Energy storage technology is a related technology that uses a medium or device to store electrical energy in the same form or convert it into another energy form, and release the electrical energy when needed. Energy storage technology is classified according to storage media and can be divided into physical energy storage, electrochemical energy storage, electrical energy storage, etc.
1. Application of physical energy storage
The application forms of physical energy storage mainly include pumped hydro energy storage, compressed air energy storage and flywheel energy storage.
The basic principle of pumped water storage is to use the gravitational potential energy of water. When energy needs to be stored, water is pumped from the downstream reservoir to the upstream reservoir through a turbine. At this time, the system consumes electrical energy and converts it into the gravitational potential energy of water. When energy needs to be released, water in the upstream reservoir drives a generator that converts gravitational potential energy into electrical energy.
Pumped water energy storage is currently the largest form of energy storage in terms of total installed capacity. It has a high technical level, high efficiency, and fast response speed, but the construction cost and cycle are long, highly dependent on geographical conditions, and requires long-distance power transmission.
Compressed air energy storage is a new type of energy storage technology. The principle is to compress air and store it in an air storage chamber when electricity consumption is low, convert electrical energy into internal energy and store it, and release high-pressure air during peak electricity consumption to drive power generation. Mechanical power generation can solve the problem of difficulty in connecting photovoltaic and wind power to the grid.
Compressed air energy storage has a lifespan of up to 40 years, low cost, and good economics, but it is closely related to geographical conditions and its suitable locations are very limited.
Flywheel energy storage technology is an energy storage technology that uses a reciprocal bidirectional motor to realize the mutual conversion between electrical energy and the mechanical energy of a high-speed rotating flywheel.
Flywheel energy storage has high reliability, good stability, and a response rate of milliseconds, but it has low energy density and a certain degree of self-discharge.
2. Electrochemical energy storage
Electrochemical energy storage is a device that uses chemical reactions to directly convert electrical energy, mainly including lead-acid batteries, lithium-ion batteries, sodium-sulfur batteries, vanadium flow batteries, zinc-air batteries, nickel-hydrogen batteries, etc.
Lead-acid batteries are one of the most widely used batteries in the world. The anode and cathode in a lead-acid battery are immersed in the electrolyte, and a potential of 2V is generated between the two levels. This is the principle of lead-acid batteries.
Lead-acid batteries have mature technology and low prices, but have low energy density and short lifespan.
A lithium-ion battery is actually a lithium-ion concentration difference battery. The positive and negative electrodes are composed of two different lithium-ion intercalation compounds. When charging, lithium ions are deintercalated from the positive electrode and embedded in the negative electrode through the electrolyte. At this time, the negative electrode is in a lithium-rich state and the positive electrode is in a lithium-poor state; during discharge, the opposite is true.
Lithium-ion efficiency can reach more than 93%, cycle life can reach more than 6,000 times, and energy density is high, but the cost and price are also high, and thermal runaway is prone to occur under extreme conditions such as high temperature, short circuit, and overcharge.
Lithium-ion battery technology is still under development, and current research is focused on further improving service life and safety, reducing costs, and developing new positive and negative electrode materials.
The anode of a sodium-sulfur battery is composed of liquid sulfur, and the cathode is composed of liquid sodium. The operating temperature of the battery needs to be maintained above 300°C to keep the electrodes in a molten state.
However, sodium-sulfur batteries have low safety and limited application scenarios. Japan's NGK Company is the only manufacturer in the world that can manufacture high-performance sodium-sulfur batteries.
3. Electrical energy storage
The application forms of electrical energy storage mainly include supercapacitor energy storage and superconducting energy storage.
Supercapacitor is also called electric double layer capacitor. It consists of four parts: current collector, electrolyte, polarizing electrode and separator. It uses ions of opposite polarity in the electrode and electrolyte to attract each other to form an electric double layer capacitor to store energy.
Supercapacitors operate in a wide temperature range and are environmentally friendly, but have low energy density, high investment costs, and a certain self-discharge rate.
The superconducting energy storage system consists of a superconducting coil placed in a cryogenic container, a power conditioning system and a cryogenic refrigeration system. Energy is stored in a magnetic field in the form of a circulating DC current in a superconducting coil.
Superconducting energy storage systems directly store electrical energy in a magnetic field with high power density, but superconducting materials are expensive and are mostly in the experimental stage.
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