Three solar design tools dominate the US solar industry: Helioscope, Aurora Solar, and PVWatts. Each serves different purposes, different user profiles, and different points in the solar sales and design workflow. Solar EPCs, installers, and design teams typically use at least two of these tools, and understanding when to use each one determines both design quality and workflow efficiency. This guide compares the three tools across features, cost, workflow integration, and use cases, and walks through how they fit into the modern US solar design workflow.
The three tools at a glance
PVWatts
PVWatts is a free web-based solar production estimator developed and maintained by the National Renewable Energy Laboratory (NREL). It takes basic system inputs (location, system size, tilt, azimuth, and system loss parameters) and produces estimated annual and monthly solar energy production for the specified location using NREL’s meteorological and irradiance datasets.
PVWatts is best for: quick production estimates, order-of-magnitude sizing checks, academic and educational use, initial customer conversations, and preliminary feasibility.
Helioscope
Helioscope is a commercial solar design and simulation tool developed by Aurora Solar (which acquired the earlier Folsom Labs product). It supports detailed shading analysis, 3D site modeling, string design, inverter and module database selection, and detailed production modeling. Helioscope is widely used across US commercial and utility-scale solar for detailed engineering-quality production analysis.
Helioscope is best for: detailed shading analysis on commercial and complex projects, string design and inverter selection, financial modeling that requires production accuracy, and bankable projects that need documented modeling for lenders.
Aurora Solar
Aurora Solar (the platform, from the company that also owns Helioscope) is a comprehensive residential and small commercial solar design platform. It combines site modeling, LiDAR-based shading analysis, permit-ready plan set generation, customer proposal generation, and workflow tools for solar installers. Aurora is designed as an end-to-end platform for residential solar workflows.
Aurora is best for: residential solar sales and design workflow, permit-ready plan set generation, customer proposals with visualizations, and installer companies wanting an all-in-one platform.
Feature comparison summary
| Feature | PVWatts | Helioscope | Aurora Solar |
|---|---|---|---|
| Cost | Free | Paid subscription | Paid subscription |
| 3D site modeling | No | Yes (detailed) | Yes (with LiDAR) |
| Shading analysis | Simple | Detailed (object-based) | Detailed (LiDAR-based) |
| String design | No | Yes | Yes |
| Production simulation | Simple annual/monthly | Detailed 8760-hour | Detailed 8760-hour |
| Permit-ready outputs | No | Documentation reports | Full plan set generation |
| Customer proposals | No | Basic | Comprehensive |
| Primary users | Educational, initial estimates | Commercial and utility EPCs | Residential installers |
When to use each tool
Use PVWatts for:
- Quick production estimate for a customer conversation
- Sanity-checking a Helioscope or Aurora production number
- Order-of-magnitude sizing before starting detailed design
- Academic, research, or educational contexts
- Systems where detailed shading analysis is not needed
Use Helioscope for:
- Commercial rooftop solar with complex shading (adjacent buildings, HVAC equipment, parapets)
- Utility-scale ground-mount with terrain and shading complexity
- Community solar projects requiring detailed production modeling for financial models
- Bankable projects where lenders require documented production analysis
- Detailed string design and inverter selection for commercial and larger residential
- Projects where you need to model multiple design scenarios quickly
Use Aurora Solar for:
- Residential solar sales and design workflow
- Generating permit-ready plan sets integrated with sales proposals
- LiDAR-based shading analysis for accurate residential production modeling
- Customer-facing proposals with visualizations and financial analysis
- Residential installer companies wanting an integrated sales-to-permit workflow
Workflow integration between the tools
In practice, solar EPCs and installers often use multiple tools in sequence:
- Initial customer contact: PVWatts or Aurora quick estimate to give an order-of-magnitude production number
- Detailed design and proposal: Aurora for residential, Helioscope for commercial
- Financial modeling: Helioscope’s detailed 8760-hour production output feeds financial models for larger projects
- Permit plan set: Aurora directly generates plan sets for residential; commercial typically requires additional AutoCAD or similar for detailed electrical and structural drawings beyond what Aurora or Helioscope produces
- Bankable documentation: Helioscope reports for lender packages on commercial and utility-scale
What none of these tools do well
Understanding tool limitations helps design teams choose appropriate workflow tools:
- None generate complete NEC-compliant electrical plan sets with detailed SLDs, conductor schedules, and equipment specifications ready for AHJ submission, these still require AutoCAD or equivalent CAD-based workflow
- None replace structural analysis using STAAD.Pro, ETABS, or equivalent for commercial and utility-scale racking and roof structural design
- None replace PE stamping workflow, a PE still reviews and stamps
- None automate utility interconnection paperwork completely, though some integrate with specific utility systems
Cost considerations
PVWatts is free. Helioscope and Aurora are paid subscription products with pricing tiers based on user count, feature access, and project volume. Pricing changes periodically; check current pricing directly with Aurora Solar (which owns both platforms). Solar EPCs evaluating tool investment should consider total workflow cost, not just software cost, the time saved on detailed design work often justifies the subscription cost even for small installers.
Where outsourced solar design fits into the tool landscape
Outsourced solar design teams typically maintain expertise across all three tools plus AutoCAD, structural analysis software, and electrical calculation tools. This allows the outsourced team to receive design inputs in whatever format the client uses (Helioscope model, Aurora sales proposal, or PVWatts estimate) and deliver AHJ-ready plan sets in the client’s preferred template.
RIH Engineering provides outsourced solar PV design using Helioscope, Aurora Solar, AutoCAD, and adjacent tools. Our team receives design inputs from client Helioscope or Aurora models and delivers permit-ready plan sets, single-line diagrams, structural calculations, and interconnection documentation to your standards. If you want to talk through how outsourced design fits your Helioscope or Aurora workflow, get in touch.
Frequently asked questions
What is PVWatts and when should I use it?
PVWatts is a free web-based solar production estimator developed by NREL. Given basic system inputs (location, size, tilt, azimuth, loss factors), it produces estimated annual and monthly solar energy production using NREL's meteorological datasets. Best for quick production estimates, sanity-checking, order-of-magnitude sizing, and educational contexts. Not suitable for detailed shading analysis or bankable production documentation.
What is Helioscope and how does it differ from Aurora Solar?
Helioscope is a commercial solar design and simulation tool focused on detailed shading analysis, string design, and production modeling for commercial and utility-scale projects. Aurora Solar is a comprehensive residential and small commercial platform combining design, LiDAR-based shading, permit plan sets, and customer proposals. Both are owned by Aurora Solar (the company). Helioscope targets commercial EPCs; Aurora targets residential installers.
Can Helioscope or Aurora generate complete AHJ-ready permit plan sets?
Aurora Solar generates permit-ready plan sets suitable for residential and small commercial submissions in many US jurisdictions. Helioscope produces documentation and reports rather than complete plan sets. Both may need to be supplemented with AutoCAD or equivalent CAD-based workflow for detailed electrical and structural drawings on larger commercial projects, and PE stamping remains a separate workflow.
How much do Helioscope and Aurora Solar cost?
Both are paid subscription products with pricing tiers based on user count, feature access, and project volume. Pricing changes periodically. Check current pricing directly with Aurora Solar (which owns both platforms). Solar EPCs evaluating tool investment should consider total workflow cost including time saved on detailed design work.
Should solar EPCs use one tool or multiple?
In practice, most solar EPCs use multiple tools in sequence. PVWatts for initial estimates and sanity checks. Aurora for residential design and permit plan sets. Helioscope for commercial and utility-scale detailed shading and production modeling. AutoCAD or equivalent for detailed electrical and structural drawings on commercial. The specific combination depends on project mix and workflow.