For most people who decide to mount solar panels on their roof, a mounting system is necessary. This short entry explains the basics of what needs to be taken into consideration when putting a solar array on your roof.
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Solar panels on my roof: what to consider
Ordinarily, if you have decided to install a solar power system, it will most likely be mounted on your roof unless you have perhaps become a solar farmer, in which case your system may be ground-mounted. In such a case, deciding where to locate and how to arrange your solar panels is a bit easier (provided you have the space, which is probably the case if you’ve got the option for a ground-mounted system) than working around the inherent limitations of your roof’s orientation, tilt angle, material, and available space.
Roof orientation and tilt angle for solar panels:
The orientation of your roof is the first thing to consider when considering whether you want to install a system. In the southern hemisphere, due north is the best option, but obviously, not all homes were designed with solar power in mind, and as a result, roof orientations differ drastically from home to home. Northeast and northwest-facing roofs are second best orientations after due north, followed by east and west. Anything further south than these will result in a severe reduction in efficiency to your panels. If your array faces due east or west, you will never see more than 85% performance from your panels–not that this should prevent you from going ahead with an install, but it is something that needs to be considered.
Likewise, the tilt angle of your roof will have a major impact on the amount of solar rays collected by your solar power system. Outside the tropics, including through most of Australia, an angle of about 32° is ideal, but anywhere between 20° and 40° should be sufficient for up to 90% operational efficiency. Many roofs fit this description, but if your roof is less than 20°, you might need to consider using mounting brackets. (Please see this previous entry about tilt and orientation for solar panels in Australia for more information.)
Roof space available for solar panels
One obvious factor to be taken into consideration when mounting panels on a roof is the amount of space available on it. A typical polycrystalline or monocrystalline panel measures about 1.6m x 1m, and depending on the capacity (size in watts) of your system, for an average 2 or 3-bedroom home, you should be able to fit enough panels to significantly offset your electricity costs on one, or in a stretch, two parts of your roof. Closeness of the panels to your home is not an absolute requirement: the roofs of sheds, garages, and balconies that stand slightly apart from your house may also provide options for placement.
What kind of roof materials are there and how are they different for mounting solar panels?
If you have a house in Australia, you probably have either a tile roof, a slate or shingle roof, or a corrugated metal roof. Tiles are hard and held together by a combination of mounting hooks and gravity–like a jigsaw puzzle. It is possible to take broken tiles out to replace them, sometimes without any special tools. Shingles and slates, on the other hand, typically have holes in them and are nailed onto the roof substrate. In both cases, they overlap each other so that water does not penetrate the building as rain falls. Corrugated metal roofs are composed of comparably large sheets that usually overlap each other, or may be one large piece. In mounting a PV system on any of these types of roofs, it is important to ensure that no gaps are left in the roof that may later result in leakage.
Mounting a solar array on all of the above types of roof is possible and in fact quite standard practice for solar power system installers, as many installations are retrofit onto the roofs of old homes.
Types of mounting systems for roof-top solar panels
The most common way to mount systems to first install brackets, the shape and size of which will vary with the mounting system manufacturer, but which will look something like the L-mounts pictured below. In the case of tile, slate, and shingled roofs, this may require cutting precise holes in the roof material for the mounting brackets to protrude from, while on corrugated roofs, the brackets will Rails are then fitted onto the mounts, which have been spaced appropriately apart so that the panels can be fitted flush together, side by side on the same set of rails. This is the most typical system for small- to medium-sized arrays, although flush mounts which support individual panels may also be used if the array is only composed of one or two panels. If you need to adjust the tilt angle of your array because the tilt angle of the roof is less than ideal, it is possible to do this with a universal mount by increasing the height of the rail higher up on the roof.
If you plan to replace your old roof anyhow, or if you are building a new home, you might want to consider photovoltaic roof tiles or shingles, which, as we discussed in our previous blog entry covering building-integrated photovoltaics (BIPV). These can be a cost effective option if you intend to replace your roof and install solar panels around the same time. Roof-integrated photovoltaics is one of the relatively more widespread forms of BIPV, and it is possible to have a solar roof installed here in Australia. (For more information, please contact us.)
© 2010 Solar Choice Pty Ltd
Resources and Links:
Image credits: Tile Roofs : Asphalt Shingles : Corrugated Roof : Conergy Suntop III: Instructions for Professional Installation (pdf)
Previous Solar Choice blog entries: Built-in Photovoltaics : Tilt angle and Orientation for solar power systems : What kind of solar panels are right for me?
He holds a master's degree in Environmental Management from UNSW, and a bachelor's degree in Philosophy from Bridgewater State University in his native Massachusetts.