Energy Storage Knowledge | What are the different types of energy storage technologies?

With the increasing proportion of renewable energy sources such as wind and solar power, electricity supply is no longer as stable and controllable as traditional thermal power. During peak solar power generation in the daytime, supply may exceed demand, while at night, when wind power drops sharply, supply may be insufficient.

Energy storage acts as an "energy manager" in this context. These storage systems are like a group of "energy power banks" with different functions: some excel at storing electricity, some specialize in thermal storage, some can withstand long periods of "standby," and some can unleash energy bursts instantly.

Currently, global energy storage technology has formed a diversified development pattern, mainly including physical energy storage, electrochemical energy storage, electromagnetic energy storage, thermal energy storage, hydrogen energy storage, and emerging technologies, each playing a role in different scenarios with its unique advantages.

Physical Energy Storage: The "Veteran" Relying on "Spatial Transformation" to Store Energy

Physical energy storage was the earliest energy storage method to be applied on a large scale. Its core is to achieve energy storage system through mechanical movement or changes in location.

Among them, pumped hydro storage is considered the "elder brother," accounting for over 90% of global installed capacity. Its principle is simple: during off-peak electricity demand, excess electricity is used to pump water from a lower reservoir to a higher-lying upper reservoir, essentially converting electrical energy into the gravitational potential energy of the water; during peak demand, the water is released to drive turbines to generate electricity, converting the potential energy back into electrical energy.

This technology is currently the most economical large-scale energy storage solution, but its drawbacks include dependence on geographical conditions (requiring terrain with elevation differences) and a relatively long construction period (typically 5-10 years).

Another type of physical energy storage is compressed air energy storage. Air is compressed using an electric motor and stored in underground caverns or large tanks. During peak demand, the compressed air is released to drive turbines to generate electricity.

Early technologies had lower efficiency because they did not recover the heat generated during compression, but the recently developed "Advanced Adiabatic Compressed Air Energy Storage" (A-CAES) recovers the heat of compression, increasing efficiency to over 70%.

In addition, flywheel energy storage takes a "lightweight" approach, converting electrical energy into the kinetic energy of a high-speed rotating flywheel. Its response speed is as fast as milliseconds, and its cycle life can reach millions of cycles. It is commonly used in scenarios with high instantaneous power requirements, such as uninterruptible power supplies (UPS) in data centers and regenerative braking in rail transit.

Electrochemical Energy Storage: A Portable and Efficient Rising Star

Electrochemical energy storage converts electrical energy into chemical energy through chemical reactions. In recent years, due to cost reductions and technological breakthroughs, it has become the fastest-growing field.

Lithium-ion batteries are currently the absolute mainstay, accounting for more than 90% of new energy storage installations. Depending on the cathode material, they are further divided into lithium iron phosphate (LFP) batteries and ternary lithium batteries (NCM). The former has high safety and low cost, mainly targeting the energy storage and commercial vehicle markets; the latter has higher energy density and is mostly used in high-end electric vehicles. However, lithium batteries still face challenges such as resource constraints (lithium, cobalt, etc.) and safety risks (such as thermal runaway).

Flow batteries, on the other hand, are a "potential stock" for long-term energy storage. It achieves a decoupled design between "capacity" and "power" by storing the electrolyte in an external tank—adding tanks increases energy storage time, making it particularly suitable for scenarios requiring continuous power supply for several hours.

Vanadium redox flow batteries (VRFBs) boast a lifespan of over 25 years, more than 10,000 cycles, and reusable electrolyte. The Three Gorges Energy Jimsar 200MW/1GWh VRFB energy storage power station has become the world's largest VRFB energy storage power station, driving the commercialization of long-duration energy storage.

Furthermore, sodium-ion batteries are emerging due to their abundant sodium resources (420 times that of lithium) and low cost. Companies like CATL and EVE Energy have chosen to enter this market, and they are expected to replace some lithium batteries in low-speed electric vehicles and home backup power supplies in the future.

Electromagnetic Energy Storage: The "Flash" with Millisecond-Level Response

Electromagnetic energy storage utilizes electric or magnetic fields to store energy. Its characteristics include extremely fast charging and discharging speeds (millisecond-level) and ultra-high power density, but relatively low energy density.

Supercapacitors store energy through the double electric layer at the electrode-electrolyte interface, boasting near-infinite cycle life. They are commonly used for high-speed rail braking energy recovery and instantaneous voltage support in smart grids. Superconducting magnetic energy storage (SMES), on the other hand, stores magnetic field energy using superconducting coils, achieving efficiencies exceeding 95%. However, it requires operation in extremely low temperatures down to -269 degrees Celsius, resulting in higher costs. Currently, it is primarily used in laboratory research and high-precision industrial equipment.

Thermal Energy Storage: The Invisible "Energy Bank"

Thermal energy storage stores thermal energy through temperature changes or phase transitions in a medium, often combined with solar thermal power generation and industrial waste heat utilization.

Sensible heat storage is the most common, absorbing heat through media such as water, molten salt, and rock, storing it after the temperature rises, and releasing energy when the temperature drops during heat release. Latent heat storage utilizes phase change materials (such as paraffin and molten salt) to absorb or release large amounts of heat during solid-liquid phase transitions, maintaining a relatively constant temperature. It can be used for regulating room temperature in building walls and dissipating heat from electronic devices. Thermochemical storage stores heat through reversible chemical reactions (such as the reaction of calcium oxide with water), with a theoretical efficiency exceeding 80%. However, it is still in the laboratory research and pilot-scale stages and has not yet achieved large-scale commercial application.

Hydrogen Storage: The "Ultimate Solution" for Cross-Seasonal Energy Storage?

Hydrogen storage is considered the "ultimate weapon" to solve the seasonal fluctuations of renewable energy. Its approach involves using surplus electricity during off-peak hours to electrolyze water to produce "green hydrogen," which is stored in high-pressure tanks or underground salt caverns. When needed, it can be used to generate electricity through fuel cells or directly in industrial and transportation sectors.

The biggest advantages of hydrogen storage are zero carbon emissions, long-term storage (months or even years), and the ability to couple multiple energy networks such as electricity, heat, and fuel.

However, current technological bottlenecks are evident: hydrogen production efficiency from water electrolysis is approximately 70%, fuel cell power generation efficiency is around 50%, and the overall efficiency is only 30%-40%; liquid hydrogen storage conditions and transportation costs are also high.

Emerging Technologies: Gravity, Air, and More Possibilities

Besides the aforementioned mature technologies, emerging directions such as gravity energy storage and liquid air energy storage are rapidly gaining traction.

Gravity energy storage uses an electric motor to lift heavy objects (such as concrete blocks or gravel) to a high position, releasing the weight to drive a generator when electricity is needed; liquid air energy storage cools air to approximately -196 degrees Celsius and liquefies it, driving a turbine to generate electricity when it expands. The Qinghai Province 60,000 kW/600,000 kWh liquid air energy storage demonstration project, located in Golmud City, Haixi Prefecture, Qinghai Province, is currently in its final commissioning phase, serving as the world's largest liquid air energy storage demonstration project.

The Future: Multi-Technology Collaboration to Build an Energy Internet

Different energy storage technologies have their own advantages and disadvantages, and in the future, a "division of labor and cooperation" pattern may emerge: pumped hydro storage and lithium batteries are suitable for grid peak shaving (4-8 hours); flow batteries, compressed air, and hydrogen storage focus on long-term energy storage (>8 hours); supercapacitors and flywheels are responsible for instantaneous power support; and thermal energy storage is deeply coupled with renewable energy generation.

According to the International Renewable Energy Agency, global energy storage capacity will reach 230 gigawatts by 2030, with long-term energy storage showing the fastest growth.

With technological iteration and cost reduction, future energy storage networks may collaborate efficiently like a neural network, ultimately realizing the zero-carbon vision of integrated "generation, grid, load, and storage."