When purchasing or building a new property, the way the house sits in the landscape is important. If you are on the Southern side of a hill, you will be a lot more limited in solar power generation than if you are on a North-facing hill. Any shade on your roof will also reduce how much power your system can generate. Ideally, you want a roof facing true North (not magnetic North) with no shading at all. To find true North, you can use a compass and then add or subtract the magnetic declination for your location.
| City | Latitude | Longitude | Magnetic declination |
|---|---|---|---|
| Darwin | 12° 28' 0' S | 130° 49' 60' E | +2° 34' |
| Brisbane | 27° 30' 0' S | 153° 1' 0' E | +11° 0' |
| Lismore | 28° 48' 0' S | 153° 16' 0' E | +11° 28' |
| Perth | 31° 55' 60' S | 115° 49' 60' E | -1° 44' |
| Sydney | 33° 52' 60' S | 151° 13' 0' E | +12° 36' |
| Adelaide | 34° 55' 60' S | 138° 35' 60' E | +7° 56' |
| Melbourne | 37° 49' 0' S | 144° 58' 0' E | +11° 38' |
| Hobart | 42° 55' 0' S | 147° 19' 60' E | +15° 5' |
The next point to think about is the optimum tilt of your solar panels. The general rule in Australia is to have them at a tilt equivalent to your latitude. However, you can improve your power output by not only calculating exactly the best tilt at your latitude, but also considering your power usage pattern across seasons. To produce the most power, your solar panels need to be exactly perpendicular to the direction of the sun rays. But of course, the position of the sun varies across seasons: it is higher in summer and lower in winter. In addition, the irradiance is lower in winter, especially around June/July, which is also when the sun happens to be at its lowest angle. So you need to consider your consumption patterns. Do you run exactly the same appliances year-round? If so, you will be better off angling your panels to optimise performance in winter, so you can partly make up for the lower irradiance. If you have a significantly higher usage in summer (e.g., running the air-con in summer but not the heater in winter), then you will be okay with flatter panels to receive more summer sun.
But generally, June/July are the months where solar systems can risk falling short, so a lot of people will choose to angle their panels for better winter performance. If this is the case for you, then the ideal tilt for your solar panels is your latitude + 15°. This is especially important for off-grid solar systems, where maximising winter power output is crucial so you can recharge your batteries.
Most roof pitches are between 15° and 25°, so you will need to install your panels on a solar frame with adjustable legs, so you can have them set at the optimal tilt. The solar frame we general recommend allows for a 15° to 30° tilt, which is in addition to your roof pitch.
So for example, if you are at a latitude similar to Lismore, you want to maximise winter power output, and your roof pitch is 20°, your install will look like this:
Latitude + 15° = roof pitch + frame tilt
28° + 15° = 20° + frame tilt
28° + 15° - 20° = frame tilt
Frame tilt = 23°
So for this example, you will need to install the panels on a tilted solar frame and set the frame at 23°
Another advantage of tilt frames is that they allow for more airflow behind the panels, which increases performance by keeping them cooler.
However, tilt frames have a downside as well: if you plan on having several rows of panels, you will create potential shading situations from one row to a higher row. So you need to weigh the pros and cons of having potentially less panels at the right tilt from having to space out your rows, or doing a flat install on the roof and simply installing more panels. Because the STCs are based on the number of kW installed, it will sometimes make more sense financially to do an easier/cheaper install with extra panels, so you can claim more STCs.
If you are in the planning stage of building a new house, here is a summary of the considerations to take into account:
- Roof facing as close to true North as possible
- Roof pitch as close to latitude as possible for best year-round performance (for install flat on roof)
- Roof pitch as close to latitude - 10° for best summer performance (for install flat on roof)
- Roof pitch as close to latitude + 15° for best winter performance (for install flat on roof). Especially important for off-grid systems.
- Install on solar frame with adjustable legs if you can’t pick your roof tilt (e.g., house already built, don’t like the look of steep roofs, safety concern for installers, etc.)
Always communicate with your solar installer ahead of time on this. Some installers will require additional safety procedures/cost to walk on roofs steeper than 25°. If you look at a steep church roof, you can easily see that it’s not a very welcoming roof to walk on. The same thing applies for the house builder – a very steep roof can be logistically difficult, so a roof with a more gentle pitch and a tilted solar frame may be the best solution, or a flat install with a few extra panels to make up for the lower performance.
If you need any advice, feel free to contact us and we can design the right solar system for your needs.