The development of energy storage technology is crucial for ensuring the large-scale development of clean energy and the safe and economical operation of the power grid. Energy storage technology adds an energy storage component to the power system, making the "rigid" power system with real-time power balance more "flexible," particularly in mitigating the volatility caused by large-scale clean energy generation connecting to the grid, and improving the safety, economy, and flexibility of grid operation. Energy storage technology is generally divided into thermal energy storage and electrical energy storage, with electrical energy storage being the primary application in the future global energy internet.
Electric energy storage technologies are mainly divided into three categories: physical energy storage, electrochemical energy storage, and electromagnetic energy storage.
Physical energy storage
Pumped storage is currently the most mature energy storage technology, with relatively low costs, and has already achieved large-scale application. The total installed capacity of pumped storage units worldwide currently exceeds 100 million kilowatts, with Japan, the United States, and China ranking among the top three. Global hydropower resources are abundant, and by making reasonable use of terrain, large-capacity pumped storage units can be constructed to better ensure the security of the power grid.
Compressed air energy storage utilizes surplus electricity generated during off-peak hours to power an air compressor, forcing air into a large-capacity storage chamber. This converts electrical energy into storable compressed air potential energy. When the system's power generation capacity is insufficient, the compressed air is mixed with oil or natural gas and burned to drive a gas turbine, generating electricity to meet peak-shaving needs. Compressed air energy storage offers advantages such as large capacity, long service life, and good economic efficiency. However, it consumes fossil fuels during power generation, resulting in pollution and carbon emissions.
Electrochemical energy storage
Electrochemical energy storage is currently the most cutting-edge energy storage technology. In recent years, electrochemical energy storage technologies such as sodium-sulfur batteries, flow batteries, and lithium-ion batteries have developed rapidly, with huge development potential and broad application prospects, and are expected to be among the first to enter the commercialization stage. Future breakthroughs are needed in battery materials, manufacturing processes, system integration, and operation and maintenance to reduce manufacturing and operating costs.
Lead-acid batteries have a history of over 140 years. They are technologically mature, inexpensive, and highly safe, making them the most mature battery energy storage technology. Currently, they account for more than half of the battery market share and are mainly used in electric bicycles. However, lead-acid batteries have low energy density, are heavy, and contain toxic materials, making them unsuitable for grid energy storage.
Sodium-sulfur batteries have high energy density, are easy to manufacture, transport and install in a modular manner, and are suitable for emergency power supply for special loads.
Flow batteries have large capacity, recyclable electrolyte, long cycle life, and can be designed with separate capacity and power.
Lithium-ion batteries are batteries that use lithium-ion compounds as the positive electrode and carbon materials as the negative electrode. Lithium-ion batteries have excellent cycle performance, long lifespan, and do not contain toxic or harmful substances, earning them the title of "green batteries." Currently, lithium-ion batteries are widely used in mobile phones, laptops, electric vehicles, and other fields. However, the cost per charge-discharge cycle exceeds 1 yuan per kilowatt-hour, making their application in power systems and large-scale energy storage still uneconomical.
Metal-air batteries are a new type of fuel cell that uses metal fuel instead of hydrogen energy in traditional fuel cells. They offer numerous advantages, including being non-toxic, pollution-free, having stable discharge voltage, high energy density, low internal resistance, long lifespan, relatively low price, and requiring less sophisticated manufacturing processes. The raw materials for metal-air batteries are inexpensive, abundant, and recyclable, making them a promising next-generation green energy storage battery.
Electromagnetic energy storage
Supercapacitors are electrochemical devices that store energy through polarized electrolytes, developed in the 1970s and 80s. The energy storage process does not involve chemical reactions, and because it is reversible, supercapacitors can be charged and discharged hundreds of thousands of times. Supercapacitors have high power density, short charge/discharge times, long cycle life, and a wide operating temperature range, but their energy storage capacity is low, making them unsuitable for large-scale grid energy storage.
Superconducting electromagnetic energy storage is an energy storage device that utilizes the zero resistance of superconductors. It has advantages such as high instantaneous power, light weight, small size, zero loss, and fast response, and can be used to improve the stability of power systems and enhance power quality. However, superconducting electromagnetic energy storage has low energy density and limited capacity, and its future prospects are still unclear due to limitations in superconducting material technology.
Development direction and prospects
Large-scale energy storage can be used for peak shaving and valley filling in the global energy internet. Large-scale, long-term energy storage facilities such as pumped hydro storage and compressed air storage can be used for peak shaving in large power grids. Flow batteries, with their large energy storage capacity, high cycle life, and long lifespan, can supplement grid peak shaving energy storage devices. Hydrogen energy storage can be used to store surplus wind and solar energy, providing power for fuel cell vehicles.
Large-scale power storage can be used to mitigate the volatility of large-scale clean energy sources. Power storage devices such as supercapacitors, superconducting electromagnetic energy storage, flywheel energy storage, and sodium-sulfur batteries are mainly used in conjunction with large-scale renewable energy sources. They can quickly respond to the output of wind and solar power, mitigate the fluctuations of renewable energy, and ensure the real-time safe operation of the power grid.
Small-scale energy storage batteries can be used in electric vehicles. While energy storage devices such as lithium batteries, new lead-acid batteries, and metal-air batteries have high energy and power densities, their poor battery uniformity makes it difficult to form large-capacity battery packs, rendering them unsuitable for large power plants; they are primarily used in electric vehicles. With extended battery lifespan and reduced costs, energy storage batteries can meet the needs of large-scale electric vehicle development. In the future, electric vehicle energy storage batteries will be connected to the global energy internet, assisting in grid peak shaving by rationally scheduling charging times, achieving off-peak charging and peak-hour discharging.
Advances in energy storage technology hinge on breakthroughs in materials technology. With continuous innovation and development of new energy storage materials, significant breakthroughs are expected in extending the lifespan of energy storage components, increasing energy density, shortening charging time, and reducing costs.
