Introduction

SunLock is an Australian designed and manufactured solar panel mounting system. Backed by a 10 year warranty from an Australian company, SunLock is the trusted and proven name in solar PV mounting systems.

Supplied with clear & comprehensive installation instructions, including engineering drawings and AS/NZS1170.2:2011 compliance certificates, a properly installed SunLock frame is the simplest way to save time and money whilst ensuring compliance with CEC guidelines.

Features

Fast - the SunLock key insert goes straight into the rail (not at a clumsy angle) and locks securely into place. Brackets and clamps can be easily loosened and adjusted to ensure panels are correctly aligned.

Compliant - installation drawings and compliance certificates are provided by Partridge Partners Pty Ltd, who are registered structural engineers; and are supplied as part of the installation manual (download from the sidebar at right).

Durable - SunLock is 6000 series aluminium (predominantly 6106-T6) which has a 25+ year service life under Australian conditions, even without anodising.

Earthed - EarthLock washers and bonding terminals are fast to install and ensure that systems using transformerless (TL) inverters are properly earthed according to CEC guidelines.

Edge zones - installation manuals include spacing tables for edge zones. This is critical, as most small domestic installations are fitted close to the edges of roofs.

Accurate - installation manuals include fixing capacity ratings for key elements including tile brackets (1.03 kN), L-feet (1.6 kN) and roofing screws for steel purlins (1.05 kN in non-cyclonic conditions, 0.63 kN in cyclonic regions).

Components

What to look for in a framing system

Background

Solar photovoltaic (PV) systems are typically mounted to existing roofs using a framing system. The framing system is a structural component and must comply with relevant codes and standards, including Clean Energy Council (CEC) guidelines. It is the responsibility of the installer to sign off that the system (including the framing) complies with these standards. Australian Standards and the Building Code of Australia exist to ensure structures are safe and durable. In the case of solar panels, the framing system must ensure that the PV panels do not detach from the roof in high winds, potentially impacting and damaging other property or injuring people.

Compliance

CEC guidelines state that framing systems must comply with all relevant codes and standards. These include:

• Australian and New Zealand standard AS/NZS1170.2:2011 defines how the wind loads on a structure are to be calculated, based on factors including the site, terrain and topography
• AS/NZS1664.1:1997 defines how an aluminium structure is to be designed to be capable of withstanding a defined load
• AS1720.1:2010 and AS/NZS4600:2005 define how the fixing capacities of timber roof screws and steel roof screws are calculated; based on factors such as size, embedment depth, timber type, and whether the wind load is non-cyclonic or cyclonic (low-high-low fluctuations)

Overall, a framing system must not just be "designed to be compliant with AS1170.2". The type and the number of fixings used (or the fixing spacing) must be specified, including the minimum embedment depth; and the load capacity of the brackets must be known (and should be stated). These items are often not included in the documentation from less reputable suppliers. If this occurs, it is essentially impossible to confirm that the solar PV frame is securely fixed to the roof frame, and therefore in accordance with CEC guidelines.

Look for installation manuals which include engineering drawings prepared by a registered structural engineer.

Edge zones

Roof edges experience higher wind loads than the centre section, and therefore more fixings are required (i.e. a smaller fixing spacing).

AS/NZS1170.2:2011 states that the "edge zone" (comprising both the edge zone and the intermediate zone) has a width "A" which is calculated based on the dimensions of the building. These are also known as the 0.2B or 0.2D zones.

A typical domestic site is shown below. The north and west facing sections of the roof are likely locations for solar panels. The width of the house "B" is ~ 10 m, and the depth "D" is ~ 13 m. The width of the edge zone is therefore 0.2 x 10 = 2 m. The "internal zone" is marked in yellow, and is very small.

The figure above shows that on most domestic sites it is impossible to install a PV system within the internal zone. Therefore, tables of fixing spacings for the intermediate and edge zones are required. However, the installation manuals from less reputable suppliers do not supply this information. They only supply tables of fixings spacings for the internal zone.

Look for installation manuals which include spacing tables for the edge zone, not just the internal zone.

Roof pitch

AS/NZS1170.2:2011 states that the wind load on a roof (or a flush mounted PV panel on a roof) varies as a function of the roof pitch. Flatter roofs (e.g. 10-20°) experience a higher wind uplift load that steeper roofs (e.g. 20-35°). This is commonly known as the airplane wing effect, where a suction or uplift force is generated just behind the crest of the wing.

The installation manuals from less reputable suppliers do not state which roof pitch was used in their calculations, and do not point out that the fixing spacings should be reduced for flatter roofs.

Look for installation manuals which clearly state which roof pitch the spacing tables are valid for (e.g. 10-20°, or 20-35°).

Thickness of steel battens/purlins

AS/NZS4600:2005 defines what fixing capacity a Tek screw has, as a function of the thickness of the steel batten/purlin which it screws into. From this, the required number of fixings (or the fixing spacing) can be calculated. Because it is time consuming to generate tables of fixing spacings for a large variety of batten/purlin thicknesses, suppliers generally assume one nominal value. Although steel purlins typically have a minimum thickness of 1.0 mm, battens can be thinner (e.g. 0.75 mm).

Less reputable suppliers ignore the fact that solar frame can also be fixed to thinner steel battens. This enables them to use a larger fixing capacity (based on 1.0 mm thick purlins) and a wider fixing spacing. However, this can lead to unsafe installations on domestic roof frames which use thinner steel battens.

Look for installation manuals which clearly state what thickness of steel battens/purlins the spacing tables are valid for (e.g. 0.75 mm) and check that this thickness is representative of domestic roof frames.

Durability

Most framing suppliers use 6000 series aluminium (alloyed with magnesium and silicon) for rails, brackets and clamps. This grade of aluminium is highly durable, with a service life of 25+ years under Australian conditions (without anodising). Aluminium builds its' own durable protective layer of aluminium oxide, and this layer will re-build after scratching or cutting.

Anodising does not significantly increase the service life of components fabricated from high quality aluminium of known metallurgical composition (such as components fabricated in Australia) under normal atmospheric conditions. In contrast, components from less reputable suppliers are fabricated from low cost aluminium of an unknown grade or of varying metallurgical composition. This poor quality aluminium often requires anodising to prevent surface corrosion within the first few years of service. Furthermore, every time the rail (or bracket or clamp) extrusions are cut to length, the cut ends aren't anodised.

Look for framing systems which are fabricated in Australia and where the supplier has sufficient trust in the quality to be able to offer mill finish (non anodised) aluminium.

Summary

Frames for PV arrays are a structural component and must comply with relevant codes and standards, including:

• AS/NZS1170.2:2011 on wind actions
• AS/NZS1664.1:1997 on aluminium structures
• AS1720.1:2010 on timber structures
• AS/NZS4600:2005 on cold-formed steel structures

To ensure that their system is both safe and compliant, customers should look for installation manuals which include the following:

• engineering drawings prepared by a registered structural engineer
• spacing tables for the edge zone, not just the internal zone
• spacing tables which clearly state which roof pitch they for (e.g. 10-20°, or 20-35°)
• spacing tables which clearly state a minimum embedment depth for roof screws into timber (e.g. 35 mm); and clearly state a minimum steel batten/purlin thickness which is representative of Australian domestic roof frames (e.g. 0.75 mm)
• clearly stated load capacities for key components such as tile brackets (e.g. 1.03 kN), L-feet (1.6 kN) and roofing screws (1.05 kN in non-cyclonic conditions, 0.63 kN in cyclonic regions)

and:

• look for framing systems which are which are fabricated in Australia from high quality aluminium; where the supplier has sufficient confidence in the quality to be able offer mill finish (non anodised) aluminium.

Surviving storms

The weak point in a solar panel mounting system is usually the number of roofing screws that hold the solar frame to the roof frame. This is especially important for tilt arrays, as they catch a lot more wind than a flush mounted system. For example, these images show a tilt frame (not SunLock) which was installed in a typical residential suburb in Queensland. It detached from the roof during a storm in November 2012, twisted and landed in a new location.





According to the photos, failure occurred in at least two locations:

• the screws holding the front feet ripped out
• the upper halves of the telescoping rear legs ripped out from the lower halves

It is quite possible that if the storm had lasted a little longer, individual PV modules could have detached from the rails and flown through the air, damaging property or injuring people. This type of damage could have been avoided if the installer had been provided with the correct number of parts and a full installation manual, taking into account factors such as:

• Correct spacing between tilt legs (to provide enough roof fixings)
• Lower fixing capacity of Tek screws into thin steel battens (compared with screwing into timber)
• Lower load capacity of telescoping rear tilt legs (compared with a fixed length rear leg)
• Use of diagonal braces to prevent sideways movement

Note that when properly installed, a SunLock tilt frame will withstand once in 500 year winds. For full details refer to the SunLock installation manual or the technical bulletin on tilt legs.