Geoballasted Ground-Mounted Solar Panels

[DuaeGuttae]

Have any of you who keep up with the solar industry (@peakbagger, @begreen, @jebatty) seen or studied any geoballasted ground-mount solar systems?

My husband and I are working with a local solar contractor on a good-sized array that will be located in a rather barren part of our property. The company typically uses poured cement footers (if that's the right term) to mount the poles, but the owner brought up this other technique as a possibility. It's intriguing, and I wondered if you all had any experience or opinions.

Our plans are to have a 13.4 kilowatt system facing south with string inverters and optimizers. We have good sun exposure year-round. Summer production is hurt here because of high temperatures, but winter production is significant. (Summer is still better, just by not as much as one might expect.)

 

[peakbagger]

I dont have any experience with them, pretty much standard up in my area are various pile solutions based on soil conditions. We have to worry about frost and high water table in some sites. As long as a local PE is willing to stamp the plans I expect there is a solution that works for your soils. If its just a contractor proposing it and there is no PE involved I would be less confident.

 

[semipro]

They're a great application as long as they're designed and installed correctly. Basically, as long as they're installed on flat ground, or very securely anchored on a slope (which kind of defeats the benefits since this means digging), and are of sufficient weight for your wind conditions, they're a great way to go. They have the benefits of being movable and handling ground movement well (frost heave, subsidence, earthquakes). Wind load calculations are relatively simple and the ballasting system vendor probably already has engineered and approved build specifications for given wind conditions. Ballasted systems are a great solution in rocky soils since you want to avoid excavation and you have a ready supply of rocks.

I have to ask though, why the optimizers? A high voltage string array sounds like it makes a lot of sense for your application. You can run voltages as high as 600 VDC now and that's useful for long wiring runs with smaller wiring and less voltage loss. If there's no chance of array shading though why the extra complexity and cost of optimizers? With the cost of panels being so low compared to other components, just add a few extra panels if you're worried about overall array efficiency. The benefit-cost ratio will probably much higher than with optimizers and you'll have far fewer components that can fail.

 

[ABMax24]

Our local installer has been doing a lot of installs like this lately (I borrowed the below images from his FB page). Obviously he uses concrete instead of rocks and isn't a "geo" system but the concept is the same.Here there's a few reasons for it, cost, it can be cheaper than installing piles. Permitting, by sitting on concrete blocks it can be considered a temporary structure to many jurisdictions and lessens the requirements compared to if it were installed on piles.

The downfall here is frost, in our ground conditions we can often get surface heaving of the ground in winter as the water in the soil expands and freezes (froze heaves), where piles would be installed deeper than the frost and remain stationary. To some it's also un-sightly having big concrete sitting above ground in the yard.

I do also agree with @semipro that you'd be better off to nix the optimizers and install more panels instead. In our area optimizers are priced at a premium and you could probably install 30% more panels just from the cost savings on the optimizers.

 

[begreen]

Our system is a traditional poles set in concrete. The labor didn't seem onerous, but it did add a little time waiting for the concrete to set. Like others have said a concern would be frost heaving. Another would be very high wind loads. Here's an article on gabion anchoring that might be of interest.

APA Solar Racking explains its concrete-free ballast ground-mount system

APA Solar Racking has changed the ground-mount ballast market by offering a concrete-free design. Featured at Intersolar this year, APA’s Geoballast Foundation was developed after years of installing ballasted solar projects. The utilization of wet concrete simply had so many hidden extra steps...

solarbuildermag.com

One thing to consider is the height of the lower edge of the array. Ours is too low, imo. Think about brush clearing and weeds.

 

[semipro]

One thing to consider is the height of the lower edge of the array. Ours is too low, imo. Think about brush clearing and weeds.

And rocks thrown up from mowers.

 

[begreen]

And rocks thrown up from mowers.

And weedeaters. Don't ask how I know.

 

[DuaeGuttae]

Thank you so much for the input. I'm really glad to have advice from folks who have more experience and knowledge in this area.

@ABMax24, the pictures you provided are just the sort of ballast that my neighbor has for his very large solar array. I think it was done because the ground is rock here. The water table and frost are not issues in this area. There are flash floods, though, at times because when the "frog strangler" rains do come, the water can't soak into the hard ground, and it runs off.

@begreen, the article you linked is just what the owner of the company was proposing. He was very forthright that he has not used this technique before, but it was recommended to him by an engineer for our site, because it is very rocky and also not easy to access. There's no hope for a concrete truck. Pictures don't really capture it, but I took a few tonight just to give some idea. We would be glad not to have additional concrete poured into our ground and could get over the aesthetics of the ballast baskets for that reason. It was just such an unfamiliar idea to me that I wanted to see if anybody had more knowledge.

This is a view of the ground where the array would be placed. We could never use a bladed lawnmower down here (not that there's a lawn), but I have on occasion used a walk behind string trimmer to attack invasive species before they go to seed. Thankfully we've really taken care of most of the infestations of horehound and Malta Star thistle, but flying rocks are definitely a concern if using a trimmer down there. How high would you recommend the front edge be, @begreen or @semipro?

This is the slope that leads down to the fairly flat area at the bottom of our property. It's just to give you a view of cross-section on the ground, so to speak. (There is a flatter way down, where the trench will have to be dug with a rock saw, but there's no access for a truck to that flat way.)


This is the spot where the array is most likely to be placed. It's fairly flat and barren, but there is a ridge above it that has a number of trees. We are slowly cutting out the Texas Cedar (Ashe Juniper), which is a "native invasive" in this area, to deal with most shading, and we are locating the array away from the neighbor's trees as much as possible.


Here's our own personal rock pit. We think the previous owners may have hired folks to move rocks to one corner of the property and then fenced it off. The neighbors told us about their "scraping" the land. We don't really know what that meant or why it would be done. We just have a lot of rocks that appear to have been put in this one place. We took the fencing and turned it into garden trellises (lovely cattle and utility panels), and we have a huge number of rocks, and it's on the same level as our potential array, just on the far side.



Nothing is set in stone (or concrete) yet, except that we are confident we want to go with this particular company. The owner did recommend the optimizers for us, and we were encouraged that he did not push microinverters as every other proposal we had received had, but we can revisit that. (I will admit that when he was explaining string inverters, string inverters with optimizers, and microinverters, he sounded just like something that I had read from @peakbagger, and that encouraged me.) I think that there will be some shading during morning and evening hours but not in peak. Does that change things?

I appreciate the feedback. Thank you.

 

[peakbagger]

Microinverters and optimizers generally deal with small local shadows,like chimneys, vent stacks or dampers on individual panels. If you have large general shadows covering multiple panels you can get similar benefits for less cost by going with string inverters with multiple MPPT inputs laying out the strings so that the potentially shaded strings are on the same MPPT. Instead of one big string inverter I would suggest two possibly three string inverters so you have more MPPT circuits. If you want emergency backup when the sun is out, I think Sunny Boy still has the Secure Power Supply (SPS) option which will energize a 15 amp outlet when the grid is down and the sun is out. If you have two or possibly three smaller inverters with SPS you possibly could have three 15 amp circuits when the grid is down. I expect very few folks actually have used them in an emergency.

If the array is a distance from the house you can cut the power loss due to resistance and save a bit on wiring by by going with string inverters mounted at the house. Set up the strings correctly and you can run up to 600 volts volts back to the house instead of 120 or possibly 240 volts. If you mount the inverters at the house you also can pick a spot preferably in a basement if you have one of at least a cool side of the house in the shade. This gets the electronics into a less harsh environment. If in the future you are interested in batteries, string inverters are going to give you more options (but its a moving target).

Installers like microinverters as they are far more "plug and play" for the installer. There is less design work at the office and fewer components to carry in the truck.

 

[DuaeGuttae]

Microinverters and optimizers generally deal with small local shadows,like chimneys, vent stacks or dampers on individual panels. If you have large general shadows covering multiple panels you can get similar benefits for less cost by going with string inverters with multiple MPPT inputs laying out the strings so that the potentially shaded strings are on the same MPPT. Instead of one big string inverter I would suggest two possibly three string inverters so you have more MPPT circuits. If you want emergency backup when the sun is out, I think Sunny Boy still has the Secure Power Supply (SPS) option which will energize a 15 amp outlet when the grid is down and the sun is out. If you have two or possibly three smaller inverters with SPS you possibly could have three 15 amp circuits when the grid is down. I expect very few folks actually have used them in an emergency.

If the array is a distance from the house you can cut the power loss due to resistance and save a bit on wiring by by going with string inverters mounted at the house. Set up the strings correctly and you can run up to 600 volts volts back to the house instead of 120 or possibly 240 volts. If you mount the inverters at the house you also can pick a spot preferably in a basement if you have one of at least a cool side of the house in the shade. This gets the electronics into a less harsh environment. If in the future you are interested in batteries, string inverters are going to give you more options (but its a moving target).

Installers like microinverters as they are far more "plug and play" for the installer. There is less design work at the office and fewer components to carry in the truck.

Thanks, Peakbagger, for taking the time to explain that and make suggestions. I think our proposal has two string inverters, one slightly larger than the other. When we next talk to the owner/installer, we'll clarify why he was recommending optimizers in our situation.

We are not planning on any sort of battery. We have an dual-fuel inverter generator for emergencies, mostly because we have a deep freeze in our garage because we buy meat in bulk, and I wasn't willing to fill it until we had a back-up. There are not usually any basements in this part of the state (and unfortunately lots of HVAC and water heaters in attics, therefore).

The array will be quite a distance from the house (more than 250'), and the installer was talking about building a rack at our utility pole up near the house to mount the inverters and second meter. We have no basement, and our revenue meter is located on the pole, not on our house. I think the utility has requirements about shut offs all facing the same direction. The pole is actually a more shaded location, even than the most northerly side of our house, so that works out. It still won't be cool in the summer, but at least it won't be baking in the sun.

 

[peakbagger]

For what its worth. If your area is lightning prone, its advisable to run a bare ground conductor in the trench from the array to the pole and then tied into the main house ground. That conductor would be tied into local ground rod at the array. A good quality surge suppressor (I like MidnIght Solar's SPDs) should be installed at the array on the conductors running to the inverters and tied to the ground rod. This keeps the system at equal ground potential so that is there is strike it will hopefully keep the surge out of the conductors and direct it into the ground. There are no guarantees with lightning but that is best practice.

 

[semipro]

How high would you recommend the front edge be, @begreen or @semipro?

Array height is a trade-off when you have the potential for shading. In our case, I wanted to raise the array as high as practical to avoid shading from trees to the south, some on land I don't own. Our lower edge ended up about head height which creates problems as my wife and I have learned quickly, the hard way. I also wanted to be able to clear the array of snow from the ground. We'll see how that goes.

I hit the lower edge of our array with the ROPS on our tractor the day after it went into operation. I broke one panel and bent another - ouch. I seem to have a long-standing habit of taking things that are new and pretty and damaging them right away. Usually its a vehicle.

I posted some photos of our carport array here: https://www.hearth.com/talk/threads/cutting-trees-for-marginal-solar-improvement.181710/post-2444666

 

[DuaeGuttae]

Array height is a trade-off when you have the potential for shading. In our case, I wanted to raise the array as high as practical to avoid shading from trees to the south, some on land I don't own. Our lower edge ended up about head height which creates problems as my wife and I have learned quickly, the hard way. I also wanted to be able to clear the array of snow from the ground. We'll see how that goes.

I hit the lower edge of our array with the ROPS on our tractor the day after it went into operation. I broke one panel and bent another - ouch. I seem to have a long-standing habit of taking things that are new and pretty and damaging them right away. Usually its a vehicle.

I posted some photos of our carport array here: https://www.hearth.com/talk/threads/cutting-trees-for-marginal-solar-improvement.181710/post-2444666

Ouch, semipro, what did you do about the broken panel? Did you have an extra? Overall, your carport looks great, and I'm tremendously impressed that you could do that yourself. We have a very similar Nissan LEAF, and we really enjoy it.

It turns out that we won't be using a geoballasted system at all. There are no local distributors, and the freight charges made it too expensive for our contractor to consider. The plan is to use concrete piers and poles.

We're still in the process of getting approvals, and it may hit an insurmountable snag with the architechtural review committee in our neighborhood. We hope not, but my conversation with the contact last week was not encouraging, when he said that they have in the past approved ground-mounted arrays as long as the top edge is no higher than four feet off the ground. We designed a system that met every requirement actually set out in our covenants, but it has to be approved in writing by this committee, so we'll see. We never imagined any sort of four-foot requirement (especially since our next door neighbors have a 72-panel system in three arrays that is clearly much taller. Hmm.)

 

[semipro]

Ouch, semipro, what did you do about the broken panel? Did you have an extra? Overall, your carport looks great, and I'm tremendously impressed that you could do that yourself. We have a very similar Nissan LEAF, and we really enjoy it.

It turns out that we won't be using a geoballasted system at all. There are no local distributors, and the freight charges made it too expensive for our contractor to consider. The plan is to use concrete piers and poles.

We're still in the process of getting approvals, and it may hit an insurmountable snag with the architechtural review committee in our neighborhood. We hope not, but my conversation with the contact last week was not encouraging, when he said that they have in the past approved ground-mounted arrays as long as the top edge is no higher than four feet off the ground. We designed a system that met every requirement actually set out in our covenants, but it has to be approved in writing by this committee, so we'll see. We never imagined any sort of four-foot requirement (especially since our next door neighbors have a 72-panel system in three arrays that is clearly much taller. Hmm.)

We have not replaced the panel yet. Shipping is quite high just for one or two panels. We do not have an extra, not in that size anyway.

Thanks for the complement. It was a lot of work but we're really enjoying the carport and the Leaf. Driving around on sunshine is really satisfying.

Maybe your neighbor's array was the impetus for the code?

 

[begreen]

Is rooftop solar out of the question?

 

[DuaeGuttae]

Maybe your neighbor's array was the impetus for the code?

The covenants are original to the time that our house was built over 20 years ago. Mostly they just specify that an array not be visible from the road, public rights of way, or neighboring properties. (Our neighbor's panels are in violation in that they are clearly visible from our house, but we bought our house knowing that, and we're not going to complain. They aren't visible from any other property, and it's possible that very few other people in the neighborhood know about them at all.)

There is a law in Texas that says a Homeowners' Association can require panels not to be higher than the fence in a yard. We think that's where the four-foot reference came from. Our plan is not for panels in a fenced yard, however. The array would be in a disused pasture that is not visible to any of the neighbors in this neighborhood. We are drafting a very polite letter with all sorts of plans that show the location and that the plan meets every stipulation in the published covenants. We hope that that will be enough for us to gain approval for our particular situation without difficulty. We did, after all, choose the location for the panels with the rules in front of us.

Is rooftop solar out of the question?

Pretty much. Our roof is already 23 years old, but it has years of life left in it according to some inspections we've had, so we're not replacing it now. It wouldn't be wise to cover it in panels, though, because it won't last another 23 years. It's also not an ideal orientation or angle with some shading (and we absolutely want to keep as much shade on the house as possible), so it would require more panels placed here and there on all sorts of parts of the roof. The final blow was also how much our Homeowner's insurance would rise for a roof-mounted system, so it didn't even make financial sense at the outset in comparison to a ground mount. We really tried to look at all the angles, and a ground-mount was definitely the best option.

 

[DuaeGuttae]

We got our approval from the architectural control committee. I'm glad that there was no insurmountable problem, and I am grateful that they didn't sit on our request at all.

Now we wait for the decision on the technical plans from the power company. That the contractor is handling entirely.

 

[DuaeGuttae]

The engineering plans were approved by the power company. Work will probably start some time next week.

 

[begreen]

The engineering plans were approved by the power company. Work will probably start some time next week.

Cool. Progress is good.

 

[DuaeGuttae]

More progress. For those of you used to heavy machinery, I'm sure it's nothing impressive, but my kids thought that the rock saw was a "machine of the apocalypse." They had to stay safely inside while it was working.



After it was done, I took this picture of my four year old standing on one of the rocks that it threw up. The soil actually was less rocky in places than they had been anticipating, but it was still plenty rocky.


I'm not sure that I can capture it, but here's a shot of one part of the trench where the rock saw just cut straight through some massive limestone and moved a whole piece out of the middle.


This is the view where the trench comes down the hill, followed by a view of where the array will be placed. The holes have been dug. My youngest has been told that he's allowed to fill in the trench with his toys at this point, and he has spent some delighted hours today near all these piles. He's never had so much loose soil to work with before.


I think the racking is supposed to arrive on Wednesday.

 

[begreen]

At that age my kids would have been in heaven with all that equipment and action.

 

[DuaeGuttae]

It turns out that huge galvanized steel tubes are also incredibly fun for kids because they can make music by slapping them. They loved the long horizontals that vibrated so slowly, and they can hear a whisper easily from one end to the other. (This was when there were only tubes, nothing else.)

The racking and panels got put up earlier this week. Now is the time that the contractor says is the most frustrating. We have to wait for the power company to schedule a time to come out so that the panels can be interconnected and tested and then shut off again. If that works properly, we then have to schedule a different person to come out from the power company to do the final inspection. He says that it could take a couple of weeks for each, so we're hoping to be running by mid November.

 

[ABMax24]

It turns out that huge galvanized steel tubes are also incredibly fun for kids because they can make music by slapping them. They loved the long horizontals that vibrated so slowly, and they can hear a whisper easily from one end to the other. (This was when there were only tubes, nothing else.)

The racking and panels got put up earlier this week. Now is the time that the contractor says is the most frustrating. We have to wait for the power company to schedule a time to come out so that the panels can be interconnected and tested and then shut off again. If that works properly, we then have to schedule a different person to come out from the power company to do the final inspection. He says that it could take a couple of weeks for each, so we're hoping to be running by mid November.

View attachment 264753

Looks Good!

I'm glad to hear it's not just our power company that is slow. I had the same scenario, system was ready to go for 2 weeks before the power company came to install the bi-directional meter. All in all it took them 3.5 months from initial approval for install to going live on the grid.

 

[moresnow]

Sounds like a frustrating process. Power company=big buss. I'd expect no less

 

[DuaeGuttae]

The panels were tested successfully and interconnected on Friday. Now they're off again until the utility schedules a final inspection. It's getting closer.

I saw an interesting sight this morning down by the panels. I think that the the air temperature was about 60 at the time, but there was bright sun hitting them, though there was still dew. There were a number of butterflies resting on the panels. I wondered if it was a good spot for them to warm themselves in the early morning before the air had warmed up.