1. Overview
Energy storage technology can be broadly categorized into physical storage and chemical storage. Physical storage includes technologies such as pumped hydro storage, compressed air, flywheel storage, gravity storage, and phase-change storage. Chemical storage includes lithium-ion batteries, flow batteries, sodium-ion batteries, and hydrogen (ammonia) storage technologies.
New energy storage refers to storage technologies that primarily output electrical power, excluding pumped hydro storage. Compared to pumped hydro storage, new energy storage technologies offer flexible siting, short construction periods, rapid response, and diverse functional characteristics.
New energy storage technologies are widely applied in various sectors of the power system, profoundly changing the operational characteristics of traditional power systems. They have become indispensable facilities for the safe, stable, and economic operation of power systems.
2. Mechanical Energy Storage
Mechanical energy storage mainly includes compressed air energy storage and flywheel energy storage.
Compressed Air Energy Storage (CAES): CAES uses surplus electricity during low-demand periods to compress air, which is stored and later released during peak demand periods to generate power by driving a gas turbine. CAES is suitable for large-scale applications such as wind farms due to its peak-shaving capabilities but requires specific geographical conditions.
Flywheel Energy Storage: This method uses electrical energy to accelerate a rotor placed in a vacuum, converting electrical energy into kinetic energy for storage. Flywheel energy storage is characterized by short discharge durations and smaller capacities, making it ideal for applications like uninterruptible power supplies (UPS) and frequency regulation. However, its energy density is relatively low, sustaining power for only a few seconds to minutes.
3. Electrochemical Energy Storage
Electrochemical energy storage is a prominent field that includes various types of batteries:
Lithium-Ion Batteries: The most mature and widely used electrochemical storage technology, currently in large-scale production and with the fastest growth and highest market share.
Lead-Acid Batteries: These batteries have electrodes made primarily of lead and its oxides with a sulfuric acid electrolyte. They are a mature technology with stable performance but suffer from long charging times, high pollution, and short lifespans.
Flow Batteries: Still in the demonstration application stage, flow batteries can be categorized based on their electrolyte systems into vanadium redox flow batteries, zinc-iron flow batteries, zinc-bromine flow batteries, and iron-chromium flow batteries. Vanadium redox flow batteries are the most commercialized, while the others are still accelerating towards industrialization.
Sodium-Ion Batteries: These batteries use the intercalation and deintercalation of sodium ions between the anode and cathode for charging and discharging. Sodium-ion technology is still experimental, undergoing further research and testing.
4. Electromagnetic Energy Storage
Electromagnetic energy storage includes superconducting magnetic energy storage (SMES) and supercapacitor energy storage, suitable for applications requiring rapid discharge and high power.
Superconducting Magnetic Energy Storage (SMES): Stores electrical energy in a magnetic field with rapid charge/discharge capabilities and high power density. Despite the availability of commercial low-temperature and high-temperature SMES products, their application in power grids remains limited due to the high cost and complex maintenance of superconducting materials, keeping them in the experimental phase.
Supercapacitors: Store electrical energy using electrostatic principles, with low voltage withstand of the dielectric material. Therefore, supercapacitors have limited energy storage capacity, low energy density, and high investment costs.
5. Chemical Energy Storage
Chemical energy storage mainly refers to hydrogen storage technologies. These convert intermittent or surplus electricity into hydrogen via electrolysis for storage, which can be converted back into electrical power using fuel cells or other generation devices when needed.
According to the "Development Path Research of Hydrogen Energy Storage Peak Shaving Stations" by Polaris, the current power generation efficiency of hydrogen fuel cell systems is about 45%. Considering the energy loss during water electrolysis, the overall system efficiency of hydrogen storage power generation is approximately 35%. Improving energy conversion efficiency is a critical challenge, and large-scale industrial development of hydrogen energy storage requires considerable time.
