Why shading is a bigger issue on commercial roofs than it looks
Flat commercial roofs look open. Large uninterrupted surfaces suggest that shading should be simple. In practice a flat roof is full of small shade sources: rooftop units, exhaust stacks, parapets, penthouses, screen walls, antennas and the modules' own rows. Because panels on a low-slope roof are usually tilted and set in rows, they can shade each other as well. The sun is low for much of the day in winter, and a small object casts a long shadow.
What satellite shading tools do
Remote shading tools combine aerial imagery with elevation or surface data and estimate shade across the roof through the year. Their strengths are real.
- Speed. They produce a result without a site visit, which is ideal for screening many buildings.
- Reach. They cover buildings that are hard to access or not yet surveyed.
- Context. They include far-field shade sources such as nearby buildings and distant trees.
Their limits come from the data underneath. Elevation data may be coarse or out of date, and small objects on the roof can be smoothed away or mislocated. Heights are inferred, not measured. If the imagery is old, new equipment and grown trees are missing, which the note on outdated satellite imagery discusses.
What on-site drone analysis adds
A drone flown over the actual roof records current conditions at high resolution, and the resulting 3D model gives object heights and positions directly. A technician on site can also confirm what an item is and how tall it really is, and can note objects the drone cannot resolve.
- Measured heights for parapets, rooftop units and stacks, instead of inferred ones.
- Correct positions for small obstructions that decide row layout.
- Current conditions, including vegetation as it stands now.
- Verification by a person who can see what the imagery cannot.
Side by side
Screening a portfolio
Use satellite shading. It is fast, it ranks buildings, and an error at this stage costs little because nobody has designed anything yet.
Setting row spacing and placing equipment
Use on-site data. Row-to-row spacing, setbacks from parapets and the position of inverters or combiners all depend on exact heights and distances. This is the decision where a small error in an obstruction height changes the layout.
Checking the final design
Run the shading analysis on the as-surveyed model, not on the screening model, so that the production assumptions in the plan correspond to the building as measured.
Far-field shade still matters
On-site capture does not make remote data obsolete. Distant trees, hills and neighboring buildings can be captured by the drone model, by site photographs and by the horizon records a technician makes. The point is not to choose one source, but to know which question each source answers well.
How to avoid disagreement between the two
When the satellite estimate and the on-site model disagree, trust the one that was measured more recently and more directly, and record why. The difference usually points to something specific: an object missing from the imagery, a height the elevation data got wrong, or a tree that has grown. Treat the discrepancy as information, not as a conflict to be averaged away.
The detail of what to capture on a flat roof is in shading and obstruction analysis on flat commercial roofs.
A practical workflow
- Screen candidate buildings with satellite shading and drop any that are clearly shaded.
- For the remaining buildings, capture obstruction heights and positions on site.
- Build the layout on the measured model and set row spacing against the measured heights.
- Run the final shading check on the same model that the plan set is drawn from.
- Record which values were measured and which were assumed.
Following this order keeps the cheap tool where it is strong and the accurate tool where accuracy decides the layout. It also leaves a clear record: anyone reviewing the design later can see which shading numbers came from a screen and which came from the building itself, and can judge how much weight each deserves.
Where Solar Survey AI fits
Our commercial on-site survey records obstructions, heights and surroundings on site, in one visit, with turnaround confirmed when we scope the job. Aerial capture and technician verification sit in the same record, so the layout and the shading assumptions in the design describe the roof that actually exists.