Battery Energy Storage Systems (BESS, battery energy storage systems) achieve the storage and release of electrical energy through electrochemical reactions. The core of this system lies in the collaborative operation of battery cells and auxiliary systems. The following is a detailed explanation of its working principle and key components:

I. Core Working Principle: Electrochemical Energy Conversion

The essence of BESS is the mutual conversion between electrical energy and chemical energy, achieved through the redox reactions within the battery:

Charging process:

External power supply inputs electrical energy, driving the chemical reactions inside the battery.
The positive electrode active material (such as lithium-ion batteries’ lithium iron phosphate) releases electrons, which flow through the external circuit to the negative electrode.
The ions released from the positive electrode (such as lithium ions) migrate through the electrolyte to the negative electrode and are embedded in the negative electrode material (such as graphite).
The electrical energy is converted into chemical energy for storage.

Discharging process:

Ions are desorbed from the negative electrode, return to the positive electrode, and release electrons to form an electric current.
The chemical energy is reconverted into electrical energy, which is output through the external circuit for use by devices.
This process is reversible, so the battery can be repeatedly charged and discharged.

II. Key Components

BESS is composed of multiple subsystems, working together to achieve the storage, conversion, and management of electrical energy:

Battery Cells:

Positive and negative electrodes: Store active substances (such as lithium, sodium, lead), and release electrons during discharge.

Electrolyte:

Conduct ions (such as lithium ions, sodium ions), and isolate the positive and negative electrodes to prevent short circuits.

Separator:

Physically separates the positive and negative electrodes, allowing ions to pass through.

Types:

Include lithium-ion batteries (lithium iron phosphate, ternary lithium), lead-acid batteries, sodium-sulfur batteries, flow batteries, etc. Different types are suitable for different scenarios.

Battery Management System (BMS, Battery Management System):

Function:

Monitor battery voltage, temperature, and current, balance the charging and discharging status of the battery pack, and prevent safety hazards such as overcharging, overdischarging, and short circuits.

Role:

Extend battery life and ensure safe operation of the system.

Power Conversion System (PCS, Power Conversion System):

Function:

Convert the battery’s output direct current (DC) to alternating current (AC) for use by external devices; or convert AC back to DC to charge the battery.

Application:

Achieve compatibility between the battery and the grid or load.

Thermal Management System:

Function:

Maintain the battery within an appropriate operating temperature range to prevent performance degradation or damage due to overheating or overcooling.

Methods:

Include air cooling, liquid cooling, etc.

III. System Operation Process

Electric energy input:

BESS receives electric energy from the grid, power station, or renewable energy sources (such as solar photovoltaic panels).

Energy storage stage:

Electric energy is converted to direct current (DC) by the PCS to charge the battery cells.
BMS monitors the charging process to ensure battery safety.

Discharge stage:

When external demand increases or the grid is unstable, the battery cells discharge.
PCS converts the DC electricity to AC and outputs it to the load or the grid.
BMS continuously monitors the discharge status to prevent overdischarge.

Smart scheduling:

Combined with software platforms (such as EMS, Energy Management System), BESS can intelligently adjust charging and discharging strategies based on grid demand, price fluctuations, or renewable energy generation.
For example: Charge during low electricity prices and discharge during peak times to reduce electricity costs; or store excess electricity from solar photovoltaic panels for use at night.

IV. Application Scenarios and Advantages

Grid-side peak shaving:

Reduce peak and fill valleys, balance grid supply and demand, and delay grid upgrade investment.
For example: Lithium iron phosphate batteries, sodium-sulfur batteries are used for grid peak shaving.

User-side energy storage:

Reduce electricity costs and participate in demand response.
For example: Lead-acid batteries, recycled lithium batteries are used for household or industrial energy storage.

Integration of renewable energy:

Store intermittent energy sources such as solar and wind power to improve the utilization rate of renewable energy.
For example: Used in conjunction with solar photovoltaic panels to solve the problem of “no electricity when there is no sunlight”.

Emergency backup power supply:

Provide backup power during grid failures or extreme weather to ensure the operation of critical loads.
For example: Provide uninterrupted power supply for hospitals, data centers, etc.

Electric vehicle charging stations:

Buffer the impact of fast charging on the grid and balance charging loads.
For example: High-power lithium-ion batteries are used for charging station energy storage.