Aluminium 40 Series Extrusion 40 x 40 mm for PV Module Lines

01What changes when the frame lives in a PV module line?

Four things, and none of them are about strength. A 40 x 40 mm aluminium 40 series extrusion at 1.30 to 2.35 kg/m is more than adequate structurally for a module line frame. What changes is that the frame now sits in a wet, chemically active, electrically sensitive, thermally cycling environment for a decade, and each of those four adjectives creates its own failure mode.

• Wet — condensation inside hollow profiles, and standing water in upward facing slots.
• Chemically active — deionised water, mild detergents and occasionally alkaline cleaners on an anodised surface.
• Electrically sensitive — an anodised layer is an insulator, so an anodised frame is not automatically bonded.
• Thermally cycling — daily expansion and contraction working every bolted joint loose over years, not weeks.

The rest of this page deals with those four in order. If you are building a dry, indoor, non-electrical frame out of the same section, most of it does not apply — and the standard frame guidance on the 40 x 40 four slot product page is the better starting point.

02Does UV degrade an anodised aluminium frame?

The oxide layer itself, no. Anodising is an inorganic oxide and it does not chalk, yellow or embrittle under UV the way a polymer coating does. That is the main reason anodised aluminium is preferred over powder coat on a line that sees daylight or strong UV from process lamps.

03What do PV line cleaning agents do to the frame?

Module lines use a narrow set of cleaning agents, and the frame is exposed to all of them as overspray and run-off. The list below covers what is normally found; the specific product should be checked against its working pH rather than its marketing description.

The deionised water row is the one people miss. DI water is chemically clean but it is hungry — it will dissolve aluminium from any unprotected surface it sits on, and it does it fastest at a cut face or a thread where there is no oxide layer. On a line that uses DI water as a final rinse, every cut face needs to be anodised, sealed, or kept out of the wet zone.

04Why is an anodised frame not automatically bonded?

Because the anodised layer is a dielectric. It is aluminium oxide, typically 10 to 15 micrometres thick, and it does not conduct. A multimeter probe touched onto an anodised surface will read open circuit, or a resistance that varies with probe pressure. So a frame assembled entirely from anodised profile with anodised brackets is a set of insulated parts that happen to be bolted together.

That matters on a PV line for two reasons: operator protection if a heater, drive or lamp fails and puts a conductor in contact with the frame, and static control around glass and polymer handling, where a floating frame becomes a charge store.

Test criterion

A commonly used acceptance figure is 0.1 ohm between the protective bonding terminal and any exposed conductive part — confirm against the standard your customer works to

Problem

Anodised interfaces read open circuit and fail the test

Fix 1

Serrated or toothed washers that bite through the anodised layer at each joint

Fix 2

A dedicated bonding stud with the anodising masked on assembly

Fix 3

Bare aluminium busbar or a separate conductor linking the frame sections

05How much deflection is acceptable when the line handles glass?

Much less than for a general machine frame. Glass is brittle, it does not yield, and it fails from a stress concentration rather than from a load. A rail that sags 3 mm under a module is not a problem for the rail — it is a problem for the module, which now sits on a curved support and carries a bending stress it was never designed for.

The practical rule is to set the deflection limit from the glass, not from the structure. A limit of span divided by 500 is a common starting point for a support rail under glass; for thin or large format modules, tighter. Then check the section against that limit rather than checking the stress.

06Where does condensation collect?

Inside the hollow profile, and in any slot that faces up. A hollow aluminium extrusion on a line that cycles between warm and cool is a chimney: moist air enters at one open end, condenses on the cool inner wall, and the water has nowhere to go. Over years it sits there and works on the inside surface, which is the one surface nobody inspects.

• Cap every open profile end. Plastic end caps are cheap and they close the chimney.
• Turn upward facing slots into covered slots, using a slot cover strip. An open slot is a gutter.
• Drill a weep hole at the low end of any run that cannot be capped, and deburr it.
• Do not seal a profile that already has water in it. Cap it dry, or the water stays in permanently.
• On a wet station, slope horizontal runs slightly so any water that does get in leaves by the weep hole rather than sitting.

07What needs checking on a maintenance schedule?

Four items, and they are all things that degrade slowly and then fail suddenly.

The bonding check is the one that gets skipped, because it needs a meter and a record rather than a look. It is also the one that matters most, because a frame that was bonded when installed can become unbonded through corrosion at a single joint and nothing on the outside of the machine will show it.

08Questions from PV line and automation engineers

Related sections and categories

Browse 40 Series Aluminium Profiles, Strut Profiles, the 40 x 40 mm four slot section, or see the 40 x 40 mm three slot closed face section for the full section data.