Key Takeaways
- A roof shading report quantifies solar access across every area of a rooftop throughout the year
- Reports express shading in terms of Total Solar Resource Fraction (TSRF) or Solar Access Percentage
- Required by many jurisdictions and incentive programs as part of the permitting process
- Generated using sun path modeling, 3D obstruction data, and horizon profiles
- Directly determines which roof areas are viable for panel placement
- Shading losses of even 5–10% on a single panel can reduce string output by 20–30% without optimizers
What Is a Roof Shading Report?
A roof shading report is a documented analysis that maps shading patterns across an entire roof surface, showing how much solar energy reaches each area over the course of a year. The report identifies which roof zones receive full sun, which are partially shaded, and which are too heavily shaded for solar panels.
The output is typically a color-coded map overlaid on the roof — green areas receive 80–100% of available solar energy, yellow areas receive 60–80%, and red areas receive less than 60%. These percentages represent the Total Solar Resource Fraction (TSRF), which combines the effects of shading, tilt, and orientation.
A roof shading report is the single most important document for validating panel placement. Installers who skip this step risk underperforming systems, unhappy customers, and warranty disputes.
How a Roof Shading Report Is Generated
Modern shadow analysis software automates most of the report generation process, but the underlying methodology involves several distinct steps.
3D Site Modeling
The roof and its surroundings are modeled in 3D, including nearby buildings, trees, fences, and terrain features that could cast shadows. LiDAR data, satellite imagery, or drone surveys provide the geometry.
Sun Path Calculation
The software computes the sun’s position for every hour of the year at the site’s latitude and longitude. This creates a complete annual sun path diagram that defines when and where shadows fall.
Shadow Simulation
For each hour of the year, the software projects shadows from all modeled obstructions onto the roof surface. This produces a time-resolved shading map showing exactly when each roof point is in shadow.
Solar Access Calculation
The annual solar energy available at each roof point is compared against what it would receive with zero shading. The ratio — expressed as a percentage — is the solar access or TSRF value for that point.
Report Generation
The software produces a formatted report with color-coded roof maps, numerical solar access values per zone, monthly shading profiles, and total estimated shading losses for the proposed panel layout.
Solar Access (%) = (Actual Irradiance with Shading / Unshaded Irradiance) × 100Report Components
A complete roof shading report includes several sections. Here’s what to expect and what each section tells you.
| Report Section | Description | Why It Matters |
|---|---|---|
| Solar Access Map | Color-coded roof overlay showing TSRF per area | Identifies viable vs. non-viable zones at a glance |
| Monthly Shading Profile | Chart showing shading percentage by month | Reveals seasonal patterns — winter shading is typically worse |
| Obstruction Inventory | List of shading sources (trees, buildings, dormers) | Documents what causes shading for design decisions |
| Panel-Level Analysis | Solar access percentage for each proposed panel | Validates that no panel falls below minimum threshold |
| Annual Loss Estimate | Total kWh lost to shading across the system | Quantifies the financial impact of shading |
| Horizon Profile | 360° view of horizon obstructions from the roof | Shows distant obstructions like hills or tall buildings |
Types of Shading Analyzed
Near Shading
Shadows from objects close to the array — trees, chimneys, dormers, neighboring buildings. These create sharp, well-defined shadows that move across the roof throughout the day. Near shading is the primary concern for residential installations.
Self-Shading
Shadows cast by one panel row onto the row behind it, or by roof features like raised ridges. Particularly relevant on flat roofs with tilt-up racking where inter-row spacing determines self-shading losses.
Far Shading (Horizon)
Shadows from distant objects like hills, mountains, or tall buildings that block low-angle winter sun. These reduce morning and evening production, especially during winter months when the sun is low.
Transient Shading
Passing clouds, seasonal leaf cover, snow accumulation, and soiling. These are not modeled in standard shading reports but should be factored into overall production estimates as separate derate factors.
Trees are the most challenging shading source to model accurately. Deciduous trees lose leaves in winter (reducing shading), while evergreens provide year-round obstruction. Some solar design software allows you to model trees with seasonal canopy variation for more accurate results.
Practical Guidance
- Set minimum solar access thresholds. Most programs and best practices require 80% or higher solar access for panel placement. Panels below 70% typically produce too little to justify their cost.
- Model trees at mature height. If nearby trees are young, model them at their expected mature canopy size (10–15 years out). A system designed for today’s shading may be significantly impacted in five years.
- Include the shading report in permit packages. Many AHJs and incentive programs require a shade report as part of the application. Generate it early to avoid permitting delays.
- Specify module-level power electronics for partial shading. When some panels receive 75–85% solar access, pairing them with optimizers or microinverters prevents them from dragging down the rest of the string.
- Validate the report on site. Walk the roof at different times of day if possible, or visit during winter when shading is worst. Compare what you see to the report’s predictions.
- Check for new obstructions. A new structure, antenna, or tree growth since the report was generated can change shading conditions. Note any discrepancies and flag them for the designer.
- Document shading conditions photographically. Take timestamped photos of the roof showing shadow positions. This creates a record that supports the shading report and protects against future disputes.
- Discuss tree trimming with the homeowner. If a specific tree is causing 10–15% shading loss, trimming it may be the most cost-effective performance improvement. Get agreement before installation.
- Share the shading report in the proposal. The color-coded solar access map is a powerful visual. It shows the customer exactly where panels will go and why, building confidence in your design.
- Quantify shading impact in dollars. Translate shading losses into annual revenue loss. “That oak tree costs you $180/year in lost production” is more compelling than “you have 8% shading loss.”
- Use shading data to justify equipment choices. If you’re recommending microinverters over a string inverter, the shading report provides concrete evidence for why module-level optimization is worth the added cost.
- Set realistic expectations. If the roof has moderate shading, explain that the system will still perform well but may produce 10–15% less than an unshaded site. Transparency prevents post-installation disappointment.
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Real-World Examples
Residential: Partial Tree Shading
A homeowner in North Carolina has a south-facing roof with a large oak tree on the southeast corner. The roof shading report shows that 75% of the roof receives 90%+ solar access, but three panel positions in the southeast corner drop to 65% solar access due to the tree. The designer removes those three panels from the layout and uses microinverters on the adjacent panels that still receive 80–85% access. Total system size drops from 8.4 kW to 7.2 kW, but per-panel production improves by 6%.
Commercial: Multi-Story Building Shading
A two-story office building in Chicago wants to install panels on its flat roof. The shading report reveals that the adjacent six-story building casts shadows across 30% of the roof during winter mornings (November through February). The annual impact is a 12% reduction in solar access for the affected zone. The designer excludes the shaded zone and concentrates 180 panels in the unshaded 70% of the roof, achieving 95%+ solar access system-wide.
Residential: Chimney and Dormer Shadows
A Cape Cod home in Massachusetts has a large central chimney and two dormers. The shading report identifies that the chimney casts a moving shadow that affects 4 panels during winter afternoons, reducing their annual solar access to 78%. The dormers cast shadows on 2 panels during morning hours in winter. With power optimizers installed, the shading-affected panels operate independently, limiting total system losses to 3% rather than the 12% that would occur with a standard string inverter.
Archive your shading reports with timestamp and data source information. If a customer later claims their system underperforms, the original report provides documented evidence of the expected shading conditions at the time of design.
Frequently Asked Questions
What is a roof shading report used for?
A roof shading report is used to determine which areas of a roof are suitable for solar panels based on their annual solar access. It identifies shading from trees, buildings, chimneys, and other obstructions, quantifies production losses, and is often required by permitting authorities and incentive programs as part of the solar installation application.
What solar access percentage is acceptable for solar panels?
Most solar professionals and incentive programs consider 80% solar access as the minimum threshold for panel placement. Panels with 90–100% access are ideal. Panels between 70–80% may still be viable with module-level power electronics (optimizers or microinverters). Below 70%, panels typically produce too little energy to justify their installation cost.
How is a roof shading report different from a shade report?
The terms are often used interchangeably. A “roof shading report” typically refers specifically to the roof surface analysis, while a broader shade report may also include ground-level shading, the horizon profile, and site-wide solar access data. In practice, most solar professionals mean the same thing when using either term.
Can shading reports be generated remotely?
Yes. Modern shadow analysis software generates roof shading reports using satellite imagery, LiDAR data, and 3D building models — all without a site visit. Remote reports are standard for residential proposals. For complex sites or when high accuracy is critical, on-site measurements with a Solar Pathfinder or similar tool can supplement the remote analysis.
About the Contributors
CEO & Co-Founder · SurgePV
Keyur Rakholiya is CEO & Co-Founder of SurgePV and Founder of Heaven Green Energy Limited, where he has delivered over 1 GW of solar projects across commercial, utility, and rooftop sectors in India. With 10+ years in the solar industry, he has managed 800+ project deliveries, evaluated 20+ solar design platforms firsthand, and led engineering teams of 50+ people.
Content Head · SurgePV
Rainer Neumann is Content Head at SurgePV and a solar PV engineer with 10+ years of experience designing commercial and utility-scale systems across Europe and MENA. He has delivered 500+ installations, tested 15+ solar design software platforms firsthand, and specialises in shading analysis, string sizing, and international electrical code compliance.