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octobre 14, 2025

Qu'est-ce que l'état de charge des batteries solaires ?

5 minutes de lecture

Les informations sur l'énergie solaire peuvent prêter à confusion. C'est pourquoi nous veillons à ce que les nôtres soient étayées :

  • Les points de vue d'ingénieurs solaires expérimentés et d'experts mondiaux de l'énergie
  • Données réelles provenant de milliers de systèmes solaires et de batteries
  • Sources vérifiées telles que les organismes de normalisation internationaux et les agences gouvernementales

In modern energy storage systems and electric vehicles, the State of Charge (SOC) of a battery is a key parameter for evaluating battery performance and available energy.

Accurate SOC estimation not only helps optimize charging and discharging strategies but also ensures system safety, extends battery life, and enhances energy management. This article introduces the definition, calculation methods, common estimation algorithms, and influencing factors of SOC, along with its practical applications in photovoltaic energy storage and electric vehicles.

What is SOC

SOC represents the percentage of stored energy in a battery or energy storage system relative to its full capacity. In a battery, SOC refers to the ratio between the current remaining charge and the fully charged capacity, typically expressed as a percentage.

This parameter helps users understand the remaining battery capacity and plan charging and discharging schedules. It is also a vital input for Battery Management Systems (BMS) in charge control, energy optimization, and safety protection—serving as a key indicator of overall system performance and energy availability.

State of charge of Battery and Electric vehicle

State of charge of different energy assets

Battery

In solar battery systems, SOC is used to monitor the remaining energy in real time, helping users plan energy usage and charging schedules efficiently to maximize energy utilization.

Electric vehicle (EV)

In electric vehicles, SOC is the core parameter of the Battery Management System (BMS), directly reflecting the vehicle’s remaining driving range. It provides essential information for driving decisions and plays a critical role in ensuring battery safety and longevity.

Electric Vehicle Dashboard Displaying Real-Time State of Charge (SOC) for Safe and Efficient Driving

Whether in solar energy storage systems or electric vehicles, maintaining SOC between 20% and 80% is considered optimal and can significantly improve battery cycle life.

How to Calculate SOC

The battery’s charge status can be represented as the percentage of remaining capacity relative to its maximum capacity.

The formula is as follows:
SOC = Remaining Capacity / Total Capacity × 100

SOC calculation method

Exemple :

The total storage capacity of GODE’s LF51200-02 LiFePO₄ Battery Pack is 10kWh. If 3kWh has been used, then: (
7kWh/10kWh)x 100 = 70% SoC.

Parameter Description:

  • Q₀(mAh): Initial Capacity
  • Q(mAh): Charge or discharge capacity
  • Qmax(mAh): Maximum storable capacity of the battery

How to Measure the State of Charge in Solar Batteries

In a Battery Management System (BMS), SOC cannot be measured directly and is typically estimated using the following models:

1. Coulomb Counting

The Coulomb Counting method tracks the charge and discharge current over time (current integration). It offers high responsiveness and simplicity but suffers from cumulative errors over long periods and relies heavily on an accurate initial SOC and efficiency correction.

2. Open Circuit Voltage Method

The Open Circuit Voltage method measures terminal voltage under rest or low-current conditions and maps it to SOC using a pre-calibrated OCV–SOC curve. It is intuitive and accurate under steady-state conditions but requires rest periods to avoid polarization-induced errors.

3. Model-Based Estimation

The Model-Based Estimation method uses physical or equivalent circuit models along with observation data to estimate or predict SOC. It reflects dynamic electrochemical behavior and maintains high accuracy under varying conditions but requires precise modeling, parameter identification, and higher computational capacity.

4. Hybrid Algorithm

The Hybrid Algorithm combines the real-time tracking of Coulomb Counting, the dynamic correction of Model-Based Estimation, and the static calibration of the OCV method. It balances real-time performance and long-term accuracy and is widely adopted in industrial BMS applications.

All GODE energy storage batteries feature LCD displays, indicator lights, or mobile applications for real-time monitoring of SOC and other parameters—no manual calculation required.

GODE Energy Storage Battery with LCD Display Showing Real-Time State of Charge

This indicator helps users assess available energy and overall system performance.

Main Factors Affecting SOC

Charge and discharge rate

The C-rate significantly affects SOC. Higher charging current increases SOC faster, while higher discharge current reduces SOC more rapidly. Excessive C-rates can impair SOC accuracy in BMS calculations.

Charging voltage

Charging voltage determines the maximum achievable SOC. A higher voltage allows faster charging but accelerates aging and raises safety risks, while too low a voltage leads to insufficient charging and underestimated SOC.

Profondeur de la décharge

Greater Depth of Discharge (DOD) results in larger SOC drops. Deep discharges accelerate capacity degradation and cause nonlinear SOC behavior. It is recommended to maintain DOD within 20%–80% to significantly extend battery life.

Self-Discharge

Even when idle, internal chemical reactions cause batteries to lose charge gradually. Higher self-discharge rates lead to faster SOC decay, especially under high temperatures or extended storage periods.

Temperature

Temperature directly impacts chemical reaction rates and internal resistance. High temperatures accelerate reactions and SOC fluctuations but increase aging, while low temperatures reduce activity and capacity, slowing SOC changes and increasing estimation errors.

Humidité

Ambient humidity indirectly affects SOC by influencing cooling and insulation. High humidity can cause terminal oxidation or insulation degradation, leading to micro leakage and slow SOC decline, while low humidity supports stable electrical performance.

Type de batterie

Different chemistries (e.g., LiFePO₄, NCM, LFP, lead-acid) exhibit distinct voltage–capacity curves. LiFePO₄ has a flat voltage plateau, making SOC estimation difficult, while NCM shows higher voltage sensitivity, simplifying voltage-based estimation.

BMS

The precision of BMS algorithms directly determines SOC reliability. If temperature, capacity fade, and dynamic voltage compensation are not properly accounted for, SOC results deviate from reality. Advanced algorithms provide real-time correction for stable and accurate SOC estimation.

Conclusion

SOC is an essential parameter in energy storage and electric vehicle systems. Through scientific estimation and high-precision algorithms, it is possible to enhance efficiency, ensure safety, and extend battery life. GODE continues to drive the transition toward a greener and smarter energy future through innovation in energy storage and BMS technology.