Understanding your seasonal shading variation
Why the same object casts such different shadows across the year
Yes, significantly. A 15 foot obstruction at 38 degrees latitude casts a shadow around 27 feet long in December but only about 4 feet long in June, since the sun sits much lower in the winter sky. This is a purely geometric effect that has nothing to do with the obstruction itself changing, only the sun's position relative to it. A NREL field study on shading obstructions modeled how a fixed obstruction's shadow position shifts throughout the year based on changing sun angle, the same geometry behind seasonal shading variation.
How a harmless summer shadow becomes a winter problem
The sun's midday elevation angle can swing by 40 degrees or more between summer and winter depending on latitude, which dramatically stretches a fixed object's shadow during the low-sun months even though the object itself never changes. A shadow that clears your array entirely in July can reach well into it by January. NOAA's Solar Calculator can trace this exact seasonal elevation swing for your specific latitude if you want the precise angle rather than a general estimate.
Why latitude changes how big this swing gets
Yes. Locations farther from the equator see a bigger swing in the sun's seasonal elevation angle, which widens the gap between a shadow's summer length and its winter length compared to locations closer to the equator. A homeowner near the Canadian border deals with a much bigger seasonal shadow swing than one in southern Florida with an identical obstruction.
Why summer-only shading checks can miss real problems
Yes. A shading assessment done only in summer can miss a significant winter shading problem, since the same obstruction that barely touches the array in June can reach much further across it in December. This is one of the more common oversights in casual, non-professional shading assessments. Check the neighboring building calculator too, since large structures often create the most dramatic seasonal swings. A proper pre-installation site assessment should account for this seasonal swing rather than checking shading on a single sunny day, which the roof inspection cost before solar estimator covers as part of a full pre-installation evaluation.
What to do with this number next
Run the general shading loss estimator for a combined estimate across your whole shading situation, or check the seasonal output calculator to see this same latitude effect applied to your total system output rather than just one shadow. The microinverter vs string inverter output tool compares what each setup would produce from the same array.