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Electric energy storage is a technology for balancing supply and demand in the power grid. The form of electric energy storage is usually not directly storing "electrical energy", but first converting electrical energy into kinetic energy, (water) potential energy, chemical energy and other forms of storage, and then converting it back into electrical energy when needed.

Electric energy storage itself is not an emerging technology, but from an industrial perspective, it has just emerged and is in its early stages. The traditional "rigid" power system's instantaneous dynamic balance of energy sources and loads is becoming increasingly difficult to sustain. In the future, the power system must have sufficient "flexibility" to adapt to the new normal of high proportion renewable energy. In this transformation process, energy storage has become one of the key supporting technologies for future high proportion renewable energy power systems due to its ability to separate the production and consumption of electricity from time and space.

1、Popular explanation

Electric energy storage technology, a technology for storing electrical energy. In the power system, the production and use of electricity are carried out simultaneously, and the quantity is balanced. But the electricity consumption is always fluctuating, and the possibility of power generation equipment failure also needs to be considered. Therefore, the capacity of the power generation equipment put into operation in the system is often higher than the electricity consumption, so excess electricity can be stored for adjustment and use when the backup electricity increases. Energy storage methods include pumped storage, battery storage, superconductive storage, mechanical flywheel storage, compressed air storage, etc. Pumped storage is the most common among them.

The stored energy can be used as emergency energy, as well as to store energy during low grid loads and output energy during high grid loads for peak shaving and valley filling, reducing grid fluctuations.

Energy storage is an essential component of future power systems and is indispensable. Energy storage can achieve time shift application of energy, smooth out intermittency of wind and light, and generate electricity immediately. By shaving and filling in valleys, revenue can be achieved. Real time coupling between power supply and demand can be changed to cross time coupling, enriching the means of power balance, achieving high-density and controllable application of low-density and fluctuating energy, achieving the effect of conventional power sources, and becoming a highly competitive energy source.

2、Technical Introduction

Electric energy storage refers to the process of storing energy through a medium or device and releasing it when needed.

3. Small energy storage and large energy storage

Small energy storage: Energy storage at the end of the power consumption process, with a small volume, high safety requirements, and low cost-effectiveness, focuses on miniaturization and safety development, and is popular in areas such as mobile phone batteries, electric vehicle batteries, and emergency power supplies.

Large energy storage: Energy storage oriented towards the supply side, with a large volume and high cost performance requirements, with a focus on developing towards cost-effectiveness.

4. Energy storage methods

4.1 Battery Energy Storage

Lead acid batteries are generally used in high-power applications, mainly for storing surplus energy in emergency power sources, electric vehicles, and power plants. Low power applications can also use rechargeable dry batteries, such as nickel hydrogen batteries, lithium-ion batteries, etc.

All vanadium flow battery is a large-scale energy storage battery that converts chemical energy to electrical energy through changes in the valence state of vanadium ions, thereby storing and releasing the forces generated by wind or solar energy. It is commonly referred to as the "power bank" in the industry. The vanadium battery industry used for power plant peak shaving and wind energy storage in developed countries such as the United States and Japan is developing rapidly, and the technology is basically mature. Compared to lithium batteries, the biggest advantage of all vanadium flow batteries is that they do not burn or explode.

4.2 Capacitor energy storage

Capacitors are also energy storage components, and their stored electrical energy is proportional to the square of their own capacitance and terminal voltage: E=C * U * U/2. Capacitive energy storage is easy to maintain and does not require superconductors. Another important aspect of capacitive energy storage is its ability to provide instantaneous high power, making it very suitable for applications such as lasers and flash lights.

Supercapacitors, also known as electrochemical capacitors, are a new type of energy storage device that lies between traditional capacitors and rechargeable batteries. Their structure is similar to that of batteries, mainly including dual electrodes, electrolytes, current collectors, and isolators. They have advantages such as high power density, long cycle life, good low-temperature performance, safety, reliability, and environmental friendliness. However, due to the low dielectric withstand voltage, there is leakage current, which limits the energy storage and holding time. At present, supercapacitors are mainly based on double-layer capacitors with porous carbon electrodes/electrolyte interfaces, or quasi capacitors generated by metal oxides or conductive polymers to achieve energy storage.

5. Application scenarios

5.1 Power supply side

Smooth output: Absorbing fluctuations in renewable energy generation or smoothing the output power of renewable energy generation.

Tracking power generation plan: Follow the ramp up of renewable energy generation to assist wind and solar power generation, making them a partially adjustable power source and improving their controllability.

In a high penetration renewable energy generation area, storing excess wind and solar power to reduce energy waste and increase the penetration and economy of renewable energy.

The stored energy can be used as a rotating backup for power grid scheduling at any time, thereby reducing the amount of backup for conventional power generation and improving their efficiency.

5.2 Transmission side

Reduce the pressure on peak shaving and frequency regulation units, provide peak shaving and frequency regulation auxiliary services for the power grid, and pay according to the regulation effect.

Energy storage devices built in different locations and multiple locations can serve as auxiliary services, optimize power flow, reduce or solve line overload and congestion, and reduce line and network losses.

Delay the construction and operation of new lines.

When there is disturbance or accident in the power grid, energy storage can be used as a regulating power source to help improve the safety and stability performance of the power grid and increase the margin of safe operation of the power grid. It can also be used as an emergency backup power source or black start power source for the power grid.

5.3 Distribution side

For independent or grid connected microgrids, energy storage devices become an indispensable equipment to maintain the normal and stable operation of the microgrid. They can be used to adjust the frequency of the microgrid, maintain frequency stability during the transition process, and be used for long-term energy management.

One of the necessary adjustment methods for active distribution networks is to improve the distribution network's ability to absorb distributed power sources and ensure power quality to ensure that the distribution network operates within a safe range.

Mobile energy storage devices can quickly transport energy storage devices to the power outage area and connect them to the grid in case of regional power outages, in order to shorten the outage time and improve the reliability of power supply.

5.4 User side

Users can use energy storage devices and time of use electricity prices to change their electricity usage time and methods, in order to reduce peak load and valley load, and lower electricity costs.

For some users who require high reliability, the consequences of power supply interruption are extremely serious, requiring the installation of a certain number of energy storage devices as backup power sources (or uninterruptible power sources).

When an electric vehicle is connected to the power grid, it can serve as an energy storage device, utilizing the function of V2G to respond to demand and return the stored energy inside the electric vehicle to the grid when needed.

Energy storage systems can also be used for energy management systems in homes and buildings.