Checking a site for shade through the day and year

Why check for shade before fixing anything down?

Because shade hurts output by more than its size suggests. A panel's output is extremely sensitive to shading.¹ You can move a panel on paper for nothing. Moving it once it's bolted down costs time and often money.

The advice from the field is blunt: don't let trees or other obstructions shade an installation.¹ So survey the site first, and survey it properly.

Where does the sun actually travel in Australia?

You need a picture of the sun's path, because shade follows the sun. Accurate knowledge of the sun's path at your location is essential for deciding where to put solar equipment.² The position of the sun also varies across regions and by season.³

Here is the rough pattern for the Southern Hemisphere.

• Summer (November to January). The sun rises in the south-east and peaks slightly north of overhead.²
• Winter (May to July). It rises in the north-east and peaks at a low angle in the north.²
• Equinoxes. It rises due east and sets due west.²

Notice what that means. In winter the sun sits low in the north, so anything tall to the north of your panels can throw a long shadow over them. In summer the sun is higher, and the same object may not reach.

Which time of year is the hardest test?

Winter. The lower angle of the winter sun can limit solar access.³ That guide is about house design, but the sun doesn't treat panels differently from windows.

A site that looks wide open in December can be shaded by a tree, shed or hill in June. If you can only inspect once, make it a winter day, or work out what winter will look like.

There's a handy shortcut for that. Two days the same distance either side of a solstice have practically overlapping sun paths.² A check in late May, say, will show roughly what late July looks like. You don't have to wait for midwinter itself.

How do I check a site, step by step?

You don't need special gear to start. A phone, a notebook and a free hour will do.

1. Find true north first. Phone maps use solar north by default, though it's worth checking your settings.³ How that differs from a compass is explained under true north and compasses.
2. Stand where the panels will sit. Not near it. At the same spot and about the same height.
3. Face north and scan the skyline. Sweep from east, through north, to west. Anything that rises into the arc where the sun travels is a shade risk.
4. Photograph it. Take a few overlapping pictures across that whole sweep, so you've got a record you can compare later.
5. Look again at a different hour. Early morning and late afternoon shadows are long, and they can reach spots that stay clear at midday.
6. Repeat in another season. Use the shortcut above if you can't wait.

If you use a phone sun-path app or a printed sun chart, treat it as a guide. Check it against what you can see, and trust your eyes over a number you can't explain.

What counts as shade?

More than trees. Look for chimneys, vent pipes, aerials, dishes, a neighbour's roofline, the house itself and the panels in front.

Even a small shadow matters, because output is so sensitive to shading.¹ The page on how shading cuts output explains why.

What if there's shade I can't avoid?

You have three honest choices. Move the panels to a clearer spot. Remove or trim the thing causing the shade, if it's yours to touch. Or accept a loss in the seasons when it falls on them.

Don't fit the panels first and hope.

Do I need a licensed electrician at this stage?

Not for looking at shadows. Once the site is chosen, though, fixed mains wiring is licensed electrical work in Australia, and it isn't a DIY job. Before anyone touches the battery, shunt, fuse or inverter cables, the battery must be isolated. Read the maker's manual first. A licensed electrician can take over if there's any doubt.