solar tilt angle

North-facing used to be the only answer for solar in Perth. Today, with time-based export rates and evening peaks, west-facing and split arrays deserve a serious look. Using modelled data for Perth, this guide compares orientations and tilt angles so you can see exactly what each choice costs or gains.

Orientation and tilt basics

Orientation (or azimuth) is the compass direction the panels face. Tilt is the angle of the panels from horizontal, which on most homes is simply the roof pitch. In the southern hemisphere, panels facing true north see the sun for the longest part of the day, which is why north is the default recommendation.

CSIRO notes that, based on solar geometry alone, annual output is maximised when panels face the equator and are tilted at an angle equal to the local latitude. Perth sits at about 32° south, so the textbook answer is north at roughly 32°. In practice, most Perth roofs are pitched lower than that, and the textbook answer ignores something that now matters a great deal: when the energy is produced.

Perth solar output by direction: the data

We modelled a 1 kW system in Perth using the European Commission’s free PVGIS tool (ERA5 climate data, 14% system losses). The results below are per kW of panels, so multiply by your system size. A 6.6 kW array facing north at 20°, for example, would produce roughly 6.6 x 1,695 = about 11,200 kWh a year under these assumptions.

Three takeaways stand out. North-west and north-east cost only about 3% compared with true north. West and east cost about 12% at a typical 20° pitch, and the penalty shrinks on flatter roofs (about 7% at 10°). South-facing panels lose the most, especially on steep roofs, although on a near-flat roof even south can still be workable.

These numbers line up with CSIRO’s national analysis, which found that pointing panels up to 45° away from the ideal direction loses only a small percentage of yearly energy in Australian capital cities, while 90° away loses more, ranging from about 9% in Darwin to about 26% in Melbourne.

How much does tilt matter?

Less than most people expect. CSIRO’s analysis of PVWatts data found that a tilt angle 20° away from optimum reduces annual yield by only around 5%, and 30° away by around 12%. For a north-facing array in Perth, our modelling shows 1,635 kWh per kW at 10° versus 1,714 at 32°, a gap of under 5%.

Steeper panels produce more in winter, when the sun is low, and less in summer. Flatter panels do the opposite. Tilt frames can raise a flat array to a better angle, but CSIRO points out that the small gain may not justify the added cost and visual impact. Flat panels also self-clean less effectively in rain, so very low angles below about 5° are best avoided.

The case for west-facing panels in Perth

Here is where the story changes. Using hourly PVGIS data, we looked at how much of each array’s output arrives between 3pm and 9pm, which matches Synergy’s DEBS peak export window and the time most households start cooking, cooling and running appliances.

A west-facing array produces about 12% less energy across the year, but roughly 50% more during the 3pm – 9pm window than a north-facing array. If that late-afternoon output replaces grid power you would otherwise buy, or earns the DEBS peak rate rather than the midday rate, the lower total can still be worth more. Synergy itself encourages new customers to talk to their installer about west-facing panels for exactly this reason.

This timing effect is closely tied to the duck curve in WA’s grid, where midday demand collapses because of rooftop solar and then rises steeply as the sun sets.

Split arrays and east-west roofs

Many Perth homes have hip roofs with faces in several directions. Splitting panels across north and west, or east and west, spreads production over a longer part of the day. An east-west array has a lower peak but a flatter, wider output curve, which suits households that use power in both the morning and late afternoon.

Split arrays need the right equipment. Each roof face should go on its own string with its own MPPT (maximum power point tracker) input, or use microinverters or optimisers, so a shaded or differently oriented face does not drag down the rest. Ask your installer to show you the string layout on the design.

How to choose the right orientation for your home

1. Map your usage. Use your Synergy bill or smart meter data to see when you use the most power.
2. Check shading first. A well-oriented roof face that is shaded in the afternoon may underperform a less ideal but clear face.
3. Use your largest unshaded faces. Panel count usually matters more than a few percent of orientation loss.
4. Factor in a battery. If you plan to add a solar battery, north can maximise the energy available to charge it.
5. Run the numbers. Compare payback for each layout using real system pricing. Our guide to the price of a solar panel system in Perth and our 6.6 kW ROI breakdown are good starting points.

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