Finally installing PV on my roof in LA: day 1

[DanKegel]

They're installing the rails and conduits today. The crew that installed the penetrations never did quite finish, so this crew is having to flash one mount and caulk another. They ran out of LG 305's, so they're substituting same number of LG 310's, so that's a bonus 125 watts, woot Panels themselves go on in a couple days.

Pics as usual at https://goo.gl/photos/s6s1n69k1EBuSejE8

[SunEagle]

Looking good Dan. Thanks for the photos.

[DanKegel]

oh noes! reverse tilt mount was supposed to be tilted towards south 20 degrees, but it's more like 2 degrees.
Trying to explain problem to my official contact at the installer now.
Pics show one of the installers measuring current tilt, and demonstrating what 20 degrees would look like.

Installer says they'll fix it. Glad I was paying attention - wish I'd caught it sooner, but at least I got it before panels were mounted.

[SunEagle]

Wow. I guess it was easy to make the mistake until they add the rails and then it became easy to see the low angle for those reverse tilt panels.

[DanKegel]

Yep. You can see how they fixed it in today's pictures ( https://goo.gl/photos/s6s1n69k1EBuSejE8 ), glad I caught it early.

They're a little flummoxed by my request to use hardwired ethernet. I made it easy for them by running the ethernet right to the solaredge box, and giving them a link to the how-to video ( https://www.youtube.com/watch?v=AyL67b7JMGk ), all I'm asking for them is to put it in a conduit and plug it in. Sounds like everybody else goes for Zigbee.

The LG310s look real pretty. The bifacials do, too, but they're not mounted yet -- the edge clamps they need aren't here yet. So no generation until those come in, maybe Monday.

Did anybody notice the identical triplets in one picture? https://goo.gl/photos/oSmhoKiqELrkS3e28

[sensij]

Nice adjustment. You've probably already planned for it, but the bifacials will have their best chance to outperform if they can be mounted so the support brackets are not shadowing the backside.

Stick to your guns on the hardwire. SolarEdge Zigbee is like early wireless routers... even if it only needs to be reset a couple times a year, it will still be a couple times more than you'd like.

[J.P.M.]

Dan: Absolutely NOMB, and I thought I'd stay out of your parade and not rain on it, but I'd have and do have a concern about the longer reverse tilt support arrangement. Who designed them ? Were they built to the drawings ? As built, unless the connection between the bracket and the panel frame is designed to take out that moment (bending) load, which is unlikely, or the bracket at the roof is a pin type connection, wind or other external loads will exert a moment load at the roof connection. That type of loading and of the magnitude the longer arm will induce is usually not something a screwed in connection to the roof of that type is designed to withstand, particularly when the loading is cyclic, or occasional and reversing, or recurring. Over time, sooner or later, the alternating stresses will cause rocking motion as things loosen up, as they will with this arrangement, and that will cause problems.

Having the longer supports oriented normal to the panel plane with a pin type connection at or close to the roof roof might have been one of several other ways to do it.

Just my $0.02.

[J.P.M.]

[QUOTE=sensij;n300608]the bifacials will have their best chance to outperform if they can be mounted so the support brackets are not shadowing the backside.

QUOTE]
How would that be done ? Anyway, assuming you're thinking about shadows, and particularly after looking at the surroundings from the photos, since it seems likely that little of the insolation that gets to the reverse side of the panels will be specular in nature, and therefore little if any shadow will be cast, except probably a bit early and late in summer, how much of a problem will it be ?

[sensij]

Yeah, it won't be shadowing any beam irradiance. Since there will be LG panels installed on the reverse tilt stand as well, those LG panels should be located over the unistrut support members, which look like they will be just a couple inches under the panel. It might not make much difference, but having empty space behind the Sunpreme's will give any diffuse light the best chance to get to a cell.

I was thinking that the panels would be installed portrait orientation, with clamps on the short ends. On further review of the Sunpreme installation manual, I'm not sure that the panel can mechanically tolerate end mounting without support in the center. The manual recommends that in a high albedo environment, the portrait orientation is good but the rails should run along the long sides, not the short sides (see notes in rightmost column of page 1, and figure 2 on page 3).

[DanKegel]

I don't think the supports were designed, they were improvised. The lower part of the long supports were designed for tilt mounts on a flat roof, not for reverse tilt on a sloped roof. The resulting install does seem kludgy... struts with knees? Really?
I'm not even sure how one would check to see if the screws were coming loose - they're not visible (except maybe from the bottom; I think at least one didn't go directly into a rafter.)
I guess I can go up and wiggle it by hand once a year and see if it feels loose.

Anyone have a favorite brand of reverse tilt mount kit, for future reference?

I hope the installer is planning to install rails parallel to the panels to clamp them to. I'll be watching, with a copy of the sunpreme data sheet handy.

The strut a couple inches below the panel will "shade" it from diffuse light. But I think only one of the panels has this problem; the other seems like it might be unobstructed. If so, this'll be a natural experiment to see how much difference it makes.

[J.P.M.]

I don't think the supports were designed, they were improvised.

More NOMB, but it reads to me as if you're going to allow that improvisation to be changed without some knowledgeable professional at least looking at it ? What are you thinking ?

If the inspector is myopic or doesn't know/care much about structural design, you might get away with it.

Not my roof and still NOMB, but I'd not use what I think I see. I'm not a fear monger, but simply put, I'd be concerned about safety.

Similar to the standoffs in a line that looks to be non parallel to the roof ridge that Sensij found, this is another example of barn job work.

[DanKegel]

Hey, I'm a babe in the woods when it comes to mounting solar panels. Do you know of a list of good steep-roof reverse-tilt mount kits I can point them to and say "If you don't have an engineer on staff to design mounts properly, you should be using one of these instead of improvising"?

And I'm not trying to get away with anything here. I'm just a guy who trusted an installer when they said they could do reverse-tilt mounts. I'd like to have some good ammo Monday when I talk to them about this.

[J.P.M.]

Hey, I'm a babe in the woods when it comes to mounting solar panels. Do you know of a list of good steep-roof reverse-tilt mount kits I can point them to and say "If you don't have an engineer on staff to design mounts properly, you should be using one of these instead of improvising"?

And I'm not trying to get away with anything here. I'm just a guy who trusted an installer when they said they could do reverse-tilt mounts. I'd like to have some good ammo Monday when I talk to them about this.

Dan: The short answer to your question is no. And, for a lot of reasons, practical, legal and ethical, I do not make recommendations dealing with specific engineering questions without a contract.

I only wrote what I did because I saw something that may be, IMO, dangerous. Part of the attitude I picked up from an engineering career that some call being a prick.

However, Google is not a prick. A quick search will lead you to many ideas and options. Not recommending anything, except that you seek qualified advice from a P.E., but Ironridge has a tilt leg assembly that may be a good idea generator for you. I've also seen some stuff by a co. called Sunmodo that seems fit for purpose. I'm sure there are others.

As you peruse websites, note that the longer (upper) strut is usually, or often, oriented normal the panel, and that the adjustable struts are usually slide (sleeve) types that keep the strut from bending.

As for your motive(s), I did not mean to imply you are trying to get away with anything. However, and not a knock, my experience is that inspector attention to detail and opinion as to what's important tends to vary some with their experience and/opinion. They are still however, always right.

I'll save my opinions about people such as yourself who seem to want to save the world with solar/R.E. without, IMO anyway, much concern for practical details or the consequences of not taking the time to deal with the details for some other time.

Until then, take what you want of the above. Scrap the rest.

[DanKegel]

Pointing out something potentially dangerous doesn't make someone a prick. It's helpful.

I couldn't find anything at all about using Ironridge or Sunmodo for reverse tilt on steep sloped roofs.

Unirac specifically advises against it:
http://unirac.com/wp-content/uploads...LICABILITY.PDF

Spice Solar's one reference to reverse tilt,
http://www.spicesolar.com/wp-content...-TILT-ELEV.pdf
shows a joint at the roof surface.

Most detailed info I found so far is from an Australian outfit.
http://www.clenergy.com/Products/Mou...ack/Solar-Roof
has an adjustable tilt leg installation guide that looks like it gives good guidance:
http://www.clenergy.com/getmedia/1e8..._V3-2.pdf.aspx
and it does indeed have a joint at the roof surface as you suggested.

Having that data isn't quite enough to go to the installer and say "you did it wrong, rip out the existing supports, void the warranty on the roof, and install something different", but I might be able to say "I don't think that reverse tilt is to code".

It'd be helpful to have a link to an article about the hazards here and/or on something more united-states oriented on how to properly design reverse tilt mounts.
And/or success reports from the field with reverse tilt mount kits in the US. I guess I should start a separate thread for that question.

[J.P.M.]

It'd be helpful to have a link to an article about the hazards here and/or on something more United States oriented on how to properly design reverse tilt mounts.

It might be, but as a practical matter, that might be getting into an area of engineering design that's somewhat particular to each application in a way that might involve some liability questions. Also, rules of thumb such as may be the result are usually not much use except for measuring thumbs, particularly if/when safety might be an issue. That's one reason why building codes tend to be proscriptive rather than performance oriented.

I'd suggest seeking out an engineering professional after some honest and sober reflection as to the self efficacy of dealing with such questions, and in so doing, erring on the side of caution as to knowing one's limits. An increased probability of property damage or personal injury or worse can be the result of ignorance.

I'm fully aware that most arrays have little, if anything in the way of actual structural or other engineering design considerations and don't fail, at least not immediately. AFAIK, most off standard designs usually rely upon, and chew into, factors of safety and careful thought that are supposed to make up for the unseen and for mistakes, but not laziness or deliberate ignorance borne of such laziness.