6 energy storage technologies introduction-principles, cons, pros and industrial chain

The characteristics and cost reduction of energy storage technologies are different. According to different application scenarios, energy storage technologies will present a pattern of simultaneous development of multiple lines. To sum up, energy storage technology can be divided into mechanical energy storage, thermal storage and chemical energy storage.

Among them, mechanical energy storage includes pumped storage and compressed air storage; The thermal storage is mainly molten salt thermal storage; Chemical energy storage includes lithium ion battery energy storage, sodium ion battery energy storage and liquid flow battery energy storage. This article will introduce various energy storage technologies in detail.

Pumped storage

Principle

Pumped storage is currently the most mature energy storage technology with the lowest cost per kilowatt hour, and also one of the mainstream energy storage technologies with the largest installed capacity. Pumped storage is a kind of mechanical energy storage.

When water is pumped from the lower pool reservoir to the upper pool reservoir during the low load period, the electric energy is converted into gravity potential energy for storage, and the reverse flow is used for power generation during the peak load period. The comprehensive efficiency is between 70% and 85%.

Pros and cons

Pros：
Currently, the most mature energy storage technology has the lowest cost per kilowatt hour. According to the calculation, without considering the charging cost and the discount rate is 0, the electricity cost of pumped storage is only 0.207 RMB/kWh, which is the lowest in various energy storage technologies.

Cons：
● Obvious constraints on geographical resources
● Relatively limited energy density
● High initial investment cost
● Long development and construction time

Industrial chain and industrialization

The main companies involved in the construction of pumped storage power plants are investors, contractors and equipment manufacturers. In addition, the installed capacity of pumped storage has grown significantly in China. According to data, by the end of 2021, the total scale of pumped storage power plants put into operation in China is 36.39GW, and the proportion of the total scale of pumped storage power plants in China in the world will increase from 17% in 2010 to 28% in 2021.

Compressed air energy storage

Principle

Compressed air energy storage system is a kind of electric energy storage system. The excess electric energy is stored by compressed air, and when necessary, the high-pressure gas is released to the expander for power generation. At present, compressed air technology is dominated by medium temperature regenerative compressed air energy storage.

Pros and cons

Pros:

With the progress of technology, compressed air energy storage can store compressed gas in the form of gas storage tank, thus getting rid of geographical constraints. In addition, the unit cost of the energy storage technologies is relatively low, and the equipment cost accounts for the majority of the system cost. It is possible to reduce the cost rapidly with large-scale application.

Cons:
The efficiency of the whole compressed air energy storage system is still relatively low. At present, the efficiency of the projects involved in operation is between 50% – 70%, and there is still a certain gap between 76% of the more mature pumped storage projects, which affects the economy of the whole project to a certain extent.

Industrial chain and industrialization

● Compressor
Compressor is one of the most important components in compressed air energy storage system, and its performance has a decisive impact on the whole system. Most compressors in large compressed air storage power plants are axial flow and centrifugal compressor units, and the compressor pressure ratio needs to reach 40-80, or even higher.

According to the report, the compressor cost of Huntorf Power Station in the United States is about 170 dollars/KW based on 2002 dollars.

● Expander

The expander is also the core component of the compressed air energy storage system in energy storage technologies. The expander in the large compressed air energy storage system has the characteristics of large expansion ratio and high load, and generally adopts the structure of multi-stage expansion and intermediate reheat.

According to the report, the investment cost of the turbine expander in the United States of America is about 185 dollars/KW among the 100 megawatt power plants priced in 2002 dollars. Since 1949, the research and development of compressed air energy storage system has been very active all over the world.

Lithium ion battery

Pros and cons

Pros:
Lithium battery energy storage is the most mature electrochemical energy storage technology in energy storage technologies with the largest installed capacity. According to data, lithium-ion batteries will account for 89.7% of China’s new energy storage installed capacity in 2021, which is one of the most representative new energy storage technologies. At present, they are widely used in 1-2 hour medium and short-term energy storage scenarios, as well as 4-8 hour energy storage projects.

Cons:

● Cost increase
The lithium-ion battery provides power and is bound with the device for storing energy. The battery cost increases proportionally without increasing power but only capacity.

● Resource constraints

With the rapid growth of global battery demand, lithium resources begin to face resource constraints. On the one hand, the total distribution of lithium resources is limited, and the crustal abundance is only 0.006%; On the other hand, the spatial distribution of lithium resources is uneven.

Lithium mines are mainly distributed in Australia and South America. According to the report, China’s lithium reserves account for only 6% of the world’s total, and the mining cost is high. Currently, lithium for battery production is highly dependent on foreign countries. At the same time, lithium resource constraints also bring about the problem of lithium resource allocation between power batteries and energy storage batteries.

Industrial chain

The lithium-ion battery energy storage industry chain is relatively mature in energy storage technologies. In the whole system, the battery cost accounts for the highest proportion. At present, due to the high price of upstream lithium resources, the cost of the current entire lithium-ion battery energy storage system has increased rather than decreased compared with the beginning of 2021.

Sodium ion battery

Principle

In energy storage technologies, the working principle of sodium ion battery is similar to that of lithium ion battery, which is a plug-in battery. During charging, Na+is disengaged from the positive pole and enters the negative pole; When discharging, Na+returns to the positive pole from the negative pole, and electrons in the external circuit enter the positive pole from the negative pole, reducing Na+to Na.

Pros and cons

Pros:

● Rich sodium resources
Compared with lithium resources, sodium resources are very abundant, so in the scenario of large-scale application, sodium ion batteries have no obvious resource constraints.

● Low cost
In energy storage technologies, the theoretical cost of cathode material and collector material of sodium ion battery is lower than that of lithium battery. After the completion of industrialization and cost reduction, its initial investment cost is expected to be lower than that of lithium battery.

Cons:
In terms of battery performance, the cycle life and energy storage efficiency of sodium ion battery are lower than those of lithium ion battery. The cycle life of sodium ion battery has been improved rapidly in energy storage technologies.

At the beginning of commercialization in 2018, the cycle life of sodium ion battery was about 2000 times. By the end of 2020, a research team has developed a sodium ion battery with a cycle life of 4500 times. However, the current mainstream lithium-ion battery has a higher cycle life. In 2021, CATL developed a lithium-ion battery with a cycle life of more than 12000 times.

Industrial chain and industrialization

As one of the new battery energy storage technologies route, sodium ion battery industry chain includes upstream resource enterprises, midstream battery materials and cell enterprises. At present, the cathode materials of sodium ion batteries mainly include sodium transition metal oxides.

In addition to the cathode and anode materials, the relevant preparation process of sodium ion battery is similar to that of lithium battery. The existing lithium ion battery industry chain can be used to accelerate the industrial development.

In energy storage technologies, the commercialization of sodium ion batteries has accelerated in recent years. In July 2021, CATL released sodium ion battery products, showing that the industry leader officially entered the field of sodium ion batteries. 

In addition, HiNa Battery has also launched demonstration projects of sodium ion battery electric bicycle, electric vehicle and energy storage power station in recent years.

Liquid flow battery

Principle

In energy storage technologies, liquid flow battery is a large-scale and efficient electrochemical energy storage technologies device. Different from other battery energy storage devices, the liquid flow battery stores reactive active substances in electrolyte solution, which can realize the separation of electrochemical reaction and energy storage site, making the battery power and energy storage capacity design relatively independent, which is suitable for large-scale energy storage.

At present, typical liquid flow battery systems include:

● All vanadium flow battery
● Iron chromium flow battery
● Zinc bromine flow battery
● Sodium polysulfide/bromine battery

Pros and cons

Pros:

● Output power and energy storage capacity can be designed separately

The power of liquid flow battery can be increased by increasing the number of single cells and electrode area. At present, the power of vanadium battery in commercial demonstration operation in China has reached 5MW.

● Long cycle life

Since the cathode and anode active substances of the liquid flow battery only exist in the cathode and anode electrolyte, there is no change in the phase of other batteries during charging and discharging.

Cons:

In energy storage technologies, the cost problem is the biggest disadvantage of current liquid flow battery. At present, the industrialization of all vanadium flow battery is fast, but it faces the problem of vanadium resource constraint; Fe Cr flow battery has no obvious resource constraints, but the current industrialization is relatively slow.

Industrial chain and industrialization

The liquid flow battery is mainly composed of the following parts:
● Electrolyte
● Separator
● Electrode materials
● Pump
● Power conversion system

In all vanadium flow battery, the cost of electrolyte accounts for more than half of the cost of energy storage battery. The separator should have excellent chemical and electrochemical stability, and should be cheap to improve the market competitiveness of the product and facilitate large-scale commercial promotion. The pump plays the role of transporting electrolyte in vanadium battery, which requires strong stability.

According to the calculation, when the energy storage duration is 8h, the value of the electrolyte of the vanadium flow battery accounts for 53%, the value of the separator accounts for 19%, the value of the graphite felt accounts for 5%, the value of the pump accounts for 4%, and the value of the power conversion system accounts for 12%.

With the drive of relevant demonstration projects, the cost of all vanadium flow battery is expected to be reduced, so as to promote its commercialization in the product technology side.

Molten salt thermal storage

Principle

Molten salt thermal storage realizes the storage and release of heat energy through temperature change, phase change or chemical reaction of heat storage medium. The thermal storage medium absorbs electric energy, radiant energy and other energy and stores them in the medium.

When the ambient temperature is lower than the medium temperature, the thermal storage medium can release the heat energy. Thermal storage technology can be divided into:

● Sensible thermal storage
● Phase change thermal storage
● Thermochemical heat storage

Pros and cons

Pros:
In energy storage technologies, as a thermal storage medium, molten salt has low cost, stable working state, high heat storage density and long heat storage time. It is suitable for large-scale medium and high temperature heat storage. A single machine can achieve a heat storage capacity of more than 100MWh.

Cons:

In energy storage technologies, molten salt stores energy by storing heat. If it needs to store electric energy, it needs to complete the conversion of “electric energy – thermal energy – electric energy” in the whole process, and the efficiency is very low.

Therefore, molten salt energy storage can only be used in scenarios where thermal energy is used for power generation, as a storage medium of energy, or in scenarios where the terminal energy demand is thermal energy rather than electrical energy.

Industrial chain and industrialization

The main components of molten salt are sodium nitrate and potassium nitrate, which are relatively common chemical materials. At present, China’s molten salt supply and chemical salt service are relatively mature. At the same time, the one-time investment scale of molten salt thermal storage is large.

Through the cultivation of the solar thermal power distribution and storage market, the molten salt thermal storage industry chain in energy storage technologies is relatively mature. If the market demand is further expanded, the investment cost of the industrial chain is expected to decrease.

In energy storage technologies, the molten salt thermal storage system is usually connected with the solar thermal power generation. In 1982, the 10MW solar tower thermal power station Solar One in the United States was put into construction and equipped with a double tank molten salt thermal storage system, which is the beginning of the molten salt tower thermal power station.

At the beginning of the 21st century, Spain built GemaSolar power station, equipped with a 15h level double tank molten salt energy storage system. Many great energy storage technology manufacturers in China also do well in the field of energy storage technologies.

Delingha 50 MW tower type molten salt solar thermal power plant project is the first batch of tower type projects put into operation in energy storage technologies in China with molten salt as the heat transfer and storage medium. It is equipped with a 7h level molten salt thermal storage system, and the designed annual power generation is 146 million KWh.