(Report Producer/Author: Great Wall Securities, Yu Ximeng)
1. The necessity of developing new types of energy storage in China
The power system is currently one of the main sources of carbon emissions in China. The goal of future power system construction is to build a new type of power system with new energy as the main body. Carbon free energy such as wind power, photovoltaic, hydropower, nuclear power, etc. will gradually replace fossil energy as the main force of power generation. As of the end of 2021, China's total installed capacity of electricity was 2.38 billion kilowatts, including 330 million kilowatts of wind and 310 million kilowatts of photovoltaic power, and approximately 1.3 billion kilowatts of thermal power (including biomass). Based on comprehensive predictions of factors such as population change, GDP growth, transformation of power installation structure, substitution of electricity, and increase in per capita electricity consumption, we predict that by 2030, the installed capacity of electricity in China will reach 3.6 billion kilowatts, including 800 million kilowatts of wind power and 1 billion kilowatts of photovoltaic power, accounting for about 50%. By 2060, the installed capacity of electricity in China will reach 9.0-9.5 billion kilowatts, including 3.3 billion kilowatts of wind power and 4.2 billion kilowatts of photovoltaic power, accounting for over 80%.
Wind power and photovoltaic power not only bring us green and low-carbon electricity, but also have randomness, intermittency, and volatility, posing higher requirements for the regulation ability of the power system. Usually, the fluctuation characteristic parameters (amplitude, frequency, and rate of change) of the net load (net value after subtracting wind and solar output from the electricity load) are used to calculate the demand for regulating capacity in the power system. Figure 2 shows the changes in the net load of the California power system as the penetration rate of new energy increases. As can be seen from the figure, as the photovoltaic output increases at noon, the net load decreases, while as the sun sets in the evening, the net load demand rapidly increases. This requires the power system to have the ability to reduce output at noon and quickly increase output in the evening. As the proportion of new energy increases, the range of power changes that need to be adjusted becomes larger and larger.
In addition to the daily regulation mentioned above, the fluctuation characteristics of net load vary at different time scales such as short time (seconds to minutes), long time (hours to days), and ultra long time (weeks, months, years). For power grid regulation, it corresponds to scenarios such as frequency regulation, daily peak regulation, and seasonal peak regulation. As the proportion of new energy installed in the power system continues to rise, the proportion of stable power sources such as thermal power and nuclear power gradually decreases. The impact of climate on hydropower output at the end of the spectrum greatly weakens the supply side's response and regulation ability. In addition, long-term deep load regulation of coal-fired power and nuclear power may pose risks to the safety of unit operation, as well as increase additional coal consumption and carbon emissions. These additional demand for supply side load regulation must be compensated for by clean energy storage installations. In addition to meeting the demand for regulation capacity, energy storage can also play a role in alleviating grid congestion, providing backup and black start for power transmission and security in the power grid. For the power generation side, energy storage can play a role in smoothing new energy fluctuations and improving new energy consumption. The energy storage installation on the load side can greatly improve the self balancing and response capabilities of the load side.
In the future, the characteristics of China's power system will be to use wind, light, water, and nuclear power as the main power sources, with sufficient energy storage installed to provide regulation capacity, and to retain fossil energy installed as part of the base load and guaranteed regulation based on the principle of miniaturization. Coupled with strong grid transmission and scheduling capabilities and intelligent load side response capabilities, it will be a brand new power system with several characteristics such as safety, stability, cleanliness, and flexibility. Energy storage will play an indispensable and important role in new power systems.
Among various energy storage technologies, pumped storage technology is mature and stable, with low full life cycle energy storage costs, and is currently the main force in energy storage installation. As of the end of 2021, out of the approximately 46 million kilowatts of energy storage installed capacity that has been put into operation in China, pumped storage capacity is approximately 37 million kilowatts, and over 60 million kilowatts of pumped storage power stations have been constructed. Nevertheless, pumped storage power stations have drawbacks or limitations such as inflexible site selection, large construction investment scale, and long construction period, which are difficult to solve through technical means. Relying solely on pumped storage energy cannot meet the requirements of the rapid increase in new energy installation in recent years, nor can it meet the requirements of future power systems for flexible spatiotemporal configuration and diversified technical parameters of energy storage. This provides sufficient development space for various types of "new energy storage". We believe that after full cultivation and development during the 14th and 15th Five Year Plans, mature "new energy storage" technologies will be on par with pumped storage in the future new power systems, playing an important role in system regulation and safety assurance in various application scenarios of source grid load.
2. Development status of new energy storage
2.1 Installation situation
As of the end of 2021, the installed capacity of energy storage projects that have been put into operation globally is approximately 210 million kilowatts, a year-on-year increase of 9%. Among them, the installed capacity of pumped storage is about 180 million kilowatts, accounting for less than 90% for the first time. The cumulative installed capacity of new energy storage is 30 million kilowatts, a year-on-year increase of 67.7%, with lithium-ion batteries installed at about 23 million kilowatts, occupying a dominant position. Among the 30 million kilowatts of new energy storage installations, the United States is the country with the largest installed capacity, approximately 6.5 million kilowatts, followed closely by China, with an installed capacity of approximately 5.8 million kilowatts. Other countries with more new energy storage installations include South Korea, the United Kingdom, Germany, Australia, and Japan.
As of the end of 2021, China has installed approximately 46 million kilowatts of electricity storage capacity, an increase of 30% compared to 2020, accounting for 22% of the global electricity system's energy storage capacity. In 2021, there will be approximately 10 million kilowatts of newly installed power storage capacity, including approximately 8 million kilowatts of pumped storage capacity and approximately 2 million kilowatts of new energy storage capacity. Among the 5.8 million installed units of new energy storage, lithium-ion batteries account for a high proportion, approaching 90%, equivalent to an installed capacity of approximately 5.2 million kilowatts. Among the other new types of energy storage, lead-acid batteries and compressed air energy storage account for a relatively large proportion. From the perspective of the new energy storage installed capacity that has been put into operation in various provinces, Jiangsu Province ranks first with an installed capacity of over 1 million kilowatts, followed by Guangdong and Shandong provinces. Other provinces with larger installed capacity include Qinghai, Inner Mongolia, Hunan, Anhui, etc.
2.2 Current status of technological development
There are many types of technologies involved in new energy storage, which are mainly divided into several categories according to different energy storage methods, including mechanical energy storage, electromagnetic energy storage, electrochemical energy storage, chemical energy storage, and heat storage. There are various completely different technological routes within each major category of technology. According to the discharge duration, it can be divided into power type electrical energy storage, energy type electrical energy storage, and thermal (cold) storage technology. This report mainly summarizes and compares the main technical and economic parameters and development status of various energy based electric energy storage technologies. Due to the relatively mature development of lithium-ion batteries and the abundance of relevant reference materials, this report focuses on introducing five energy storage technologies that focus on energy based applications, including compressed air energy storage, gravity energy storage, liquid flow battery energy storage, sodium ion battery energy storage, and hydrogen energy storage. The technical principles, characteristics, and A detailed analysis was conducted on key technical indicators, economic potential, and application prospects.
Technical principles. Compressed Air Energy Storage (CAES) is a form of mechanical energy storage. During the low valley of the power grid, the surplus electrical energy is utilized to drive the compressor to produce high-pressure air, which is stored in the gas storage chamber and converted into pressure potential energy of the air; When the power grid is at a peak or when users demand electricity, air is released from the air storage chamber and then enters the expander to output shaft power to the outside, driving the generator to generate electricity and converting the pressure potential energy of the air into electrical energy. The high-pressure air in the CAES energy storage system needs to be heated to increase power density before entering the expander for work. According to the different heat sources of heating, it can be divided into compressed air energy storage systems that burn fuel (i.e., traditional compressed air energy storage systems with supplementary combustion), compressed air energy storage systems with heat storage, and compressed air energy storage systems without heat sources.
The Advanced Adiabatic Compressed Air Energy Storage System (AA-CAES) introduces heat storage technology on the basis of traditional CAES systems, utilizing heat storage media to recover the compression heat generated during the compression stage and storing high-temperature storage media. During the energy release stage, the high-temperature storage media preheats high-pressure air through a heat exchanger. The heat storage system replaces the supplementary combustion of the combustion chamber to heat the air, thereby achieving the goal of reducing system energy loss and improving efficiency. In addition, some AA-CAES systems use liquid compressed air stored in storage tanks, overcoming the limitations of natural conditions.
2.2.1 Compressed air energy storage
Compressed air energy storage technology is a relatively fast developing and mature technology among the new energy storage technologies discussed in this report, and has entered the stage of a 100MW demonstration project. Early compressed air energy storage systems relied on gas reburning and natural gas storage caves, but currently there is no need for reburning and can be applied to artificial gas storage spaces. Compressed air energy storage technology is of the same origin as gas turbine technology, and the main pain point lies in equipment manufacturing and performance improvement. The performance improvement of large-scale compressed air equipment, expansion equipment, heat storage equipment, storage tanks, and other equipment is the key to improving efficiency, economy, and reliability. During the 14th Five Year Plan period, the efficiency of the compressed air energy storage system is expected to increase to 65%~70%, and the system cost will be reduced to 1000~1500 yuan/kW · h. At the end of the 15th Five Year Plan and beyond, the system efficiency is expected to reach 70% or above, and the system cost will be reduced to 800-1000 yuan/kW · h.
Technical advantages and disadvantages. The compressed air energy storage system has the advantages of large capacity, long working time, good economic performance, and multiple charging and discharging cycles. The compressed air energy storage system is suitable for building large energy storage power plants (>100MW), with a discharge duration of over 4 hours, making it suitable as a long-term energy storage system. The compressed air energy storage system has a long lifespan, capable of storing/releasing energy tens of thousands of times, with a lifespan of over 40 years; And its efficiency can reach around 70%. Compressed air energy storage technology is of the same origin as steam turbine and gas turbine systems, with strong technical universality, good equipment development foundation, easy control of construction and operation costs, and good economic efficiency.
Industry chain and cost: The upstream of compressed air energy storage mainly involves the production, processing, assembly, and manufacturing of raw materials and core components (molds, castings, pipelines, valves, tanks, etc.), which are part of the mechanical industry. However, it involves the characteristics and performance requirements of compressed air energy storage itself, and the design and processing requirements for basic components are relatively strict. The midstream is mainly an industry related to the design and manufacturing of key equipment (compressors, expanders, combustion chambers, heat storage/heat exchangers, etc.), as well as system integration and control. It belongs to a technology intensive high-end manufacturing industry, with characteristics such as multi-disciplinary and technological intersection. Downstream is mainly the user's use and demand for compressed air energy storage systems, involving multiple industry fields such as conventional power transmission and distribution, large-scale access to renewable energy, distributed energy systems, smart grids, and energy internet.
At present, the cost of 100 megawatt level compressed air energy storage power is about 4000-6000 yuan/kW, and the energy cost is about 1000-2500 yuan/kWh. The cycle efficiency can reach 65-70%, and the operating life is about 40-60 years. The initial investment cost of the compressed air system mainly includes system equipment, land costs, and infrastructure. The system equipment includes compressor unit, expander unit, heat storage system (heat exchanger, heat accumulator, heat storage medium, pipeline), electrical and control equipment, gas storage room, etc.
2.2.2 Liquid flow battery
Liquid flow batteries have the advantages of large capacity, good safety, and decoupling between power and capacity, making them suitable for large-scale long-term energy storage. All vanadium flow battery is currently a mature flow battery system, and the multivalent nature of vanadium makes it face fewer technical problems, making the technology more mature. However, the cost of the main active substance vanadium accounts for a high proportion of the system cost, which limits its cost reduction. The progress of all vanadium flow batteries is currently rapid in China, and the 5MW/10MWh project has been operating safely and stably for more than 8 years. The 200MW/800MWh project has entered the debugging phase. Other forms of liquid flow batteries are currently in the demonstration stage of kW~MW level.
The cost of all vanadium flow batteries currently ranges from 2500 to 3500 yuan/kWh. If considering the residual value of vanadium electrolyte accounting for 70% of the original value and long-term energy storage for more than 8 hours, the price is expected to decrease to 800-1400 yuan/kWh. But in the past year, the price of vanadium pentoxide has significantly increased, which has greatly increased its cost pressure. Zinc based and iron based systems have the characteristics of large reserves of active substances and low prices. However, there are many technological and scientific research issues, and compared to all vanadium batteries, the technology is more complex, requiring longer time for research and development demonstration.
In theory, ion pairs with varying valence states can form various redox flow batteries. According to the classification of liquid flow forms, liquid flow batteries can be divided into dual flow batteries and single flow batteries. According to the deposition and phase transition, it can be divided into deposition type batteries and non deposition type batteries. According to the classification of active materials, they can be divided into all vanadium flow batteries, zinc based flow batteries (zinc bromide, zinc iron, zinc nickel, zinc air, etc.), iron chromium flow batteries, all iron flow batteries, and so on. Compared to all vanadium flow batteries, other flow battery technologies have slightly lower maturity and still face problems such as deposition of active substances, electrolyte exchange, low power density, inability to fully decouple capacity and energy, hydrogen and oxygen evolution.
Vanadium pentoxide and separator account for 60-80% of the raw material cost. And as the energy storage time increases, the proportion of vanadium pentoxide cost gradually increases. The vanadium pentoxide market is currently a typical spot market, and short-term fluctuations in vanadium prices will directly affect the cost of all vanadium flow batteries. Therefore, a relatively stable vanadium price is conducive to cost control in the flow battery industry. Although the initial investment cost of all vanadium flow batteries is relatively high, the electrolyte performance of all vanadium flow batteries decays slowly and can be recycled through online or offline regeneration. Moreover, the value of vanadium in the electrolyte exists for a long time (with relatively high residual value), and its recyclability and high residual value rate have certain advantages for initial investment cost allocation and subsequent annual operation and maintenance costs.
Company and demonstration projects. All vanadium flow batteries have many demonstration projects. In 2012, Dalian Rongke Energy Storage implemented the global large-scale 5MW/10MWh all vanadium liquid flow energy storage system for the Liaoning Woniushi wind farm, which was the first to achieve technological industrialization at home and abroad. The design life of this project is 10-15 years, and there is almost no significant decrease in energy efficiency after operation. The maintenance cost is low, and the operation effect is significant, further verifying the maturity of all vanadium flow battery technology. Afterwards, more large-scale all vanadium flow battery demonstration projects were put into construction and operation. At present, all vanadium flow batteries in China have entered the demonstration and application stage of 100 megawatt level technology.
The Dalian National Demonstration Project, Hubei All Vanadium Flow Battery Energy Storage Project, and Datang Zhongning Shared Energy Storage Project have all reached the level of one hundred megawatts. The National Demonstration Project of Dalian Liquid Flow Battery Energy Storage and Peaking Regulation Power Station is a 100MW level large-scale electrochemical energy storage national demonstration project approved by the National Energy Administration. The power station is the first phase of the "200MW/800MWh Dalian Liquid Flow Battery Energy Storage and Peaking Regulation Power Station National Demonstration Project", and adopts the all vanadium liquid flow battery energy storage technology independently developed by Dalian Institute of Chemistry. The first phase of the 100MW/400MWh grade all vanadium flow battery energy storage power station has completed the main project construction in 2022 and entered the single module debugging stage. It is expected to be put into commercial operation this year.
The State Power Investment Xiangyang High tech Energy Storage Power Station project is invested and constructed by State Power Investment Hubei Lvdong Vanadium New Energy Co., Ltd. in Xiangyang High tech Zone, Hubei. The project will commence on August 29, 2021, and is expected to be completed before 2022. Among them, the 100MW all vanadium flow battery energy storage power station project with an investment of 1.9 billion yuan, with a construction land area of about 120 acres, is expected to reach full production capacity within five years, achieving a total output value of 2.095 billion yuan and tax revenue of 52 million yuan. In addition to all vanadium flow batteries, China has also carried out demonstration applications of other types of flow batteries, but the project capacity is generally small and is still in the early stage of demonstration application.
2.2.3 Sodium ion batteries
Sodium ion batteries have the advantages of low theoretical cost, similar characteristics to lithium-ion batteries, and good safety, making them suitable for replacing high-cost lithium-ion batteries in application scenarios with strict cost requirements. The resources required for the positive and negative materials of sodium ion batteries are abundant in the earth's crust, evenly distributed, and more economically and environmentally friendly for mining. They are considered by the industry to be more economical battery technology than lithium-ion batteries. At present, sodium ion battery technology is mainly divided into three routes, namely layered transition metal sodium ion oxides, Prussian blue, and polyanionic sodium ion compounds. All three routes are laid out by industry leading enterprises and are in the stage of laboratory to large-scale industrialization transformation. At present, China is in a world leading position in the field of sodium ion batteries. Enterprises such as Zhongke Haina, Ningde Times, and Cube New Energy have all achieved initial mass production of sodium ion batteries and launched mature product lines.
In terms of performance parameters, the energy density of products developed by various sodium ion battery manufacturers has exceeded 140Wh/kg, and is still approaching the current level of lithium-ion batteries. In today's high price of lithium carbonate (currently priced at 500000 yuan/ton), the price of sodium carbonate remains at 2000 yuan/ton, and the cost of battery cells remains at 0.4~0.5 yuan/Wh. The industry estimates that the final cost of sodium ion batteries will be 20~40% lower than that of lithium-ion batteries. Sodium ion batteries have demonstrated high safety performance in laboratory environments and are compatible with lithium-ion battery processes, making it easier for existing manufacturers to transform.
The cost of positive materials dominates the cost of battery cells. Based on data from the first half of 2022, the estimated cost of copper iron manganese layered oxides is about 29000 yuan/ton, nickel iron manganese layered oxides are about 42000 yuan/ton, and Prussian white oxides are between 22000 and 26000 yuan/ton. Negative material hard carbon varies greatly depending on the supply chain resource prices of manufacturers, ranging from 100000 to 200000 yuan/ton. Currently, many manufacturers claim that there is significant room for a decrease in hard carbon costs. The cost of electrolyte is also an important component of battery cost. The electrolyte salt of sodium ion batteries is generally sodium hexafluorophosphate (NaPF6). Referring to the current cost of 3000 yuan/ton of sodium carbonate, the cost of electrolyte is expected to be less than 20000 yuan/ton. Sodium ion batteries can use aluminum foil as the collector for both positive and negative charges, and the current price is between 30000 to 40000 yuan/ton.
2.2.4 Gravity energy storage
The gravity energy storage of solid media is the main development direction for the commercialization of gravity energy storage in the near future. The new gravity energy storage technology of water media is still in the theoretical research stage, and there are currently no commercial products for new water media gravity energy storage besides traditional pumping and storage. The lifting blocks used by Energy Vault as a means of storing electricity have mastered relatively mature technology and have started to be applied in small-scale demonstration projects, but there has not yet been a large-scale application, and its technical maturity needs to be verified by demonstration projects. If there is a successful demonstration, block gravity energy storage has the advantages of high scalability and low electricity cost, and has a relatively broad application prospect in medium to long-term energy storage. Gravity energy storage in mines utilizes abandoned mines for energy storage, and the height difference in mines is usually greater than that of artificial structures. If abandoned mines hundreds of meters deep are deployed for gravity energy storage, their energy storage efficiency and energy storage density can surpass the method of deploying gravity energy storage using artificial height differences.
2.2.5 Hydrogen energy storage
Technical principles. Hydrogen energy storage belongs to chemical energy storage, which uses electrical energy to convert low-energy substances into high-energy substances for storage, thus achieving energy storage. At present, common chemical energy storage mainly includes hydrogen energy storage and energy storage by further synthesizing hydrogen into fuels (methane, methanol, etc.). These energy storage carriers themselves are fuels that can be directly utilized. Therefore, there is a clear difference between chemical energy storage and other aforementioned electric energy storage technologies (both input and output are electrical energy): if the terminal can directly utilize substances such as hydrogen and methane, such as hydrogen fuel cell vehicles, cogeneration, chemical production, etc. In the long run, these energy storage carriers can be converted into electrical energy for the power system when needed due to their stable properties. At present, in chemical energy storage technology, hydrogen energy storage is relatively mature, relying on electrolytic water hydrogen production equipment and hydrogen fuel cells (or hydrogen doped gas turbines) to achieve mutual conversion of electricity and hydrogen energy. When storing energy, excess electricity is used to electrolyze water to produce hydrogen and store it. When releasing energy, hydrogen fuel cells or hydrogen generators are used to generate electricity.
Hydrogen energy storage requires the conversion of electricity to hydrogen electricity, which involves four stages: "production, storage, transportation, and use", and the entire process is relatively complex. In the hydrogen production process, electric hydrogen production technology includes four types: alkaline water electrolysis (ALK), proton exchange membrane water electrolysis (PEM), anion exchange membrane water electrolysis (AEM), and solid oxide water electrolysis (SOEC). The first three types are room temperature (60-90 ℃) electrolytic cells, while SOEC is high-temperature (600-1000 ℃) electrolytic cells. Alkaline electrolyzers use alkaline electrolytes added to water to increase water conductivity and improve electrolysis efficiency. Its structure is simple, technology is mature, and price is cheap. It is currently the mainstream method of hydrogen production by electrolysis of water, but its disadvantage is low efficiency. The efficiency of the electrolysis cell is about 75%, and the system efficiency is 60-70%. At the same time, it is limited by the mechanical strength of the diaphragm, and the flexible power adjustment speed is limited. Proton exchange membrane technology uses proton exchange membranes to replace the original membrane and electrolyte. Due to the thin proton exchange membrane and fast proton migration speed, it can significantly reduce the volume and resistance of the electrolytic cell, resulting in an electrolytic cell efficiency of about 80%.
Due to the current high price of proton exchange membranes and their strong acidity when soaked in water, only acid resistant precious metals such as platinum can be used for electricity production. Therefore, the cost of hydrogen production through proton exchange membrane electrolysis is relatively expensive. The structure of an anion exchange membrane electrolyzer is similar to that of a proton exchange membrane electrolyzer, mainly consisting of an anion exchange membrane and two transition metal catalytic electrodes. It is generally used as an electrolyte in pure water or low concentration alkaline solution. Anion membrane exchange membrane is an important component of AEM electrolysis water system, and it is also a major difference between this technology and PEM technology. Its function is to transfer anionic OH - from negative to positive, while blocking the direct transfer of gas and electrons between electricity. Solid oxide electrolytic cell technology utilizes solid oxides as electrolytes to allow water vapor to pass through porous anions at high temperatures (600-1000 ℃). Hydrogen ions gain electrons and become hydrogen, while oxygen ions lose electrons on the cations through solid oxides and become oxygen. Due to the enhanced ion activity in high-temperature environments, its electrolysis efficiency is high, reaching up to 90%. This method is still in the experimental research stage.
In addition, green hydrogen can also be converted into ammonia or methanol for storage through the synthesis of ammonia or hydrogen to methanol process. When used, hydrogen can be produced through ammonia catalytic cracking and methanol catalytic cracking, or ammonia and methanol can be directly applied. The boiling point of liquid ammonia is -33.5 ℃, while the boiling point of methanol is -64.8 ℃. Therefore, the liquefaction and storage costs are much lower than those of hydrogen. On the other hand, the synthesis and cracking technologies of ammonia and methane are mature, and only partial optimization and adjustment are needed for renewable energy hydrogen production processes. More importantly, the carbon dioxide used in the synthesis of methanol can be obtained through carbon capture technology (CCUS), achieving "negative carbon emissions" in the production process, which has significant advantages in terms of carbon reduction.
Hydrogen power generation technology mainly includes two types: hydrogen generators and hydrogen fuel cells. Hydrogen generators mainly use hydrogen (or a mixture of hydrogen and natural gas) as fuel, utilizing the principles of internal combustion engines. Through the processes of suction, compression, combustion, and exhaust, they drive the generator to generate current output. Hydrogen fuel cell is a power generation device that utilizes the reverse reaction of electrolyzed water to directly convert the chemical energy of hydrogen into electrical energy through electrochemical reactions. In comparison, fuel cells have higher power generation efficiency, lower noise, no pollutant emissions, and are easy to achieve miniaturization, with a broader development prospect.
Hydrogen fuel cells are mainly divided into alkaline fuel cells, proton exchange membrane fuel cells, solid oxide fuel cells, and other types. Alkaline fuel cell (AFC) is a type of fuel cell system that has been developed and successfully applied. It usually uses potassium hydroxide as an electrolyte and is often used as a power source for special purposes such as space exploration and flight. Proton exchange membrane fuel cells are composed of proton exchange membranes, electrocatalysts, gas diffusion layers, double plates, and other components. They have the advantages of low operating temperature, fast start-up, and high power density. They are currently developing rapidly and widely used in the fields of hydrogen vehicles and hydrogen power generation. Solid oxide fuel cells belong to high-temperature fuel cells, which have an all solid-state battery structure. They have high overall efficiency, wide adaptability to fuel, and are suitable for cogeneration. Currently, the focus of research is on optimizing the battery structure and improving preparation technology.
Technical advantages and disadvantages. There is a clear difference between chemical energy storage and other aforementioned electric energy storage technologies: if the terminal can directly utilize substances such as hydrogen and methane, such as hydrogen fuel cell vehicles, cogeneration, chemical production, etc., these energy storage carriers do not need to be converted into electricity in the power system, which can improve overall energy efficiency. If hydrogen, ammonia, and methane must be converted back into electrical energy, due to the long process chain, their energy utilization efficiency is low, their fixed investment is high, and their economy is worse than other energy storage methods.
Chemical energy storage is more suitable for application scenarios with long-term and large capacity surplus on the power generation side, such as during the high water period of hydropower and the peak power generation of large-scale photovoltaic projects. Due to the ability to continuously convert electrical energy into substances such as hydrogen, ammonia, and methanol, chemical energy storage has significant advantages in terms of energy storage power and capacity, while matching transportation capacity. Hydrogen or other synthetic fuels are physical substances that are easier to store than direct electricity. For example, the unit mass calorific value of hydrogen can reach up to 1.4 × 108J/kg, high hydrogen storage energy density, capable of achieving large-scale energy storage. The drawbacks of chemical energy storage are low efficiency in electricity to electricity conversion, high cost of storage and transportation equipment, and the fact that fuels such as hydrogen and methane are flammable and explosive, posing certain safety hazards during storage. Chemical energy storage involves three stages: production, storage, and power generation. Taking hydrogen energy storage as an example, it mainly includes electric hydrogen production, hydrogen storage and transportation, and hydrogen power generation.
The cost of hydrogen storage and transportation is mainly influenced by factors such as storage method, transportation method, and transportation distance. The single cost of gaseous hydrogen storage (3-35MPa) is 2-3 yuan/kg, the single cost of liquid hydrogen storage is 20-25 yuan/kg, and the single cost of synthetic ammonia hydrogen storage is 6-8 yuan/kg. The cost of transporting high-pressure gaseous hydrogen by road is 80-100 yuan/km, while the cost of transporting high-pressure gaseous hydrogen by road is 10-15 yuan/km. The cost of shipping liquid hydrogen by sea is about 0.5 yuan/km. The cost of transporting hydrogen for a hydrogen pipeline with an inner diameter of 500mm and a design pressure of 4MPa is approximately 0.5-1 yuan/km per ton. The power generation unit, taking proton exchange membrane fuel cells as an example, has a stack cost of 2000-4000 yuan/KW, which accounts for approximately 60% of the total system cost. The expensive prices of precious metal catalysts and perfluorosulfonic acid membranes are the main reasons for driving up the cost of fuel cells. Reducing the amount of platinum in the catalyst, developing non precious metal catalysts, and low-cost non fluorinated proton exchange membranes are the key to reducing costs.
2.2.6. Other advanced energy storage technologies
Solid state lithium-ion batteries. Technical principles. Solid state battery is a lithium-ion battery technology that uses solid materials to form electricity and electrolytes. Its working principle is the same as traditional (liquid) lithium-ion batteries, both of which belong to the category of "rocking chair batteries". Through reversible redox reactions, lithium ions repeatedly travel between positive and negative charges, achieving the storage or release of electrical energy. The positive electrode of solid-state batteries can be composed of carbon, titanate, metal lithium and its alloys, while the negative electrode can be composed of metal oxides, sulfides, vanadium oxides, etc. Currently, sodium sulfur batteries (metal sodium is negative electrode, sulfur is positive electrode) β- The technical route of using aluminum oxide tubes as solid electrolytes is representative.
Technical characteristics. Good safety performance is a major advantage of solid-state batteries compared to traditional (liquid electrolyte) lithium batteries. Its solid-state electrolyte is non flowable, has good thermal stability, strong resistance to damage, and will not produce leakage or flammable and explosive gases under damage conditions, greatly improving the safety issues faced by lithium batteries. The high theoretical energy density is also an important reason for the industry's attention to solid-state batteries. In theory, solid-state electrolytes have a higher material density compared to liquids, which means a higher energy density. Currently, laboratory data for solid-state batteries has exceeded 400 Wh/kg, significantly better than the average level of lithium batteries. In addition, with its excellent physical and chemical stability as an electrolyte, solid-state batteries under laboratory conditions also exhibit good low-temperature performance and long cycle life. At present, due to issues in production technology, PACK process, and conductivity of electrical material contact surfaces, the energy density of solid-state batteries that meet mass production standards is not yet as high as mature lithium-ion batteries. Due to immature industrial chains and complex processes, the current cost of solid-state batteries far exceeds that of liquid lithium-ion batteries.
2.3. Comprehensive evaluation of the economic benefits of new energy storage technologies
We can compare various energy storage technologies from multiple technical and economic indicators, evaluate their applicability in different application scenarios, and serve as important reference data for predicting their future development direction. The technical and economic parameters for evaluating energy storage systems mainly include: design power/energy, initial investment cost, full life cycle operation and maintenance cost, number of cycles, and cycle efficiency
