Menictas, who leads the Energy Storage and Refrigeration Laboratory in the School of Mechanical and Manufacturing Engineering at UNSW, says there are a number of factors which are making research and development of LDES systems ever more important.
"One of the key things is enhanced grid stability. Renewable energy sources like solar and wind are intermittent, meaning they do not produce power all the time, such as at night or when the weather is calm.
"LDES batteries can store excess electricity and release it when needed, which helps smooth out the energy supply.
"Then there is the question of resilience and being able to provide power for critical services – like a hospital or maybe even a data centre.
"Overall, what's becoming clear is that we need to be able to store more energy that can then deliver electricity for a longer period of time. What's increasingly important is for those systems to have eight, 10 and even 12-hours of storage."
Professor Jie Bao, from UNSW's School of Chemical Engineering and Director of the ARC Research Hub for Integrated Energy Storage Systems, says there are a number of different LDES battery technologies being developed which could ultimately be used in different scenarios.
"There isn't necessarily one best energy storage solution. There are different use cases and each of them might have a different solution," he says.
"The different technologies can also be complimentary, and can be implemented in tandem and properly coordinated.
"But there are also very common challenges. One is the raw materials, such as lithium or vanadium, that we need to source and another is simply the scale of manufacture to build the number and size of batteries we now need."
Here we explain some of the various LDES battery technologies being developed around the world, as well as some of the challenges that still need to be overcome.
LDES battery storage benefits
One of the key benefits is enhanced grid stability. Renewable energy sources like solar and wind are intermittent, meaning they do not produce power all the time. LDES helps smooth out the energy supply by storing excess electricity and releasing it when needed, reducing the risk of power outages.
LDES batteries enable more renewable energy integration into power grids. With better storage solutions, wind and solar energy can be utilised more effectively, reducing dependence on fossil fuels and accelerating the transition to a low-carbon economy.
LDES batteries also plays a role in reducing peak demand stress. Electricity demand varies throughout the day, often peaking in the evening. By providing stored energy during these peak times, LDES systems can reduce strain on the grid.
They can also support remote areas and communities with unreliable power by providing a steady and sustainable energy source, particularly in regions prone to natural disasters.
Promising LDES battery technologies
Vanadium flow
Vanadium flow batteries, developed at UNSW by Professor Maria Skyllas-Kazacos in the 1980s, are now becoming popular around the world, with increased power and energy capacity
The world's largest vanadium flow battery, a 175 MW/700 MWh system in Dalian, China, was developed by Rongke Power and completed in December 2024. Meanwhile, in the UK, a 5 MW array has been built which connects into the national grid system.
A vanadium flow battery stores energy in liquid electrolytes containingvanadium ions at four different oxidation states. The positive and negative electrolyes which are stored in separate tanks are circulated through battery stacks where the power conversion takes place. \ When charging or discharging, electrons transfer between the electrolytes through an external circuit, enabling energy storage and release without significant degradation.
Vanadium flow batteries can scale up easily, allowing a large the energy capacity for power supply for extended periods.
However, they have lower energy density than some other LDES options.
Lithium-ion
In contrast, lithium-ion batteries offer high energy density and fast response times, making them already popular for vehicles, consumer electronics and medical devices.
However, they degrade more quickly over time and may only last 500-3000 charging cycles before suffering noticeable capacity loss – compared to a reported 200,000 cycles for a vanadium flow battery.
There are also additional safety concerns with lithium-ion batteries related to thermal runaway leading to fires, while they are reliant on a scarce raw material and recycling is costly and complex.
Even so, the Hornsdale Power Reserve in South Australia and the Victorian Big Battery in Geelong both utilise lithium-ion Tesla Megapacks. The latter can store enough energy to power over one million Victorian homes for up to half an hour.
Iron flow
Iron flow batteries, which store energy in a liquid electrolyte typically made of iron, salt, and water, are an affordable and environmentally friendly option for long-duration energy storage.
These promise around 10,000 cycles with minimal degradation over time.
However, they have lower energy density than lithium-ion or vanadium flow and require more space for the same energy storage capacity.
Organic flow
Another potential option are organic flow batteries, which are still very much in the research phase, with carbon-based molecules being tested for use instead of metals such as vanadium or lithium.
While they may provide a cheaper, non-toxic energy storage solution, there are still big question marks about their energy density at scale and durability.
Limitations and challenges of LDES batteries
Despite their benefits, LDES battery development faces some significant challenges.
One major challenge is the high initial costs, with many of the technologies requiring substantial upfront investment in infrastructure, making large-scale deployment difficult.
LDES technologies, like other storage systems, experience energy loss during the storage and retrieval process, due to factors like self-discharge, internal resistance, and inefficiencies in the charging and discharging cycles.
Material and supply chain constraints also present significant issues for some LDES batteries. Certain technologies depend on rare or expensive materials, which can lead to supply chain vulnerabilities, as well as environmental concerns.
While many LDES technologies show great promise, some are still in the experimental phase and require further research and development before they can be widely adopted.
Environmental impact of LDES batteries
While LDES batteries could be the key to a cleaner energy future, its environmental impact varies depending on the technology used.
One major benefit is the lowering of carbon emissions, as the use of fossil fuels to produce electricity can be greatly reduced.
However, some of the main battery technologies rely on rare or critical minerals – such as lithium, vanadium and cobalt – which raises environmental concerns if the mining practices are not carried out sustainably or cause significant greenhouse gas emissions themselves.
In addition, proper recycling and disposal methods are needed to prevent environmental harm, especially in relation to lithium batteries. Flow batteries, in contrast, have a lower environmental impact due to the ability to recover and reuse electrolytes.
Key Facts:
UNSW experts explain why long-duration energy storage batteries are likely to be crucial in the transition to more environmentally friendly energy systems.
