Solar 2022: Other People's Arrays

So… @Canem and I got something loaded onto trailers today (pulled by Fords - all the interesting stuff I get involved in seems to include a lot of Fords).

His trailer’s an awful lot nicer than the one I use. Though I have plans to do a full refresh on the one I use, at some point.

This is 35.5kW of solar panels, in the form of 100x 144 half-cell 355W panels. The plan is to build five ground mount arrays at two different locations (other people’s homes, they’ll of course be doing the electrical interconnection work on their primary residence, as allowed out here). One will be ~14kW, one will be ~21kW.

After building my arrays, the reasonable topic of “Ok, how would you improve this?” came up in conversation - and while I’m happy with my arrays, and how I did things, I can come up with some ways to improve it. The biggest is that my wooden A-frames, while fairly cheap to build when I bought lumber, are incredibly labor intensive, and are “insanely overbuilt,” to what is probably a flaw. No problems, I like things that way, but we can improve it. Especially since metalworking isn’t my thing, but I now know someone who does some properly fine metalwork and welding. :wink:

The general concept is to build ground mount A-frames, as cheaply as we possibly can, while maintaining robust structural strength and, of course, code compliance and legality. Out here, most people have land - so a ground mount array, clear of the shade, typically won’t be a problem. As a major bonus, you now eliminate any roof work, which makes things a lot more reasonable for quite a few people, myself included. Ask me to help with a ground mount array, I’m excited. Ask me to go on a roof, there’d better be a damned good reason. I’m no longer likely to bounce if I fall off a roof, I’m likely to spend some serious time in a hospital.

This thread serves as a discussion and at least partial build log thread, though. I’m digging into the design and math for a couple scenarios, and trying to optimize cost throughout. If it’s cheaper to mount the inverters to the arrays and run AC back to the house (conveniently skipping the local “understanding” about a short vertical run to the inverters), then so be it. But expect some fun NEC math here!

Goal: Two large installs built and online by the end of 2022, with much learned about how to further improve the process.

FWD: pv magazine International: Solar trailer for off-grid applications from France. Solar trailer for off-grid applications from France – pv magazine International

Huh, that looks legit, just a bit heavy! Sure you shouldn’t be posting that in the solar trailer thread? :wink:

Excellent. Both arrays have power company approval, now to get the plans drawn up and submitted!

Yeah. I mean your piles alone…

Me, lumber would still be pretty cheap, but I would have used precast patio anchors and 2x4s :wink:

For the eyeballing of onelines for errors:

Solar array drawings. Please point out any errors/omissions/weird stuff you spot!

They’re based on what I got approved, so should be mostly fine, but another set of eyes is good, I’ve ported everything to OpenOffice, which is a circle of hell.

My only questions are;

I believe the 10.1 is after compensating for a +70C max temperature.
IIRC the conversion for Voc was 1.2 @ -25C. Although I guess I’d better go check, as I get that as a Voc of 562V

Ah, yep that’s what I was missing :slight_smile:

I got ~560v @ -40° C. Still fine since it looks like the Sunny boy can handle 600v.

Yeah per NEC 2017 690.7(A) the factor at -25C is 1.2 and 1.25 at -40C.
So 46.8v * 1.2 = 56.16.

Are you using the electrical numbers at STC or NMOT?

Or 53.8v based on the -0.30%/C from the datasheet.

We rarely see below 0F, -10F is about the coldest I’ve seen. -20 or -25C is fine.

There’s a coefficient of short circuit current - current goes up with increasing temperatures.

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i just bumped this post by accident. I have designed almost the exact array, similar panels and the same inverter as i don’t have any more room on my roof. ( filled with solar thermal tubes) I stopped because of the high cost of the wiring . did you end up with the inverter at the array, or sending dc to the house? and how far is the array from the house? thanks for the info in advance.

You can do it however you want, and it’s up to you to optimize wire cost.

My array has the inverters at the house, about 120-150’ of underground run. I believe @Canem is planning to put the inverters at the array, and run AC underground to the house. There’s not a huge win to either method - you need more wires for running DC to the house, but they’re going to be 12AWG. You need fewer wires for AC, but they’ll be 8 or 10 AWG (and if you can convince your inspector to let you undersize the neutral for the inverters, there are some more savings to be had).

Would be willing to make a post discussing your solar tubes? :slight_smile:

i think at the distance i was planning, i had to use #6 wire which adds up real fast. i could put together something for the solar thermal. i have 75 tubes in a boiler loop that heats an endless pool and a floor in the same room. I had to do it myself as i could not find anyone that would attempt it. I live in Montana. The only other one I have seen as large is at a car wash in Columbia Falls, MT.

I’ll be at about 170’ from the house, with the inverters at the array in a pasture out away from the trees. That works out to be 10AWG for AC wiring that distance from a Sunny Boy 6 inverter.

Does your inverter have that emergency power outlet that lets you create a small amount of power during power outage? did you wire that to bring in that circuit in the event of no power situation?

Yes, ‘Secure Power Supply’ outlet they call it. For my purposes I’m routing 12awg all the way to the house for that too so the plugs can be by the house main breaker panel, so each inverter has the 10AWG wires supplying grid power and 12awg for the backup outlet [1800watts max IIRC]. And double everything, as I’ve got 2 inverters (It’s 2, 20-panel 7kw arrays on the same long frame).

thanks for the answer. one last question and i’ll stop … for a while. looking at the diagram you posted, it shows all this fit into 3/4" schedule 80 pvc? that must have been a tight fit. what wire type did you use to get this to fit? ( i know its 10 g but i am wondering about the wire code itself. )

You can cram a lot in a 3/4 Sch80 conduit.

I ran 1" for my stuff, to make pulling easier. The main problem is that once you start getting too many wires in a conduit, you have to start derating for conduit fill reasons, and that’s a nuisance in a hurry.