Energy storage technology, as the name suggests, refers to the process of storing the energy. It can be likened to a large-scale energy buffer, utilizing various storage methods. It captures excess energy during periods of overproduction and releases it during shortages, ensuring a stable supply. Whether mitigating renewable energy’s intermittency or enabling efficient utilization, storage plays a pivotal role.
From the generation perspective, solar photovoltaic panels produce abundant electricity during daylight but cease at night. Similarly, wind power fluctuates with wind availability—high output during strong winds and minimal during calm periods. This intermittency poses challenges to stable supply.
On the demand side, daytime peaks occur when offices and factories operate, while usage declines at night. This temporal mismatch between supply and demand leads to wasted excess energy without storage. Energy storage acts as a stabilizing intermediary: storing surplus during overproduction and releasing it during shortages to balance supply, enhance efficiency, and reduce waste.
When the grid fails or emergencies occur, energy storage systems can respond quickly, powering important equipment and users with emergency electricity to maintain stable operation.
Economically speaking, energy storage also makes good economic sense. Stocking up on power when it's cheap and using it when prices are high helps users cut energy costs. For large enterprises, using storage systems wisely can further lower production costs and improve their bottom line.
Energy storage technologies vary by conversion method: physical, chemical, and electromagnetic.
Utilizes mechanical methods such as pumped-hydro, compressed air, or flywheels.
1. Pumped Hydro Storage: Pumped hydro storage is currently the most widely used physical energy storage technology. It works by pumping water from a lower reservoir to an upper reservoir during periods of low electricity demand, converting electrical energy into potential energy for storage. During peak demand periods, the water from the upper reservoir is released back to the lower reservoir, powering hydroelectric generators to convert the potential energy back into electricity. The advantages of pumped hydro storage include mature technology, large capacity, long lifespan, and overall efficiency of 70%-85%. The downside is the high requirement for geographical conditions, as suitable terrain is needed to construct the upper and lower reservoirs.
Compressed air energy storage uses electricity during periods of low grid demand to compress air, which is then stored in underground salt caverns or other storage facilities. During peak demand periods, the compressed air is released to power turbines and generate electricity. This method works well for large-scale applications and can integrate with renewable energy sources like wind power, as wind's mechanical energy can directly drive the compressor rotation, eliminating intermediate electrical conversion and improving efficiency. However, it also requires specific geographical conditions, particularly large caverns for storing the compressed air.
Flywheel energy storage uses an electric motor to rapidly spin a flywheel, converting electrical energy into kinetic energy for storage. When needed, the flywheel drives a generator to produce electricity. Its advantages include long lifespan, high efficiency, and rapid response time, responding in milliseconds. However, its energy density is low, providing power for only seconds to minutes, and it experiences some energy loss due to bearing wear and air resistance.
Lithium-ion batteries should be familiar to everyone, as they are used in smartphones and laptops. They offer high energy density, long service life, and a wide operating temperature range, and they dominate the electrochemical energy storage market. However, they also have drawbacks, such as high costs and safety concerns.
Lead-acid batteries are a traditional type of battery, with electrodes mainly made of lead and its oxides and an electrolyte consisting of sulfuric acid solution. Their materials are widely available, they are low-cost, and commonly used as backup power in electrical systems. However, they have lower cycle life, a shorter lifespan, and can cause environmental pollution if not properly handled during production or recycling.
Sodium-sulfur batteries use metallic sodium as the anode, sulfur as the cathode, and a ceramic tube as the electrolyte separator. They offer advantages such as small size, high capacity, long lifespan, and high efficiency. They are widely used in power storage applications like peak shaving, emergency power, and wind energy storage. However, they require high operating temperatures, typically between 300–350°C.
Flow batteries, often referred to as redox flow batteries, are called all-vanadium flow batteries (or vanadium batteries) when both electrodes use vanadium salt solutions. Their advantages include such features as flexible design, fast charge-discharge response, excellent performance, long lifespan, easily recyclable electrolyte solutions, greater flexibility in installation locations, safety, environmental friendliness, high energy efficiency, and fast startup time. However, they have relatively low energy density and larger space requirements.
Electromagnetic energy storage mainly includes superconducting energy storage and supercapacitor energy storage.
Superconducting magnetic energy storage (SMES) is a method of directly storing electrical energy without conversion. It works by directing electric current into an inductive coil made of superconducting materials, where the current can theoretically circulate indefinitely without loss until needed. This storage method achieves high energy conversion efficiency (up to 95%) and fast response times, activating within milliseconds. However, the high cost of superconducting materials and the expense of maintaining ultra-low temperatures currently limit its large-scale application.
Supercapacitor energy storage is a novel energy storage device that combines features of traditional capacitors and rechargeable batteries. Its structure resembles that of a battery, consisting of four main components: dual electrodes, an electrolyte, current collectors, and a separator. Supercapacitors offer advantages such as high power density, long cycle life, excellent low-temperature performance, safety, reliability, and environmental friendliness. However, due to low dielectric breakdown voltage and leakage current, their energy storage capacity and retention time remain limited.
