Gravity energy storage-working, comparison and prospect

In the past, the importance of energy storage was not fully reflected in the traditional energy era, in which coal was the main power generator. With the transformation and upgrading of the power system and the large-scale use and construction of renewable energy represented by solar energy and wind energy, the energy storage industry also ushered in a new development prospect.

Globally, the installed capacity of energy storage is growing steadily, and under the favorable policy, the installed capacity of energy storage is also growing at a high speed. Especially in the field of new energy storage technologies including gravity energy storage, hydrogen energy storage and flywheel energy storage, a number of new directions of energy storage have emerged, which has attracted extensive attention.

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Among them, gravity is a relatively weak force, while the energy density of pumped storage system is low. In order to store energy on a large scale, terrain with large drop and a large number of water sources are required, which cannot be built in areas where water sources are scarce and in the marine environment.

Therefore, according to the principle of gravity potential energy storage, combined with its advantages of large capacity, long-term energy storage and high energy storage efficiency, many gravity energy storage systems have been designed and built.

This article will introduce the working principle and development prospect of gravity energy storage, and analyze the advantages and disadvantages of gravity energy storage by comparing lithium ion batteries.

Gravity potential energy is the core of gravity energy storage technology

Gravity potential energy is the core of gravity energy storage technology. The first mechanical equipment to use gravitational potential energy was an ordinary pendulum clock, which was invented by Huygens in 1656. However, it took 251 years to store energy by using gravitational potential energy.

In 1907, Switzerland built the first pump energy storage system. Its working principle is gravity. Initially, the pump energy storage hydropower was obtained by burning fossil fuels. Although the cost is low (because it produces electricity during off peak hours), there is still a problem of resource waste.

The water is pumped from the lower reservoir to the upper reservoir through the gravitational potential energy, and the gravity will flush the water back to the lower reservoir during the peak period, and generate electricity in this process. Today, such systems are still used for renewable energy.

After more than a century, the method of pumped storage has been widely used. China has also started to research and build pumped storage power plants since the late 1960s. Up to now, the installed capacity has exceeded 40 million kilowatts, which has reached the leading position in the world.

The pumped storage system needs to take into account the terrain and water source factors. It is preferred to build in areas with large drop and abundant water sources. Therefore, it is impossible to build in some areas where water sources are scarce, including the marine area.

Therefore, researchers need to combine the working principle of gravity potential energy and the advantages of energy storage capacity, and consider developing different forms of gravity energy storage systems to solve the main problems of renewable energy without using water.

Principle of gravity energy storage

Gravity energy storage can save the energy provided by the sun and wind, and then deliver it to the demand side at the appropriate time, while making the system cheap and wear resistant. The principle of gravity energy storage charging mode is very simple.

The system uses the power received from the outside to lift the load from the bottom to the top, which is the way that gravity potential energy accumulates in the load. When it is necessary to extract energy and obtain power, the motor switches to the generator mode and provides energy for the user when the load falls under the action of gravity.

The load will not drop immediately. It is designed to drop slowly, that is, the system can provide energy for several hours. In fact, it all depends on the weight of the load and the height of the elevator. At the same time, it only takes a few seconds to switch from charging mode to discharging mode, and the system can quickly respond to the peak load.

Based on this working principle, in 2021, the first prototype of gravity energy storage test was successfully developed, also known as the demonstration sample. The system was installed in Edinburgh Port, England.

Its design is similar to an elevator, except that it is not a cabin but two 25 ton loads inside. They will slowly rise to a height of 15 meters under the action of solar energy and electric motor energy, and then drop rapidly under the influence of gravity within a few seconds.

Of course, the load drops faster than normal, and the device can only supply power to nearby villages for a few seconds. Its power is 250 kilowatts, but such systems may provide a peak power of 1 to 20 megawatts for 8 hours. It is estimated that a 20 megawatt grid can power 63000 homes per hour.

Pros and cons of gravity energy storage compared with lithium ion battery

Compared with lithium ion battery, gravity energy storage is based on underground shaft and has the following advantages:

● Long service life

Lithium ion batteries degrade rapidly according to the number of charging and discharging cycles within five to ten years. The service life of gravity batteries can be as long as 50 years without too much maintenance and repair costs.

● Higher security

The extraction of lithium and other metals and the harsh working conditions are not conducive to the health of the staff, and the lithium inventory is drying up. In addition, accidents caused by lithium ion batteries still occur.

● Small accommodation space

The holding space required by gravity battery is small, and it is suitable for many old coal mine areas, because there is often not much available space to install large area lithium ion batteries in these areas.

Of course, there are two sides to the technology, and there are also shortcomings in vertical gravity energy storage.

On the one hand, the production technology process of loads made of concrete is not environmentally friendly. Researchers can use pressed building debris and recycle concrete and other suitable materials.

Another factor to consider is environmental factors. Not all places have ready mines, which means that new mines must be drilled to build some batteries or high-rise buildings, which increases the cost of the project.

Gravity energy storage technology has broad development prospects

In addition to shaft gravity energy storage technology, some companies are developing energy storage systems using gravity tower structures, and some companies are developing locomotive ramp track system projects.

They are all committed to developing gravity technology and gradually accelerating commercial progress. Some gravity energy storage systems are also gradually entering the test and commercial stage.

From a technical perspective, gravity energy storage is a good energy storage solution, especially for solar and wind energy. The synergy of natural forces enables us to obtain more energy without affecting the surrounding ecosystem.

In addition, gravity batteries do not require specific terrain like pumped storage hydropower. Gravity energy storage technology has a broad development prospect. After the successful construction and operation of the gravity battery, it will be much easier to expand its scale.