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Xiho
Jul 07 2025
SOC: The smart navigator of energy storage system, understanding the "language" of battery.
At the core of every lithium battery lies a key indicator - SOC (State of Charge). It is like a "heartbeat monitor" for the battery, telling you how much energy is left in the battery cell in percentage. If a lithium battery has a total capacity of 10kWh and currently has 5kWh left, its SOC is 50%. From mobile phones to grid-level energy storage systems, SOC is everywhere and is the "invisible commander" of energy management.
1. How to measure SOC?
The SOC of lithium batteries cannot be measured directly and needs to be estimated by combining algorithms and sensor data. Common methods include:
(1) Coulomb integration method: Integrate the charge and discharge current to dynamically track the change in charge. The advantage is strong real-time performance, but the current measurement error will accumulate.
(2) Open circuit voltage method (OCV): Use the corresponding relationship between the voltage and SOC of the battery cell after it is left to stand to estimate. It has high accuracy but needs to be left to stand for several hours and is not suitable for dynamic conditions.
(3) Kalman filter method: Fusion of current integration and voltage models to offset errors through a prediction-correction mechanism. Applicable to automotive-grade lithium battery management systems with an accuracy of ±3%.
(1) Coulomb integration method: Integrate the charge and discharge current to dynamically track the change in charge. The advantage is strong real-time performance, but the current measurement error will accumulate.
(2) Open circuit voltage method (OCV): Use the corresponding relationship between the voltage and SOC of the battery cell after it is left to stand to estimate. It has high accuracy but needs to be left to stand for several hours and is not suitable for dynamic conditions.
(3) Kalman filter method: Fusion of current integration and voltage models to offset errors through a prediction-correction mechanism. Applicable to automotive-grade lithium battery management systems with an accuracy of ±3%.
2. Three core functions of SOC
(1) Determine the charging and discharging strategy
The energy management system (EMS) of the energy storage system intelligently dispatches energy based on the SOC value: stop charging when SOC > 95% to prevent the lithium battery from overcharging; prohibit discharging when SOC < 20% to avoid over-discharging and damaging the battery cell. For example, in a home photovoltaic storage system, if the SOC is too low, the solar energy system will be used for power supply to protect the battery health.
(2) Ensure safe operation of the system
Real-time monitoring of SOC can prevent thermal runaway (such as fire or explosion) caused by overcharging/over-discharging of the lithium battery. Modern energy storage systems control SOC within the safety threshold through mechanisms such as OVP (overvoltage protection) and OCP (overcurrent protection).
(3) Optimize energy scheduling
In a multi-source coordinated system (such as photovoltaic + grid + energy storage system), SOC determines the direction of energy flow:
Low SOC → Prioritize charging with the solar system;
High SOC → Send excess photovoltaic power to the grid or load.
For example, Tesla Powerwall will dynamically switch charging and discharging modes according to SOC to maximize the utilization of green electricity.
From lithium batteries in the palm of your hand to energy storage systems supporting cities, SOC has gone beyond simple "power display" and has become the core link between physical batteries and digital management. It makes the green power storage of solar systems smarter, makes the endurance of electric vehicles more reliable, and makes the trillion-watt-hour grid-level energy storage system operate safely.
The energy management system (EMS) of the energy storage system intelligently dispatches energy based on the SOC value: stop charging when SOC > 95% to prevent the lithium battery from overcharging; prohibit discharging when SOC < 20% to avoid over-discharging and damaging the battery cell. For example, in a home photovoltaic storage system, if the SOC is too low, the solar energy system will be used for power supply to protect the battery health.
(2) Ensure safe operation of the system
Real-time monitoring of SOC can prevent thermal runaway (such as fire or explosion) caused by overcharging/over-discharging of the lithium battery. Modern energy storage systems control SOC within the safety threshold through mechanisms such as OVP (overvoltage protection) and OCP (overcurrent protection).
(3) Optimize energy scheduling
In a multi-source coordinated system (such as photovoltaic + grid + energy storage system), SOC determines the direction of energy flow:
Low SOC → Prioritize charging with the solar system;
High SOC → Send excess photovoltaic power to the grid or load.
For example, Tesla Powerwall will dynamically switch charging and discharging modes according to SOC to maximize the utilization of green electricity.
From lithium batteries in the palm of your hand to energy storage systems supporting cities, SOC has gone beyond simple "power display" and has become the core link between physical batteries and digital management. It makes the green power storage of solar systems smarter, makes the endurance of electric vehicles more reliable, and makes the trillion-watt-hour grid-level energy storage system operate safely.
