Trees, Chimneys and Solar Panels: What a Shade Assessment Should Show

A tree beside the house does not automatically rule out solar. A roof that looks clear at lunchtime does not automatically make a good design either. I want to know where the shadow falls, when it arrives and which panels it affects.

Before paying extra for a particular inverter or panel, ask for a shade assessment that explains the layout. The useful result is a design decision you can follow, with the assumptions written down.

This is especially relevant to established Melbourne homes with mature gardens, neighbouring buildings and chimneys. Start with the roof, then choose the equipment. Our solar overview explains the wider planning process.

Ask for more than one sunny roof photograph

Shade changes with the position of the sun and the season. Trees and buildings also differ in height and distance from the roof. A single aerial image cannot show that whole pattern.

The Australian Government’s solar design guide explains why timing, obstructions and future tree growth belong in the assessment.

I would ask the designer to identify the obstructions on the actual roof plan. A chimney, neighbouring extension and tree canopy should be recognisable, rather than disappearing beneath a neat rectangle of proposed panels.

Then compare morning, midday and afternoon across the year. Ask which roof sections stay useful through winter, and whether the proposed layout relies on pruning that has not been agreed or may not be permitted.

Photos taken safely from the ground can help explain a concern. They supplement the assessment; they are not a reason to climb onto the roof or measure electrical equipment yourself.

Make the assumptions visible

A shade map is a model. Its usefulness depends on the roof dimensions, obstruction heights and other information behind it. I would want the proposal to say what was measured on site and what came from mapping data.

SunSPOT’s guidance distinguishes detailed mapping from user-entered shade assumptions. That is a useful reminder to ask where any estimate gets its inputs.

Ask to see the expected effect on generation by month or roof section, where the design tool provides it. An annual total can hide a weak period that matters to your household’s electricity use.

Keep weather assumptions, system size and other losses consistent when comparing layouts. Otherwise, a difference attributed to shade may partly come from changing something else in the calculation.

Understand what the string layout changes

A string is a connected group of panels. With a string inverter, I would ask which panels are grouped together and why. Similar sun and shade conditions are a useful starting point, alongside the equipment’s design limits.

That does not mean one shaded panel simply switches off an entire roof. Shade behaviour depends on the panel, how the shadow crosses it, and the electrical configuration. A blanket claim is not a substitute for a design.

The government’s inverter guide explains strings, microinverters and optimisers.

Our plain-English inverter explainer adds context.

Have the designer show the proposed groups on the roof plan. You do not need to become an electrician to ask why panels with different conditions have been combined, or whether another layout would reduce that compromise.

When panel-level electronics deserve a look

Microinverters work at individual panels. Power optimisers manage panels individually within a compatible inverter system. Both can help with some uneven shading and complicated roof layouts, but neither creates missing sunlight.

For a roof with persistent shade across most of the useful area, paying more for electronics may still leave a disappointing result. I would first compare a smaller array in better light, another roof section, and the proposed full layout.

For a mostly clear roof with a small moving shadow, compare the estimated extra generation with the extra installed cost. Include monitoring, equipment access and who handles future service work in that discussion.

Panel-level monitoring can help locate a weak part of an array. It does not, by itself, prove whether the cause is shade, dirt or a fault. The pattern still needs interpretation.

What I would want beside the quote

I would use the same short set of questions for every proposal. Our installer selection guide covers the wider workmanship and aftercare questions.

• Which objects shade the proposed panels, and when?
• Which information was measured, and which inputs were estimated?
• How do the panel groups and inverter choice respond to those conditions?
• What changes if the most shaded panels are left out?
• What extra cost buys what estimated benefit, using the same assumptions?

Decide on the layout before the upgrade

My recommendation is to pay for a justified design, not a promise that a premium component will solve every shadow. A straightforward system can be the right choice where the roof is simple and the shade is limited.

If shade is substantial or the proposal depends on changing a tree you do not control, resolve that uncertainty before signing. A clear answer now is more useful than a confident annual estimate built on a doubtful assumption.