Site Sunlight Analysis: A Reproducible Shadow Study
Run a preliminary site solar analysis with a worked wall example. Compare summer and winter direct-sun hours, document inputs and understand model limits.
Last reviewed September 20, 2026A useful sunlight analysis connects a decision to a receiving point, measured geometry and a date. This worked study asks a narrow question: how does a wall due south change direct-sun duration at one point in London? It is a synthetic experiment, not a survey of a real property.
Open a worked example
Each link restores the stated place, moment and modeled assumptions in the studio.
Inputs for a useful comparison
Observer: 51.5080° N, 0.1281° W, Europe/London, receiver height 0 m. Model one opaque vertical screen 12 m due south, 9 m tall and 20 m wide, with its normal at 180°. No terrain, trees, other buildings or window-facing filter. Compare 21 June and 21 December 2026.
Choose the result before choosing the tool
Sun-path analysis answers where the sun is. Shadow analysis asks whether a modeled object intercepts the ray. Direct-sun duration counts unblocked time at a point. Irradiance describes incident energy per area; photovoltaic yield adds module, orientation, temperature and system behavior. Those outputs are related but not interchangeable.
- For a garden, compare receiving points and morning versus afternoon exposure.
- For a window, also specify the outward-facing bearing and receiving height.
- For a possible solar-panel position, use this study to screen obstructions, then evaluate irradiation and system performance separately.
Keep the experiment reproducible
Hold the coordinates and obstacle geometry fixed while changing the date. Use the scene links below the introduction to restore this example. The times are local noon: June uses BST, December GMT. The exposure totals integrate the entire local day, not just the selected noon instant.
To reproduce the open-point baseline, remove the wall from the restored scene. To reproduce the wall case, reopen its scene link. Save each variation with a clear name and export its field sheet before editing.
Use a site worksheet before making a decision
Record the point, time zone, date, obstacle dimensions, receiving height and where every measurement came from. Mark unknown heights as unknown. A missing imported building is not evidence of a clear sightline.
Check the predicted transitions against observations on site. If the purpose is a formal daylight report, planning submission or an energy investment, this preliminary model is not a substitute for the appropriate measured inputs and analysis.
Method and a worked example
SunCarta samples the geometric solar center every two minutes across the actual local civil day. A sample counts as direct sun only when the center is above 0° and its ray is not intercepted by the finite screen. This duration is not the conventional sunrise-to-sunset daylight duration, which uses a different solar-limb/refraction definition.
On 21 June 2026, the open point receives 984 modeled minutes (16 h 24 m); adding this wall leaves 984 minutes, so the modeled loss is zero. On 21 December, the open point receives 456 minutes (7 h 36 m), while the wall case receives 104 minutes (1 h 44 m): 52 minutes before noon and 52 after noon. The modeled loss is 352 minutes (5 h 52 m). These are sampled model outputs, not measured sunshine records.
How to interpret the comparison
The same obstacle can have almost no effect on summer direct-sun duration and a large winter effect. The wall subtends about 36.9° vertically on its centerline (arctan(9/12)); in winter the low sun is intercepted across much of its path. In summer it passes above the wall when its bearing crosses the screen. The screen is finite, so winter light can still reach the point around its edges.
Limits of the estimate
A real building has depth, a roof and multiple facades; this example uses one zero-depth vertical screen. Trees change with leaf cover. Uneven ground and the actual skyline matter. This preliminary geometry study does not calculate irradiance, photovoltaic yield, room illuminance or compliance with daylight or planning standards.
What to do next
Open both scenes, then switch to the same location and your measured geometry. Read the direct-sun windows, explore monthly sample days and export a field sheet with your assumptions. For electricity estimates, use an irradiance and PV-performance model rather than multiplying these hours by panel capacity.
Questions about this method
Is sunlight analysis the same as solar-panel analysis?
No. Direct-sun hours describe geometry at a point. Solar-panel output also depends on irradiation, orientation, temperature and system losses. SunCarta’s shading study does not estimate kWh.
Why is direct-sun duration shorter than sunrise-to-sunset daylight?
The direct-sun integrator requires the geometric solar center to be above 0°. Standard sunrise and sunset use a conventional limb/refraction definition; the two durations need not match.
Can I reproduce the numbers?
Yes. Open the June and December scenes, read the direct-sun totals and remove the wall to compare the open-point baseline. Keep the coordinates, receiving height and dates unchanged.