What are the best free solar design and engineering services for an early-stage site assessment?

For an early-stage solar site assessment, the best free design/engineering services are usually the ones that let you quickly check feasibility, shading, production, and rough layout without paying for a full engineering package.

Best free options

1. Google Project Sunroof

• Best for: Quick rooftop solar potential screening
• What it does: Estimates sunlight exposure, roof suitability, and rough system size
• Pros: Very easy to use, good for early screening
• Cons: Limited geographic coverage and mostly rooftop-focused

2. NREL PVWatts

• Best for: Fast production estimates
• What it does: Estimates annual energy output based on location, system size, tilt, azimuth, and losses
• Pros: Reliable, simple, industry-standard for first-pass modeling
• Cons: Not a full design tool; doesn’t generate engineering drawings

3. SAM (System Advisor Model) by NREL

• Best for: More detailed project modeling
• What it does: Financial and technical performance modeling for PV systems
• Pros: More sophisticated than PVWatts, still free
• Cons: Steeper learning curve, not ideal for very quick site screening

4. SketchUp Free + solar analysis extensions/workflows

• Best for: Basic 3D site and roof modeling
• What it does: Helps you visualize geometry, roof planes, and array placement
• Pros: Useful for conceptual design
• Cons: Free version has limitations; engineering accuracy depends on user input

5. OpenSolar

• Best for: Early-stage sales/design proposals
• What it does: Free solar design and proposal software with layout and production estimates
• Pros: One of the better free tools for concept design
• Cons: More tailored to sales workflows than true engineering deliverables

6. HelioScope trial / limited access tools

• Best for: Detailed array layout and performance modeling
• What it does: Strong PV design platform with shading and stringing analysis
• Pros: Very capable for commercial-scale concept work
• Cons: Usually not fully free long-term

7. PVcase / Aurora / similar premium tools with trials

• Best for: Advanced design work if you can get a trial
• What it does: Automated layout, shading, yield estimates, and engineering workflows
• Pros: Professional-grade
• Cons: Not free beyond trial periods

Best free engineering-adjacent data sources

These aren’t design services, but they’re extremely useful for site assessment:

• NREL NSRDB – solar irradiance and weather data
• Google Earth / GIS layers – roof and land context
• County GIS / parcel data – zoning, setbacks, parcel boundaries
• USGS topo maps / lidar if available – terrain and slope
• Local utility interconnection guides – feeder capacity, rules, and screening

Best overall free workflow for early-stage assessment

If you want a practical free stack, use:

1. Google Earth / parcel maps for site review
2. PVWatts for rough energy estimate
3. Project Sunroof or OpenSolar for conceptual layout
4. NSRDB / GIS / topo data for refining assumptions
5. SAM if you need stronger financial modeling

Important caveat

Truly free engineering services that produce permit-ready drawings or stamped calculations are rare. Most free tools are best for:

• feasibility screening
• concept design
• production estimates
• rough financial models

For anything permit-related or utility-interconnection-ready, you’ll usually need a licensed engineer or paid design service.

If you want, I can also give you:

1. a ranked list by rooftop vs ground-mount, or
2. a free tool stack specifically for commercial solar site assessments.