What is SOC%
SOC (State of Charge) is a critical parameter used to measure the remaining charge or energy stored in a battery, expressed as a percentage of the battery’s full capacity. It gives a real-time indication of how much usable energy is available in the battery.
SOC Formula
The basic formula for SOC is: SOC(%)=(Current Capacity (Ah)/Maximum Capacity (Ah))×100
Where:
- Current Capacity: The amount of charge currently stored in the battery.
- Maximum Capacity: The full charge capacity of the battery (can degrade over time).
Key Points About SOC
- Range:
- 100% SOC means the battery is fully charged.
- 0% SOC means the battery is completely discharged.
- Safe operating ranges depend on the battery type (e.g., LiFePO₄ batteries should typically stay within 20–90% SOC to maximize lifespan).
- SOC vs. DOD (Depth of Discharge):
- DOD is the complement of SOC: DOD(%)=100%−SOC(%)
- For instance, if SOC is 70%, the battery is 30% discharged (DOD).
- Measurement Methods:
- Voltage-Based: Estimates SOC using battery voltage. This method is simple but less accurate, as voltage can vary with load and temperature.
- Coulomb Counting: Tracks the charge entering and leaving the battery. It’s more precise but requires accurate sensors.
- Smart Monitoring: Advanced Battery Management Systems (BMS) integrate voltage, current, and temperature to estimate SOC.
- Importance of SOC:
- Energy Management: Helps users know how much energy is available for use.
- Battery Protection: Prevents overcharging (SOC > 100%) or over-discharging (SOC < 0%), which can damage the battery.
- System Optimization: In renewable systems, SOC is critical for load balancing and determining when to charge or discharge batteries.
Practical Example
A 12V, 100Ah battery:
- Fully charged: SOC = 100% (12V, 100Ah available).
- Half-charged: SOC = 50% (12V, 50Ah available).
- Fully discharged: SOC = 0% (0Ah available).