In the quest for cleaner and more efficient energy solutions, innovators are exploring alternative methods of energy storage. One such emerging technology is gravity-based energy storage, an idea that leverages the power of gravity to store and release electricity.
While lithium-ion batteries have become the go-to solution for energy storage, they come with limitations. These batteries have a finite number of charge and discharge cycles, typically lasting only a few years before capacity degradation sets in. Additionally, the production and disposal of lithium-ion batteries raise environmental concerns.
Gravity-Based Energy Storage
Gravity-based energy storage systems offer a compelling alternative to traditional battery technology. These systems work by harnessing the potential energy of heavy objects, such as massive weights or blocks, and convert it into electricity.
The basic idea behind a gravity battery system is lifting a heavy object using energy from other sources such as a large mass of concrete or a weight high into the air, to the top of a deep shaft, on a pulley, letting it fall when energy is needed and converting its potential energy into electricity using an electric generator.
This is often done when there is plenty of green energy, the batteries use the power to lift a heavy weight either high into the air or to the top of a deep shaft. Then when the power is needed, winches gradually lower the weight, and produce electricity from the movement of the cables.
For what it is, it is an attempt to improve on an old idea: pumped hydroelectric power storage. Dams often require a reservoir with water pumped to it at times of low demand, usually at night and then released to generate electricity. But hydroelectric dams require specific terrain, expensive infrastructure, and planning approval. In the gravity battery, water is replaced by a solid weight.
Let's take a closer look at how these innovative companies are approaching this concept:
From Switzerland, Energy Vault takes a different approach by using a tower of 35-ton bricks and a six-armed crane. According to Energy Vault, the bricks are "proprietary cement/polymer-based composite bricks that can be made of ultra-low-cost materials: soil, mine tailings, coal ash, incinerated city waste, and other remediation materials." Each of this brick is designed to weigh 35 metric tons and is engineered to have a specific gravity at least twice that of water and enough compressive agility.
Their original system consists of a combination such bricks and a tall tower. A surplus of power, from either solar or wind used to power a mechanical crane to raise the blocks 35 stories into the air. These bricks then stay suspended there until power is needed again when they are then lowered to work like a hydroelectric dam, that is, pulling on cables that spin turbines, thus producing electricity. According to Energy Vault, the blocks will have a storage capacity of up to 80 megawatt-hours and be able to continuously discharge 4 to 8 megawatts for 8 to 16 hours.
The control system manages the complex choreography, ensuring a constant energy output. In August 3, 2023, Energy Vault announced the completion of its first gravity energy storage system in Jiangsu, China. It is a 25 MW/100 MWh storage system that makes use of the company’s new ribbon-based lifting systems.
Its EVx, the Energy Vault system, installed in 2020 in Switzerland in a demonstration project, performed at round-trip efficiency of about 75%.
The tower is controlled by computer systems and machine vision software that control the charging and discharging cycles. While Energy Vault hopes to reach a range of storage durations from two to 12 hours, this first commercial installation in China will use a 4-hour duration.
This Scottish startup has developed a unique 'underground' approach to gravity-based energy storage. Their system involves suspending a 50-ton iron weight using cables within a vertical underground shaft. Electric motors can lift the weight, storing potential energy. When needed, the weight is released, and the motors become generators, sending power back to the grid. Gravitricity's system offers rapid response times, making it suitable for balancing the grid during fluctuations in demand.
Gravitricity designed its systems to be housed in old mine shafts rather than towers. In the UK, it could go to depths of 750m (2,461ft) - twice the height of the Eiffel Tower in Paris. In in African countries, they expect to install them in holes underground holes constructed for the systems with depths that could exceed 2km (1.2 miles).
New Energy Let's Go and Gravity Power
The California-based Gravity Power uses an iteration of the hydroelectric dam. Renewable energy is used to pump water under a heavy piston and lift it. When power is needed, the piston weight is released, forcing the water through a hydroelectric generator. German company New Energy Let's Go uses a similar design.
These companies are all developing different types of gravity batteries, but they all share the same goal: to create a more efficient and sustainable way to store energy.
Advantages of Gravity-Based Storage
Gravity-based energy storage has several advantages:
Unlike traditional batteries, winches, cables, and heavy weights can maintain their performance for decades, reducing the need for frequent replacements.
These systems have a smaller environmental footprint compared to lithium-ion batteries, as they rely on readily available materials like steel and concrete.
Initial estimates suggest that gravity-based energy storage systems can be cost-competitive over their lifetime when compared to lithium-ion batteries.
While the technology is still in its early stages and faces enormous challenges, such as scaling up and regulatory hurdles, it holds promise as a sustainable and efficient energy storage solution. As the world transitions to renewable energy sources and strives to reduce greenhouse gas emissions, innovative technologies like gravity-based energy storage are expected to play a vital role in creating a more sustainable energy landscape. While these systems are not yet widely deployed, they represent a promising step toward a cleaner and more reliable energy future.
In conclusion, gravity-based energy storage is an exciting and evolving field that has the potential to reshape the way we store and utilize electricity. With ongoing research and development, we may see these innovative systems become an integral part of our global energy infrastructure, helping us transition to a greener and more sustainable future.