Ground mount recommendations

[Jack Rabbit Off Grid]

I think since I am unable to dig that deep I’m going to do something like this but out of wood. I’m going to mount my panels landscape so their surface area is going to be 28’w by 7’ tall. How would I calculate how large to make my concrete blocks? I found a calculator for pounds per square foot. I’m thinking of probably 8 legs. 200# ea 300#?

 

[Samsonite801]

I think since I am unable to dig that deep I’m going to do something like this but out of wood. I’m going to mount my panels landscape so their surface area is going to be 28’w by 7’ tall. How would I calculate how large to make my concrete blocks? I found a calculator for pounds per square foot. I’m thinking of probably 8 legs. 200# ea 300#?

Hey if you need more weight, you could also distribute it sideways, by building a frame on the bottom that holds standard cinderblocks (or the solid ones). I remember when I was doing wireless internet, and we would install non-penetrating roof mounts, they had like a frame holder (simple angle iron rectangles), and you could put 10 cinderblocks on the smaller ones, and 20 on bigger ones (and more on even larger ones), to hold a large terrestrial dish antenna mount, without drilling any holes in the roof, but the weight was super heavy, you could even stack them double high on the cinderblocks if you needed more weight.

 

[Zerocool00]

I just spent two months after work, installing 20,600w or 48 ea QCells at 45° PV array angle on a shale/clay 36° slope, using 48 ea 4x4 post (8’-16’ L), sprayed termite spray, dried them sealed all posts with Black synthetic rubber, dug with post hole diggers/chisel as deep as possible, for shallow holes I poured concrete above ground inside a 12”-14” cylinder, Sealed top of concrete to posts with synthetic rubber, 34 pieces Unistrut, 22 ea 2x4x12’ bracing, 150+ lbs of concrete per post, 112 ea 3/8” x 2.5” ss bolts, 112 ea Belleville washers, 96 ea 3/8” x 4” galv lag bolts. It’s withstood 40 mph winds so far. Going around perimeter with 1x10 oak boards, spaced about 4” apart for a wind block, visual appeal, panel perimeter security and extra weight. Wiring now...

This sounds exactly like what I was planning. Could you share some photos?

 

[pvdude]

I used snapnrack.com for my ground mount.
Sandy soil here, boring piers was easy.
Rated for 170mph winds.
We get about 110-120 mph here in hurricanes, hope that the thing stays in place!



However, on page 12 they also show a “beam footing option” that does not require deep holes.
It uses tons of concrete mass to keep the array on the ground in wind.

https://snapnrack.com/wp-content/uploads/2019/07/S200-Install-Manual_v1.24.pdf

 

[SunnyNM]

I used snapnrack.com for my ground mount.
Sandy soil here, boring piers was easy.
Rated for 170mph winds.
We get about 110-120 mph here in hurricanes, hope that the thing stays in place!

View attachment 84827
View attachment 84828
However, on page 12 they also show a “beam footing option” that does not require deep holes.
It uses tons of concrete mass to keep the array on the ground in wind.

https://snapnrack.com/wp-content/uploads/2019/07/S200-Install-Manual_v1.24.pdf

Very nice. This looks very similar to what I need. Cost?

 

[pvdude]

Cost was about $900 for all the Snapnrack aluminum. Rails were about $500 of that. Shipping about $150.
I have since discovered that https://www.rexelusa.com/ (local store) sells Snapnrack, so now I order from them, free delivery!

Buying the steel pipe (schedule 40, 21ft, 10 pieces) was a trip, the local steelyard would only quote prices good for that day only, inflation had the steel prices changing so often.
$800, free delivery, a year ago. No idea how much steel had gone up since.

 

[MichaelK]

Here is a pic of my rotating array V4.0 design. I drilled a hole 36" deep and sunk the 10' post in concrete. It is extremely sturdy. This array can hold six panels in landscape orientation, though I have them here in portrait because I wanted 120VDC. What I'm finding is the by rotating my arrays East and West over the course of the day, I can more or less double output. Most importantly, with the arrays facing SE, I can start my wellpump at 7:30am.

 

[Zwy]

I think since I am unable to dig that deep I’m going to do something like this but out of wood. I’m going to mount my panels landscape so their surface area is going to be 28’w by 7’ tall. How would I calculate how large to make my concrete blocks? I found a calculator for pounds per square foot. I’m thinking of probably 8 legs. 200# ea 300#?

Just pour a flat slab on top if your surface is solid rock. This provides ballast. If you want it anchored to the rock, drill holes with hammer drill into the rock and use some of the epoxy used for fastening machinery to cement, then tie into rebar. Something similar to the Hilti injectable. https://www.hilti.com/c/CLS_FASTENER_7135/CLS_INJECTABLE_ADHESIVE_ANCHORS_7135/r4929903

 

[WYtreasure]

Plastic snow fence is one inexpensive, quick, easy and ugly way to block a lot of wind. The dark green with smaller holes and more plastic works real well even in 70+ mph winds.
There are also wooden slats woven together with wire. That is a snow fence that stands up to every wind I have ever seen.

 

[BillG]

The standard engineering we get for NORCAL ground mount systems is 12" diameter by 4.5' deep holes (!)
Total overkill IMO, but several different engineers, for several different big name solar outfits (who outsource GM's because they are such a PITA to dig) all end up spec'ing the 4.5' deep holes which take 1/4 cubic yard of mud each.
The easier but less asthetic way to go if theres rock is a concrete surface mount ballast system. (basically forming large rectangular footings on the surface, one for each front/back pair of posts.)

If the soil conditions are good, using a 12" auger is an absolute breeze. If there's rock, it's a frigging nightmare to dig 4' piers. major excavation work required measured in days instead of minutes for auguring...

 

[onokai]

I built a ground mount with wood and unistruts. No wood ground contact-very solid-been thru big wind events as well.
details are here: all bolted-poured concrete filled sono tubes with simpson strong tie post supports. All wood is bolted with galvanized bolts

Ground Mounted 9,600 watt Sol Arc do it yourself solar system-Solar Pirate

Here are the details of my 24 x400 9600 watt jinko panel system. I started with a solar assessment tool for the site Its a handy device loaned out from a local energy supplier. Our side hill was a perfect south facing site. Due to the slope I also slanted it a bit to the west a few degrees. We...

diysolarforum.com

 

[Jack Rabbit Off Grid]

Since my last post I have scrapped all previous design ideas. Since then I have purchased a 2.5T mini excavator so now pouring a solid level slab is now an option. I have also since ordered 2 Tamarack 5 panel single pole ground mounts.

I am going to level two spots and pour 5’x5’x2 1/2’ thick pads. Haven’t decided if I’m going To weld a 1’x1’ flat bolting flange to the bottom of the posts and concrete anchor them down or just stick the posts in the concrete yet?

 

[onokai]

I had grass under array and it all died-still grows slightly on south side and needs a bit of gas trimming now and then
Cement slab is overkill in my opionion maybe a cement or PT curb filled with crushed rock on top of weed mat (matt only needed at edges due to more light there)

 

[MarkSolar]

Since my last post I have scrapped all previous design ideas. Since then I have purchased a 2.5T mini excavator so now pouring a solid level slab is now an option. I have also since ordered 2 Tamarack 5 panel single pole ground mounts.

I am going to level two spots and pour 5’x5’x2 1/2’ thick pads. Haven’t decided if I’m going To weld a 1’x1’ flat bolting flange to the bottom of the posts and concrete anchor them down or just stick the posts in the concrete yet?

I think you're on the right track. We live on glacial till and putting in ground screws was a nightmare even with the largest skid steer I could find. If I had it to do over I'd pour a slab. The other benefit of a slab is it's pretty reflective, so you have the option of getting bifacial panels and benefiting from the extra production.

I would use the bolt on flange. When you put metal in concrete there is a lot of corrosion, so 1/2" bolts will last a lot longer than even a heavy wall pipe. The plate also gives you some adjustment capability to get the pole plumb. If you look at how they mount light poles and sign posts, they use a plate. I worked concrete for awhile, we would get that plate with the four bolts installed and jamb nutted to the plate so it was one piece. We'd use a string line to locate the plate in the concrete and push it in as soon as we poured. The other option if you weld would be to weld the pipe to a flat plate, that gives you a little more room to get things in the exact right spot.

Unless you're experienced it can be hard to pour a 2.5" slab. It's hard to keep the wire down, and to push the rocks down to finish it. Its also harder to get the L bolts for that plate set at the right depth. If you're hiring a contractor they won't have a problem.

 

[WYtreasure]

Unless you're experienced it can be hard to pour a 2.5" slab. It's hard to keep the wire down, and to push the rocks down to finish it. Its also harder to get the L bolts for that plate set at the right depth. If you're hiring a contractor they won't have a problem.

Jack Rabbit said 2.5 FEET, not 2.5 INCHES.

That's one serious chunk of concrete.

 

[MarkSolar]

Jack Rabbit said 2.5 FEET, not 2.5 INCHES.

That's one serious chunk of concrete.

OMG, missed that, could that be a typo? That would be a 5 ton slab to hold down 5 panels. If it were 2.5 inches thick it would be about 750# which might be a bit light by itself but there's also the weight of the panels and racking so it's probably about 1000#, which seems like it would be close to adequate.
My seat of the pants calculation says large 5 panels are about 90 sqft, a 60mph wind on a vertical flat wall is about 10psf, so that would be 900#. For 120mph wind it's about 40psf so that would be 3600# force on a wall. The uplift will be less than that amount but don't know the angle so can't make a guesstimate.

 

[onokai]

My guess is Jack Rabbit is down under (Aus) with a 2.5 digger mate mini excavator

 

[Canxane]

Contact someone who builds fences (check craiglist). Your basic corner post fence is a 4 or 5 inch schedule 80 or higher steel pipe that is pounded into the ground and the "h braces" are welded. The same guy can pound the posts wherever you want, at whatever height you need. He will also weld the cross members. It is a basic job for a fence builder. You can then stick any rail system you want on it. Much faster and cheaper than any other options, not to mention must stronger. No concrete, the posts are level and straight. Stick some geotextile cloth under it and dump a load of gravel on the fabric to keep the weed pressure down under the array. Then you don't need to mow or do any maintenance underneath. Looks better too.

The pounded posts, and all the welding was under $500 labor for the entire day. The adjustable rack lets me change the tilt.

 

[MarkSolar]

Contact someone who builds fences (check craiglist). Your basic corner post fence is a 4 or 5 inch schedule 80 or higher steel pipe that is pounded into the ground and the "h braces" are welded. The same guy can pound the posts wherever you want, at whatever height you need. He will also weld the cross members. It is a basic job for a fence builder. You can then stick any rail system you want on it. Much faster and cheaper than any other options, not to mention must stronger. No concrete, the posts are level and straight. Stick some geotextile cloth under it and dump a load of gravel on the fabric to keep the weed pressure down under the array. Then you don't need to mow or do any maintenance underneath. Looks better too.

The pounded posts, and all the welding was under $500 labor for the entire day. The adjustable rack lets me change the tilt.

A pounded post has almost no pullout strength, which is the most important thing for a solar rack. If there is any kind of permitting involved it's hard to imagine that getting approved.
I have a pounder that fits on the back of my tractor and in my area where there's lots of rocks it just doesn't work. If I'm lucky enough to find a spot to get a post in, the chances of it being plumb are almost zero.

 

[Warpspeed]

In a very windy stormy environment, it may be worth thinking about mounting panels horizontal and at a much reduced height.
In fact in a full evil grey sky, up beats any other orientation for power output.
Use one of the on line solar calculators to calculate average monthly power at your location for various panel orientations.
Horizontal will definitely produce a lower total yearly average, but it may not be as much less as you might expect. The shortfall might even be made up for with more panels purchased from the savings in framework.
Possibly worth looking into, even if the idea does not have much appeal initially.