Auto-Stringing

Auto-Stringing is an advanced solar design automation feature that automatically determines how solar modules should be electrically connected into strings based on inverter requirements, voltage limits, current thresholds, and layout configuration. Instead of manually calculating string lengths or mapping connections, the software uses algorithms to create optimal and code-compliant stringing patterns—saving time, reducing errors, and ensuring electrical performance.

In modern solar workflows, Auto-Stringing is an essential tool for designers, EPCs, and installers, especially when working with complex layouts, multi-inverter systems, module-level electronics, or variable roof geometries. Platforms like Solar Designing use Auto-Stringing to instantly create string maps that match NEC rules, inverter specifications, and performance requirements.

Key Takeaways

Auto-Stringing automates the electrical design of module strings, saving time and reducing human error.
Ensures strings stay within inverter voltage and current specifications.
Balances MPPT loads for optimal inverter performance.
Essential for residential, commercial, and utility-scale PV workflows.
Combines perfectly with automated layout and shading tools.

What Is Auto-Stringing?

Auto-Stringing is the automated process of connecting solar modules together into electrical strings according to design constraints and inverter characteristics. Instead of manually grouping modules into series strings, the software determines:

The ideal number of modules per string
Which modules belong to each string
How strings are routed to each inverter or MPPT
Maximum and minimum string voltage
Current limits and safety margins
DC/AC ratio considerations

By analyzing temperature coefficients, irradiance conditions, module layout, and equipment specifications, Auto-Stringing produces a string configuration that is both technically sound and energy-efficient.

Related concepts include Stringing & Electrical Design, Inverter Sizing, and Solar Layout Optimization.

How Auto-Stringing Works

Auto-Stringing typically follows a structured engineering workflow:

1. Analyze Module and Inverter Specifications

The system identifies required parameters such as:

Max DC voltage (e.g., 600V, 1000V, 1500V)
Min MPPT voltage
Max DC current
MPPT count
DC/AC ratio

2. Evaluate Temperature Conditions

Cold temperatures increase voltage, so the algorithm calculates worst-case conditions using:

Module Voc
Temperature coefficient
Site temperature data

3. Determine Maximum Modules per String

Auto-Stringing ensures strings stay below the inverter’s voltage limits in cold conditions.

4. Group Modules Based on Layout

Modules are grouped by:

Roof plane
Ground array block
Orientation
Row alignment

5. Assign Strings to MPPTs or Inverters

The system ensures:

Balanced DC input
Even current distribution
Optimal clipping behavior

6. Create Visual String Maps

The designer receives a complete, color-coded string map ready for permitting, installation, and proposal integration.

See String Map Auto-Generation for mapping visualization.

Types / Variants of Auto-Stringing

1. Fixed-String Auto-Stringing

Follows strict rules for string length and layout.

2. MPPT-Optimized Auto-Stringing

Balances strings across multiple MPPT channels.

3. Bifacial & Tracker-Aware Auto-Stringing

Accounts for irradiance differences, row spacing, and mismatch risk.

4. Module-Level Power Electronics Integration

Adjusts rules when microinverters or DC optimizers are used.

5. Multi-Inverter Auto-Stringing

For large rooftops, ground-mounts, and utility-scale designs.

How It’s Measured

Auto-Stringing quality is evaluated based on:

1. String Voltage Range

Must fall between inverter MPPT min/max voltage.

2. Current Matching

Ensures no imbalance across MPPTs.

3. Number of Strings per MPPT

Affects clipping and inverter efficiency.

4. DC/AC Ratio

Impacts energy yield and clipping duration.

5. Mismatch Risk

Lower mismatch = higher system performance.

Typical Values / Ranges

Depending on region and system scale:

Residential

8–15 modules per string
1–2 MPPT inverters

Commercial

14–22 modules per string
2–4 MPPTs per inverter

Utility-Scale

20–28 modules per string
1000V/1500V systems
Central or high-capacity string inverters

Actual values depend on temperature, inverter specs, and module data sheets.

Practical Guidance for Solar Designers & Installers

1. Always validate string voltages in cold-climate conditions

Cold increases voltage and may exceed inverter limits.

2. Keep strings within the same plane

Avoid mixing modules across roof facets with different orientations.

3. Balance MPPT inputs

Equal number of strings per MPPT ensures stable performance.

4. Use Auto-Stringing as a starting point

Then refine manually for:

Shaded modules
Different roof planes
Fire setbacks
Walkways

5. Combine Auto-Stringing with layout tools

Use Solar Designing for automated placement and Shadow Analysis for shading-aware stringing.

6. Review inverter datasheets carefully

Temperature-adjusted calculations are essential for safety.

7. Generate installer-ready documentation

String maps should tie directly into permitting and installation workflows.

Real-World Examples

1. Residential Rooftop System

Auto-Stringing calculates that a 10 kW system can safely place 13 modules per string based on cold-weather design limits.

2. Commercial Flat Roof

A 200 kW system is automatically grouped into 36 balanced strings, evenly distributed across MPPT inputs for optimal performance.

3. Utility-Scale Solar Plant

A 75 MW project uses Auto-Stringing to automatically assign strings across central inverters, achieving a uniform DC/AC ratio across multiple blocks.