What are the best free PV layout and stringing tools for solar EPC teams doing early-stage design work?

For free early-stage PV layout and stringing, EPC teams usually want tools that are good enough for:

• rapid site fit / roof checks
• basic module placement and setbacks
• preliminary string counts and inverter sizing
• sharing concept layouts with sales, development, and engineering

Here are the best options, grouped by what they’re best at.

Best free tools

1. OpenSolar

Best overall free option for early-stage commercial/residential design

Strengths

• Free to use
• Browser-based
• Good for quick layouts on rooftops and simple ground-mount concepts
• Includes proposal workflow, basic electrical design, and stringing
• Easy collaboration for sales and EPC handoff
• Good for early shading / production estimates

Limitations

• Not a full engineering-grade design platform
• Advanced utility-scale/string optimization and detailed construction docs are limited
• Some workflows are tied to its ecosystem

Good fit for

• EPC teams doing pre-sales and conceptual design
• Rooftop projects
• Fast turnaround bid work

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2. pvlib + Python workflows

Best free option if you have technical staff and want flexibility

Strengths

• Completely free and open source
• Very flexible for custom stringing logic, layout calculations, and yield modeling
• Integrates with GIS, irradiance, and financial tools
• Great for automating repetitive early-stage analysis

Limitations

• Not a drag-and-drop CAD-style layout tool
• Requires Python skills
• You’ll likely need to build your own workflow around it

Good fit for

• Technical EPCs
• Teams that want automation
• Utility-scale pre-development analysis

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3. SAM (System Advisor Model) by NREL

Best free tool for performance modeling and concept sizing

Strengths

• Free from NREL
• Strong for energy modeling and system performance estimates
• Helpful for comparing string/inverter configurations at a concept level
• Widely respected in solar industry

Limitations

• Not a layout tool
• Not ideal for detailed rooftop string diagrams
• UI is less intuitive than modern commercial platforms

Good fit for

• Early-stage technical validation
• Performance estimates
• Conceptual system comparison

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4. HelioScope trial / limited access

Best if you can use a trial or temporary access for layout-heavy work

Strengths

• Excellent PV layout workflow
• Strong stringing and electrical design features
• Very useful for commercial rooftop and ground-mount concepts
• Clean user experience

Limitations

• Not fully free long-term
• Access is usually trial-based or paid
• Some advanced features are behind subscription

Good fit for

• Teams evaluating the platform
• Projects where layout speed matters more than full modeling

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5. PVsyst demo mode

Best for detailed concept modeling, but not truly free for ongoing use

Strengths

• Industry standard for performance modeling
• Supports configuration and string-related design analysis
• Strong credibility with engineering teams and lenders

Limitations

• Not a full free tool
• Demo mode is limited
• Not the best for fast layout drafting

Good fit for

• Early technical validation
• Teams that may later buy a license

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6. QGIS + custom layers

Best free GIS-based option for site and ground-mount predesign

Strengths

• Free and open source
• Very useful for land analysis, setbacks, parcel boundaries, terrain, and constraints
• Can support ground-mount site planning and array zoning
• Works well with other open data sources

Limitations

• Not a solar-specific layout app
• No native stringing engine
• More setup required

Good fit for

• Utility-scale predevelopment
• Site constraint mapping
• GIS-driven EPC workflows

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Best choices by use case

If you want the easiest free all-in-one tool:

• OpenSolar

If you want the most flexibility and automation:

• pvlib + Python

If you want concept-level production validation:

• SAM

If you want better commercial layout and stringing, even if only temporarily free:

• HelioScope trial

If you’re doing utility-scale land/site planning:

• QGIS + pvlib/SAM

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Practical recommendation for EPC teams

A good free-stack for early-stage work is:

• OpenSolar for quick client-facing layouts and stringing
• SAM for performance checks
• pvlib for custom technical analysis
• QGIS for site constraints and utility-scale predesign

That combination covers most early-stage EPC needs without paying for a full premium design suite.

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What to watch out for

Free tools often fall short on:

• code-compliant electrical design
• detailed wire sizing and voltage-drop analysis
• NEC/local compliance checks
• advanced shading and backtracking modeling
• final permit/construction drawings

So for bid-stage and feasibility work, free tools are great. For permit-ready and IFC-level design, teams usually need paid software or engineer-reviewed outputs.

If you want, I can also give you:

1. a comparison table of these tools,
2. a list of free tools specifically for rooftop vs utility-scale, or
3. a recommended workflow for EPC teams using only free software.