Impact of SOC Estimation Error

An initial high level look at the impact SOC estimation errors.

SoC from OCV lookup

State of Charge (SOC)

State of Charge, abbreviated as SOC and defined as the amount of charge in the cell as a percentage compared to the nominal capacity of the cell in Ah.

Errors in SOC accuracy can impact the operation of the battery in a number of ways:

  • incorrect remaining energy
  • poorly balanced cells
  • reduced charge and discharge power
  • reduced lifetime
  • operation outside of safe working limits

In an electrified vehicle these errors can result in:

  • wrong range estimation
  • erratic range estimation
  • longer charge times
  • sudden loss of power
  • reduced battery lifetime

In a stationary energy storage system these errors can result in the following financial impacts [2]:

  • Trading on wrong energy and power volumes: An over or underestimated SOC can lead to trading decisions that sell either too much or too little energy or power. This leads to suboptimal asset use and decreased revenue.
  • Penalties for non-compliance with market conditions: Batteries are contracted on energy and grid services markets based on their ability to deliver a certain power output for a specified time. Inaccurate SOC can result in the battery underperforming, leading to financial penalties. In the worst-case scenario, operators can even be excluded from markets.

The impact of SOC estimation error can be significant. Mostly the issues are around poor estimations of remaining energy, hence the impact on all devices will be uncertainty in how long it can operate for. The trouble is that depending on the use the impact can be anything from annoyance to endangering life.

This post has been built based on the support and sponsorship from: Thermo Fisher ScientificEatron TechnologiesAbout:Energy and Quarto Technical Services.

The current state of the art in SOC estimation technigues suggests that the errors are around +/-1%, but is that for all chemistries under all operating conditions? Is that level of accuracy good enough for all applications going forward?

References

  1. A Closer Look at State of Charge (SOC) and State of Health (SOH) Estimation Techniques for Batteries, Analog Devices
  2. The Financial Implications of Inaccurate SOC in LFP Batteries, ACCURE

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