An Electrical Single-Line Diagram (SLD) is a simplified, standardized schematic that represents the entire electrical architecture of a solar PV system using single lines and symbols. Instead of showing every wire, conductor, or component in detail, an SLD condenses the electrical system into an easy-to-read map that communicates how electricity flows from solar panels to inverters, disconnects, breakers, meters, and the utility grid.

In solar design workflows, SLDs are essential for permitting, AHJ approvals, engineering reviews, utility interconnection applications, and installation planning. They are typically created alongside the layout during the design process in advanced platforms such as Solar Designing and reviewed as part of project planning workflows like the Solar Project Planning Hub.

• An Electrical Single-Line Diagram (SLD) is a simplified yet detailed electrical blueprint for solar PV systems.
• It shows the full electrical flow from solar panels to the grid using standardized symbols.
• SLDs are required for permitting, utility interconnection, engineering review, and installation.
• They include voltage ratings, current ratings, protection devices, conductor paths, and grounding details.
• Accurate SLDs improve safety, clarity, and approval speed for all solar projects.

What Is an Electrical Single-Line Diagram (SLD)?

An SLD is a visual blueprint that shows the electrical structure of a system using a single line to represent each electrical path. It organizes the full electrical system into a clear sequence, typically featuring:

• Solar panels and strings
• Combiner boxes or fuse holders
• Inverters (string, hybrid, or central)
• AC disconnects
• Breakers and protection devices
• Main distribution panel or switchgear
• Metering equipment
• Utility point of connection

The purpose of an SLD is to give engineers, inspectors, installers, and utilities a clear understanding of system topology, fault protection, conductor paths, grounding, and safety compliance.

Related terms include Stringing & Electrical Design, Inverter Sizing, and Mounting Structure (for BOS considerations).

How an SLD Works

An SLD works by presenting the full electrical system in a logical, top-down flow, using standardized symbols and simplified representations.

1. DC Side Representation

The diagram begins with the solar modules, often grouped into strings and sub-arrays.

It shows:

• Module count per string
• String grouping
• Combiner boxes (if used)
• DC disconnect switches
• Conductor size, OCPD, and voltage ratings

This connects to the inverter’s DC terminals.

2. Inverter Stage

SLDs indicate the type, quantity, and rating of inverters:

• String inverters
• Central inverters
• Hybrid inverters
• Microinverter grouping (represented differently but included when needed)

This is where DC is converted to AC.

See: Solar Inverter

3. AC Side Representation

The AC portion often includes:

• AC disconnect
• AC breaker
• Critical load panel (for hybrid systems)
• Distribution panel or switchgear
• Transformer (commercial/utility)

4. Utility Grid Interface

The SLD ends at the point of interconnection:

• Meter socket
• Service panel
• Utility transformer
• Service drop/service lateral

Utilities require SLDs for approval and interconnection agreements.

5. Safety and Grounding

SLDs also illustrate:

• Grounding electrode conductor (GEC)
• Equipment grounding conductor (EGC)
• Bonding points
• OCPD ratings

Types / Variants of Single-Line Diagrams

1. Residential SLD

Simplified representation showing:

• PV array
• Inverter
• AC disconnect
• Main distribution panel
• Net-metering connection

Often used for AHJ permit submissions.

2. Commercial SLD

More detailed, including:

• Multiple inverters
• Panelboards
• Switchgear
• Production meters
• Transformers
• Monitoring systems

3. Utility-Scale SLD

Highly technical diagrams including:

• Central inverters
• MV switchgear
• Breaker schemes
• SCADA interface
• Transformers and substations

4. Battery / Hybrid SLD

Shows:

• Battery banks
• Hybrid inverters
• ESS disconnects
• Critical load panel

Useful for systems designed with Load Analysis.

How SLDs Are Measured (Key Data Included)

SLDs don’t use measurement units like kW or meters to quantify the diagram itself, but they include technical specifications such as:

Voltage Levels

• DC max system voltage
• AC voltage (120V/240V/208V/400V/480V)

Current Ratings

• String current
• Inverter output current
• Breaker ratings

Power Ratings

• DC system size (kWp)
• Inverter AC output (kW)

Wire and Conductor Sizes

Based on load calculations and voltage drop (see Voltage).

Protection Devices

• OCPDs
• Fuses
• Breakers
• Disconnect switches

Typical Values / Ranges

Residential Systems

• String voltage: 250–450V DC
• AC voltage: 120/240V
• Main breaker: 100–200A

Commercial Systems

• String voltage: 800–1000V DC
• AC voltage: 208V / 400V / 480V
• Switchgear protection: 30A–600A+

Utility-Scale

• DC voltage: 1000–1500V
• AC voltage after step-up: 4.16kV–34.5kV
• Central inverter sizes: 1–5 MW

Practical Guidance for Solar Designers & Installers

1. Always match SLDs to AHJ requirements

AHJs vary in their required symbols, labeling, and detail.

For jurisdiction research, see: AHJ Compliance.

2. Ensure conductor sizes match load

Use tools such as the Voltage Drop Calculator.

3. Keep AC and DC paths clearly separated

Improves readability and speeds up approval.

4. Use consistent, standardized symbols

Avoid custom icons that may confuse inspectors or utilities.

5. Confirm inverter and breaker alignment

Ensure sizing matches the calculations from Inverter Sizing.

6. Integrate SLD creation into the design workflow

SurgePV produces SLD-ready data automatically as part of layout and electrical design:

Solar Designing

7. Use SLDs to communicate with field teams

Installers rely on SLDs to understand wiring paths and safety locations.

Real-World Examples

1. Residential Rooftop SLD

A 7.5 kW home system includes:

• 18 panels in two strings
• A single 7.6 kW inverter
• AC disconnect
• Main panel connection via a 40A breaker

The SLD accompanies the permit package for AHJ review.

2. Commercial Flat Roof SLD

A 250 kW system uses:

• Multiple three-phase string inverters
• A production meter
• Switchgear with fuse-protected feeders
• Step-down transformer

The SLD is required for utility interconnection approval.

3. Utility-Scale SLD

A 20 MW solar farm shows:

• Central inverters feeding MV switchgear
• Step-up transformers
• Protection relays
• SCADA integration points

Utilities use this SLD for grid studies and safety review.

• Stringing & Electrical Design
• Inverter Sizing
• Solar Inverter
• Voltage
• Load Analysis