The storage duration and method of storing electrical energy in an energy storage system are closely related to the type of technology used and its design purpose. Common energy storage technologies in the market include battery energy storage, pumped storage, compressed air energy storage, flywheel energy storage, and supercapacitor energy storage. Different energy storage purposes determine the required energy storage duration. For example, energy storage systems used to smooth grid fluctuations typically require only a few minutes to a few hours of capacity, while peak shaving and valley filling applications may require longer storage capacity. Next, I will provide a detailed overview of these aspects:
1、 Methods and duration of storing electrical energy
1. Battery energy storage: Battery energy storage converts electrical energy into chemical energy through chemical reactions for storage, and then converts the chemical energy back into electrical energy when discharged. It is currently the most widely used energy storage technology. The storage duration is affected by the type, capacity, and discharge rate of the battery. Lithium iron phosphate batteries are highly favored for their high energy density and long cycle life, and are suitable for energy storage in short to medium time ranges, typically ranging from a few hours to several days.
2. Pumped storage: When electricity demand is low, pumped storage pumps water from low water level reservoirs to high water level reservoirs for storage. When demand increases, it generates electricity by releasing water, forming a good energy regulation mechanism. This technology can store a large amount of energy and is commonly used as a long-term regulation tool in power systems. The storage time can extend from a few hours to several days or even longer, making it very suitable for scenarios that require long-term energy storage, such as balancing between peak and off peak electricity demand.
3. Compressed air energy storage and flywheel energy storage: Compressed air energy storage uses electricity to compress and store air in underground caves or storage tanks when electricity demand is low, and releases compressed air to drive turbines to generate electricity when electricity demand increases. Flywheel energy storage is achieved by driving a flywheel to rotate at high speed through an electric motor, utilizing the inertia of the rotating body to store energy. When needed, the flywheel can be used to drive a generator to generate electricity. The storage time of these two technologies is generally short, suitable for quickly responding to changes in grid demand, and the storage time is usually a few minutes to several hours.
4. Supercapacitors for energy storage: Supercapacitors store energy by utilizing high specific surface area electrodes and the double layer principle to store charges, making it easy to achieve rapid charging and discharging of electrical energy. Its fast charging and discharging capability and short-term high-power output are the characteristics, and the storage time is generally short, usually from a few minutes to several hours.

2、Due to the differences in operational complexity and specific technical details among different types of energy storage systems, the operational steps of energy storage systems can be roughly summarized as follows:

1. When renewable energy generates excess electricity, it charges the energy storage equipment and inputs the excess electricity into the energy storage system.
2. Convert excess electrical energy into other forms (such as chemical energy, potential energy, kinetic energy, etc.) and store them in energy storage devices.
3. Real time monitoring of the energy storage system status to ensure safe and efficient operation.
4. Release stored energy from energy storage devices to the grid or for other purposes based on grid demand or specific application scenarios.
3、 The role and importance of energy storage systems mainly include:
1. By storing and releasing electrical energy, it helps the power grid manage the balance of electricity supply and demand more efficiently, especially in power grids with a high proportion of renewable energy.
2. In the event of a power failure or outage in the power grid, providing backup power sources enhances the grid's ability to accept renewable energy sources such as wind and solar energy, and improves the reliability and flexibility of the power system.
3. Storing energy during low electricity demand and releasing it during peak hours helps reduce reliance on traditional peak power plants.
4. Promoting the application of distributed energy (such as solar photovoltaics), enabling users to store and use their own electricity, is conducive to the widespread application of clean energy and promotes the transformation of energy structure.
5. By optimizing electricity production and consumption patterns, reducing energy costs, improving energy efficiency, and reducing dependence on traditional fossil fuels.