What to do about high (cell) voltage spread alerts in your BESS

Understanding and Addressing High Cell Voltage Spreads in Your Battery Storage

Experiencing high cell voltage spreads in your battery system can be concerning, but understanding the potential causes and taking quick action can help ensure the safety and optimal performance of your system.

What Causes High Cell Voltage Spreads?

Several factors can contribute to high cell voltage spreads and alerts that lead to the voltage spread crossing the safety threshold.

Weak Cells or Low-Quality Cells: Within a BESS, individual battery cells can have slight variations in capacity or internal resistance, either due to lower quality or due to manufacturing problems turning it into a weak(er) cell.

During charging and discharging, the capacity or energy drawn from the different cells would ideally be the same, but if the cells poses different absolute capacities due to lower quality, the resulting voltage levels of weak cells will be different to normal cells leading to a voltage spread.

Self-discharge of cells: All batteries exhibit a natural self-discharge phenomenon, where they lose some charge even when not actively in use. This rate can vary between cell chemistries and temperatures.

Over time, the voltage of individual cells can drift due to self-discharge. Cells with higher self-discharge rates (caused by manufacturing issues) will see a larger voltage drop compared to others, contributing to an increasing voltage spread.

Non-functioning of BMS balancing: The Battery Management System (BMS) plays a crucial role in maintaining cell voltage balance. It monitors individual cell voltages and performs cell balancing when necessary. This balancing process involves pulling all cells down to the same voltage level or actively moving charge in-between cells to achieve the same voltage level.

If the BMS balancing process is not functioning properly, voltage differences between cells can accumulate over time. This can lead to significant voltage spread within the BESS, potentially impacting performance and lifespan.

What You Can Do:

If you experience high (cell) voltage spread alerts, these steps might help:

Perform balancing: Regularly perform preventative maintenance on the BMS to ensure proper functionality and accuracy of its sensors. Use the TWAICE Health Analytics and the upcoming TWAICE Performance Manager to control the evolution of the voltage spread before and after a balancing process.

Control and adjust thermal setpoint if needed: Maintain optimal operating temperatures within the BESS to minimize self-discharge rates. Implement a thermal management system that regulates temperature throughout the battery strings and containers. Leverage TWAICE Health Analytics and the upcoming TWAICE Performance Manager to validate a homogeneous temperature across the BESS.

Cross-check recurring alerts: Check if a component is regularly experiencing lower voltage threshold crossing alerts, which can be an indication for weak cells or cells with a higher self-discharge. Using the TWAICE Safety Monitoring and Analytics, sort the Alert Log by components to identify recurring patterns for certain components.
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Remember!

Early detection and intervention are crucial to preventing damage to your battery system and ensuring its continued safe and reliable operation. By understanding the potential causes of high cell voltage spread alerts and taking appropriate action, you can maintain the health and performance of your battery investment.