How does the tool decide when panels are shaded?

For each hour of the day it computes the sun's elevation and azimuth, then marks that hour shaded whenever the sun is lower than the obstruction's elevation angle and falls within the obstruction's angular width. Midday hours count more because the sun delivers more energy then.

Why does it use the equinox sun path?

The equinox is a fair middle-of-the-road reference: winter sun runs lower and causes more shading, summer sun runs higher and causes less. Using the equinox gives an annual-average style estimate without needing a full year of weather data.

What is the obstruction elevation angle?

It is the angle from the horizontal up to the top of the obstruction as measured from the array. A tall tree close to the panels has a high elevation angle; a distant ridge on the horizon has a low one. A Solar Pathfinder or inclinometer measures it directly.

Why enter the share of array affected separately?

A shadow that covers a quarter of the modules does not erase a quarter of all output unless wiring matches. With module-level optimizers or microinverters the loss tracks the shaded area closely, so the affected-share input lets you reflect your layout.

Is this accurate enough to design around?

It is a fast planning estimate to compare sites and obstructions, not a bankable production number. For a final design run a TMY-based simulation in tools like PVsyst or SAM and confirm with an on-site shade reading.

Solar Array Shading Loss Estimator

A single tree or chimney to the south-east can quietly erase a chunk of a solar array’s morning production. This estimator turns an obstruction’s position and size into an irradiance-weighted estimate of how much annual energy it costs, so you can judge a site before committing to a layout.

How it works

The tool samples the sun’s path across the day and tests each moment against the obstruction’s geometry:

for each daylight moment:
  elevation, azimuth = sun position (equinox, your latitude)
  shaded = sun elevation < obstruction elevation
           AND |sun azimuth − obstruction azimuth| ≤ width / 2
  weight = sin(elevation)         (clear-sky irradiance proxy)
shaded fraction = shaded weight / total weight
annual loss ≈ shaded fraction × affected array share

Weighting by the sine of solar elevation means a blocked midday hour, when the sun is strongest, costs far more than a blocked hour just after sunrise.

Example and notes

A 25° tall obstruction at azimuth 135° (south-east), 40° wide, that shadows a quarter of the array yields a few percent of annual loss because it only bites during low-sun morning hours. Move that same obstruction due south at the same height and the loss climbs sharply, because it now blocks the high-value midday sun. Remember winter losses run higher than this equinox estimate, so for heating-season-critical systems, scout obstructions on the lowest-sun day too.