Irradiance Heat Mapping
Irradiance Heat Mapping is the process of visually representing how much solar energy (irradiance) reaches different surfaces of a roof, site, or terrain over time. The heat map uses color gradients—typically ranging from cool colors for low irradiance to warm colors for high irradiance—to show shading intensity, sunlight availability, and energy potential across a surface.
In solar design, irradiance heat mapping is a critical tool for identifying the most productive panel locations, optimizing azimuth and tilt, and avoiding shaded or low-yielding areas. Modern tools such as Solar Designing and Shadow Analysis compute these heat maps using 3D models, LiDAR data, obstruction profiles, and advanced sunlight simulation engines.
This method significantly improves the accuracy of solar layouts, production modeling, and financial projections by revealing the real solar resource at a granular, pixel-level resolution.
Key Takeaways
- Irradiance Heat Mapping provides a visual guide to where sunlight is strongest and weakest on a surface.
- It is essential for panel placement, shading avoidance, and energy accuracy.
- Supports performance modeling, ROI estimates, and proposal clarity.
- Used across residential, commercial, and utility-scale solar design.
- Works best alongside tools like Shadow Analysis, Auto-Design, and Solar Layout Optimization.
What Is Irradiance Heat Mapping?
Irradiance Heat Mapping is a visualization technique that shows how much sunlight different parts of a surface receive during the day, month, or entire year. It helps designers understand:
- Which areas receive consistent sunlight
- Which areas are affected by shading
- How roof geometry impacts irradiance
- How obstructions (trees, chimneys, parapets) influence output
Each pixel of the heat map assigns a value to represent irradiance levels, typically in W/m² or kWh/m² per day/month/year.
Irradiance heat mapping directly supports other concepts like
Shading Analysis, and
How Irradiance Heat Mapping Works
1. 3D Model Creation
The software builds a digital 3D representation of the roof, site, or terrain.
2. Sun Path Simulation
Uses geographic coordinates and time data to trace the sun’s movement throughout the year.
3. Shading Calculation
The model evaluates shadows cast by:
- Trees
- Buildings
- Roof structures
- Terrain features
This is closely related to Shadow Analysis.
4. Irradiance Computation
The engine calculates:
- Direct irradiance
- Diffuse irradiance
- Reflected irradiance
- Plane-of-array irradiance
5. Heat Map Rendering
A visual map is generated with color-coded irradiance ranges.
High irradiance → orange/red
Medium → yellow/green
Low → blue/purple
Types / Variants of Irradiance Heat Mapping
1. Annual Irradiance Heat Map
Shows long-term solar potential across the entire year; used for system sizing and energy modeling.
2. Monthly Heat Map
Reveals seasonal shading differences—useful for winter shading vs summer production.
3. Hourly Heat Map
Used for in-depth shading diagnostics and troubleshooting.
4. POA (Plane-of-Array) Heat Map
Simulates irradiance on tilted surfaces, tracking the true panel orientation.
See POA Irradiance.
5. Bifacial Heat Mapping
Evaluates rear-side irradiance for bifacial systems.
6. Terrain-Based Heat Mapping
Used in ground-mount and utility-scale designs to understand slope effects.
How Irradiance Is Measured
Irradiance heat maps typically measure:
Global Horizontal Irradiance (GHI)
Total sunlight on a horizontal surface.
Direct Normal Irradiance (DNI)
Sunlight hitting a surface perpendicular to the sun’s rays.
Diffuse Irradiance (DHI)
Sky-scattered light.
Plane-of-Array Irradiance (POA)
Actual sunlight received by the solar modules.
Units Used:
- W/m²
- kWh/m²/day
- kWh/m²/year
Heat maps are often the foundation for production modeling tools such as Solar Designing and Generation & Financial Tool.
Typical Values / Ranges
High Performing Roof Areas
- 900–1,200 kWh/m²/year
- South-facing, minimal shading, clean plane
Moderate Irradiance Areas
- 700–900 kWh/m²/year
- East/west facing or partial seasonal shading
Low Irradiance Areas
- 0–600 kWh/m²/year
- Heavy shading, near obstructions, north-facing planes
Ground-Mount & Utility-Scale
- Terrain influences irradiance by 3–15%
Practical Guidance for Solar Designers & Installers
1. Always review heat maps before placing panels
This ensures modules are only placed in productive areas and avoids low-yield sections.
2. Combine heat mapping with shading tools
Use Shadow Analysis for deeper insights.
3. Optimize module placement using Auto-Design
Auto-design tools can intelligently fill high-irradiance zones:
See Auto-Design.
4. Use heat maps to justify system design in proposals
Clients respond better to visual data in Solar Proposals.
5. Use heat maps to build accurate financial projections
Higher irradiance → better ROI; use the Solar ROI Calculator.
6. Avoid placing modules in deeply shaded areas
Even with module-level electronics, poor irradiance reduces yield.
7. Validate results for commercial and utility projects
Use detailed 3D models and LiDAR data for accuracy.
Real-World Examples
1. Residential Roof Analysis
A designer performs an irradiance heat map on a home with multiple dormers.
The map shows high sunlight on the main southern plane but low irradiance behind a chimney.
Panels are placed only in high-yield zones, increasing annual output by 14%.
2. Commercial Flat Roof System
A factory rooftop heat map reveals significant shading from HVAC units.
The design team adjusts walkways and array spacing to avoid shading, improving performance and reducing mismatch losses.
3. Ground-Mount Solar Farm
Heat mapping identifies low-irradiance pockets caused by terrain dips.
Rows are repositioned, improving system performance by 6–9%.
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