Shade costs a solar system more than the size of the shadow suggests. Panels are wired in series, so a small shadow over one panel, or even one corner of it, can pull down the output of the panels connected to it. A few hours of shade on a clear day is enough to show up in your bill.
The good news is that shading is one of the easier problems to fix once you know where it’s coming from. Here’s what causes it, how to spot it and what your options are.
Why a small shadow does so much damage
A solar panel is a chain of cells wired in a row, and current has to pass through all of them. When part of the chain is shaded, it becomes a bottleneck: the shaded cells let less current through, and the rest of the panel and string can only work as hard as that weakest point.
Panels have built-in bypass diodes that let the current skip a shaded section, which limits the loss. But the sections usually run along the panel in bands, so a shadow across the bottom edge of a panel, such as a roof ridge, a fence or a hedge, can knock out all of them at once.
How much you lose depends on your system:
- Standard string inverter: panels are wired together, so shade on one panel can drag down the whole string.
- Microinverters or power optimisers: each panel works on its own, so shade only affects the panel it lands on.
If you don’t know which you have, your installer’s paperwork or your monitoring app will show it.
What causes shading on the Sunshine Coast
| Source | When it matters most | What helps |
|---|---|---|
| Trees and palms | Year-round, and worse as they grow | Trimming, or removal where appropriate |
| Neighbouring roofs and buildings | Winter, when the sun sits lower | Usually can’t be changed; optimisers limit the loss |
| Chimneys, vents, antennas and solar hot water tanks | Early morning and late afternoon | Moving the item, or redesigning the layout |
| Dirt, leaves and bird droppings | Any time | Cleaning |
Trees are the most common cause. They grow, so a system that worked perfectly at installation can be partly shaded five years later. This is especially true in leafy areas like Noosa, where heavier tree cover is part of the job.
Winter makes it worse. Panels in Australia face north, and in winter the sun is lower in the northern sky. Shadows get much longer, so a tree or building that doesn’t touch your panels in summer can shade them by June.
Dirt is a kind of shade. A patch of bird droppings or a pile of leaves blocks light in the same way, and it can cause the same overheating problem, called a hot spot. We cover that in 7 common solar panel problems. Unlike a tree, it’s fixed with a clean.
How to tell if your panels are shaded
The easiest check is your inverter or monitoring app. Look at a clear day and check the shape of the output curve:
- A smooth, rounded curve means no shading.
- A dip at the same time every day suggests something is casting a shadow at that time. Match the time of the dip with the direction of the sun to find the culprit.
- A gradual decline over months with no dip points to dirt or a growing tree.
Our guide on how to check if your solar panels are working walks through the monitoring steps. You can also walk around at the time of the dip and look at the roof from the ground, and check again in winter, when shadows are at their longest.
What you can do about it
- Clean the panels. Rule out dirt first, because it’s the cheapest fix. See signs your solar panels need cleaning.
- Trim or remove the source. Overhanging branches are the easiest to fix. Use a qualified arborist, and check council rules and speak to your neighbour if the tree isn’t yours, since some trees are protected.
- Talk to your installer about optimisers or microinverters. If you can’t remove the shade, these limit the damage by letting each panel work independently.
- Consider the layout. Moving a few panels to a sunnier part of the roof can pay off if one section is shaded for most of the day.
Does shade damage the panels?
Usually, no. Shade mostly costs you power, not hardware. The exception is a hot spot, where a shaded or blocked cell overheats because the rest of the panel is pushing current through it. It’s rare when the panel is shaded by a tree, which moves, and more likely when something sits on the same spot for a long time, such as droppings, a stuck leaf or a stubborn stain.
Not sure if it’s shade or dirt?
That’s the most common question we get, and it’s hard to answer from the ground. Our Solar Health Check compares your output with what a system your size should produce, and tells you whether the cause is dirt, shade or something an electrician should look at.
If it turns out to be dirt, a clean is a simple fix. Our rate is $110 for up to 10 panels on a single-storey roof, then $8 per panel after that (excluding GST), with a before-and-after photo report of every panel. See the full pricing, or get a free quote and we’ll reply the same day.
FAQs
Do solar panels work in the shade?
Yes, but at a much lower output. Panels can still produce power from indirect light, but direct sunlight is what they’re designed for. Shade on part of a panel can cut its output by more than the size of the shadow.
How much does shading reduce solar output?
It depends on how much of the system is shaded, for how long, and whether you have microinverters or optimisers. A little shade on a system with optimisers might cost you very little. The same shade on a standard string system can cost a lot more.
Can I trim a tree that’s shading my panels?
If it’s on your property, usually yes, but use a qualified arborist and check your council’s rules first, as some trees are protected. If the tree is on a neighbour’s property, speak to them before doing anything.
Does cleaning fix shading?
Only if the “shade” is dirt, leaves or droppings. A cleaner can’t remove the shadow of a tree or a neighbouring roof.
How do I know if my system has optimisers or microinverters?
Check your installer’s paperwork or your monitoring app. If you can see output for each panel individually, you almost certainly have one of them.