Sodium-ion batteries
Sodium-ion batteries have obvious advantages. First, the raw materials are abundant, with sodium abundance in the earth's crust being about 435 times that of lithium. Other raw materials are also readily available and lower in cost compared to lithium iron phosphate batteries. Second, the manufacturing process and industrial chain of lithium batteries can be applied, enabling rapid industrialization. Third, they have excellent performance, including high safety, excellent fast charging performance, and good low-temperature performance.
However, sodium-ion batteries also have obvious drawbacks: they are large in size, have low energy density, and have a shorter cycle life than lithium-ion batteries.
In summary, sodium-ion batteries have enormous potential in the field of large-scale energy storage, which does not have high requirements for product energy density, is extremely sensitive to product materials and production costs, and does not have strict requirements for product volume.
Currently, Chinese companies are making remarkable progress in the industrialization of sodium-ion batteries. Zhongke Haina ranks among the world's leading companies in sodium-ion battery energy storage technology; lithium battery giants such as CATL are accelerating the industrialization process by entering the sodium-ion battery energy storage market; and Huayang Technology has put the world's first batch of sodium-ion battery cell production lines into operation.
Flow battery
Based on the active materials of the positive and negative electrodes, flow batteries can be classified into vanadium redox flow batteries, zinc-bromine flow batteries, iron-chromium flow batteries, etc. Among them, vanadium redox flow batteries and iron-chromium flow batteries are the mainstream in commercial applications.
Due to its structural design, flow batteries separate the positive and negative electrolytes during operation, allowing them to circulate independently without interference. This results in advantages such as long cycle life, wide applicability, high capacity, high safety, and reusable electrolyte.
The disadvantages are a narrow operating temperature range and low energy density. Taking the vanadium redox flow battery as an example, its energy density is 15~30Wh/L, which is about one-tenth or even one-twenty-sixth of that of lithium-ion batteries.
In the field of long-term energy storage, iron-chromium redox flow batteries have particularly obvious advantages. They are less toxic and corrosive, have a cycle life of up to tens of thousands of cycles, which translates to a service life of more than 20 years. Moreover, their overall cost is close to that of pumped hydro storage, making them a huge potential in the field of long-term energy storage.
According to incomplete statistics from Vico.com, the flow battery energy storage projects that have been completed include the 200MW/800MWh Dalian Flow Battery Energy Storage Peak Shaving Power Station National Demonstration Project, the 10MW/40MWh State Power Investment Corporation Tuoshan Grid Source Friendly Wind Farm Energy Storage Project, and the 1MW/2MWh Huadian Tengzhou New Energy Thermal Power Co., Ltd. Project.
Gravity energy storage
Gravity energy storage belongs to mechanical energy storage. Its working principle is to use the height difference to raise and lower the energy storage medium, thereby realizing the mutual conversion of gravitational potential energy and electrical energy.
Gravity energy storage has advantages in three main aspects. First, it has low initial investment costs, only about 3 yuan/Wh, which is lower than pumped hydro storage. Second, it has high safety, with no stringent environmental requirements, and can be built in remote areas. Third, it has a long lifespan, with an average lifespan of 30-35 years.
The disadvantages are a large footprint and low energy density. It is suitable for small islands and isolated areas with high electricity costs, low energy storage needs, and periodic energy storage requirements.
my country's pioneer in gravity energy storage is Tianying. On September 8, 2022, it announced a strategic cooperation with the Tongliao Municipal People's Government and the China Investment Association to build the Tongliao Wind-Solar-Storage-Hydrogen-Ammonia Integrated Zero-Carbon Industrial Park and Zero-Carbon Industrial Equipment Manufacturing Center, which includes gravity energy storage projects.
Compressed air energy storage
Compressed air energy storage refers to the use of electricity to compress and store air during periods of low grid load, and then releasing the compressed air during periods of high grid load to drive a steam turbine to generate electricity.
Depending on the working medium, storage medium, and heat source, compressed air energy storage can be divided into traditional compressed air energy storage systems, compressed air energy storage systems with heat storage devices, and liquid-gas compressed energy storage systems.
The advantage of compressed air lies in the flexibility of site selection. Power plants can be built in caves, salt caverns, abandoned mines, expired oil and gas wells, which can greatly reduce the cost of raw materials and land.
Compressed air energy storage is a relatively mature technology, and several demonstration projects have been implemented in China.
On September 23, 2021, a 10MW salt cavern compressed air energy storage peak-shaving power station was officially put into operation in Feicheng Economic Development Zone, Shandong Province.
On May 26, 2022, the world's first non-combustion compressed air energy storage power station—the Jintan Salt Cavern Compressed Air Energy Storage National Pilot Demonstration Project—was officially put into operation in Jintan District, Changzhou City, Jiangsu Province.
Flywheel energy storage
The core components of flywheel energy storage are the flywheel itself and the bidirectional motor that reverses the electric/generator functions.
The working principle of flywheel energy storage is as follows: the reversible bidirectional motor works to drive the flywheel to rotate at high speed, converting electrical energy into mechanical kinetic energy for storage; when electrical energy is needed, the rotating flywheel is used to drive the motor to generate electricity and output electrical energy, thereby realizing the mutual conversion and storage of electrical energy and mechanical kinetic energy.
The advantages of flywheel energy storage include long lifespan, easy installation, easy maintenance, large energy storage capacity, high energy density, and no limitation on the number of charging cycles.
At the same time, it also has great limitations. Compared with other technologies, it has lower energy density, lower safety, and the rotor and bearing design needs to be improved.
Considering its advantages and disadvantages, flywheel energy storage can be widely used in uninterruptible power supplies, emergency power supplies, battery-free magnetic levitation flywheel energy storage UPS, electric vehicle batteries, power grid peak shaving and frequency control, and other fields.
Currently, there are already concrete examples of small-scale flywheel energy storage prototypes being put into use. For example, on April 11, 2022, two 1-megawatt flywheel energy storage devices were successfully put into use at Wannianquan Road Station on Qingdao Metro Line 3.
However, in terms of large-scale energy storage, flywheel energy storage still needs further research and development before it can be successfully commercialized due to the current state of technological research.
Future Outlook
In the future, the global energy storage market will be huge, and no single energy storage technology is destined to occupy the entire market share.
Depending on factors such as cost, performance, and applicable conditions, different energy storage technologies will have their own development in their respective energy storage sub-sectors.
Sodium-ion batteries offer flexible deployment options and have great potential in industrial and commercial energy storage; flow batteries may shine in the field of long-term energy storage; gravity energy storage will be cost-effective in remote mountainous areas and islands; compressed air energy storage can significantly reduce initial investment costs in abandoned oil fields and mines; and flywheel energy storage has the opportunity to gain a share in the power storage field.
