Finally, the start of my 25kw Ground Mount grid-tie system

live4soccer7

Solar Enthusiast
Joined
Jun 15, 2020
Messages
257
Perhaps someone will have an opinion or suggestion on this.

I can use 4mm2 (12 gauge) wire from the panels to the inverters. This is about a 300-350' run. I was thinking of stepping this up to 6mm2 (10 gauge) for two reasons.

1. I will get less of a voltage drop
2. It will allow me to run more current through it down the road if I have to upgrade/change panels in an array. Surely panels will only get more efficient and powerful.
 

wattmatters

Solar Addict
Joined
Apr 16, 2021
Messages
854
I used 6mm² gauge in my little off-grid set up which is ~100' run. In my case I have to parallel x 3 so current is high(ish) and my inverter's operating voltage range is low and narrow, so it mattered more. Saved me from running two sets of smaller gauge wire.

In your case you don't appear to be overly budget constrained so I'd go with the fatter cable. But if you want to "future proof" then probably the best thing for that is ensuring a way you can run more/different cable if needed. IOW focus on the conduit and access pits for doing cables runs or a trench line that won't be covered by structures later on.
 

live4soccer7

Solar Enthusiast
Joined
Jun 15, 2020
Messages
257
Thanks. I'll definitely be trenching and running conduit so I can pull different/more wire down the road. I am keeping the trench out of any areas where there could possibly be a building. I'm still waiting on the panel pricing from CED. Everything is somewhat hinging on that right now.
 

wattmatters

Solar Addict
Joined
Apr 16, 2021
Messages
854
I have no idea what gauge cable my grid tied system uses, but it is roof mounted so not the distance you have. Still the furthest panel must be a 100' run.
 

SteinVT

New Member
Joined
Jul 30, 2021
Messages
25
Location
Vermont
I'm in the middle of building up a ground mount system similar to MarkSolar's. It's a Sunmodo rack with Adani bifacial panels, all purchased from my local CED Greentech in Burlington Vermont. Originally I was going to go the cement route, but I am very happy with the ground screws. A crew came in with a big Bobcat and put in the 16 screws in a couple of hours. Using the calculator on the Sunmobo website suggested a bunch of concrete would be needed. I would still be digging.

The screws were put in accurately enough that only minimal screwing around was needed to get everything lined up. Here is a picture of our work in progress. This represents 2 and 1/2 days of work by myself and my very understanding wife.
Solar Array.jpg

We had to leave on a trip but will be back new week and we hope to finish it up. Still working on the design for the connection to the house. - Mark
 

live4soccer7

Solar Enthusiast
Joined
Jun 15, 2020
Messages
257
That's looks fantastic. I'm really liking the idea of the sunmodo setup. What kind of bobcat attachment did they have? I have access to a bobcat, so it would be great to know what they used to screw in the posts. Pic?
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,365

I'm curious about your top-clamps to panel frame, from rails running parallel to that part of frame.
I want to do something similar, instead of traditional landscape panel orientation on two rails. Benefit of the configuration you have is number of rails = number of panel columns + 1, rather than number of panel columns x 2.

My concern is that flexing or tilting of rails allows frame to pull away from glass laminate. Laminate only goes a fraction of an inch into slot in frame. Only the two horizontal pipes prevents that.
With traditional configuration, rail itself keeps clamp spacing fixed.

I imagine using additional tie straps joining shorter ends of panel frame to hold spacing.
Mine would be bottom clips not top clamps.
 

SteinVT

New Member
Joined
Jul 30, 2021
Messages
25
Location
Vermont
I'm very much a DIY guy, but. I think I would leave this one to the professionals. The attachment to the Bobcat was more than a torque head, there is a lot of mechanism to keep everything straight. It takes two guys, one in the Bobcat and the second running the mechanism. The whole time a screw is going in, he monitored two bubble levels and adjusted about six levers. But they went in straight and true. $3850 for 16 screws. I would do again in a heartbeat. - Mark
 

MarkSolar

Solar Enthusiast
Joined
Mar 3, 2021
Messages
189
What kind of bobcat attachment did they have? I have access to a bobcat, so it would be great to know what they used to screw in the posts. Pic?
I used a bobcat with an auger (attached), the auger happened to have an output shaft that fit inside the ground screws without much slop. Every auger model is different, you'll have to check your output shaft to see if it will fit. Sunmodo has some info in their instructions on which augers will work out of the box. They offer adapters that you can buy/rent to adapt your auger to the ground screw. I had a bit of trouble finding the right shear pin to connect the auger to the ground screw because the standard one wasn't quite long enough. I think I ended up using a cat 2 tractor top pin link that I had in a junk box, but can't remember for sure. That pin needs to be really hardened, especially if your auger output is much smaller than the ID of the ground screw.

It sounds like the attachment they used on SteinVT system measures the torque of the installation, that's the only way to know for sure what the pullout strength is. That number is in the ground screw specs. You can also measure that torque by hand if you put a large digital torque head on the ground screw and get a really long pipe to turn it by hand and measure the torque. A lot of installers use a mini excavator with an attachment that looks like a pile driver to put in the ground screws. Those really do a nice job because the track helps hold the screw plumb during the install and you get more downforce with a mini.
 

Attachments

  • Bobcat.jpg
    Bobcat.jpg
    1.8 MB · Views: 9
Last edited:

SteinVT

New Member
Joined
Jul 30, 2021
Messages
25
Location
Vermont
I'm curious about your top-clamps to panel frame, from rails running parallel to that part of frame.
I want to do something similar, instead of traditional landscape panel orientation on two rails. Benefit of the configuration you have is number of rails = number of panel columns + 1, rather than number of panel columns x 2.
I think the design of the Sunmodo clamps does a good job of capturing the side rails of the panel. Hopefully that won't be a problem.
Screen Shot 2021-08-20 at 9.39.35 AM.png
We went with the portrait mode because of the bifacial panels. Our setup is 16 * 2P. If we had gone landscape, we probably could have gone 8 * 4L. That would have required 16 rails where we needed 17. - Mark
 

MarkSolar

Solar Enthusiast
Joined
Mar 3, 2021
Messages
189
My concern is that flexing or tilting of rails allows frame to pull away from glass laminate. Laminate only goes a fraction of an inch into slot in frame. Only the two horizontal pipes prevents that.
I had the same concern. My panel data sheet spells out 1/8" tolerance for out of plane flatness which seems overly optimistic. Getting the horizontal pipes in the "right" position was a process. I put a string line down the edge of each one and then installed the lower diagonal brace to fix the position of the lower pipe. Then the panel rails themselves act as diagonal braces for the top pipe position. One nice thing about Sunmodo is you have several ways to adjust the vertical height of the pipes, so that helps. Once all the diagonal braces and rails are in place, the horizontal pipes can't move and the whole thing is rigid. I ran a string along my panel faces to convince myself they were all flat.
 

MarkSolar

Solar Enthusiast
Joined
Mar 3, 2021
Messages
189
Perhaps someone will have an opinion or suggestion on this.

I can use 4mm2 (12 gauge) wire from the panels to the inverters. This is about a 300-350' run. I was thinking of stepping this up to 6mm2 (10 gauge) for two reasons.

1. I will get less of a voltage drop
2. It will allow me to run more current through it down the road if I have to upgrade/change panels in an array. Surely panels will only get more efficient and powerful.
Run the numbers using a DC voltage drop calculator. My intuition is you need 8gauge for that distance unless you can always keep the voltage really high. I used this calculator but there's tons of them online:
 

SteinVT

New Member
Joined
Jul 30, 2021
Messages
25
Location
Vermont
I ended up borrowing a laser to set the height of the posts and therefore the horizontal rails. The next trick was getting the vertical rails perpendicular to the horizontal rails. After a bunch of trail and error, I ended up using a four foot T-square for rough placement and matching diagonal measurements for final positioning.

To place the panels, we insert it Into the bottom position and slide up. These bifacial panels are heavy and it’s the only way my wife and I could do it. They seem to sit flat on the four clamps. - Mark
 

MarkSolar

Solar Enthusiast
Joined
Mar 3, 2021
Messages
189
To place the panels, we insert it Into the bottom position and slide up. These bifacial panels are heavy and it’s the only way my wife and I could do it. They seem to sit flat on the four clamps. - Mark
I did the same thing. Mine was 3 rows high in landscape mode, so I had a tall strong friend come over and he slid one up to the top and I used quick clamps to keep it up and out of the way. Same thing for middle row, then I fixed the bottom row in place with clamps and then lowered the top two rows down on top of the first. One mistake I made in my orientation is that the junction box on the panels is not in the middle, so I should have installed every other column of panels in the opposite orientation to make the plus to minus cable connections come out clean. The way I did it I had to run them sort of diagonally across the panel. I would have taken every other column apart except you can't use those clamps more than once and I didn't feel like buying half of them a second time.
 

live4soccer7

Solar Enthusiast
Joined
Jun 15, 2020
Messages
257
Does anyone have any experience with the SMA Sunny Boy SPS aspect of the inverters? I believe it is an add on, but I don't know that any of the other inverters on the market offer that. I would be highly valuable to have 2000W at your disposal during the day without the grid and battery packs. That's equivalent to a 15A circuit in your home.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,365
No experience, just read about it.
Apparently needs a switch and an outlet. Maybe not much more.
There was a time when Rapid Shut Down disabled Secure Power, but I think SMA says now it is compatible. (But I don't know how that works, where it gets power for signaling, what is different to re-enable it. Could just be firmware, if RSD allows a low voltage through.)

All the more reason to have strings of multiple orientations connected. That will keep available power high longer.
 

live4soccer7

Solar Enthusiast
Joined
Jun 15, 2020
Messages
257
After looking at fronius, I was thinking of going with 3 fronius 15.5kw units. Now I'm thinking of just going back to sunny boys or maybe just one fronius and the rest sunny boys to allow the use of power when things go down. That happens several times a year and we are at the "end of the line" on the power grid, so they aren't typically in too much of a hurry to get power to us if there are larger fish to take care of. Having even one SPS would allow us to get pellet stoves going, keep the fridge/freezer cool on cycles though the day, and charge devices. I have some UPS units for electronics, but those are main just to allow clean shutdowns of equipment.
 

MarkSolar

Solar Enthusiast
Joined
Mar 3, 2021
Messages
189
My thoughts on the SPS were that our power outages tend to occur during storms or at night. It's also dependent on me being there to plug something in, so I might as well buy a small generator if I have to be there anyway to hook it up. I guess if it came as a free feature of the inverter I wouldn't turn it down, but the cost didn't seem to justify the marginal value. I have a 2000W Honda generator for construction use, it's easy to start and really quiet, I'd rather know I have that available any time.
 

live4soccer7

Solar Enthusiast
Joined
Jun 15, 2020
Messages
257
My thoughts on the SPS were that our power outages tend to occur during storms or at night. It's also dependent on me being there to plug something in, so I might as well buy a small generator if I have to be there anyway to hook it up. I guess if it came as a free feature of the inverter I wouldn't turn it down, but the cost didn't seem to justify the marginal value. I have a 2000W Honda generator for construction use, it's easy to start and really quiet, I'd rather know I have that available any time.
I hear you on that. I have a little "genny" as well. I think it is a honda 2000 too.

Still waiting to hear back from CED. I might have to give another branch a call as I'd like to start moving forward and I don't really want to until I know exactly what I am getting.
 
Top