As the world moves towards a more renewable and decentralised energy system, energy storage is becoming increasingly important. 

Energy storage technologies allow us to store energy when it’s available and release it when it’s needed, providing a range of benefits for the grid, businesses, and households.

One of the primary reasons efficient energy storage is crucial for the green transition is the need to manage variable energy supply. Renewable energy sources like wind and solar are intermittent and don’t provide a consistent energy supply. Energy storage can help smooth out these fluctuations by storing excess energy when it’s available and releasing it when needed.

As many renewable energy sources are becoming cheaper and cheaper, storing them and using them later can be very cost-efficient for society. 

Energy storage can also provide backup power during emergencies and help reduce peak demand, which occurs when many people use electricity simultaneously. 

By storing excess energy during off-peak hours and releasing it during peak hours, energy storage can help prevent blackouts and reduce the need for expensive infrastructure upgrades or reliance on fossil fuels.

Improving energy storage infrastructure and overcoming the issues posed by the intermittent renewable energy supply is essential to achieve decarbonisation targets and can drastically help eliminate our fossil fuel dependence. 

Thermal Energy Storage

Thermal energy storage (TES) is an innovative technology that offers a promising solution for storing and releasing heat energy. It allows us to leverage renewable energy sources such as wind and solar by utilising the energy they generate to heat a “thermal battery” that can store the heat for several hours or even days.

This stored energy can be used to generate electricity when needed, especially during periods when renewable energy sources are not readily available. This approach is a game-changer for renewable energy as it enables us to use it when it’s most cost-effective, which typically occurs during sunny or windy periods. 

As a result, the overall cost of electricity can be reduced, and the grid’s stability can be improved.

One of the main benefits of TES is that it offers a simple approach to energy storage. Thermal batteries are typically constructed from abundant materials that are cheap to assemble and maintain and can operate for many years.

For instance, a lot of TES companies, such as Antora Energy, use solid carbon, which is extremely cheap and highly accessible. The existing supply chain of solid carbon is over 30 million tons a year, 50 times the available quantity of lithium. 

The technology is also highly scalable, meaning it can be adapted to suit various applications, from large-scale power plants to smaller residential buildings.

Pumped hydroelectric storage

Pumped hydroelectric storage (PHS) is currently one of the most widely used forms of energy storage. PHS involves pumping water from a lower reservoir to a higher one during low electricity demand, such as at night, using excess electricity generated from renewable sources. 

During periods of high demand for electricity, the stored water is released to the lower reservoir which generates electricity by turning turbines. This process enables excess electrical capacity to be stored efficiently and inexpensively, allowing it to be released when it is most needed.

According to the International Energy Agency (IEA), the total installed capacity of PHS worldwide was around 160 GW in 2021, making it the most widely deployed grid-scale storage technology. 

Indeed, PHS accounts for over 90% of the world’s electricity storage, at approximately 8,500 GWh in 2020. 

The majority of PHS plants currently in operation provide daily balancing, ensuring a steady supply of electricity during peak demand. However, there is potential for PHS to be used in larger-scale applications, such as supporting the integration of intermittent renewable energy sources into the grid.

The United States has the largest capacity of PHS, with many plants scattered across the country. The world’s largest PHS plant, the Bath County Pumped Storage Station, is located in Virginia, with a capacity of more than 3 GW, a 24 gigawatt-hour storage capacity, the equivalent of one year of electricity use for 6,000 homes. 

Despite its benefits, PHS does have some limitations, including the need for suitable topography and access to large amounts of water. Nevertheless, PHS remains a key technology for energy storage and has enormous potential to help accelerate the transition to a more sustainable energy future.

Green hydrogen 

The production of green hydrogen through electrolysis powered by renewable energy sources like solar and wind offers a promising solution for long-term energy storage. 

Hydrogen produced from this process can be stored and converted back to electricity when needed, providing balancing power for the grid. Most importantly, it can be burned when required without releasing any GHG emissions.

One of the significant advantages of hydrogen is its ability to be stored for months without losing power through discharge, making it an attractive option for long-term energy storage. In comparison, lithium-ion batteries can only store energy for a couple of hours.

Related Articles: Droughts in East Africa: Stronger and ‘100 Times More Likely’ Due to Climate Change | Complex vs Complicated: Why Understanding the Difference Is Critical for Innovation in Sustainability | ‘Global Blue Deal’: Why the Ocean Needs It

On the other hand, the “power-to-gas-to-power” process required by green hydrogen has a high energy storage capacity, but it is less efficient and more expensive than other storage technologies. 

Indeed, converting the power to gas and back to power has an efficiency of 18%-46%, according to the Massachusetts Institute of Technology. To put that into perspective, pumped-storage hydropower has an efficiency closer to 70%-85%

Despite being a promising option for energy storage, the logistics and infrastructure to scale up its production are not yet developed enough. 

Bringing production costs down and at a larger scale could provide a significant step towards reducing carbon dioxide emissions and even creating a circular economy. 

Many projects are already in the works as more industry leaders, such as John Ketchum at NextEra Energy Resources, see green hydrogen as a “really long-term solution.” NextEra is already working on 50 potential green hydrogen projects. 

In the EU, many projects have been implemented, such as the Green Skills for Hydrogen, an EU-backed skill conversion and training program aimed at equipping workers with the necessary tools and skills to adapt to the new technology. 

Gravity Batteries

Gravity batteries are a new form of energy storage technology that leverages the power of gravity and regenerative braking to send renewable energy to the grid. 

The batteries work by using renewable energy to lift a heavy object into the air or to the top of a deep cavity in the ground, and then lower the weight when energy is in high demand. The movement of the cables to bring the object up and down will produce electricity on demand, thus overcoming the issue posed by inconsistent energy production.

Unlike conventional batteries such as lithium-ion, gravity batteries do not experience self-discharge, meaning they can store energy for months or even years.

Researchers have discovered that abandoned mines worldwide can be repurposed to store energy, providing a unique solution for excess energy generated during good weather conditions.

One of the significant benefits of using abandoned mines for energy storage is the ability to use existing infrastructure. 

Mines are already connected to the power grid, reducing the cost and complexity of implementation. 

A recent study by the International Institute for Applied Systems Analysis (IIASA) suggests that these decommissioned mines could provide up to 70 terawatts of energy storage, which is enough to match the entire world’s daily electricity consumption. 

With an estimated 550,000 abandoned mines in the U.S. alone, this technology has immense potential.

Some companies are already building gravity batteries that don’t require mines and can be dropped anywhere. This technology would make energy storage more accessible, affordable, and scalable, opening up new possibilities for renewable energy.

In the UK, a trailblazer project, Gravitricity, has been testing a gravity battery in Edinburgh by using a 15-meter steel tower to bring the heavy weight up and down using solar power. 

Although the project operated only for 10 seconds, it demonstrated that the theory could be put into practice. 

Jill Macpherson, the project’s senior test and simulation engineer, elaborated on the successful experiment: 

“The demonstrator was rated at 250kW – enough to sustain about 750 homes, albeit for a very short time. But it confirmed that we can deliver full power in less than a second, which is valuable to operators that need to balance the grid second by second. It can also deliver large amounts more slowly, so it’s very flexible.”

The promise of such batteries is unmatched, as they can be implemented all around the world, including in Africa; as said by Gravitricity’s founder, Charlie Blair: 

“If this technology is one that really makes a difference it’s going to make a difference globally. It’s going to keep the lights on in Africa, as they build the grid, just as much as it will in Europe.”

Building holes specifically for these gravitational batteries in Africa could allow them to go as deep as 2 km. In Africa, integrating these batteries into the network could drastically improve access to electricity. In Europe, it could provide an efficient solution to storing renewable energy. 

While gravity batteries are a promising technology, there are still many barriers to adoption. Cost is a significant concern, as is the need to optimise the technology for different environments and use cases. 

Further research and development are required to improve the efficiency and reliability of these batteries. Nonetheless, the potential of gravity batteries to provide long-term energy storage using existing infrastructure is a compelling reason to explore this technology further.

Developing efficient and large-scale technology for energy storage will help society overcome one of the most prominent issues with using renewable energy — the inconsistencies in supply that are unable to match peaks of demand. It is thus crucial to keep progressing in energy storage research worldwide and collaborate to achieve a long-term solution.