Thermal expansion?

[Brettw]

Do I need to allow for thermal expansion when installing solar panels?
I'm building a stand alone wood rack to hold my panels.

 

[MurphyGuy]

Yes, but not much. A 1/2 inch between them is more than enough.

 

[Brettw]

Yes, but not much. A 1/2 inch between them is more than enough.

Thank you.
My panels are 41 inches wide, is 1/2" still enough?

 

[Brett V]

The clamps I used provided about 1/2" between the panels and I've gone from temperatures in the 90's to low teens with no problems. I have big 72 cell panels and believe they're 41" wide.

 

[MurphyGuy]

Thank you.
My panels are 41 inches wide, is 1/2" still enough?

1/2 inch is plenty. I have both 60 cell and 72 cell panels and left 1.5 inches between the columns. After 5 years in Michigan with temps going from -30 to +96 degrees, I have never detected any shrinkage or expansion. I'm sure its there, but you'd need a caliper or micrometer to measure it.

 

[Brett V]

1/2 inch is plenty. I have both 60 cell and 72 cell panels and left 1.5 inches between the columns. After 5 years in Michigan with temps going from -30 to +96 degrees, I have never detected any shrinkage or expansion. I'm sure its there, but you'd need a caliper or micrometer to measure it.

I can't imagine -30 degrees. I grew up in Pittsburgh and remember complaining about temps in the teens some mornings going to wait for the school bus.
My stepmother grew up in Duluth and she used to say "kid, you don't know what colds is".

 

[sunshine_eggo]

The clamps I used provided about 1/2" between the panels and I've gone from temperatures in the 90's to low teens with no problems. I have big 72 cell panels and believe they're 41" wide.

View attachment 122870

Based on what I see in your mount, there are solid spacers or clamps filling the gap between the frames. This does not allow for expansion.

1/2 inch is plenty. I have both 60 cell and 72 cell panels and left 1.5 inches between the columns. After 5 years in Michigan with temps going from -30 to +96 degrees, I have never detected any shrinkage or expansion. I'm sure its there, but you'd need a caliper or micrometer to measure it.

Across the stated temperature range a 41" wide panel would increase by just over 1/2 inch from low to high.

I would argue that none is needed.

Sure, panels expand with heat and shrink with cold, but so does what they're attached to. Aluminum panel frames attached to aluminum rails will see zero relative expansion. Aluminum to wood or steel will, but even when there is a difference, the materials give a little and never experience anything near their yield strength or UTS. I've seen commercial ground and roof mounts that allow for zero expansion.

Yes, if you mount solar panels with zero clearance between two immobile blocks of stone, you will likely regret your choice, but if your array has free ends like in any ground or roof mount installation, you're good.

Consider that panels themselves are made of dissimilar materials. Glass and Aluminum have markedly different CTE.

 

[MurphyGuy]

I can't imagine -30 degrees. I grew up in Pittsburgh and remember complaining about temps in the teens some mornings going to wait for the school bus.
My stepmother grew up in Duluth and she used to say "kid, you don't know what colds is".

-30 is not normal here. Zero is normal during the deep January freeze, even -10 is common. Extremes down to -15 might happen once a year if conditions are right but it's not every year. We hit -40 once about 6(?) years ago and my wife burned her lungs shoveling snow with me. I've been in it before and had a face mask on to temper the chill before it hit my lungs, but she didn't.

Per your post, like I said, I've never detected the gap between my panels growing or shrinking. As the other poster said, the entire rack grows and shrinks as well.

 

[Brettw]

Thanks for all the replies!

 

[fromport]

I would argue that none is needed.

According to one of the manufacturers of rails system (prosolar) you can go up to 30 panels side by side before you would run into any kind of problem.

 

[Brett V]

Based on what I see in your mount, there are solid spacers or clamps filling the gap between the frames. This does not allow for expansion.

They are solid T shaped aluminum clamps made for solar panels.

 

[sunshine_eggo]

They are solid T shaped aluminum clamps made for solar panels.

which would not allow for expansion.

 

[Brett V]

which would not allow for expansion.

I never said they did. I don't think thermal expansion is an issue at all. I'm sure it's happening to some extent, but at such a small amount as to be irrelavent.

 

[400bird]

Across the stated temperature range a 41" wide panel would increase by just over 1/2 inch from low to high.

What?
That sure is a lot of thermal expansion.
I'd say the OP and everyone needs some room for thermal expansion, but not much.

By some random 30 second dig, 0.533mm would be a rough expansion number for the aluminum frame 41" wide. (Glass has lowe thermal expansion)
That would put the long dimension at roughly 1mm of expansion.
That is if my random Google and 30 seconds of math is correct. But I don't think we'd see 1/2" of thermal expansion in a panel.

 

[sunshine_eggo]

What?
That sure is a lot of thermal expansion.
I'd say the OP and everyone needs some room for thermal expansion, but not much.

By some random 30 second dig, 0.533mm would be a rough expansion number for the aluminum frame 41" wide. (Glass has lowe thermal expansion)
That would put the long dimension at roughly 1mm of expansion.
That is if my random Google and 30 seconds of math is correct. But I don't think we'd see 1/2" of thermal expansion in a panel.

You are correct. I used this reference:

Thermal Expansion: Table of Coefficient of Thermal Expansion of Building Materials - linear expansion of glass, metal, wood, masonry & plastic in response to temperature changes

and I didn't check it against any other source. They list Aluminum as 10e^-5 instead of -6, so my decimal was off by one place.

 

[RV8R]

Based on what I see in your mount, there are solid spacers or clamps filling the gap between the frames. This does not allow for expansion.



Across the stated temperature range a 41" wide panel would increase by just over 1/2 inch from low to high.

I would argue that none is needed.

Sure, panels expand with heat and shrink with cold, but so does what they're attached to. Aluminum panel frames attached to aluminum rails will see zero relative expansion. Aluminum to wood or steel will, but even when there is a difference, the materials give a little and never experience anything near their yield strength or UTS. I've seen commercial ground and roof mounts that allow for zero expansion.

Yes, if you mount solar panels with zero clearance between two immobile blocks of stone, you will likely regret your choice, but if your array has free ends like in any ground or roof mount installation, you're good.

Consider that panels themselves are made of dissimilar materials. Glass and Aluminum have markedly different CTE.

I suppose it really matters, where it matters. In that I mean; the length of the array, the thermal expansion coefficient of the components involved, ect.

I recently drove by some pretty large solar farms near the Salton Sea & also in Idaho (at least I think it was Idaho). These were pretty impressive farms with 1000s of panels & seemingly mile(s) long. Expansion & contraction was “engineered“ into the design.

I did not worry about expansion with my tiny 6 panel 600W array. With a much larger system, I would figure it out.

 

[Bluedog225]

The clamps I used provided about 1/2" between the panels and I've gone from temperatures in the 90's to low teens with no problems. I have big 72 cell panels and believe they're 41" wide.

View attachment 122870

I’d appreciate seeing pics of your support structure from the other side.

 

[Steve_S]

There are 2 (probably more) ways that panels can be mounted.
Most Common is they are mounted onto Aluminium Rails with the appropriate mid & end clamps. In such a config, thermal issues are minimal as the aluminium will be stable across temperature variations. The feet holding the rains can be attached to wood framing or to the appropriate roofing type connectors if roof mounted. NOTE: Never attach Aluminium to PT Wood ! Isolate the aluminium and use Stainless Screws/Bolts to attach to PT Wood.

2nd option is to attach to wood directly, there are different types of mounts to do so. Some mount panels independently and some are for pairs of panels. There are MANY options with some being more forgiving than others. Wood, regardless of type will always expand & contract a bit through the seasons and if you haven't used Rails then this should be taken into account. NOTE that if the wood Twists and you have not used rails, this is when "stuff happen" and people start making Blue Air !

 

[meetyg]

NOTE: Never attach Aluminium to PT Wood ! Isolate the aluminium and use Stainless Screws/Bolts to attach to PT Wood.

Why not? what are the implications?

I have a old (painted) pergola. I suppose it's made of PT wood.

 

[Steve_S]

https://www.ussteel.com/documents/40705/43746/ACQ+Pressure+Treated+Lumber+Effect+on+Sheet+Steel.pdf/58b32449-adaa-6e0a-de38-b552944f7a56?t=1604458476292

There are tons of articles on using various metals with CCA & ACQ Pressure Treated wood. It disintegrates aluminium quite quickly, and is highly corrosive to many metals, hence why they use coated screws or hot dip galvanised or stainless.