Guides

How to account for trees in a solar shading study

Published 8 October 2026. About 6 minutes to read.

Buildings stay the same size. Trees grow, lose their leaves, and let some light through. They are the objects most often modelled badly in a shading study, and the ones clients argue about most.

Winter shadows are long

A shadow's length on flat ground is the object's height divided by the tangent of the sun's altitude. At solar noon on the winter solstice, the sun's altitude is about 90° minus the latitude minus 23.4°.

• At 34° latitude (Cape Town, Sydney or Los Angeles), the noon sun is about 32.6° high. A 10 m tree casts a 15.6 m shadow.
• At 52° latitude (London, Amsterdam or Calgary), the noon sun is about 14.6° high. The same tree casts a shadow of about 38 m.

Those are noon values. Two hours either side of noon, the sun is lower still and the shadows are longer. A tree that seems far from the house can reach the roof for much of a winter's day.

Model the tree it will become

A solar system is expected to run for 20 to 25 years. A young tree near the array will be much bigger by year ten. Ask the client whether a tree will be pruned, kept or removed, and model the size you expect over the life of the system rather than the size today. If you are unsure, run both and show the difference in the report. It is a far easier conversation before installation than after.

Crowns let some light through

Unlike a wall, a tree crown is not solid. How much light passes through depends on the species, the density of the foliage and the path length of the sunlight through the crown. A low winter sun shining through the full width of a dense crown is almost completely blocked. A high summer sun passing through the edge of an open crown is not.

Deciduous trees are bare in winter, but the trunk and branches still block a noticeable share of direct light. Do not assume a deciduous tree causes no shading when the sun is lowest.

Shape matters

A conifer is narrow at the top and wide at the bottom. A spreading tree has a broad, high crown and a long bare trunk. A palm has a small crown on a tall trunk. These shapes cast very different shadows at different sun heights, so a single cylinder or sphere for every tree can over- or under-estimate shading.

Measuring trees on site

• Height: a clinometer app on a phone, or a laser rangefinder, from a known distance.
• Crown radius: pace out the crown's drip line, or measure it on satellite imagery.
• Trunk height: the height of the lowest main branches.
• Position: mark the trunk on the satellite view, not the centre of the crown, which can lean.

Trees in Lekker Sun

Lekker Sun has five tree shapes (round, columnar, conifer, spreading and palm), with crown radius, total height, trunk height and foliage density. Each ray towards the sun loses light in proportion to how far it travels through the crown, and the trunk blocks it completely. That gives a realistic estimate of partial shading from trees, rather than treating them as solid blocks.

This guide is general information to help you plan and compare options. It is not engineering, electrical or financial advice. Always follow the equipment manufacturer's instructions and your local wiring rules, and have a qualified installer check the design.