Professional design + production-modeling software
Aurora Solar
What it does: The dominant residential solar design platform in the US. LIDAR-based 3D roof modeling, AI-assisted obstruction detection, hourly shading simulation (8,760 hours/year), production estimates with weather-station data. Generates customer-facing proposals with savings projections.
What it tells you: If your bid was designed in Aurora, the production estimate is generally trustworthy — Aurora's shading sim is the industry gold standard. Bids show "Aurora" branding or a 3D roof view image. Ask for the Aurora design link if your installer offers one.
HelioScope (Folsom Labs / Aurora)
What it does: Engineering-grade simulation tool. Used predominantly for commercial and small utility-scale projects. Detailed component-level losses, shading, mismatch losses. Now part of Aurora Solar.
What it tells you: Almost certainly a commercial or large residential bid. Detailed engineering report typical.
OpenSolar
What it does: Free residential design + proposal platform with optional paid features. Used heavily by smaller installers who can't justify Aurora subscription. Decent shading simulation but not as detailed as Aurora.
What it tells you: Mid-tier engineering quality — better than nothing, less rigorous than Aurora. Common in independent installer shops.
Solargraf (Enphase)
What it does: Sales-focused design tool with built-in financing integration. Owned by Enphase (so its proposals tend to favor Enphase microinverter equipment).
What it tells you: Sales-process-driven proposal. The engineering rigor is acceptable but not as deep as Aurora; the financing/savings side is well-developed.
PVcase Roof / PVcase Ground (Esdec)
What it does: AutoCAD-based solar design for commercial rooftop and ground-mount projects.
PVsyst
What it does: The international gold standard for simulation. Component-level losses, mismatch, soiling, snow, temperature derating. Used predominantly for commercial and utility-scale due to complexity.
Free / open-source production tools
NREL PVWatts
What it does: National Renewable Energy Laboratory's free hourly production calculator. Default reference for "what should this system produce?" Type your address, system size, tilt, azimuth → get annual kWh estimate. Doesn't model shading well — that's a separate calculation.
How to use it: Run your installer's bid through PVWatts yourself. If the installer's annual kWh is more than 10% above PVWatts, ask them to justify it with shading data and equipment-specific losses. If it's more than 5% below, the installer is being conservative (good for buyer protection).
Google Project Sunroof
What it does: Uses Google's aerial imagery + LIDAR to estimate your roof's solar potential. Decent first-pass for "is my roof good for solar?" but not a substitute for an actual site visit.
NREL System Advisor Model (SAM)
What it does: NREL's flagship desktop simulation tool. Hourly modeling with detailed financial analysis (loan, lease, PPA, cash). Used by analysts and serious DIY-modelers.
Shading-analysis instruments
Solar Pathfinder
What it does: Optical instrument that maps obstructions (trees, chimneys, neighbors' roofs) onto a sun-path chart. The classic "is this spot shaded?" tool. Reading from the Pathfinder feeds into shade-loss calculations.
Solmetric SunEye
What it does: Digital camera-based shade measurement. Captures fish-eye images, overlays sun-paths, computes solar access percentage by month. The professional successor to the physical Pathfinder.
HORIZON / Suncalc apps
What it does: Sun-path visualization for any address + date. Useful for back-of-envelope shading checks and seasonal modeling. Not a replacement for installer's shading instrument.
Permit-package tools (used by installers + DIY)
GreenLancer
What it does: Outsourced permit design + stamping for solar projects. Many small installers use GreenLancer to generate the AHJ (Authority Having Jurisdiction) permit package.
SolarAPP+
What it does: NREL-developed automated permitting platform adopted by 100+ jurisdictions. Same-day approval for compliant residential PV. Speeds up the install timeline significantly where adopted.
Commercial / utility-scale tools
Beyond residential: enterprise-grade tools used for commercial 100kW+ and utility-scale projects:
- PVsyst — international standard simulation (covered above).
- PVcase — AutoCAD-integrated commercial design.
- RatedPower — utility-scale plant design.
- Folsom Labs (HelioScope, now Aurora) — commercial production sim.
- SAM — NREL desktop financial modeling.
What to ask your installer about design
- "Which design tool produced this proposal?" Aurora, HelioScope, OpenSolar, Solargraf, or in-house spreadsheet? The answer tells you the engineering depth.
- "Did you do a real shading analysis?" Either (a) Aurora's LIDAR-based 8760 sim, (b) Solar Pathfinder / SunEye reading on site, or (c) physical site walk with photos. "We just used Google Earth" is not enough for a 25-year investment.
- "What's your annual kWh estimate vs PVWatts at my address?" Ask them to run PVWatts. A bid that runs 10%+ above PVWatts without shading justification is suspect.
- "What weather data are you using?" PVWatts uses NSRDB (National Solar Radiation Database). Aurora and PVsyst use TMY3 typical-meteorological-year data. Both are reasonable.
- "Did you account for snow, soiling, and temperature losses?" Annual derate is typically 10–14% from STC nameplate. Bids that show 90%+ of nameplate are usually missing real-world losses.
For DIY homeowners
If you want to run the production math yourself before getting installer quotes:
- NREL PVWatts — type your address, system size, tilt, azimuth. Default to mid-range losses (14% combined).
- Google Project Sunroof — quick first-pass roof potential.
- Suncalc.org — visualize sun paths for your address across seasons.
- NREL SAM if you're comfortable with desktop tools and want detailed financial modeling.
Then compare your numbers to whatever installers quote — if they're wildly different, ask why.
Frequently asked questions
Can I see my installer's Aurora design?
Aurora generates a public-facing customer link for each project. Many installers share this proactively; if yours doesn't, ask. The link gives you the 3D roof view, panel layout, and production simulation.
What's a good production estimate vs PVWatts?
Within ±5% of PVWatts is typical for unshaded south-facing roofs. ±10% for moderately shaded or non-ideal orientations. More than ±10% deviation needs explanation — either the installer modeled additional losses or they're using a non-standard loss assumption.
Why do two installers quote different production for the same address?
Differences in shading sim, panel-degradation assumption, soiling loss, temperature coefficient, weather data source, and clipping assumptions all stack up to 5–15% production-estimate variance for the same system on the same roof. The most-rigorous bid (typically Aurora-designed) is usually within a few percent of reality. Outliers in either direction warrant a follow-up question.