Selecting low profile or standard height channel strut

[kaid]

I have a 16' fiberglass travel trailer and will be mounting three 120 watt panels directly on to aluminum Unistrut. I'd like to use the low profile 13/16" strut to keep height down for aerodynamics and aesthetics but also know that airflow and ventilation is a good thing. Most of the posts I've seen here that use low profile strut mount the panels onto another cross beam of strut or a tilting mount - both of which raise the panel another bit off the roof.

Curious to hear the wisdom of the crowd here about why I may want to go with standard height strut at 1 5/8" instead of the 13/16" low profile.

 

[sunshine_eggo]

I have a 16' fiberglass travel trailer and will be mounting three 120 watt panels directly on to aluminum Unistrut. I'd like to use the low profile 13/16" strut to keep height down for aerodynamics and aesthetics but also know that airflow and ventilation is a good thing. Most of the posts I've seen here that use low profile strut mount the panels onto another cross beam of strut or a tilting mount - both of which raise the panel another bit off the roof.

Curious to hear the wisdom of the crowd here about why I may want to go with standard height strut at 1 5/8" instead of the 13/16" low profile.

11/16" increase in gap will likely make negligible difference in aero, cooling or aesthetics; however, I would still opt for the greater gap. Poor ventilation of hot panels flat on a roof make them hotter, perform worse and degrade faster.

 

[OzSolar]

I have a 16' fiberglass travel trailer and will be mounting three 120 watt panels directly on to aluminum Unistrut. I'd like to use the low profile 13/16" strut to keep height down for aerodynamics and aesthetics but also know that airflow and ventilation is a good thing. Most of the posts I've seen here that use low profile strut mount the panels onto another cross beam of strut or a tilting mount - both of which raise the panel another bit off the roof.

Curious to hear the wisdom of the crowd here about why I may want to go with standard height strut at 1 5/8" instead of the 13/16" low profile.

Shallow is less rigid which may or may not be an issue. The big challenge I have with it is when using it in standard applications, like mounting a disconnect on a wall, is that there's almost no room to get your hardware to tighten down before it bottoms out.

That can be somewhat mitigated with careful hardware selection until you need a 5/8" bolt. 1/2" won't and 3/4" bottoms out.

 

[HRTKD]

I've considered using the lower profile strut on the roof of my RV. With the panels mounted flat, there isn't an effective way for heat to dissipate without a breeze. The increased height may be helpful for that.

I've seen the low profile aluminum strut, but not the regular size strut in aluminum. Do you have a link/source for that?

 

[kaid]

I've considered using the lower profile strut on the roof of my RV. With the panels mounted flat, there isn't an effective way for heat to dissipate without a breeze. The increased height may be helpful for that.

I've seen the low profile aluminum strut, but not the regular size strut in aluminum. Do you have a link/source for that?

I've seen it at McMaster-Carr and Grainer - haven't priced shipping yet.

McMaster-Carr

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https://www.grainger.com/product/GRAINGER-APPROVED-Strut-Channel-Solid-Wall-Aluminum-45YW25

They both have the slotted channel as well but with VHB I'm going solid.

Shallow is less rigid which may or may not be an issue. The big challenge I have with it is when using it in standard applications, like mounting a disconnect on a wall, is that there's almost no room to get your hardware to tighten down before it bottoms out.

That can be somewhat mitigated with careful hardware selection until you need a 5/8" bolt. 1/2" won't and 3/4" bottoms out.

I'm planning to use 1' pieces of strut. Less rigid is a benefit with the slightly irregular shape of the roof but I don't know it will matter with short pieces.

Good to know on hardware - thanks!

11/16" increase in gap will likely make negligible difference in aero, cooling or aesthetics; however, I would still opt for the greater gap. Poor ventilation of hot panels flat on a roof make them hotter, perform worse and degrade faster.

I put the panels up on the roof to see how much of a difference and while up close it's obvious it is probably far less obvious from the ground. the roof also curves a bit so the edges will have a larger gap. In the pictures, I'm also only holding up one corner rather than the whole side - hard to hold the tape and the panel at the same time. I also hope the curve will help promote airflow.

This is a small camper - the roof is visible from standing on the ground where it's far less visible in those class A's with the large arrays!

 

[AmyG]

They both have the slotted channel as well but with VHB I'm going solid.

Just for clarification - does this mean you plan to use VHB tape to attach the 1 foot sections of strut to your roof?

 

[kaid]

Just for clarification - does this mean you plan to use VHB tape to attach the 1 foot sections of strut to your roof?

Yes, with the caveat that I haven’t yet checked the necessary square inches with 3M to support the weight. It’ll be bonded onto new (2022) fiberglass gel coat.

 

[AmyG]

Yes, with the caveat that I haven’t yet checked the necessary square inches with 3M to support the weight. It’ll be bonded onto new (2022) fiberglass gel coat.

Not to hijack the purpose of your original post, but that would make me nervous. I think the reason that most of the posts you've seen about strut describe mounting cross pieces for panel brackets is because the lower struts are bolted or screwed to the frame, and then the cross pieces allow spacing required for the panels.

 

[kaid]

Not to hijack the purpose of your original post, but that would make me nervous. I think the reason that most of the posts you've seen about strut describe mounting cross pieces for panel brackets is because the lower struts are bolted or screwed to the frame, and then the cross pieces allow spacing required for the panels.

Is that concern related to the length of strut & VHB specifically or VHB in general? I do intend to reach out to 3M on recommended in^2, but thought I was already being a little overkill. AM Solar's stainless mounts are 2.5" x 1", so with 4 mounts there is 10 in^2 of tape. Assuming 1" wide tape, I would have 12" x 1" on the front corners and 6" x 1" on the back corners (this 12" section is shared with the neighboring panel), for 36 in^2 of tape per panel.

And I would much rather be corrected now than once the adhesive goes on!

 

[AmyG]

Is that concern related to the length of strut & VHB specifically or VHB in general?

Well, both. You'll find different opinions on this forum about using VHB tape alone vs tape in conjunction with another method like screws. Personally, tape alone would be too risky for me. Larger surface area is obviously better, but even with full length struts I'd want some screws or bolts into the frame to be able to pull my trailer down the interstate without being worried that something would fly off and hurt someone. Any chance there is frame under some of the places you plan to put strut that you could screw into? If not, I'd say read through some posts about using tape from the more experienced folks on the forum and decide what you're okay with.