Solar panels are installed differently based on their geographic locations throughout the world. The premise behind this is simple; the sun is in a different place in the sky, so panels need to be directed according to this positioning.
The ideal situation is when the sun is hitting the panels at a perfectly perpendicular angle (90°). This maximizes the amount of energy striking the panels and being produced. The two factors that such an angle is controlled by are the orientation (North/South/East/West) and the angle of the panels from the surface of the Earth. So in Australia, what angle and orientation are best?
The tilt involves primarily the angle that the panels are facing up into the sky. On a flat roof, the tilt is 0°, whereas if the angles were to be facing a wall, it would be 90°.
According to the Your Home Technical Manual the ideal tilt angle for a solar PV array depends on the building’s electrical load profile (i.e. when you use electricity during the day). The below description refers to tilt frames, but its recommendations are worth bearing in mind when considering installing a panel array on a roof without tilt frames.
As a rule of thumb, if the main loads are in winter months when solar availability is reduced, tilt angles should be more vertical (approximately equal to latitude plus 15°) to maximise exposure to the low winter sun. If major loads are cooling and refrigeration the tilt angle should be reduced (approximately latitude minus 10°) to maximise output during summer. For grid connect systems the summer optimum angle should be used to maximise annual output of the modules.
So if you have heavy summer AC loads in your home or business, the ideal would be to tilt the panels your latitude minus 10°. If your winter heating loads are supplied by electricity (as opposed to gas or wood), on the other hand, then tilting your panels back at latitude plus 15° would be better. If the loads are roughly equal in summer and winter, tilting the panels at latitude should be fine.
In effect, however, most grid-connected solar systems are likely to be installed at whatever angle the roof happens to be tilted at (unless the roof is completely flat, in which case the panels should be given a slight tilt). This is because the additional cost of tilt frames is not always justified by the additional solar system energy yields – it may be more cost-effective (space permitting) to simply add an additional solar panel or two.
Efficiency of solar systems at different tilt angles and orientations for Sydney.
Australia, being in the Southern Hemisphere, experiences a sun that is predominantly coming at us from the North. There is of course deviance throughout the seasons, but ideally solar panels should be facing as close to true North as possible to reduce the impact that the Winter seasons have on efficiency. Once again referring to the graph above, one can see that even North Easterly and North Westerly facing panels will be largely operating at around the 90% of their rated outputs. However, once angles start approaching East North East or West North West orientation, the numbers start reducing rapidly.
A directly East or West facing panel will never operate at better than 85% of its rated output. To put this in perspective, rather than getting back the usual 4.5kWh average daily energy per 1kW of solar, the system will only produce 3.835kWh. For example, a 3kW system would lose a full 2kWh a day if it were facing more East or West than North. This would equal 88c worth of surplus energy in QLD and SA a day, $1.20 in surplus to Victorians, a minimum of $1.00 less in the ACT and $1.20 in NSW. A lot of energy that is not captured, and a lot of money that is wasted.
When tilt frames are a justifiable expense
So we can see that both of these factors are important in their own right. What the majority of houses and installations need to remember is that a combination of a not so great orientation and a poor tilt will add on to one another, making the consideration of both factors the only reasonable way forward. Tilt frames that counteract a sub-optimal tilt and orientation will cost you a little extra. How much will depend on how many panels make up the system, and how the installer sources and prices the labour and parts required.
The bottom line is that the bigger a system is, the more justifiable that expense becomes. With a 1.5kW system and below you can get away with forgoing the frame, but anything larger and the fact is that the cost of a tilt frame will be paid for with the increased efficiency and day-to-day output of your system. Shopping around to get a number of quotes is the best way to find a reasonable price for the frames, but expect to pay a minimum of $400-$500.
Top image via Your Home Technical Manual
© 2010 Solar Choice Pty Ltd
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