Overview of the Shading Analysis Methodology
This SolarPlus shade analysis tool performs a high-resolution, physics-based shading analysis to quantify energy loss across all PV modules in a 3D solar design. By combining site geometry, solar position algorithms, and ray-tracing methods, it evaluates the impact of surrounding obstructions (such as buildings, vegetation, or terrain) on energy production over an entire year. The analysis is driven by typical meteorological year (TMY) irradiance data and simulates thousands of sun rays per hour to determine how much direct and diffuse irradiance reaches each module.
The methodology involves three key stages: scene construction, ray casting, and translation to energy loss. These stages ensure that the output is both computationally efficient and physically accurate—providing engineers with shading loss values suitable for design decisions, feasibility assessments, and bankable performance reports with a high degree of confidence.
Scene Construction
At runtime, all surfaces—including roof geometry, obstructions, and PV modules—are converted from their map-defined positions (latitude/longitude/altitude) into a local 3D scene. Roofs are extruded to represent physical thickness and tilted using survey or design parameters. Trees and other obstructions are modeled as solid 3D forms with appropriate heights and widths and placed using real-world geolocation and panels are similarly rendered with tilt angles and orientation.
Each panel is sampled using six representative points, capturing the spatial shading variability across its surface. The 3D geometry is structured to allow rapid sun-ray intersection testing across the full site, enabling simulations to scale efficiently across hundreds or thousands of modules without compromising accuracy.
Ray Casting
For each hour of each month of the TMY data set, the tool calculates solar azimuth and altitude, then casts rays from a distant solar origin toward each panel’s sample points. A quick pre-check eliminates rays that cannot possibly intersect the scene, reducing computation without loss of precision.
Each surviving ray is tested for obstruction. If blocked before reaching the module, it is flagged as shaded. These results are compiled into three diode zones per module (with optional sub-division for half-cell layouts), enabling a nuanced estimate of performance loss due to direct shading. The diffuse component is similarly adjusted based on the worst-lit region of each module, using a conservative empirical transposition factor. This process reflects both hard shading and partial, low-angle or seasonal shading events.
Translation to Energy Loss
Unshaded POA Irradiance
The theoretical (unshaded) POA is:
POA_unshaded = DNI × f~transmittance~ + DHI~sky~ + DHI~ground~nx
Where:
DNI
is the direct normal irradiancef~transmittance~
is the angular transmittance factorDHI~sky~
andDHI~ground~
are diffuse components
Shading Adjustments (with high-resolution shading data)
If hourly shading simulations exist, the following logic is applied per module:
Beam Component (Energy-Weighted Zone Averaging):
f~shade~ = Σ (POA × zone_fraction) / Σ (POA) E~beam,shaded~ = DNI × f~transmittance~ × f~shade~ × f~selfshade~
f~shade~
is energy-weighted from the set of diode-level shading fractions.
Diffuse Component (Worst-Case Zone Dampening):
f~diffuse~ = 1 − (1 − min(f~zone~)) × DIFFUSE_TRANSPOSITION_FACTOR E~diffuse,shaded~ = (DHI~sky~ + DHI~ground~) × f~diffuse~
This approximates loss in sky/ground irradiance due to the most shaded part of the module.
No Shading Data (Fallback Case)
If no shading simulation data exists:
f~shade~ = 1
(no beam reduction)f~diffuse~ = 1
(no diffuse reduction)
📌 Final Shaded Irradiance Used in Simulation:
POA~effective~ = E~beam,shaded~ + E~diffuse,shaded~
The resulting shaded POA is then passed into the core performance engine, which applies module-specific electrical models—including temperature-corrected IV curves, tolerances, and degradation factors—to estimate actual current and voltage. Aggregation methods (minimum, average, or diode-based power) are used to compute string output under partial shading conditions.
Because irradiance and shading are evaluated hour-by-hour using real solar geometry and obstruction profiles, the resulting loss factors are highly representative of expected system performance. This gives high confidence that the model captures critical edge cases (e.g., low winter sun, tree proximity, inter-row shading) and provides realistic, defensible annual yield estimates—while maintaining sub-minute run times even for large commercial systems.
Half-Cut Cell Simulation Logic in Shading Analysis
Modern photovoltaic modules often use half-cut cell technology, where each bypass-diode zone (typically three per module) is physically split into two halves — effectively creating six electrical substrings. This architecture reduces resistive losses and improves performance under partial shading conditions.
In the shading simulation, each module is represented by six spatially distributed sample points. These points are classified into three diode zones (zones 0–2) based on their long-axis position, and—if half-cut mode is enabled—each zone is further divided into upper and lower halves. This split enables the simulation to differentiate whether shading impacts just the top or bottom portion of a diode zone, which is critical for capturing realistic behavior in half-cut designs.
Diode Fraction Computation
For each zone:
If half-cut is off: the zone’s output is determined by the ratio of lit to total points in that zone.
If half-cut is on: the output of each diode zone is computed as the average of the lit fractions of its upper and lower halves. This simulates the fact that power can still flow through one half of a zone even if the other is shaded.
This approach results in smoother, more forgiving shading behavior, especially for string currents. For example, a shadow grazing just the bottom half of a panel would cause less performance drop in a half-cut module than in a full-cell equivalent, aligning with manufacturer data and field measurements.
Interpreting the shade analysis table:
The shade analysis table displays the results of the ray tracing analysis of the 3D scene and shows monthly-hourly results as percentage solar access values.
Note these are not the solar production derating values but instead represent the overall average solar access across all modules on all orientations to give a generalised view of the shading effect.
When relating this to the final shading derating value, note that a significant shading effect early and late in the day is bring applied to a generally a lesser solar production output due to the reduced irradiance impinging on the panels are those times.
Where to view shading analysis results:
Reports > Design Review > Insights Detail template
In this report you will see the solar derating table with the solar production derating value for shading.
Below that you will see the shade derating table with monthly-hourly solar access values in a heatmap view.
Proposals
In the library proposals you will see an assumptions list including the solar shade derating value.
The following tags can be used to display shading values in your proposals:
[[shade_derating_table]] - the monthly-hourly heatmap table
[[shade_derating_perc]] - the production loss percent attributed to shading
[[pv_access_percent]] - the solar access after shaving (the opposite of the shade derating percent)
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