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BESS hierarchy: electrical and physical levels

Learn why TWAICE introduced a new system-centric BESS hierarchy and how its physical and electrical views map your components.

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We are happy to announce that we introduced a new hierarchy structure for the TWAICE BESS Analytics platform to better represent the entire BESS system.

This article aims to explain the main updates, new hierarchy levels, and how they affect the features in the platform.

Why a New Hierarchy?

The BESS hierarchy defines how all components of an energy storage system, from cells to transformers, are structured and connected, forming the foundation for data aggregation, visualization, and analytics across the platform.

As TWAICE evolves from battery analytics to a comprehensive data analytics platform for BESS, the way we model energy storage systems has also evolved. The new hierarchy forms the foundation for enabling deeper insights, broader integrations, and more flexibility in how customers manage and optimize their assets.

From Battery-Centric to System-Level View

The previous hierarchy focused mainly on batteries (cells, modules, and racks), which limited visibility into other critical components such as PCS (Inverter) and transformers.
The new hierarchy expands this view to represent the entire BESS, linking electrical and physical layers for a complete system perspective.

The new structure enables:

  • Extended monitoring: Adds visibility into more components such as PCS, transformers, HVAC, and sensors, giving users a truly system-wide view of performance.

  • More accurate KPIs and alerts: KPIs and anomaly detection now powered by the new hierarchy, ensuring metrics and alerts accurately reflect system behavior.

  • Feature improvements: Platform features are now powered by new structure mirroring actual BESS configurations, helping teams identify and locate issues faster on site.

Physical and Electrical Hierarchies

One of the biggest updates we introduced is new hierarchy types to better represent how BESS systems are both electrically wired and physically organized.

These two complementary hierarchies provide different but connected perspectives on system behavior and performance.

🔌 Electrical Hierarchy

Shows how components are electrically connected and how energy flows through the system from cells and modules up to PCS units, transformers, and the grid. It highlights relationships that influence power flow and efficiency.

🏗️ Physical Hierarchy

Displays how components are physically arranged, for example, which racks or PCSs are located within each enclosure or container. This view helps users quickly locate issues and link them to specific physical assets on the field.

Physical hierarchy option also enables us to onboard additional sensors such as HVAC sensors which are dedicated to enclosures (containers), allowing more comprehensive monitoring.

👉🏻 Together, these hierarchies enable users to pinpoint where an issue occurs and understand how it affects the broader system. We use this flexibility across our platform and features to make analysis, navigation, and decision-making easier and more intuitive.

Updated Hierarchy Levels

Battery Energy Storage Systems (BESS) follow a hierarchical structure of components and sensors. Below, typical BESS data model levels supported by TWAICE with updated hierarchy are given with definitions.

Note: Customers can customize naming of the component levels.

👉 Please get in touch with your TWAICE contact for more details or guidance.

🏗️ Physical Levels

Name Common Alternative Names Definition
Site Plant Used for grouping of multiple BESS, and other energy systems, such as wind and solar, at the same site.
Enclosure Container, Cluster Represents the physical housing unit that contains key electrical and battery components such as racks, PCS modules, and auxiliary systems (e.g., HVAC, fire suppression).

👉 Physical hierarchy can contain any of the electrical components (explained below) within “enclosures”.

🔌 Electrical Levels

Name Common Alternative Names Definition
System Storage, System Represents the complete BESS installation as a single operational unit. Includes all electrical and control subsystems required for operation.
Meter AUX Meter, Power Meter, Measurement Point Device or logical point used for measuring electrical parameters (e.g., power, energy, voltage). Often corresponds to utility or submetering equipment.
Transformer Step-up Transformer, MV Transformer Converts AC voltage levels between the grid and the BESS system (typically low-voltage to medium-voltage). Key interface between site and utility.
AC Combiner Cluster, AC Junction Box, AC Panel, AC Blok, Blok, AC Bank Aggregates AC outputs from multiple PCS units to the transformer or grid interface.
PCS Inverter, Power Conversion System Converts DC power from batteries to AC power for the grid, and vice versa. Typically consists of multiple PCS modules.
PCS Module Inverter Module, Power Block Subcomponent of the PCS representing an individual module. Allows fine-grained monitoring and control.
DC Combiner Node, DC Junction Box, DC Panel, DC Box, Array, BSU, DC Bank Combines multiple DC inputs from racks to the PCS Module(s). Used for current collection and protection.
Rack Group String Group, DC Branch, Battery Bank Logical grouping of multiple battery racks, used for monitoring or control aggregation.
Rack PCS PCS Rack, Converter Rack, String PCS Battery rack directly associated with a PCS input. Represents DC paths linked to specific converters.
Rack String, Pack A chain of modules electrically connected in series or parallel. Commonly represents a container’s internal substructure.
Rack Module PCS PCS Battery Module, Converter Module, String Module PCS Module within a rack that is directly associated with PCS-specific connections or control paths.
Rack Module Battery Module, Rack Module, String Module A standard unit of connected cells forming part of a rack; often includes integrated BMS and monitoring electronics.
Cell Battery Cell The smallest electrochemical unit containing active materials. Fundamental energy-storing component of the BESS.

Changes in Features

Hierarchy Diagram: Toggle between electrical and physical hierarchies

🎯 Goal and Why It Matters

Now you are able to toggle between both electrical and physical hierarchies freely, making it easy to locate issues faster in your preferred workflow.

Find all the details in Hierarchy Diagram article.

Performance - Recoverable Energy: Aggregation update, improved sibling effect detection

🎯 Goal and Why It Matters

The goal of this update is to improve the accuracy and clarity of how recoverable energy is calculated and displayed, reflecting real electrical dependencies and similarly including the physical location of the underperforming components to act faster on the field.

🔄 What Changed

Previous aggregation:
Rack → Node / Inverter

New aggregation:
Rack → DC Combiner → AC Combiner

The left table starts with AC Combiner, showcasing underperforming components that limit usable energy.

One level deeper from AC Combiner, the right table now aggregates recoverable energy from all racks connected to a DC Combiner.

Sibling Effect: this update significantly improves the detection of the sibling effect and provides a more realistic reflection of system performance:

  • When one rack underperforms, it constrains the usable energy of all sibling racks sharing the same DC Combiner.

  • With this update, the limiting rack’s recoverable energy value is multiplied by the number of racks within the DC Combiner. This ensures the total recoverable energy reflects the true electrical dependency between racks.

More details can be found in: The “Sibling Effect” in Battery Energy Storage: A Hidden Performance Bottleneck.

The details page is enriched with enclosure data for context on the physical housing of affected racks, enabling faster investigation on site.

Performance - Imbalances & Temperatures: Aggregation by enclosure

🎯 Goal and Why It Matters

The goal of this change is to make imbalance insights more actionable in the field.
Previously, KPIs such as State of Charge (SoC) spread and temperature spreads, were aggregated at the node or inverter level — an electrical view that didn’t directly map to physical locations.

With this update, aggregation now happens at the enclosure level, aligning data with the physical structure of the BESS. This allows users and field engineers to locate underperforming components, knowing exactly which enclosure to inspect on the field.

🔄 What Changed

Previous aggregation:
Rack → Node / Inverter

New aggregation:
Rack → Enclosure

KPIs are now rolled up to the enclosure level, showing how each physical unit performs. This shift improves traceability and practical relevance, making heatmaps and imbalance views easier to interpret from a real-world perspective.

⚠️ Important Note:

However, for some system architectures — especially where rack-to-enclosure mappings are one-to-one or one-to-many, this aggregation may not be meaningful.
In these cases, TWAICE provides flexibility to aggregate KPIs at the DC Combiner level, maintaining accuracy and visibility across diverse system designs.

👉 Please get in touch with your TWAICE contact for more details.

Safety: Improved anomaly detection logic

🎯 Goal and Why It Matters

The goal of this update is to make safety anomaly detection more accurate and representative of the actual electrical configuration of a BESS system.
Previously, Safety KPIs — such as temperature, resistance, and self-discharge — were compared between racks . While this provided valuable insights, it didn’t always reflect how anomalies propagate through the system electrically.

Now, Safety aggregates and compares data at the DC Combiner level — the true electrical point where rack behavior converges, improving the consistency and detection logic.

🔄 What Changed

Before: Comparisons between individual racks
Now: Aggregation and anomaly detection at DC Combiner level

By analyzing KPIs across each DC Combiner, the Safety feature can now detect temperature or resistance anomalies more reliably, by analyzing groups of racks that are electrically connected.

⚠️ Important Note:

Systems with a 1:1 rack-to-DC Combiner mapping currently have a limitation in detecting self-discharge anomalies — these cases cannot yet be identified as of now.
We are actively working to enhance the algorithm to address this scenario.
👉 Please get in touch with your TWAICE contact for more details or guidance on this limitation.

Data Explorer: New component names

Data Explorer now reflects updated hierarchy and component names in the selection panel.

Please get in touch with us for any question or feedback!