What are string design and string plan?
The path from PV system planning to a finished installation document consists of two closely linked steps: string design and the string plan.
String design (under Inverter) – Here you define which inverters are used, how the panels are connected in strings, and which MPP trackers (MPPT) the strings are connected to. Eturnity Expert provides both automated inverter design and manual string design for this purpose.
String plan (under Technical plans > String plan) – Based on the completed string design, you create a professional PDF document here that visualises the string wiring on the roof – with colour coding, labels, legend, and title block.
Previously, string tables and wiring diagrams were created manually in CAD programs or by copy-pasting into spreadsheets. For each string, the open-circuit voltage (Voc) had to be calculated individually and updated with every change – a process that could take several hours on larger projects. Eturnity Expert generates this information automatically from the project data.
Who is this feature for?
Technical planners – who finalise the electrical design after order signing and prepare installation documentation
Project managers – who need string wiring plans for the installation team and authority submissions
Back-office staff – who compile documentation packages without having to carry out the electrical design themselves
License note: If you do not see this feature in your product, it may not be included in your current license. Please request a trial or contact support@eturnity.com to learn more.
Prerequisites
PV technology is enabled in the project
A 3D layout has been completed – string design works exclusively based on the 3D data model (not 2D/legacy)
Panels are placed on the roof surfaces
Important: String design and string plan support only projects with 3D layout. When 2D legacy mode is active, a notice appears prompting you to switch to 3D mode.
Overview: The complete workflow
The complete workflow is divided into the following phases:
Complete the 3D layout – Model roof surfaces, place panels, draw obstacles
Inverter design – Select inverters (automatically or manually)
String design – Assign panels to strings, check MPPT assignment, validate compliance
Create string plan – Configure the visualisation, customise the legend, export PDF
Core principle: All changes to the electrical wiring (inverters, strings, MPPT assignment) are made in string design. The string plan is exclusively a documentation and visualisation tool – no design changes can be made there.
Part 1: String design – Inverter design and string configuration
Navigate to string design
In the project navigation, go to Inverter. Here you will find two work areas:
Inverter configuration table – The overview page with the current inverter configuration and the entry point for automated design
String design canvas – The graphical interface where you can see and manually edit the string wiring on the roof
Automated inverter design
Automated inverter design is the fastest way to a complete string design. The wizard guides you through the configuration in just a few steps:
Start: Click Automate design in the inverter configuration table. The system first checks whether your project is suitable for automated design.
Optimizer selection (optional): If desired, select a DC optimizer from the catalogue. This step can be skipped if no optimizers are required.
Inverter selection: Filter and search for suitable inverters by manufacturer, power, and type (PV, hybrid, battery). Select one or more inverters from the list.
Review proposals: The system calculates optimal configuration proposals and shows you the results – including number of inverters, wiring details, and prices. Select the appropriate proposal.
Note: Automated design is not available if the project uses manual roof surfaces, the PV system is empty, or the selected inverter is not supported. In these cases, a notice appears explaining the reasons.
After selecting a proposal, the string design is automatically created on the canvas. You can then further adjust it in manual string design.
Manual string design
Manual string design gives you full control over the string wiring. It consists of three main areas:
Canvas (work area)
The canvas shows the roof surfaces with the placed panels. Here you assign panels to individual strings by clicking. Each string is automatically colour-coded so you can identify assignments at a glance.
Sidebar (inverter hierarchy)
The left sidebar shows the complete hierarchy of your system:
Inverter – With model name, AC power (kW), DC input power (kW), and compliance status. From here you can add, edit, delete, or reorder inverters.
MPPT (MPP tracker) – Each inverter contains one or more MPP trackers. The display shows the number of connected strings and connections as well as the panel count per tracker.
Strings – Each string is shown with its name (e.g.
1.1.1), colour, panel count, and compliance status. Click to select a string; use Shift+click to select multiple strings at once.
String nomenclature: The label follows the pattern Inverter.MPPT.String. For example, 1.1.2 means: Inverter 1, MPPT 1, String 2. This nomenclature is automatically used on the string plan and in the legend.
Toolbar
The toolbar at the top provides the following functions:
Automate design – Switches to the wizard for automated inverter design
Switch polarity of the selected strings – Reverses the polarity of selected strings (only available for strings with more than one panel)
Direction – Opens a dialog to choose the wiring direction: Horizontal or Vertical. This determines the direction in which new strings are created on the roof.
Delete selected PV panels [DEL] – Removes individual panels from a string
Delete selected strings [DEL] – Deletes entire strings
Undo / Redo – Undo (Ctrl+Z) and Redo (Ctrl+Y) for all actions
Export – Exports the string design as a DXF file
System Overview – Shows a compact overview of the entire PV system
Inverter design settings – Opens the project-specific settings for inverter design
Manage inverters and optimizers
Click Add inverter or Add optimiser at the bottom of the sidebar.
Select a product from the catalogue.
Confirm the selection – the inverter or optimizer is added to the configuration.
To edit, click the edit icon next to an existing inverter and adjust the settings.
Tip: If you edit an inverter that already exists in the library, the system displays a warning so that no unintended changes are made to the default configuration.
Compliance check and validation
Eturnity Expert automatically checks your string design for electrical correctness. The compliance status is displayed at three levels – at the inverter, the MPPT, and the individual string:
Status | Meaning |
Valid (Green) | The configuration is electrically correct and within all limits. |
Warning (Yellow) | The configuration works, but there are indications of potential issues (e.g. power ratio close to the limit). |
Error (Red) | The configuration exceeds permitted limits (e.g. maximum MPP voltage, short-circuit current). These errors must be resolved before commissioning. |
Info (Blue) | Informational notices that do not require correction. |
Manual | The design was created manually and has not been automatically validated. |
Common compliance messages relate to:
Unassigned panels – Panels that have not yet been assigned to a string
MPP voltage limits – The open-circuit voltage of a string exceeds the maximum input voltage of the inverter
Power ratio (DC/AC) – The ratio of DC input power to AC output power is outside the recommended range
Unassigned battery – A battery is configured but not correctly assigned
Tip: In the header of the sidebar, you will find a summary of all compliance messages grouped by type. Click on individual inverters, MPPTs, or strings to see the specific messages.
Part 2: String plan – Visualisation and PDF creation
Once the string design is complete, you can create the string plan – a technical document that visualises the string wiring on the roof and can be exported as a PDF.
Navigate to the string plan
In the project navigation, go to Technical plans > String plan.
The page canvas opens – the same canvas type as the roof plan, but in string mode.
Note: The string plan uses the same canvas as the roof plan. The two tools are deliberately separate to keep the interface clear and organised.
Add building or roof surface
Click Add roof and choose one of the two options:
Entire project – Shows all roof surfaces with the complete string wiring in a bird's-eye view (north orientation).
Individual roof – Shows a specific roof surface with the strings on it (aligned to the longest edge).
As soon as a roof view is added, the strings appear automatically colour-coded – each colour corresponds to a string from the string design.
Tip: For the string plan, the Entire project option is often chosen, as all strings are visible at a glance. The creation process is completed with just two clicks: add building and activate labels.
String labels and annotations
Enable String labels in the layer settings to display the labels for individual strings on the plan. The labels use the same nomenclature as in string design:
Format:
Inverter.MPPT.String(e.g.1.1.1,1.1.2,1.2.1)The first number represents the inverter, the second the MPP tracker, and the third the string
The labels can be shown and hidden via layer visibility.
Configure the legend
The legend is generated automatically and contains the most important information about each string:
Panel type and power – Which panel is used and the rated power
String assignment with colour code – Each string with its colour, label, and associated inverter/MPPT
Panel count per string – How many panels are connected in each string
Open-circuit voltage (Voc) per string – Calculated and displayed automatically
Power per string – The total power connected to each string
Why open-circuit voltage (Voc) matters: During commissioning, the installer measures the open-circuit voltage of each string on the roof. This measured value must match the value on the string plan – this ensures that the wiring has been carried out correctly. Eturnity Expert calculates this value automatically. In CAD programs, this calculation had to be performed manually for each string and updated with every change.
Customise the legend
Show/hide sections – For the string plan, you can, for example, hide roof information and show only the panel and string data, to focus on the wiring.
Adjust font size – In the page settings, you can increase the legend font size.
Move legend – The legend can be freely positioned on the canvas.
Special case rule: If only a single roof surface is displayed on a page, but the string on it belongs to an inverter that also has strings on other roofs, the legend still shows all strings of that inverter. This prevents only part of the wiring from being shown, which would be misleading for the installer.
Control layer visibility
For each roof view on the string plan, you can specify which layers are visible:
Roof outlines (often hidden for the string plan)
Panels / Panel fields
Obstacles
String colour coding and labels
Panel index labels
Roof name labels
Compass and scale
Recommendation: For a clear string plan, hide the roof outlines and obstacles and focus on panels, strings, and the string legend. This way, the plan contains only the information relevant to the wiring.
Annotations and page design
On the page canvas, the same design tools are available as for the roof plan:
Arrows – For notes on cable penetrations or wiring routes
Frames – To highlight or separate areas
Text – For free labels and supplementary notes
Image – For external images (e.g. cross-section drawings of mounting systems)
Since the string wiring is automatically taken from the string design, fewer manual annotations are typically needed in the string plan than in the roof plan.
Title block and page settings
The title block is automatically populated with company, project, and system data and can be moved freely on the canvas. In the current version, title block fields are not directly editable; changes are made via the project settings.
Use Page settings to control:
Page format – A4, A3, A2, or custom
Orientation – Portrait or landscape
Show/hide legend
Show/hide title block
Manage multiple pages
For more complex projects, you can create multiple pages:
Add page – Each page can be configured independently.
Duplicate – Duplicate a finished page and adjust layer visibility or labels.
Rename page – Assign meaningful page titles (e.g. "String plan – Overview", "String plan – Roof South").
Delete page – Remove pages that are no longer needed.
Practical example: For larger buildings, create a first page with the entire building as an overview and further pages with individual roof surfaces for a detailed view of the string wiring.
Track layout changes
If the 3D layout or string design is changed after the string plan has been created, an Outdated notice appears. With a single click on Update, the plan is synchronised with the new data – without manual rework.
Export PDF
Click Generate PDF.
Assign a file name (e.g. "String plan – Installation team" or "String plan – Authority").
The PDF is saved in the project's file manager and can be downloaded from there.
You can create multiple PDFs with different page selections and file names – for example, one version for the installation team and one for the authority.
Note: Currently there is no way to automatically merge the roof plan, string plan, and single line diagram into a single PDF. All generated documents are saved individually in the file manager.
Frequently asked questions
Why can't I change strings directly in the string plan?
The string plan is a pure documentation tool. Changes to the string wiring – e.g. reassigning panels or creating new strings – must be made in string design (under Inverter). There, all electrical dependencies (compliance, open-circuit voltage, power ratio) are updated automatically. The string plan then adopts this data at the next update.
Why does the legend show strings that are not visible on my page?
If only a single roof surface is displayed on a page but the string visible there belongs to an inverter that also has strings on other roofs, the legend shows all strings of that inverter. This ensures that the installer gets a complete picture of the wiring and no strings are missing.
What do the compliance status indicators in string design mean?
The colours indicate the electrical validation status: Green = correct, Yellow = warning (works, but check), Red = error (must be resolved), Blue = information. Details can be found in the "Compliance check and validation" section above.
Can I change the string naming?
String naming currently follows the standard pattern Inverter.MPPT.String (e.g. 1.1.1). Customisation of the nomenclature (e.g. 1.A.1) is planned for a future version.
What should I do if the string plan does not work in the browser?
Safari has a known browser bug that prevents drawing elements on the canvas. For full functionality, please switch to Chrome, Edge, or Firefox.
Are optimizers shown on the string plan?
Displaying optimizers on the string plan is planned for a future version. Currently, optimizers can be configured in string design but do not yet appear on the string plan document.
Known limitations
No Safari support: Drawing elements on the canvas does not work in Safari (browser bug). Please use Chrome, Edge, or Firefox.
No version history: There is no automatic version management. Older versions can be archived as PDF in the file manager.
Title block not directly editable: Title block fields cannot be edited directly in the string plan. Changes are made via the project settings.
Optimizers not yet on the string plan: Optimizers are taken into account in string design but do not yet appear visually on the string plan document.
No merged master PDF: Roof plan, string plan, and single line diagram cannot be automatically merged into a single document.
String nomenclature not customisable: String naming cannot currently be changed individually.
3D projects only: String design and string plan support only projects with 3D layout.
Next steps
After creating the string plan, you can generate further technical documents for your project: