What is a Energy Management System (EMS)?

What is an Energy Management System (EMS)?

Checklist of what a EMS should do.

Definition (given by Bureau Veritas) and functionalities.


Definition of an EMS (Bureau Veritas):

Energy management system (EMS): Electronic system connected to a battery pack that monitors and/or safely manages the battery pack’s electrical and thermal state by controlling its environment, and that provides a means of communication between the battery system and other macro-system controllers, such as a battery support system (BSS), battery management system (BMS), or vehicle management system (VMS).


For “off-grid” applications, a VMS can be replaced by all of the installation’s charge and load equipment.


An EMS should be able to:

  • monitor and manage the battery pack’s electric and thermal state
  • estimate the potential need for battery pack (dis)connection
  • ensure a safe environment for the battery, the installation, and people
  • protect against equipment failure, human errors, environmental incidents
  • communicate with external systems and operators
  • optimize battery life and energy availability
  • perform diagnostics: log battery life history


An EMS must protect the battery itself against the failure modes described in the article “How your battery will dye“. It must also ensure multi-level protection as described in the article “Multi-level protection


Basic Functionalities of an EMS

Cell Voltage and Temperature Measurements
  • Voltage and temperature are the main factors that lead to battery failure.
  • Even a small difference in voltage or temperature between cells may indicate a serious problem.
    • As cell voltage remains mostly flat across its range of use, accuracy must be maintained within 1mV
    • The voltage of all cells must be measured using the same reference. (This rules out the use of an EMS with a separate measuring board for each cell.)


Warning in the event of abnormal conditions (level 3 protection)

You must be alerted to any deviation from optimal battery conditions, such as:

  • voltage or temperature differentials across cells
  • voltage above the chargers’ bulk/absorption settings
  • voltage below your standard discharge cycle
  • pack and cell temperature outside the optimal range

Warnings must be audible and visible from the main living area, and they must indicate the nature of the fault. A warning can be reset automatically if conditions return to normal (with hysteresis).

Communication with external equipment (level 4 protection)

At the very least, the EMS should be able to communicate three types of command to (1) disable charging, (2) disconnect loads, and (3) isolate the battery. In addition, it should be able to control external systems such as generators, heaters, or coolers.

Commands may take different forms:

  • activating a switching device (relay or circuit-breaker)
  • directly controlling certain equipment, such as battery chargers, converters, or regulators.

It is important to note that a given command such as “disable charging” may need to take different forms depending on the type of chargers used (cut alternator field, directly control a charger or regulator, activate a relay, and so on).

Cell Balancing

Often overlooked in off-grid energy storage installations, this is one of the most important features for optimizing battery life and energy availability.

In off-grid storage conditions, cells will not rapidly fall out of balance, but that will inevitably occur over time. If that situation is not remedied, battery capacity will be reduced and some cells will age faster, further accelerating the imbalance.

Alarm in the event of extreme conditions (level 5 protection)

Extreme conditions are situations where the battery starts to age more rapidly or where there is a risk to external equipment or people.

The alarm must be audible and visible from the main living area and indicate the nature of the fault.

The alarm must be persistent, requiring an operator reset.

Activation of safeguard procedures (level 6 protection)

Procedures that are triggered by an alarm (possibly after a wait time):

  • activation of a backup power supply
  • battery isolation

These procedures can only be deactivated manually after the fault has been remedied.


Internal and External Self-Tests

Self-tests are critical for ensuring that the entire protection system is operational. They include checking:

  • EMS internal component operation (e.g., measurement components, measurement references, outputs)
  • proper warning and alarm settings
  • connections and communication between system components
  • external equipment functioning

Without these basic functionalities, your EMS may be useless just when you need it the most.


TAO EMS has all these functionalities, and TAO Monitor goes a few steps beyond.


EMS—Advanced Functionalities

These functionalities put you in control of your installation and give you a true energy management system.

Personalized Events

In addition to warnings and alarms, you can define situations you want brought to your attention and optionally trigger certain actions:

  • based on voltage, temperature, SOC or current conditions
  • configuration to control EMS outputs and/or send CAN messages to external equipment


  • switch on the water-heater or water-maker when SOC exceeds a threshold
  • disconnect non-essential equipment when SOC or voltage falls below a threshold
  • activate a LED when discharge current exceeds a threshold
  • activate a fan or Pelletier cooling system when temperature exceeds a threshold
Lifetime History Log

Keep records for the lifetime of the system:

  • measurements, including cell voltage and temperature, current, SOC, cell internal resistance
  • activation and deactivation of warnings and alarms
  • all personalized events
  • standard events, such as EMS power-up, SOC reset, and many more.
In addition to fault analysis and diagnostic capabilities, a lifetime history log allows for on-site or remote support. This could be a money-saving feature if your battery fails prematurely and you need to prove that your battery has been used according to the manufacturer’s specifications.
Monitor Screen
  • view battery and cell status (voltage, temperature, current, SOC, cell internal resistance, cycle count, SOH)
  • edit EMS parameters
  • review the event log
  • statistical data and graphs
Remote Access
  • access all EMS functions remotely via a web browser (phone, tablet, computer)
  • run diagnostics and simulation
  • connect to a wifi network (or create an access point)
  • access historical data and events on the cloud

This feature enables you to monitor your installation when you are not on site. It also helps technicians to diagnose some system malfunctions and faults.



TAO Monitor has all of these advanced functionalities

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