When the only option is to put the panels on a south-facing roof – is it still useful to put the panels on?

Australia: Can you really go solar with south-facing roof?

We all know that when installing solar panels here in Australia, the north would always be the best pick. If north is not an option, northwest and northeast are generally the next best options. Then, depending on circumstances, you can go west and due east.

But is it still useful to put the panels on when your only option is a south-facing roof?

If you will ask an installer, the conventional wisdom is that he would say no. He might add that solar should never be installed on a south-facing roof. Well, solar panels work best when they’re directly facing the sun. The sun sheds the most light during the middle of the day when it’s to the north of Australia.

Interestingly, almost all of the solar calculators do not have south-facing options. Many of them, however, are now trying to update their system. But as solar PV system prices have come down in recent years, the prospects of installing on a south-facing roof look reasonably good. This is true especially if the roof has is also facing slightly to the east or west.

Solar radiation level for south-facing roofs

With the PVWatts calculator, we took a look at a handful of Australian cities (chosen for their latitudes). We checked how many kilowatt-hours (kWh) of sunlight fall on panels of different orientations & tilt angles. The figure is technically known as ‘incident solar radiation’. But you can think of it as the raw solar fuel for your panels. Note that PVWatts’ outputs are based on historical weather data for each location.

We looked at north, east, west, south, southeast & southwest at a tilt angle of 20°, which is relatively close to flat. The flatter a south-facing roof is (i.e. the closer to horizontal), the better it will be for solar.

We also looked at a tilt angle of 40° for the south-facing orientations. This is mainly to show that a south-facing roof with a steep pitch is probably not a good place for solar panels. The results backed us up on this theory. They showed poor solar radiation levels for south-facing roofs at this steep tilt.

The other results were also relatively unsurprising. It is handy to see the differences brought into sharp relief, though. The tables below of course confirm that north, east & west are the best orientation for solar panels. But they also show that even south-facing roofs could offer viable returns as well.

Solar radiation figures for north & south-facing roofs in select Australian capital cities

As an example, a roof facing due south in Brisbane will receive almost as much sunlight as a north-facing roof in Hobart.

(Results are color-coded: Green for highest, white for middle, red for lowest)

Brisbane-solar-output-comparison

Hobart-solar-output-comparison

Melbourne-solar-output-comparison

Sydney-solar-output-comparison

You might ask, what about tilt frames?

None of the scenarios discussed in this article take into account the fact that tilt frames can turn a south-facing roof into a north-facing solar array. The main considerations, in this case, would be about:

  1. additional costs (would the additional solar yields offset the higher system price?);
  2. the durability of the frames (are they properly suited for the worst-case high-wind scenarios in your location/climate?);
  3. and aesthetics (how would the frames look on your roof?).

Factors you need to consider

The point is this: Don’t write off solar for your home just because you haven’t got any unshaded roof space that faces north. Solar is possible especially if you live north of Melbourne, where there’s plenty of sunshine most of the time.

The amount of solar radiation you receive is not the only factor, however. It’s important to note that solar PV systems in Melbourne promise attractive financial returns for households. This is despite relatively low solar radiation levels.

In fact, solar even makes sense for Melbournites despite the low cost of grid electricity and the relatively high price of solar systems there – factors that can often confound the business case for having solar installed.

So if you live in Brisbane or Sydney, for example, going solar with a southeast-facing roof could be potentially more attractive than going solar with a north-facing roof in Melbourne. Both Sydney and Brisbane are home to higher grid electricity prices and lower solar system prices. Going solar in these cities is an easy choice.