Corrosion issues Aluminum rails - Stainless brackets

[Peter460]

I stay within 400m of the Atlantic seaboard in Cape Town and concerned about corrosion of the the whole PV panel / frame assembly. Popular framing system used here is the SolarPower system - however I am concerned that the Stainless Steel brackets ( to the wooden roof trusses ) are going to cause corrosion problems with the Aluminium rails and PV modules. Any comments ?

Peter

[emartin00]

Most of the aluminum rails are anodized. Anodizing protects the aluminum rail very well.
Aluminum and stainless are generally considered compatible as the electrochemical potential is below .6V

[Peter460]

Most references say Max 0.15 V difference in harsh environments - now Stainless Steel has index of 0.50 V and aluminium has values between 0.75 - 0.95 - total differences of between 0.25 - 0.45 V - not good for a harsh environment. Not sure how stable the anodising layer is and weather it gives long term protection. Having worked in the on several military projects anything over 0.15 V is a problem.Is there a way to isolate the two surfaces with grease?

https://en.wikipedia.org/wiki/Galvanic_corrosion

[diogenes]

A long time ago we used to use an anti oxidant cream to connect aluminum and copper wiring, that might be a consideration.

[foo1bar]

A long time ago we used to use an anti oxidant cream to connect aluminum and copper wiring, that might be a consideration.

In that case you were trying to electrically connect them - in this the best solution is to mechanically connect them without electrically connecting them.

I don't have a solution - but I don't know whether it's really a problem.

I'd look for an old install in the area and take a look at it.

And I'd contact the racking manufacturer and ask them about it - all their midclamps/endclamps are likely stainless - so they should be able to give you some reassurances.

[sensij]

In that case you were trying to electrically connect them - in this the best solution is to mechanically connect them without electrically connecting them.

I don't have a solution - but I don't know whether it's really a problem.

I'd look for an old install in the area and take a look at it.

And I'd contact the racking manufacturer and ask them about it - all their midclamps/endclamps are likely stainless - so they should be able to give you some reassurances.

Did you look at the Miller Solar link? I was skeptical too, but clearly, conditions can exist in some installations that can cause a problem. Even if the mounting could be resolved by designing with aluminum fasteners (which would require more and/or larger fasteners than the standard design), you still have a need to electrically ground the panel frames. Maybe aluminum lugs and conductors instead of copper? This might be a good application for frameless panels, like those made by Sunpreme.

An alternative would be to somehow encapsulate each dissimilar metal joint so that water can not penetrate... no easy answer that I can see.

[Peter460]

I wonder it its best to bond the Aluminum to Stainless bits electrically and then to earth? Here in Capetown there does not appear to be any legal requirement to electrically ground the PV but what is best practice? Does omitting earthing modern PV's still shorten their effective lifespan

[emartin00]

I wonder it its best to bond the Aluminum to Stainless bits electrically and then to earth? Here in Capetown there does not appear to be any legal requirement to electrically ground the PV but what is best practice? Does omitting earthing modern PV's still shorten their effective lifespan

Not grounding has little to do with the lifespan of the modules. It's about safety. If a wire gets cut or nicked, and makes contact with the metal, you want the ground wire to be its chosen path, not someone who is on the roof.

[inetdog]

For galvanic compatibility with aluminum in a connection to a standard steel rack system, the most common fastener used is stainless, with stainless washers to prevent direct contact.
There are other options, such as zinc coated (galvanized steel) but the right stainless alloy is less vulnerable to coating abrasion which can lead to galvanic corrosion.