Answer
Solar shade analysis assesses how obstructions affect the sunlight available to a proposed PV array. On-site observations, horizon images and three-dimensional models can supply different evidence. Solar Access, TOF and TSRF describe resource conditions; annual electrical production requires additional modeling. Choose a method by the decision, site-data gaps and required review, rather than a generic accuracy ranking.
A shade assessment should tell the designer what evidence was collected, what result was calculated and which decision that result supports. A realistic shadow map can help with placement. A resource report can describe access to sunlight. Neither alone proves the annual electrical output or satisfies every project’s approval requirements.
This guide compares assessment approaches and explains how to read their evidence. For the broader sequence of checks, see the shading-analysis design workflow.
What Does Solar Shade Analysis Measure?
Start with the report’s actual definition, period, analyzed surface and reference condition. “Shading loss” may refer to a geometric obstruction, reduced irradiance or an electrical-model result. Those quantities should not be exchanged without checking their basis.
Solmetric’s orientation application note explains these resource metrics for its documented SunEye method:
| Metric | Meaning to check in the report |
|---|---|
| Solar Access | Access to solar resource after shade, using the stated surface and method |
| Tilt and Orientation Factor, TOF | Insolation at the actual orientation relative to the method’s optimum, excluding shade |
| Total Solar Resource Fraction, TSRF | Resource available with shade and actual orientation relative to an unshaded optimum |
For that basis, TSRF combines Solar Access and TOF. If both inputs are percentages:
TSRF (%) = Solar Access (%) × TOF (%) / 100
For an illustrative Solar Access of 92% and TOF of 96%, the result is 88.32% TSRF. These are assumed inputs demonstrating the formula, not a site measurement or incentive decision. Check the software’s reference orientation and weather basis before comparing reports from different methods.
Annual resource is not the average of monthly percentages
Solmetric explicitly explains that annual Solar Access weights the monthly results by insolation. Simply averaging the percentages can give the wrong answer.
For a hypothetical two-period example, assume unshaded resource of 100 kWh/m² and 300 kWh/m², with Solar Access of 50% and 100%, respectively. Accessible resource is 50 + 300 = 350 kWh/m², compared with 400 kWh/m² without shade. The combined fraction is 87.5%, while the simple percentage average is 75%. This is an arithmetic illustration, not an annual weather dataset.
See how to read a solar shade report for the detailed report review.
Six Assessment Approaches to Compare
These categories overlap. Imagery, LiDAR or a drone survey can supply geometry to the same model; a model can also use field observations. They are not six mutually exclusive packages with a universal accuracy hierarchy.
| Approach | Evidence or task | Main review question |
|---|---|---|
| Sun-path chart and observed horizon | Screening obstruction directions against solar paths | Does the chart and observed viewpoint represent the site? |
| Reflective-dome instrument | A local obstruction view over a sun-path diagram | Was the setup correct and were relevant positions sampled? |
| Digital horizon photograph | A retained image of obstructions at a stated location | Are orientation, position and interpretation documented? |
| 3D scene and shading model | Roof, array and obstruction geometry evaluated at sun positions | Which geometry and irradiance/electrical effects are represented? |
| Remote imagery and elevation data | Source information for constructing the site model | What are the capture date, coverage and missing objects? |
| Drone-derived reconstruction | Additional site imagery or geometry for a model | What evidence establishes the survey’s suitability for this decision? |
On-site instruments and images
The Solar Pathfinder manufacturer’s manual describes a reflective dome, latitude-specific sun-path diagrams and a retained tracing of the observed obstruction view. Correct orientation, leveling and viewpoint matter. Its method is not an annual production meter.
A reading or photograph represents its observation position. An array spread across several planes or beside close obstructions may require additional positions to represent changing views. Record where the data was collected rather than assigning one sample to every module without explanation.
3D modeling and remote geometry
A model can represent modules and obstructions, calculate sun positions and derive shading factors. SAM’s shading documentation provides a concrete example of beam and diffuse inputs and a 3D shade calculator. Those are documented SAM functions, not implied capabilities of every platform.
Remote images, elevation datasets and drone reconstructions are inputs to the scene. Their value depends on which required objects they capture. A detailed roof model can still omit a nearby tree or recent addition. A clearer image does not by itself establish height accuracy, current vegetation or complete coverage.
Ask the provider to identify observation dates, control or comparison evidence, object assumptions and unresolved geometry. A survey’s positional accuracy and an energy estimate’s uncertainty are different quantities. Do not translate one into the other with a generic percentage.
From a Shadow to an Electrical Energy Estimate
A useful assessment preserves the steps between the scene and production:
- Identify the geometry. Record the site, surfaces, module positions and obstruction evidence.
- Define solar and weather inputs. Preserve coordinates, time convention, weather source and modeling period.
- Define irradiance treatment. Explain which components and shading factors enter the model.
- Represent the electrical case. Identify modules, internal layout where relevant, string/MPPT assignments and equipment limits.
- Review the integrated output. State which annual or monthly result was produced and its limitations.
Sandia’s plane-of-array guidance distinguishes beam, sky-diffuse and ground-reflected contributions. A visible direct shadow is not an explanation of every component.
NREL’s partial-shading research distinguishes irradiance loss from electrical mismatch. Module-level electronics can mitigate some mismatch, but the benefit depends on the system’s layout and topology. They cannot supply sunlight blocked by an obstruction. For the physics, see how shading affects solar panels.
Do not assume that all tools use the same time step, diffuse treatment or partial-shading model. For example, SAM documents different electrical-shading support for different input-table types. Read the chosen method’s limitations before interpreting a geometric factor as electrical loss.
What Does Validation Evidence Actually Establish?
Ask four questions about any accuracy claim:
- What quantity was tested? Solar Access, geometry, irradiance or electrical production?
- What was the reference? A field instrument, survey, modeled case or production meter?
- What was the sample? Which locations, sites, source data and configurations?
- What was the statistical result? Mean agreement, distribution, tolerance or a bound for individual readings?
A documented historical example
NREL’s December 2015 Aurora evaluation compared annual Solar Access estimates at 81 roof locations across eight houses in Los Angeles and Denver with averaged readings from two Solmetric SunEye devices. It reported statistical equivalence within ±5 Solar Access values for the studied locations and ±3 in the Denver group where LiDAR was available.
That is a historical comparison of a resource metric with field-device readings. The statistical test examined confidence intervals of mean differences. It is not a guarantee that every reading is within those values, a validation of every current software version, or proof of ±3% annual electrical production accuracy.
Use a vendor or research result only within its tested scope. A study of one tool does not certify another tool, and a validation study does not make missing site evidence disappear. No generic cost, turnaround time or accuracy ranking is established here for the six approaches.
Choose Evidence for the Decision
| Decision | Evidence to establish before relying on the result |
|---|---|
| Early screening | Source coverage, approximate constraints and explicit unresolved site inputs |
| Layout comparison | Comparable scene, weather and equipment assumptions; declared design changes |
| Proposal production estimate | Reviewed geometry and electrical case linked to the model output |
| Program or financing submission | Exact current requirements and accepted metric/method from the relevant reviewer |
| Site change or final handover | Updated evidence and review of affected model outputs |
Additional field evidence is useful when it resolves a material unknown. That may involve obstruction dimensions, roof geometry or a vegetation condition absent from the remote data. Do not require or reject a drone survey solely because a roof crosses an arbitrary tree-distance or accuracy threshold.
For an incentive or lender submission, obtain the current written requirements. Record the administrator, document version, accepted method, required metric, aggregation and any conditions. Program rules differ and change. This page does not reuse a historical threshold or approved-tool list as a current universal rule.
Likewise, there is no universally “good” TSRF that proves financial viability. Economics also depend on installed capacity, modeled electrical production, costs, consumption and the actual tariff or contract.
Keep the Shade Report Connected to the Design
Compare feasible module placements and electrical configurations using a declared basis. If a layout change adds or removes modules, show capacity as well as total energy. Preserve unresolved objects as assumptions, then review affected results when new evidence arrives.
Before exporting a report, check that the scene, module positions, electrical configuration and production case belong to the same reviewed revision. Prevent duplicate application of loss factors and explain limitations in the customer-facing result. The shading-analysis mistakes checklist provides practical correction checks.
Evaluate a Shade-Assessment Workflow
Bring a representative site and the evidence requirements above. Ask which available inputs, analysis outputs and exports support your project and how their limits are documented.
Book a DemoUse the SurgePV shadow-analysis page to begin that product evaluation.
Frequently Asked Questions
What is solar shade analysis?
It assesses how obstructions affect the sunlight available to the array. Its outputs can support layout and production modeling, but a shadow image or resource percentage alone does not establish annual electrical production.
How accurate is solar shade analysis?
Accuracy must name the measured quantity, reference method, sample and conditions. Agreement in annual Solar Access is not the same as agreement with metered electrical production. No universal error percentage for every tool, site or method is established here.
Is remote analysis equivalent to an on-site survey?
A documented remote method can be compared with on-site readings for specified conditions. That does not establish equivalence for every roof or unresolved obstruction. Check source dates, geometry, observation positions and the validation study before deciding whether additional field evidence is needed.
What is a good TSRF for solar?
There is no universal acceptance threshold. Check the exact program, lender or project specification, including the metric definition and aggregation method. A resource threshold does not by itself establish project economics or approved electrical design.
Do microinverters or optimizers increase Solar Access?
They can change electrical mismatch behavior, but they do not remove an obstruction or restore blocked sunlight. Assess their contribution through an electrically compatible production model rather than substituting an assumed improvement into the resource metric.
Sources
Primary research and reference material used for this desk-research article.
Where this fits
This article is part of SurgePV's Solar Design hub, which works through the topic from first principles to the decisions a project team actually has to make.
