What Is the Shading Factor?
The shading factor measures how much sunlight is blocked by nearby obstacles at a given point on a roof or panel, directly impacting your solar panels' energy output. A lower shading factor means more sunlight reaches your panels, maximizing energy production.
For example, if a tree or building blocks 20% of the sunlight at a given point, the shading factor at that location is 20%. The goal is to minimize this value to optimize system performance.
Shading Factor vs. Shading Loss
It's important to distinguish between the shading factor and shading loss:
Shading factor is the fraction of irradiation blocked before sunlight is converted into energy.
Shading loss refers to the actual electricity loss due to shading after sunlight has been converted into energy.
While these values are often treated as linearly connected for simplification, real-world shading losses may vary. Factors such as partial shading of strings and the use of optimizers can influence shading losses beyond what the shading factor alone suggests. In Expert, we use a straightforward linear approach to keep calculations clear, predictable, and easy to integrate into the project simulation.
Where You'll See the Shading Factor
The shading factor is calculated as part of the Shading analysis in the 3D Panel Layout. Once enabled, it is visualized in two ways:
Heatmap: A color-coded shading factor overlay on every roof you've drawn, making it easy to spot the areas with the most and least sun exposure.
Per-panel values: In the 2D view, each panel is colored and labeled based on its own annual shading factor, so you can compare panels directly against each other.
Note: Panel-level shading factor values are only meaningful for comparing panels on the same roof — don't compare shading factor values across different roofs of a project.
To check the shading factor at any single point without placing panels there, use the Shading factor selector: click the button, then click on the roof to read the exact value at that spot.
The shading factor calculated here automatically feeds into the PV > Shading / snow losses page, where it is combined with snow losses into your project's energy simulation. You can leave this on automatic — so it recalculates whenever you move panels or edit the roof — or switch to manual and enter monthly values yourself.
How Is the Shading Factor Calculated?
Shading factor calculation involves three key steps:
Data collection: The system gathers details about buildings and obstacles you've modeled, while horizon data and direct, diffuse, and reflected irradiation come from PVGIS — a trusted solar data source developed by the European Commission's Joint Research Centre, ensuring accuracy based on decades of validated satellite and ground measurements.
Point-by-point calculation: The software calculates the shading factor for each point on the roof, then aggregates it per panel.
Visualization: These outputs drive the shading heatmap and per-panel values described above.
A couple of things worth knowing about how the calculation behaves:
Moving panels, resizing panel fields, or editing the roof updates the shading factor automatically and in real time — no need to re-run anything manually.
Panels themselves are not treated as obstacles for each other in the calculation, so on a flat roof without surrounding obstacles, panels won't show shading purely from being close together.