According to the form of energy storage, the types of energy storage technology paths includes electric energy storage, thermal energy storage and hydrogen energy storage, among which electric energy storage is the most important energy storage method. According to different storage principles, electrical energy storage can be divided into electrochemical energy storage and mechanical energy storage.
Different technical paths have their own advantages and disadvantages, and are suitable for different application scenarios. Electrochemical energy storage is mainly used in the fields of new energy consumption, peak-valley price difference arbitrage, power system peak regulation and frequency regulation, and UPS. Mechanical energy storage generally has a long service life, but its response time is significantly slower than that of electrochemical energy storage and electromagnetic energy storage. It is mainly used in the field of power system peak regulation. This article mainly introduces the comparison of the Three types of energy storage technology paths.
1. Hydrogen energy storage
Hydrogen energy storage is one of types of energy storage, its basic principle of is to electrolyze water to obtain hydrogen and store it. When electricity is needed, the stored hydrogen is converted into electricity by fuel cells or other methods and sent to the grid. Hydrogen production by electrolysis of water requires a large amount of electric energy, and the cost is much higher than that of traditional hydrogen production methods. However, due to the instability of renewable energy grid integration, China has serious problems of abandoning wind and light. Hydrogen is produced by using surplus electric energy generated by wind power and photovoltaics.
It can effectively solve the cost problem of hydrogen production by electrolysis of water, and solve the consumption of wind and electricity, so hydrogen energy storage is gradually becoming the focus of my country's energy technology innovation. However, China currently lacks convenient and effective hydrogen storage materials and technologies, and the energy conversion efficiency of hydrogen energy storage is low, so it is currently less used. Whether these two problems can be solved will be the key to whether hydrogen energy storage can gain more shares in the future.
2. Mechanical energy storage
Mechanical energy storage is one of the types of energy storage that stores energy through physical methods, and converts mechanical energy into electrical energy when needed. Mechanical energy storage mainly includes gravity energy storage, pumped hydro storage, flywheel energy storage and compressed air energy storage.
① Gravity energy storage
In types of energy storage, the gravity energy storage medium is mainly divided into water and solid matter, and the energy storage medium is lifted and lowered based on the height difference to realize the charging and discharging process of the energy storage system. In addition to the more mature pumped storage, the mainstream gravity energy storage method is the energy storage tower proposed by Energy Vault (EV). It uses a crane to stack concrete blocks into a tower, and stores and releases energy by lifting and dropping the concrete blocks.
② Pumped storage
The pumped storage power station consists of upper and lower reservoirs. When the power load is low, the excess electricity is used to pump water to the upper reservoir, and the water is released at peak times. The mechanical energy generated when the water flows from the upper reservoir to the lower reservoir is used to generate electricity, thereby achieving the role of peak regulation. Pumped storage in types of energy storage can realize large-scale storage of energy, so it is widely used in power system peak regulation. However, due to its slow response speed, high initial investment, and limited geographical location, the future development space is limited.
③ Flywheel energy storage
When the flywheel energy storage is storing energy, the electric energy drives the motor to run, and the motor drives the flywheel to accelerate the rotation, and the flywheel stores energy in the form of kinetic energy; when the energy is released, the high-speed rotating flywheel drives the motor to generate electricity to complete the conversion from mechanical energy to electrical energy.
Among the types of energy storage, the flywheel energy storage has a large specific power, a service life of 15-30 years, and a response speed of milliseconds. Therefore, flywheel energy storage is mainly used for frequency modulation and UPS. However, because of its low energy density and the backup time cannot exceed 30 minutes, it cannot be applied to large-scale energy storage power stations.
④ Compressed air energy storage
Compressed air energy storage technology is derived from gas turbine technology. When the power consumption is low, the motor drives the compressor to compress the air and store it in the air storage chamber, so that the electric energy is converted into the internal energy of the air for storage. During peak power consumption, high-pressure air is released from the gas storage chamber, enters the fuel chamber and burns together with the fuel, drives the turbine to work, and drives the generator to generate electricity.
In types of energy storage, compressed air energy storage is another technology suitable for GW-scale large-scale electric energy storage after pumped hydro storage. In addition to high storage energy, it also has the advantages of high energy density and power density, low operating cost, and long service life. However, similar to pumped hydro storage, compressed air energy storage is also limited by geographical conditions, requiring highly airtight caverns as gas storage chambers, which further limits the development of compressed air energy storage.
3. Electrochemical energy storage
In three types of energy storage, electrochemical energy storage is to complete the mutual conversion between electrical energy and chemical energy through electrochemical reactions, so as to realize the storage and release of electrical energy. At present, the main energy storage batteries mainly include lead-acid batteries, flow batteries and lithium-ion batteries. In the future, sodium-ion batteries will gradually be used in energy storage as the industry chain matures.
① Lead-acid batteries
A lead-acid battery is a secondary battery with lead dioxide as the cathode, metallic lead as the negative electrode, and sulfuric acid solution as the electrolyte. It is the earliest secondary battery used on a large scale. Lead-acid batteries have low energy storage costs, good reliability, and high efficiency. They are widely used in UPS and are also one of the types of energy storage route for large-scale electrochemical energy storage in China in the early stage. However, due to the short cycle life of lead-acid batteries, low energy density, narrow operating temperature range, slow charging speed, and the impact of lead metal on the environment, the future application of lead-acid batteries will be greatly restricted.
② Flow batteries
The technical paths of flow batteries include vanadium redox flow batteries, iron-chromium flow batteries, zinc-bromine flow batteries, etc. Among them, vanadium redox flow batteries have the best comprehensive performance and the highest degree of commercialization. The cathode and anode electrolyte storage tanks of the flow battery are separated independently and placed outside the stack. The cathode and anode electrolytes are pumped into the flow battery stack through two circulating power pumps through pipelines, and the electrochemical reaction continues to occur, and the storage and release of electrical energy is completed by converting chemical energy and electrical energy.
The power of the flow battery depends on the size of the electrode reaction area, and the storage capacity depends on the volume and concentration of the electrolyte, so the design of the size of the flow battery is more flexible and changeable. In terms of long-term energy storage, vanadium redox flow batteries will have a cost advantage, and have differentiated competitive advantages over other types of en energy storage paths such as lithium batteries.
③ Lithium-ion batteries
Lithium-ion batteries realize energy storage through the intercalation and deintercalation of lithium ions in the cathode and anode materials. Lithium-ion batteries have high energy density and long life, so they are gradually becoming one of the mainstream types of energy storage route of electrochemical energy storage. According to the different cathode materials, lithium-ion batteries are divided into lithium cobaltate, lithium manganate, lithium iron phosphate and ternary batteries.
Lithium iron phosphate battery has significant comprehensive advantages in the field of energy storage, its energy density is moderate, its safety and service life are superior to other battery types, and its cost is low. Due to the scarcity of metal cobalt, the price of lithium cobalt oxide batteries is much higher than that of other batteries, and the cycle life and safety are poor, so there are few applications in the field of energy storage. The energy density of lithium manganate battery is similar to that of lithium iron phosphate battery.
Although the price is lower than that of lithium iron phosphate battery, its low life cycle cost per unit of electricity is higher than that of lithium iron phosphate battery, so it is rarely used. The energy density of ternary batteries is much higher than other battery types, and the service life can reach 8-10 years, but the safety is relatively poor, and the cost is much higher than that of lithium iron phosphate batteries. Therefore, in the field of types of energy storage that does not require extremely high energy density, the ternary batteries application prospect is weaker than that of lithium iron phosphate batteries.
④ Sodium-ion batteries
The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, using the intercalation process of sodium ions between the cathode and anode to achieve charge and discharge. Compared with lithium iron phosphate batteries, sodium-ion batteries have higher safety performance, low-temperature performance, and fast-charging performance, and lower costs, and sodium resources are far more abundant than lithium resources and are distributed all over the world.
If sodium ions can be widely used, China will largely get rid of the current situation of limited lithium resources. The disadvantages of sodium-ion batteries are mainly reflected in the low number of cycles and the immature industrial chain. At present, the cycle life of sodium batteries is generally 2000-3000 times. The immature industrial chain leads to higher upstream prices, and the cost advantage of sodium batteries cannot be revealed.
In general, pumped storage, lithium batteries, sodium batteries and vanadium redox flow batteries types of energy storage have a large room for development. Specifically, in terms of large-scale peak shaving, pumped storage has a full life cycle cost advantage and will continue to be the mainstream choice. The latter three will be widely used in conjunction with wind power and photovoltaics. Vanadium redox flow batteries are mainly used for long-term energy storage of more than 4 hours, and sodium batteries will form a certain replacement for lithium batteries in large-scale energy storage power stations. Lithium batteries will still dominate in commercial and home energy storage that is highly sensitive to energy density.