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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.
&#; 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.
&#; 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.
&#; 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.
&#; 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.
&#; 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.
&#; 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.
&#; 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.
&#; 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 - times. The immature industrial chain leads to higher upstream prices, and the cost advantage of sodium batteries cannot be revealed.
4. Conclusion
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.
Related articles: energy storage lithium battery companies, sodium-ion battery companies in the world
In a narrow sense, for the storage of electrical energy, energy storage refers to a series of technologies and measures that use chemical or physical methods to store the generated energy and release it when needed.
So, in which fields is energy storage currently used more often? How many types of energy storage are there?
Three major energy storage areas - power systems, automobiles and home battery backup power
In the field of power system energy management, the preferred technology for energy storage is pumped storage, chemical batteries in liquid flow may be the first to have commercial conditions, followed by lithium-ion batteries, lead-acid batteries need to further improve performance in technology, and sodium-sulfur batteries have long been monopolized by Japan, and there is greater uncertainty in the prospects for commercial application.
From the current energy storage system demonstration study, to stabilize the power supply to provide uniform power output, it is necessary to support approximately 20% of the new energy generation capacity, and 6-8 hours of storage time battery storage system. It is expected that by , a combined total of 2 billion kilowatts of energy storage will be required on the generation side and the consumption side.
It is predicted that by , the installed capacity of global energy storage systems will reach approximately 45 GW/81 GWh. Although the size of this storage capacity appears to be very insignificant compared to the total installed capacity of global power generation, the power system has already undergone a qualitative change due to the emergence of energy storage systems.
Currently, power plant-level storage capacity is mainly used to replace less efficient generation capacity. At the same time, the rapid growth of off-grid energy storage capacity is bound to change the relationship between consumers and power plants.
In the field of electric vehicles, energy storage technology with application prospects is dominated by lithium-ion batteries, and lead-acid batteries also have a certain market. The electric vehicle field needs 453 million kilowatts of energy storage equipment. The global electric vehicle market size has shown rapid development, from only 6.8 million units in to 64.3 million units in , with a compound annual growth rate of 75.36%.
With the continuous breakthrough of new energy vehicle range technology and the gradual reduction of the cost of core components, new energy vehicles in the global passenger car market began to achieve scale in , and it is from then on that the global electric vehicle market scale has also ushered in a new round of explosive growth.
The home energy storage sector can also be understood as a set of large batteries that store electrical energy for the home. This is a very mature market for Europe, Australia, the United States and Japan.
Currently, the major global markets for home energy storage systems are in the United States and Japan.
The area of American dwellings is usually larger, the household uses more electricity, and the number of households with new energy generation systems such as wind and light is also high.
Due to the high electricity consumption and the large price difference between peak and valley electricity rates, home energy storage systems are often used by American households to store electricity during low electricity prices and use it during high electricity prices to save money on electricity bills.
In addition, in remote areas, as well as in areas with a high incidence of natural disasters such as earthquakes and hurricanes, home energy storage systems are used as emergency power sources to eliminate the inconvenience of frequent power outages due to disasters or other reasons.
5 Categories and 11 Types of Energy Storage Technologies
Mechanical Energy Storage
Mechanical energy storage applications as long as the form of pumped storage, compressed air energy storage and flywheel energy storage.
1, Pumped Storage
When the grid is low, the use of excess power as a liquid energy media water from low elevation reservoirs to high elevation reservoirs, high elevation reservoirs when the grid peak load water back to the lower reservoir to promote the turbine generator power generation.
At present, the world average of proportion of pumped storage units in the total installed capacity of a country is about 3%. By the end of , the total capacity of energy storage units worldwide was 128 GW, of which pumped storage was 127 GW, accounting for 99%.
By the end of , China had 50,325,000 kW of pumped storage power plant units, 23,385,000 kW of operating capacity, and 26,940,000 kW of capacity under construction, accounting for about 3% of the country's total installed capacity of 1.65 billion kW. (Another 8 are under construction, with a capacity of 8.94 million kilowatts under construction)
2&#;Flywheel Energy Storage
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In a flywheel energy storage system, electrical energy is used to accelerate a rotor placed in a vacuum enclosure, i.e. a large mass cylinder made of solid material (up to tens of thousands of revolutions/minute), thus storing electrical energy in the form of kinetic energy (using the inertial energy stored in the large rotor).
Flywheel energy storage is mostly used in industrial and UPS for power distribution system operation for frequency regulation, can be used as a UPS without battery, when the power supply failure, rapid transfer of power to maintain the frequency stability of the small system for a short period of time to ensure power quality (power supply interruptions, voltage fluctuations, etc.).
3&#;Compressed Air Energy Storage
Compressed air storage uses air as a carrier of energy, large compressed air storage uses excess power to compress and store air in an underground structure (such as underground caves), and then when needed to mix compressed air with natural gas, combustion expansion to drive gas turbines to generate electricity.
To date, only Germany and the United States have operational compressed air energy storage stations. The Hundorf station in Germany was commissioned in , with a compressed power of 60MW and a generating power of 290MW (later upgraded to 321MW), with a compressed time/generating time = 4, 2 hours of continuous operation, tens of thousands of stars, and a 97% start-up reliability rate.
In addition, Germany is building an adiabatic compressed air energy storage power plant, not yet commissioned in the United States Mcintosh, Alabama Alabama, commissioned in , 110MW, compression time/generation time = 1.6, such as the continuous output of 100MW can be maintained for 26 hours, there has been a collapse accident due to geological instability. In addition, the United States is building several large compressed air energy storage power plants, which have not yet been put into operation.
Recently, the research and development of compressed air energy storage is on the rise, and the National Grid Corporation has set up a project to study 10MW compressed air energy storage.
The Electrical Energy Storage
The only form of electrical energy storage applications are supercapacitor energy storage and superconducting energy storage.
1, Supercapacitor Energy Storage
Developed according to the electrochemical double-layer theory, also known as a double-layer capacitor, the distance between the two charge layers is very small (generally less than 0.5mm), the use of a special electrode structure, so that the electrode surface area increased ten thousand times, resulting in a great electric capacity.
Supercapacitor energy storage has been developed for more than 50 years, and the technology has progressed rapidly in the last two decades, making its electric capacity greatly increased compared with that of traditional capacitors, reaching several thousand farads in magnitude, and the specific power density can reach ten times that of traditional capacitors.
Supercapacitor energy storage stores electrical energy directly in the electric field without energy form conversion and fast charging and discharging time, which is suitable for improving power quality. Due to the low energy density, it is suitable to be used in combination with other means of energy storage.
2&#;Superconducting Energy Storage
The superconducting energy storage system is made of a superconducting material, placed in a cryogenic vessel (Dewar Dewar ) in the coil, power conditioning system (PCS) and low-temperature refrigeration system and so on.
The energy is stored in the magnetic field as a DC current circulating in the superconducting coil.
Superconducting energy storage is suitable for improving power quality, increasing system damping, and improving system stability performance, especially for suppressing low-frequency power oscillations.
However, due to its expensive and complex maintenance, although there are commercial low-temperature and high-temperature superconducting energy storage products available, the application in the power grid is rare and mostly experimental.
Electrochemical Energy Storage
Electrochemical energy storage mainly includes a variety of secondary batteries, including lead-acid batteries, lithium-ion batteries, sodium-sulfur batteries and liquid flow batteries, etc. Most of these batteries are technically mature and have become the focus of attention in recent years, and have also gained many practical applications.
1, Lead-acid Batteries
Lead-acid batteries are one of the most widely used batteries in the world. The anode (PbO2) and cathode (Pb) inside the lead-acid battery are dipped into the electrolyte (dilute sulfuric acid), and potential of 2V is generated between the two poles.
Lead-acid batteries are often used for the accidental power supply or backup power supply in power systems, and most stand-alone photovoltaic power generation systems used to be equipped with such batteries. Currently, there is a trend of being gradually replaced by other batteries (such as lithium-ion batteries).
2&#;Lithium-ion Battery
Lithium-ion battery is actually a lithium-ion concentration difference battery, positive and negative electrodes by two different lithium-ion embedded compound structures.
When charging, Li + from the positive electrode embedded in the negative electrode through the electrolyte, the negative electrode is in the lithium-rich state, the positive electrode is in the lithium-poor state; when discharged, the opposite, Li + from the negative electrode embedded in the positive electrode through the electrolyte, the positive electrode is in the lithium-rich state, the negative electrode is in the lithium-poor state.
Because of the application of lithium-ion batteries in portable and mobile devices such as electric cars, computers and cell phones, it has now almost become the most widely used battery in the world.
The high energy density and power density of lithium-ion batteries are the main reasons why it can be widely used and noticed.
Its technology is developing rapidly, and in recent years, mass production and multi-occasion applications have led to a rapid decline in its price and thus to its increasing use in power systems.
Lithium-ion battery technology is still under continuous development, and current research is focused on further improving its service life and safety, reducing costs, and developing of new positive and negative electrode materials.
3&#;Sodium-sulfur Batteries
The anode of the sodium-sulfur battery consists of liquid sulfur, and the cathode consists of liquid sodium, separated by a ceramic material beta aluminum tube. The operating temperature of the battery needs to be kept above 300°C to keep the electrodes in a molten state.
NGK in Japan is the only manufacturer in the world that can produce a high-performance sodium-sulfur battery. Currently, 50kW modules are used, and MW-class high-capacity battery modules can be formed from multiple 50kW modules.
In Japan, Germany, France, the United States and other places have built about 200 such energy storage power plants, mainly for load leveling, peak shifting, improving power quality and renewable energy generation, the battery price is still high.
4, All-vanadium Liquid Flow Battery
In liquid flow batteries, energy is stored in the electroactive species dissolved in the liquid electrolyte, which is stored in a tank outside the battery. The electrolyte stored in the tank is pumped into the battery stack, and through electrodes and thin films, electrical energy is converted into chemical energy or chemical energy is converted into electrical energy.
There are several systems of liquid flow batteries, of which the vanadium redox flow battery (VRFB) has received the most attention.
This battery technology was first invented by the University of New South Wales in Australia and later transferred to VRB in Canada.
After , the technology was acquired by the Chinese company Pnang, whose products have been applied in some pilot projects in China and abroad.
The power and energy of the battery are not correlated, the stored energy depends on the size of the storage tank, thus it can store energy for hours to days, and the capacity can reach MW level, which is suitable for application in power systems.
Thermal Energy Storage
In a thermal energy storage system, thermal energy is stored in the medium of an insulated container and can be converted back to electricity when needed later, or can be used directly without being converted back to electricity.
There are many different technologies for thermal energy storage, which can be further divided into sensible heat storage and latent heat storage.
In sensible heat storage, the medium used for heat storage can be liquid water, and the hot water can be used directly or for room heating, etc. The temperature of the hot water varies during operation.
The latent heat storage is done by Phase Change Materials (PCMs), which is the medium for storing thermal energy.
Since the heat stored in thermal energy storage can be very large, it will be useful in the utilization of renewable energy generation. Molten salts are often used as a phase change material in collector solar thermal power plants. In addition, there are many other types of thermal storage technologies under development that serve many different purposes.
Chemical-based Energy Storage
Chemical-type energy storage mainly refers to the use of hydrogen or synthetic natural gas as a carrier of secondary energy.
Hydrogen is obtained by using wind power to be discarded to produce hydrogen, electrolyzing water, and decomposing it into hydrogen and oxygen. Later, hydrogen can be used directly as a carrier of energy, and then hydrogen can be reacted with carbon dioxide to become synthetic natural gas (methane), using synthetic natural gas as another secondary energy carrier.
The process of synthesizing hydrogen and carbon dioxide into methane is also known as P2G technology (power to gas). Germany is keen to promote this technology, and demonstration projects are already in operation in Germany. Natural gas-fueled cogeneration or combined cooling, heating and power systems have become an important part of distributed generation and microgrids, and play an important role in smart distribution grids, where hydrogen and synthetic natural gas provide sufficient fuel for distributed generation.
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