To create a single line diagram for a BESS, you draw a simplified electrical schematic that shows the battery system, inverter or bidirectional converter, protection devices, metering, and grid connection point, all represented by standardized symbols on a single line rather than three separate phase conductors. The diagram must capture how energy flows in both charge and discharge directions, which is what sets it apart from a conventional PV SLD. This article walks through every key question engineers ask when producing a BESS SLD, from required components and notation to step-by-step drafting and common pitfalls.
What components must appear on a BESS single line diagram?
A BESS single line diagram must include the battery modules or racks, the battery management system (BMS), the bidirectional inverter or power conversion system (PCS), AC and DC protection devices, metering equipment, a transformer where applicable, and the point of common coupling (PCC) with the grid. Each of these elements plays a distinct role in safe and compliant system operation.
Starting on the DC side, the battery racks are grouped into strings and connected to a DC busbar. The BMS is shown as a control interface rather than a power-carrying component, but it must be referenced on the diagram because it governs charge and discharge limits, cell balancing, and fault isolation. DC fuses or circuit breakers protect each string, and a DC disconnect switch allows safe isolation during maintenance.
The power conversion system sits at the heart of the diagram. Unlike a standard solar inverter, the PCS operates bidirectionally: it converts DC from the batteries to AC when discharging and converts AC from the grid to DC when charging. This bidirectional flow must be clearly indicated on the SLD, typically with arrows or notation showing both directions.
On the AC side, the diagram must show the AC protection devices (circuit breakers, fuses, surge protection), revenue-grade metering, and any step-up transformer required to match grid voltage. The PCC is the final connection point and must be labeled clearly, as it defines the boundary between the BESS system and the utility grid. Anti-islanding protection and grid interconnection relays are also mandatory inclusions in most jurisdictions.
How is a BESS SLD different from a standard PV single line diagram?
The key difference between a BESS SLD and a standard PV single line diagram is bidirectional energy flow. A PV SLD shows electricity moving in one direction, from panels through an inverter to the grid. A BESS SLD must represent energy flowing both from the grid into the battery during charging and from the battery to the grid or load during discharging, which changes the logic, symbols, and protection requirements throughout the diagram.
In a PV SLD, the source is always the solar array. In a BESS SLD, the source alternates depending on operating mode. This means the protection coordination strategy is fundamentally different: fault current can originate from either the grid side or the battery side, and the diagram must reflect protection devices capable of interrupting faults in both directions.
A BESS SLD also introduces components that simply do not exist in a standalone PV design. The BMS, state-of-charge indicators, thermal management references, and fire suppression system connections may all need to appear or be referenced. When a BESS is co-located with a PV array, a common configuration in 2026 utility-scale projects, the SLD must show how the PV inverter, the PCS, and the grid interconnection point all interact, which adds significant complexity compared to either system drawn in isolation.
What are the standard symbols and notation used in BESS single line diagrams?
BESS single line diagrams use IEC 60617 or IEEE/ANSI standard symbols depending on the project’s regional requirements. Battery banks are typically represented by a series of stacked horizontal lines (the standard battery cell symbol), while the PCS or bidirectional inverter uses a circle with a sine wave and arrows indicating both AC and DC conversion directions. Circuit breakers, fuses, disconnects, and transformers follow the same conventions used in any electrical SLD.
Beyond the core symbols, BESS diagrams rely on specific notation to convey system parameters. Each major component should be labeled with its rated voltage, current, and power capacity. The battery system label typically includes nominal voltage, usable energy capacity in kilowatt-hours, and maximum charge and discharge rates in kilowatts. The PCS label includes rated AC power output, DC input voltage range, and efficiency class where relevant.
Relay and protection device notation follows ANSI device numbering. Commonly used numbers in BESS SLDs include Device 27 (undervoltage relay), Device 59 (overvoltage relay), Device 81 (frequency relay), and Device 87 (differential protection). These numbers are placed next to the relevant protection device on the diagram so that protection engineers and utility reviewers can immediately identify the relay functions without reading a separate legend.
Color coding is optional but widely used in practice. DC conductors are often shown in red and blue (positive and negative), while AC conductors use black, and grounding conductors use green. Consistent color use reduces the risk of misreading the diagram during commissioning or maintenance.
How do you draw a single line diagram for a BESS step by step?
Drawing a BESS single line diagram follows a structured sequence: start with the battery DC side, work through the power conversion system, then build out the AC side to the grid connection. Establishing this left-to-right or bottom-to-top flow before placing any symbols prevents the common mistake of having to restructure the diagram midway through.
- Define system boundaries and voltage levels. Identify the DC bus voltage of the battery system, the AC output voltage of the PCS, and the grid interconnection voltage. Note whether a step-up transformer is required and at what ratio.
- Place the battery bank symbol. Represent the battery racks using the standard cell symbol, grouped into strings. Label each string with its voltage and capacity. Show the BMS as a connected control element.
- Add DC protection devices. Insert string fuses or circuit breakers between each battery string and the DC busbar. Add a DC main disconnect between the busbar and the PCS input.
- Draw the power conversion system. Place the bidirectional inverter or PCS symbol at the center of the diagram. Use arrows or bidirectional notation to indicate both charge and discharge paths. Label the PCS with its rated power and voltage specifications.
- Build the AC side. Connect the PCS AC output to an AC busbar. Add AC circuit breakers, surge protection devices, and metering. If a transformer is required, place it between the AC busbar and the grid connection.
- Add the point of common coupling. Label the PCC clearly and show the grid interconnection relay with its ANSI device numbers. Include anti-islanding protection and any utility-required disconnect.
- Add grounding and earthing references. Show system grounding points on both the DC and AC sides. This is a common omission that causes problems during utility review.
- Complete the legend and title block. List all symbols used, voltage levels, protection device ratings, and revision history. A complete title block with project name, system capacity, date, and revision number is mandatory for permit and interconnection submissions.
What are the most common mistakes in BESS single line diagrams?
The most common mistakes in BESS single line diagrams are omitting bidirectional flow indicators on the PCS, missing protection devices on the DC side, failing to show the BMS connection, and using inconsistent or non-standard symbols that confuse utility reviewers. These errors routinely cause permit rejections and interconnection delays.
Treating the BESS SLD like a PV SLD is the root cause of most errors. Engineers who are experienced with solar-only designs sometimes omit the DC-side protection entirely or show the PCS as a standard inverter without indicating its bidirectional capability. Utility engineers reviewing the diagram for interconnection approval will flag both issues immediately.
Another frequent mistake is incomplete labeling. A diagram that shows the correct symbols but omits rated voltages, capacities, or protection device ratings forces the reviewer to request additional information, adding weeks to the approval process. Every component on the SLD should be fully labeled with its electrical parameters.
Grounding is consistently underrepresented. Both the DC battery system and the AC output side require clearly shown grounding connections, and the grounding electrode system should be referenced on the diagram. Omitting this detail is a common reason for plan check corrections on commercial and utility-scale BESS projects.
Finally, engineers sometimes fail to account for the co-located PV case. When a solar array and a BESS share the same interconnection point, the SLD must show how both systems interact at the AC busbar, how metering is arranged, and how protection devices coordinate across both energy sources. A diagram that shows only one system when both are present will not pass utility review.
What software tools are used to create BESS single line diagrams?
BESS single line diagrams are most commonly created in AutoCAD, BricsCAD, or dedicated electrical design platforms such as ETAP, SKM PowerTools, or Revit MEP. The choice of tool depends on the project scale, the level of protection coordination analysis required, and whether the SLD needs to integrate with broader electrical or structural design workflows.
For engineering firms that already work in AutoCAD or BricsCAD, these platforms remain the standard for producing SLDs because they offer precise control over symbol libraries, title blocks, and drawing standards. Firms handling large volumes of PV and BESS projects benefit from purpose-built plugins that automate repetitive drawing tasks within the CAD environment they already use, eliminating the need to switch between tools or re-enter data manually.
ETAP and SKM are preferred when the project requires load flow analysis, short-circuit calculations, or arc flash studies alongside the SLD. These tools generate the diagram as part of a broader electrical model, which means protection device ratings and relay settings can be validated directly against the system model rather than calculated separately.
For smaller commercial BESS projects, some engineers use Visio or even purpose-built online SLD tools that provide drag-and-drop symbol libraries. These are faster for simple systems but lack the parametric control and integration with engineering calculations that larger utility-scale projects demand.
If you are working on PV projects that include BESS integration and want to explore how purpose-built solar engineering software can reduce your design time, Virto Solar’s platform is built specifically for engineers working in AutoCAD and BricsCAD environments. For questions about how our tools fit your specific workflow, reach out to our team directly.
Frequently Asked Questions
Do I need a separate single line diagram for the DC side and AC side of a BESS, or can everything be shown on one drawing?
In most cases, a single comprehensive SLD is preferred and accepted by utilities and permitting authorities, as it shows the complete energy flow path from battery to grid on one sheet. However, for large utility-scale systems with complex DC architectures — such as multiple battery blocks with individual PCS units — engineers sometimes produce a system-level SLD and supplementary DC block diagrams. Always check your local Authority Having Jurisdiction (AHJ) and utility interconnection requirements, as some explicitly specify the level of detail and number of drawings required.
What level of detail does a utility typically require on a BESS SLD for interconnection approval?
Utilities generally require that the SLD show all protection devices with their ANSI device numbers and ratings, the point of common coupling clearly labeled, revenue-grade metering placement, anti-islanding protection, and the rated capacity of the BESS in both kilowatts and kilowatt-hours. Some utilities also require that the diagram reference the IEEE 1547 or UL 9540 compliance of the system. Reviewing the utility's specific interconnection technical requirements document before starting the SLD will save significant revision time.
How should I represent state-of-charge (SOC) and BMS data on a BESS SLD without cluttering the diagram?
The BMS is best represented as a control interface block connected to the battery bank and PCS with dashed lines, which conventionally indicate control or signal connections rather than power-carrying conductors. You do not need to show individual SOC values on the SLD itself — instead, reference the BMS model number and note that SOC monitoring and cell balancing are managed by the BMS per the manufacturer's specifications. Detailed BMS communication architecture, if required, is typically captured in a separate controls or communications diagram rather than the power SLD.
What changes on the SLD when a BESS is configured for behind-the-meter use versus front-of-meter grid export?
For a behind-the-meter BESS, the SLD must clearly show the load connection point and how the system interacts with the facility's main service panel, including any load management or backup power switching. The metering arrangement also changes: behind-the-meter systems may use a revenue meter at the utility service entrance rather than at the PCS output. Front-of-meter systems, by contrast, require the SLD to emphasize the grid interconnection relay, export controls, and utility-side metering in greater detail, as these are the primary points of regulatory and commercial interest.
Can I reuse an existing PV single line diagram as a starting template for a co-located BESS project?
You can use a PV SLD as a starting point, but significant modifications are required and simply adding a battery symbol to an existing PV diagram is one of the most common causes of interconnection rejections. At minimum, you must add the PCS with bidirectional flow notation, DC-side string protection, BMS reference, updated metering to account for both energy sources, and revised protection coordination that reflects fault current contributions from the battery. It is often faster and less error-prone to draft the BESS portion fresh and then integrate it with the existing PV SLD at the shared AC busbar.
Are there specific NEC or IEC code sections I should reference when creating a BESS SLD?
In the United States, BESS SLDs should reference NEC Article 706 (Energy Storage Systems), which covers installation requirements for battery systems, as well as NEC Article 705 for interconnected power production sources. UL 9540 (Standard for Energy Storage Systems) is frequently cited for equipment compliance. For IEC-based projects, IEC 62933 covers electrical energy storage system requirements, and IEC 60617 governs the standard symbols used on the diagram. Including the applicable code references in your SLD title block or notes section demonstrates compliance readiness and speeds up the utility review process.
How do I handle SLD revisions when the BESS system design changes after the initial permit submission?
Any design change that affects protection device ratings, system capacity, voltage levels, or the interconnection configuration typically requires a revised SLD to be resubmitted for approval before construction proceeds. Maintain a clear revision history in the title block, incrementing the revision number and noting the nature of each change and the date. Using CAD-based design tools with version control or cloud collaboration features makes it significantly easier to track changes, distribute updated drawings to the project team, and maintain a clear audit trail for the AHJ and utility.
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