Six core technology routes of new energy storage

On January 6, the relevant department issued policies related to the new power system. The policy puts forward the following points in the field of large-scale, high-security new stored energy technology and equipment.

Focus on long-life, low-cost and high-safety electrochemical energy storage key core technologies and equipment integration optimization research, improve the safety of lithium batteries, reduce costs, and develop diversified technical routes such as sodium ion batteries and flow batteries. Vigorously promote the development of technologies such as compressed air energy storage, flywheel energy storage, and gravity energy storage in the direction of large-scale, high-efficiency, and flexible operation.

China’s new stored energy will develop in the way of coexistence of multiple technology routes, and each energy storage technology route will develop around four directions: high safety, low cost, high performance and high environmental protection. This policy proposes six technical routes for new energy storage. What are their characteristics and what kind of development potential do they have?

Lithium battery energy storage

According to data, as of the end of September 2022, China has put into operation a cumulative installed capacity of 6663.4MW of new energy storaging projects, of which the cumulative installed capacity of lithium-ion battery stored energy is 5950.42MW, accounting for 89.30%. Lithium-ion battery is currently the electrochemical stored energy with relatively mature technology and the fastest development momentum. Lithium-ion batteries are undoubtedly the C-bit technology route for the development of new energy storage in the future.

Lithium-ion batteries are composed of positive electrodes, negative electrodes, separators and electrolytes. And here’s an article about How do lithium ion batteries work. At present, the positive electrodes of mainstream products usually use nickel-manganese-cobalt ternary materials or lithium iron phosphate, and the negative electrodes are mostly carbon materials such as graphite. Lithium-ion batteries have the advantages of high energy density, no memory effect, fast charging and discharging, fast response, flexible configuration, and short construction period. They are widely used in new energy generation side, grid side, and user side energy storage projects such as wind power photovoltaics.

● Industry chain

The lithium-ion energy storage industry chain consists of upstream equipment vendors, midstream integrators and downstream application terminals. The equipment includes batteries, EMS, BMS, PCS, thermal management, etc. Integrators include stored energy system integration and EPC. The application side is mainly composed of power supply side, grid side and user side.

● Direction of development

Lithium-ion batteries, especially lithium iron phosphate batteries, are the most cost-effective technical direction in terms of safety, energy density, cost, and development path. The material system of lithium-ion energy storage batteries is mainly lithium iron phosphate, and lithium batteries are continuously evolving towards large capacity.

According to the requirements, the energy density of energy storaging batteries is ≥145Wh/kg, and the energy density of battery packs is ≥110Wh/kg. Cycle life ≥ 5000 times and capacity retention ≥ 80%. The current electrochemical energy storage technology, especially lithium battery stored energy technology, has entered a new cycle of change. New products and technologies such as large cells, high voltage, water cooling/liquid cooling are gradually on the stage, and stored energy systems continue to evolve towards large capacity. , At the same time, sodium-ion batteries may occupy a place in the future due to their cost advantages.

Sodium battery energy storage

● Working principle

Sodium ion battery is a secondary battery that relies on the movement of sodium ions between the positive and negative electrodes to complete the charging and discharging work. The working principle of sodium-ion batteries is similar to the “rocking chair” principle of lithium-ion batteries. When charging, sodium ions are deintercalated from the positive electrode and inserted into the negative electrode through the electrolyte; the opposite is true when discharging, which is similar to the working principle of lithium-ion batteries.

In recent years, due to the soaring price of lithium carbonate, the core raw material of lithium-ion batteries, in terms of raw materials, sodium resources are large and widely distributed, and the price of raw materials is relatively low. The performance of sodium-ion batteries is relatively good. Has a certain potential.

● Performance analysis

The positioning of sodium-ion batteries and lithium iron phosphate batteries is relatively similar.

The energy density of lithium iron phosphate batteries is mainly 150-210Wh/kg, and the energy density of ternary lithium batteries is higher, exceeding 200Wh/kg. At present, the energy density of mainstream sodium-ion batteries is generally 100-200Wh/kg, which is not as good as Lithium batteries, but there is a partial overlap with the energy density range of lithium iron phosphate batteries, far exceeding lead-acid batteries.

The larger volume of sodium ions will also cause unstable cycle performance. At present, the cycle life of sodium batteries is generally 2000-3000 times, which is much higher than that of lead-acid batteries, but it still has a cycle life of 3000-6000 times compared with lithium iron phosphate batteries. gap. On the whole, the performance indicators of sodium-ion batteries and lithium iron phosphate batteries are the closest, and their positioning is relatively similar.

● Industrial chain

Sodium-ion batteries are mainly composed of positive electrodes, negative electrodes, separators and electrolytes, and are basically compatible with lithium-ion battery production equipment, reducing the difficulty of industrialization.

China’s sodium-ion battery industry chain is still in its infancy, and its industrial layout is not yet mature. The structure of the sodium-ion battery industry chain is similar to that of lithium batteries, including upstream resource companies, midstream battery material and battery cell companies.

Flow battery energy storage

● Working principle

Flow batteries currently include all-vanadium flow batteries, iron-chromium flow batteries, zinc-bromine flow batteries, zinc-iron flow batteries, all-iron flow batteries, sodium polysulfide bromine flow batteries, lithium-ion flow batteries, zinc-nickel flow batteries and other technologies.

The all-vanadium redox flow battery is the most mature and most likely to achieve large-scale commercialization of the technical route. The all-vanadium redox flow battery is a liquid-state redox renewable battery with metal vanadium ions as the active material. The positive and negative active materials of the all-vanadium redox flow battery are stored in separate electrolyte storage tanks. When the battery is charged and discharged, the positive and negative electrolytes undergo redox reactions on both sides of the ion exchange membrane. At the same time, through the action of the pump outside the stack, the electrolyte in the liquid storage tank is continuously sent to the positive and negative chambers to maintain the concentration of ions and realize the charging and discharging of the battery.

Vanadium redox flow battery has the advantages of high system security, long life, easy expansion, short project construction period, and flexible site selection. It is one of the promising technology routes for large-scale long-term energy storaging.

● Cost analysis

The initial investment cost of the all-vanadium redox flow battery stored energy system decreases with the increase of the energy storage time.

When the time is 1 hour, the initial investment cost of the flow battery energy storaging system is 7,500 yuan/kWh, but when the time is extended to 4 hours, the total price of the all-vanadium redox flow battery stored energy system is 3,000 yuan Yuan/kWh. It can be seen that the longer the working time of the all-vanadium redox flow battery energy storage system, the lower the unit kWh price.

The electrolyte solution of all-vanadium redox flow battery can be regenerated and recycled, and its residual value is relatively high. From the perspective of the whole life cycle cost, taking the vanadium redox flow battery energy storaging system with an energy storaging time of 4 hours as an example, the actual cost is 1875 yuan/kWh. When the time is 10 hours, the actual cost is only 1020 yuan/kWh.

● Industrial chain

The all-vanadium redox flow battery industry chain has initially formed, including upstream raw material suppliers, midstream vanadium battery integrators, downstream EPCs and users. The upstream involves the preparation of stacks and electrolyte raw materials, including V₂O₅, ion exchange membranes, electrodes, bipolar plates, etc.; the midstream involves the preparation of electrolytes, stacks, and battery manufacturing, of which the value of electrolytes accounts for 40%~80%, The ion exchange membrane accounts for 30%-40% of the stack cost.

● Development potential

At present, China has 100 megawatt-scale all-vanadium liquid flow energy storage power stations put into operation. According to statistics, there have been 20  projects since 2019, including 10 projects above 100 MWh.

On September 20, 2022, China’s first GWh-level vanadium flow energy storaging power station started construction-the 250,000-kilowatt/1,000,000-kilowatt-hour all-vanadium flow battery energy storaging project in Chabuchar County. In May 2022, the first phase of the Dalian liquid flow battery energy storage peak-shaving power station national demonstration project with a total construction scale of 200MW/800MWh will be connected to the grid and put into operation. The project is located in Shahekou District, Dalian City, Liaoning Province, and the first phase construction scale is 100MW/400MWh.

Compressed air energy storage

● Working principle

Compressed air energy storage is a physical stored energy method that uses air as thestored energy medium.

The working principle is that when there is excess power, the air is compressed and stored in underground gas storage caverns (caves can be salt caverns, abandoned mines, gas storage tanks, caves, expired oil and gas wells, newly built gas storage wells, etc.), and the electrical energy is converted into compressed air. potential energy. When electricity is needed, the high-pressure air is heated and enters the expander to become normal-pressure air. During this process, the generator is driven to generate electricity, and the compressed potential energy of the air is converted into electrical energy for output.

Compressed air stored energy has the advantages of large scale, long service life, short construction period, and relatively flexible site layout. It is expected to become an important supplement for pumped storage in the field of large-scale power stations.

● Cost analysis

Judging from the projects that have been completed and are currently under construction, the system efficiency of 10 MW can reach more than 60%, the system design efficiency of 100 MW or more can reach 70%, and the efficiency of advanced compressed air energy storage system can approach 75%. In terms of construction cost, according to the data, the initial construction cost of 100MW compressed air stored energy is 4000-5000 yuan/kW, 1000 yuan/kWh, and the kWh cost is between 0.15-0.25 yuan.

● Industrial chain

In the industrial chain of compressed air energy storaging, the upstream is equipment and resource supply, and the core core equipment includes air compressors, turbo expanders, heat storage and heat exchange systems, etc., and gas storage and salt cavern resources are also needed; Project construction; the downstream is the power grid system, and the compressed air energy storaging power station is connected to the power grid system, serving industrial power consumption, commercial power consumption, residential power consumption and other departments, and plays a role in peak regulation, valley filling, frequency regulation, phase regulation, energy storaging, Emergency backup and other key functions.

● Development potential

According to data, as of the end of September 2022, the proportion of compressed air energy storaging in China’s new energy storage is 2.9%, and the installed capacity is about 193.24MW. The improvement of efficiency and the reduction of cost are the basis for the commercial development of compressed air energy storaging.

According to public data, a total of 35 compressed air energy storage projects filed, signed, under construction, and put into operation in 12 provinces including Shandong, Henan, Hebei, Jiangsu, Zhejiang, and Guangdong were incompletely counted, and most of them were projects in progress; 25 of them had According to the public scale data, the total scale of these 25 projects has exceeded 8.2GW.

Flywheel energy storage

● Working principle

Flywheel energy storaging, a physical stored energy technology that stores energy by rotating a “gyroscope”. The working principle is to use the inertia possessed by the high-speed rotating flywheel to store energy. When charging, the flywheel motor accelerates to rotate, converting electrical energy into mechanical kinetic energy of the flywheel and storing it; when discharging, the high-speed rotating flywheel drives the generator to convert mechanical kinetic energy into electrical energy.

The flywheel stored energy system has the advantages of fast response, long life, good temperature adaptability, high efficiency, large capacity, and environmental friendliness.

● Development potential

According to data, as of the end of September 2022, the cumulative installed capacity of flywheel energy storaging projects in operation in China is only 6.66MW.

Compared with other stored energy technologies, the cost of flywheel energy storaging is still relatively high, and the proportion of installed capacity in the market is still very small. However, the materials are mainly steel and electronic components, and the cost of raw materials is relatively low, and the cost will decrease after large-scale manufacturing; in addition, the equipment can accurately measure and control the mechanical loss, and the maintenance cost is relatively low.

FES is currently mainly used in power grid peak regulation and frequency modulation, rail transit, aerospace, military industry, UPS power supply, energy storaging electric vehicle charging piles and other fields. In 2023, the application scale of FES in power grid frequency regulation will increase.

In the process of power grid frequency regulation, the flywheel system can quickly and effectively perform active/reactive power compensation with changes in the power grid, stabilize fluctuating loads, buffer power generation output transients, and escort the stability of the power grid. The value of flywheel stored energy to power grid frequency regulation is more of an accompanying role. At present, the more common application is to cooperate with thermal power and other units for peak regulation and frequency regulation, as an accompanying auxiliary adjustment method.

Gravity storage

● Working principle

Gravity energy storage is to use the height difference of buildings, mountains, and terrain to realize the conversion between electric energy and gravitational potential energy by transporting “heavy objects” up and down, and then store and generate electricity.

● Development potential

The conversion efficiency of the gravity energy storage system is 80%-90%, and the service life is 25-40 years. According to the data, the initial investment cost of the project is about 3,000 yuan/kWh, and the cost per unit of electricity is about 0.5 yuan/kWh, which has certain cost advantages.

As a relatively unpopular new stored energy technology route, gravity energy storage has the advantages of short construction period, high conversion efficiency, long life, and low cost of electricity. With the implementation of 100-megawatt projects, it will gradually embark on the road to commercialization.