South-facing solar panels Perth: when does it make sense?

A south-facing solar array in Perth generates roughly a third less than the same system facing north: about 67 to 69% of the north-facing output at a typical 20 to 25 degree roof tilt. That penalty is real, but it is smaller than most people expect, and south-facing still pays off in three common situations: when you have no usable north roof, when you are adding a second array to spread generation across the day, and on low-pitch roofs where the orientation penalty shrinks. The one rule worth remembering: if you have a clear, unshaded north roof, use it first. If you don't, south is still viable.

Perth installers default to north because north faces the sun all day. But many homes have their best roof area facing south, either by the way the house sits or because the north roof is shaded, has a chimney, or is already full. Here is what south-facing actually means for your numbers.

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How much less does south-facing solar produce in Perth?

Perth sits at about 32 degrees south. A north-facing roof at 20 to 25 degree tilt catches the most energy across the year. A south-facing roof at the same tilt catches less, because it faces away from the sun for most of the day and lives on morning and afternoon light plus diffuse sky.

How much less? Roughly a third. Here is the picture for a 6.6kW system in Perth:

East and west land at about the same place, around 87% of north, because the morning and afternoon sun reaches them fairly evenly. South sits lower, at roughly two-thirds of north. So a south-facing 6.6kW system gives up around 31 to 33% compared with the same panels facing north. That is a bigger gap than east or west, but it is nowhere near a write-off.

If you want the orientation picture across every roof direction, our Perth solar roof orientation guide lays out the full set, and common solar orientation myths in Perth clears up where the panic about non-north roofs goes wrong.

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When is south-facing solar still worth installing?

Despite the penalty, south-facing solar makes sense in several Perth situations.

When you have no usable north roof

If your north-facing roof is shaded, too small, or already occupied, south may be the only real option. Common blockers:

• Shaded by a tree, a neighbouring structure, or a dormer
• Too small for a meaningful array (under 3kW)
• Taken up by a skylight, chimney, or solar hot water collector
• Not structurally suitable

Generating around 6,900 kWh a year from south beats generating zero from a north roof you can't use. If shading is the issue rather than space, it is worth confirming first: our Perth neighbour shading guide covers how much a tree or two-storey next door actually costs you.

When you want a second array to supplement north

Already have a full north-facing array and want more capacity? A south-facing addition can earn its place. It generates in the early morning and late afternoon when north output is lower, which flattens your generation curve across the day. That broader window makes it easier to time an EV charge or run the pool pump on solar rather than grid power.

Homes with large south-facing roof sections and high energy demand, think EV, pool, ducted air conditioning, benefit most from this. For the wider picture on expanding an existing system, see adding panels to existing solar in Perth.

When you have a flat or low-pitch roof

Perth has a lot of low-pitch roofs at 5 to 10 degrees. On a nearly flat roof the orientation penalty shrinks: a south-facing roof at 5 degrees pitch loses far less than a south-facing roof at 20 degrees, because a flat south array sits close to its own best angle. On a genuinely flat roof, tilt frames can sometimes point the panels north regardless of which way the building faces. Our flat roof solar guide for Perth and solar panel tilt guide cover the racking choices.

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When is south-facing solar not the right call?

When you have good north options and are choosing on convenience

Have a clear, unshaded north roof and the decision is really about cost or tidiness? Choose north. The roughly one-third output gap is too large to give up for looks or a simpler install.

When a battery quote assumes the wrong solar output

The WA Battery Scheme rebate of $130/kWh, capped at $1,300, doesn't care about panel orientation: it is based on battery capacity. But battery payback does depend on how much solar you have to charge the battery. A south-facing system producing around a third less solar has a different charging profile than a north-facing one.

So if your installer quotes battery savings on north-facing assumptions for a south-facing roof, the numbers will be off. Ask them to re-run it on your actual south-facing output estimate. Our Perth battery ROI guide and battery sizing guide show what the maths should look like once the right solar figure goes in.

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How does south-facing output change with the seasons?

South-facing panels run the opposite seasonal pattern to north-facing ones:

Winter is the hard season for a south roof. Perth's winter sun tracks low across the northern sky, so a south-facing roof in July may produce very little, just early-morning and late-afternoon light. That seasonal swing matters more if your bills peak in winter.

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How should a south-facing array be designed in Perth?

A few design choices make a real difference to what a south roof delivers.

Tilt angle. For south-facing panels in Perth, a lower tilt of 10 to 15 degrees usually beats the standard north-facing 20 to 25 degrees. Flatter sits a south array closer to its best angle and cuts the loss.

String configuration. South-facing panels should sit on their own MPPT input, not strung in with north-facing panels. Mix orientations on one MPPT and the weaker south panels drag down the north ones, costing you output. Any reputable Perth installer will keep separate MPPTs or separate strings for a mixed-orientation system. Our guide on how solar strings and MPPTs work explains why.

Monitoring expectations. Set your monitoring baseline on the south-facing estimate, not a default north number. Compare a south system against a north benchmark and it will look like it is under-performing when it is doing exactly what it should.

Shading. South-facing roofs in Perth are often less troubled by neighbour shading, which usually comes off the north side of nearby buildings. In a dense suburb, a south roof can occasionally be cleaner of shade than the north one.

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What do the Perth economics look like for a south-facing system?

Take a 6.6kW system on a south-facing roof at 20 degree pitch:

The payback figures assume you use most of your daytime generation in the home rather than exporting it. If you export a larger share, both columns stretch out. The south payback runs longer than north but is not prohibitive, especially when the system is displacing pricey daytime loads or there is simply no north roof to use.

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A south-facing array in Perth gives up roughly a third of the output of the same north-facing system, around 67 to 69% of north at a typical tilt. It still earns its place when the north roof is unavailable or too small, when you are adding a second array to broaden your generation hours, or on a low-pitch roof where the penalty shrinks. The payback runs a little longer, that is all. The rule that holds: if you have a clear north roof, use it first. If you don't, south-facing is still worth doing, just ask your installer to quote it on south-facing modelling, not the default north-facing assumption.