Gravity energy storage is a type of long duration energy storage. The future development potential of this longer-lasting and larger-scale energy storage technology is immeasurable.
1. Crane energy storage
A 70-meter crane stands in the endless desert. Six mechanical booms hang about 30 tons of bricks, which slowly fall from high to low. The bricks are composed of mine tailings, coal ash and other waste. This is the first gravity energy storage prototype located in Arbedo-Castione, Switzerland, and is a great initiative of Energy Valut.
In 2022, EV Company will shift from high towers to 20-story behemoths-modular buildings (EVRC). This crystal fortress built like building blocks controls the input and output of electricity through the mechanized process of “rising” and “descending” and an energy management system to store and release electricity.
2. Elevator energy storage
Last year, scientists from the International Institute for Applied Analysis in Austria proposed the concept of “elevator” energy storage technologies (LEST). Elevator energy storage generally has 2 interconnected storage sites, one at the base of a high-rise building and the other at the top of the building. Energy is collected when the elevator goes down and released when the elevator goes up.
Generally speaking, the heavier the object carried by the elevator, the greater the gravitational potential energy and the more electrical energy converted. Therefore, some heavy objects need to be stored in the elevator.
Some people will say that this is too troublesome: first, heavy objects will occupy people’s time and space, and second, the elevator needs to carry out a series of dragging in and out work, which is simply not feasible.
In fact, this is not the case. The elevator energy storage system is very smart. It determines the daily use of the elevator. When the elevator is less used, or during a window period, heavy objects are carried, and the equipped trailer robot will also be responsible for picking up heavy objects. Heavy objects are generally stored in some remote spaces.
3. Mine energy storage
In February this year, the same Austrian team mentioned above proposed an underground gravity energy storage system (UGES) based on mines. When electricity prices are high, sand can be filled into underground mines to generate electricity. When electricity prices are cheap, , and take sand from the mine to store energy.
The underground gravity energy storage system is a whole composed of shafts, electric motors, generators, upper and lower storage points and mining equipment. Generator sets on either side of the shaft move each elevator up and down, generating electricity on the way down and using some of the power on the way back up.
For maximum efficiency, the elevator loads sand at the surface, removes it at the bottom of the mine, and returns empty. The elevators also carry some of the sand back to the surface when there is excess energy in the grid.
Generally speaking, the deeper, wider and larger the mine, the greater the energy storage capacity and the more power available.
4. Railway energy storage
In April 2016, American energy company Advanced Rail Energy Storage (ARES) won a $55 million project from the Nevada Bureau of Land Management to use rail locomotives for energy storage.
The company built a six-mile stretch of uphill railroad track, complete with heavily loaded locomotives, which were made of solid machine-concrete, each weighing about 4,300 tons and capable of reaching a top speed of 16 miles per hour. When storing electricity, the remaining electricity is used to push the locomotive to the “station” on the top of the slope, and the electrical energy is stored as gravitational potential energy; when generating electricity, the locomotive is released downhill, and the gravitational potential energy is converted into electrical energy to start generating electricity.
It is estimated that the configuration cost of this system is about 60% of that of a pumped hydropower station with equivalent performance, and its service life is 40 years. The company also disclosed that the conversion efficiency of the system is as high as 86%.
5. Cable car energy storage
From a distance, “cable car energy storage” looks like a mountain cable car. The cable car energy storage solution was first proposed in 2019 and consists of steep hillsides, cranes, storage containers (waste, sand and gravel), cables, etc.
The principle of storing electricity is similar to that of “railway energy storage”. When storing electricity, the remaining electricity is used to drive the engine to move the cable car filled with sand and gravel from the bottom of the hillside to the top of the mountain, and the electrical energy is converted into gravitational potential energy.
When generating electricity, the cable car is lowered from the top of the hillside to the bottom, and the potential energy is converted into electrical energy.
In addition, it can also be combined with hydropower to fill the storage container with water during peak power consumption periods, which can achieve long-term energy storage and continuously store energy for several months. Public data shows that the energy storage capacity can reach 0.5-20MWh, and the power generation power is 500~5000kW.
6. Deep sea energy storage
In 2016, the new ocean pump storage system developed by Germany’s Fraunhofer Institute for Wind Energy and Energy Systems Technology (IWES) conducted its first water test on Lake Constance on the German border.
The working principle is: a hollow sphere with a diameter of 30 meters, a wall thickness of 2.7 meters, and a storage capacity of 12,000 cubic meters is placed on the seabed and uses high-pressure seawater in the deep sea to store energy.
When storing energy, seawater is pumped out of the sphere by an electric pump. When generating electricity, high-pressure seawater flows from the pipe into the hollow sphere, driving the turbine to generate electricity.
At that time, researchers launched a four-week deep-sea test in Lake Constance. Experimental results show that at the same volume increment, the power storage capacity increases linearly with depth. At a depth of 700 meters, the power storage capacity of a 30-meter-diameter offshore energy storage system is approximately 20MWh.
In coastal areas, especially near the coast in densely populated areas such as the Bohai Sea region, there is great potential for the use of marine pump storage systems.
7. Energy storage lamp
Gravity energy storage is not only used in industrial energy storage and commercial fields, but also aims to tap living space. While we enjoy the convenience of electricity, there are still more than 1.3 billion people in the world, about 18% of the population, who do not have access to electricity, and most of them can only rely on kerosene for lighting. Someone used a gravity energy storage system and invented a gravity lamp, which can store energy with just a brick.
The gravity lamp hangs a bag filled with stones and sand, and is pulled downward by gravity to drive the device to generate electricity. If it falls for 3 seconds, it can produce 25 minutes of light. This project is still being trialled in 25 regions around the world. Entering commercialization is just around the corner.
8. Pumped water energy storage
Pumped hydro storage is an ancient and common method of energy storage, and the heavy object used is natural water. Through the mutual conversion of water potential energy and electric energy, energy storage and conversion are carried out.
It has large storage capacity (100-3000MW), high efficiency (65-85%), long life (40-60 years), and the energy storage cycle is not affected by Limitations and other advantages. In 1882, Switzerland built the world’s first pumped storage power station. Going forward, the installed capacity of pumped hydro storage will continue to grow globally.
However, problems such as site selection issues, input-output imbalance, and cumbersome approval procedures have become prominent, severely restricting the development of pumped storage power stations.
9. Summary
Gravity energy storage is a type of long-term energy storage. The future development potential of this longer-lasting and larger-scale energy storage technology is immeasurable. These seemingly novel energy storage technologies may truly change the global energy storage in the near future. As the recently released energy storage policy warns: without long-term energy storage, carbon neutrality will not be achieved.
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