Does anyone know of a source for concrete ballasted ground mount hardware in the PNW? I'm looking at 3 rows of vertically oriented panels, 8 panels per row. The following hardware is what I am interested in but they only seem to quote for 100kW and larger installs. https://patriotsolargroup.com/products/bolt-ground-mount-4-panel/#engine-tab-features . I want the adjustable tilt angle for seasonal tilt and have a local pre-cast concrete supplier that can cast the ballasts to set on a graveled surface. I have basalt rock covered in cinders, so the concrete ballasts make the most sense. Not interested in the plastic tubs as I need 18" ground clearance to meet local code. Thanks in advance, Bill
Ballasted ground mount hardware sales in the Pacific North West
- Thread starter Bill541
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OffGridForGood
Catch, make or grow everything you can.
Just buy some galv channels and Z-bar and build your own?
hwy17
Anti-Solar Enthusiast
The EG4 brightmount is similar to that but with 4 bases.
Not great if you need permits though as it doesn't come with engineering docs.
Not great if you need permits though as it doesn't come with engineering docs.
I'm about ready to do that if I cannot locate a regional supplier with reasonable shipping rates. I may ditch the seasonal tilt requirement and fix it at 35-40 degrees.
I looked at the EG4 mounts and even with 4 bases, it won't meet the 110 MPH wind design speed for our area. I do like building with Aluminum though!
Thanks for the feedback!
hwy17
Anti-Solar Enthusiast
If you're looking to meet engineered wind design speeds I would just head straight to compare unirac and ironridge. Those are the two available commodity solutions will sell to you.
Edited: Oh, right, ballasted. Tough spot.
Edited: Oh, right, ballasted. Tough spot.
Well, Unirac and Iron Ridge design tools force you into a large wind sail array configuration (3 panels high typically) and huge ballasts. They call for each ballast point to be about 1 cubic yard of concrete (~ 4,050 lbs) which is way overkill for what I want to do. I want a single panel in portrait vertically (77 inches) and 8 panels per row (~ 320") with 3 ballast points at 40 degree tilt angle. I doubt it would take 12,150 lbs of ballast to hold it down in a 110 MPH wind which is likely to never happen. I'm an electrical engineer, not a structural engineer so I could really use some structural formulas for this application, any links would be appreciated!
Edited concrete weight: ~2,000 lbs/yd for concrete rubble, 4,050 lbs/yd for a solid slab.
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OffGridForGood
Catch, make or grow everything you can.
The stability is just moments, wind force x area x a coefficient x the height lever arm needs to be less than the mass of the ballast slab x the overturning distance.
Lets consider a 'slice' of your array:
-consisting of a section of PV, a single post, and ballast slab. See rough sketch attached.
The wind force wf is a function of windspeed and you can look this up from national tables.
The force will act on the net area of the panels (Apv)- you can reduce the area the wind acts on by tilting the panels more parallel to the ground for example. For this example we will just use the full area without reductions.
The applied force will act on the system as if concentrated at the centre of the PV array, we will assume the column height is this same central point
Putting this together: wf x Apv x h = the overturning force applied.
The base is a gravity block not attached to the rock below, it will resist overturning by gravity alone. This resistance will act at the centre of gravity of the block, we will call this distance from the leading edge to the centre of gravity 'd' - see the sketch.
The mass of the block we will call M, this mass will act as if it were concentrated at the centre of gravity point.
Putting this together: d x M = the resistance to overturning.
For your array to be stable we need the resistance to be greater than the overturing force, and to be 'safe' we usually go 1.5x for the resistance.
Lets run an example:
Say the PV area applicable to one post is 49 sqft, the post is 7 feet tall and the wf is 25 lbs per sqft. = 8575 ft.lbs
Lets also say the concrete base will be 6-feet wide, d=3 feet. how heavy does the concrete block need to be to not tip over?
3M > 8575 the mass needs to be at least 2858 lbs. but this would result in no factor of safety, which would normally be x1.5
so make the concrete block 1.5 x 2858 = 4287 lbs and now you have some safety margin for 25lbs/sqft wind force.
Remember this is just for one slice of the PV array - the panels associated with a single column, you can multiply by as many posts as you like, as long as you maintain the same geometry for each. Typical wf forces for exposed areas can be much higher than 25lbs/sqft so you should look up some data for your area and assess the exposure you have. ie a row of panels with a rock outcrop or trees sheltering them from wind can reduce the windspeed and thus lower the overturning force.
There are other failure modes, such as sliding, or if you were on soft ground the leading edge 'toe' of the ballast slab could sink instead of overturning on the corner, your post has to be stiff enough that is doesn't just buckle at the connection to the concrete ballast slab, and the array itself - if cantilevered ahead of the post can add to the overturning forces. Review your set up and check these items.
@OffGridForGood, thank you for your overturning example. I was reading this tech note applying ASCE 7-16 to solar panel wind loading. https://skyciv.com/docs/tech-notes/loading/solar-panel-wind-load-calculation-asce-7-16/ Your example takes it to the next step by transitioning the force down to the ballast. I also see ASCE 7-10 being applied for panel wind loading but do not know which is more accepting by the industry, perhaps both? In the Skyciv link above, he provides another link to his on-line calculator. Again what is missing are the forces applied to the mount structure on the ground. Looks like I have some more reading and pencil sharpening to do! Thanks again!
ASCE 7-10 and 7-16 is a great place to start figuring out the wind pressure on solar panels. From what I understand, this really only tells us the force placed on the face of the solar panel at 90 degrees to the panel face. What I'm interested in knowing are the lift and drag forces placed on the mounts.
Here are two videos about the forces on solar panels and mounts. His approach makes a lot of sense to me...
Calculating wind force on panels:
Calculating lift and drag on panel mounts:
In the second video, getting the lift and drag coefficients was key. The following is a paper where they did wind tunnel testing on solar panels at angles up to 40 degrees and graphed lift and drag forces. This just may be enough information, along with ASCE 7-10 or ASCE 7-16, to be able to make a spreadsheet to estimate the forces on solar panel mounts.
If we are going to DIY panel mounts, it would be good to have some numbers to back up the "Yea, that ought to hold" construction!
-Bill
Here are two videos about the forces on solar panels and mounts. His approach makes a lot of sense to me...
Calculating wind force on panels:
Calculating lift and drag on panel mounts:
In the second video, getting the lift and drag coefficients was key. The following is a paper where they did wind tunnel testing on solar panels at angles up to 40 degrees and graphed lift and drag forces. This just may be enough information, along with ASCE 7-10 or ASCE 7-16, to be able to make a spreadsheet to estimate the forces on solar panel mounts.
If we are going to DIY panel mounts, it would be good to have some numbers to back up the "Yea, that ought to hold" construction!
-Bill
I ran panel velocity pressure calculations using ASCE 7-10 and ASCE 7-16. My installation has a 40 degree tilt angle, panel center 4.125 feet above ground, 3,352 ft elevation, basic wind speed of 98 mph, and panel array dimensions 25.9 ft x 6.6ft.
ASCE 7-10 Velocity Pressure q = 0.00256*Kz*Kzt*Kd*(V^2) = 17.740 psf
ASCE 7-16 Velocity Pressure qh = 0.00256*Kz*Kzt*Kd*Ke*(V^2) = 15.775 psf
ASCE 7-16 velocity pressure has one more term Ke which compensates for the density of air at elevation.
ASCE 7-16 also differs in calculating the design wind pressure (p). p = qh*G*CN where G is a gust factor (usually 0.85) and CN is a net pressure coefficient which varies by wind direction. There is a CN coefficient for the panel Windward side (CNW) and another for the Leeward side (CNL). ASCE 7-16 also uses two load cases (A & B) but I'm not sure how they differ. From what I understand we are to use the worst of the cases. In my example, with a North wind, I have a worst case windward panel force of -30.8 psf and a worst case leeward panel force of -24.1 psf. The negative number means it is a lifting force.
I believe ASCE 7-16 is the best fit for ground mount solar panel modeling. Now I'm undecided how best to characterize the requirements of the ballast. Initial estimates using lift and drag coefficients give me:
Windward drag force (lbs) -1610.5
Windward lift force (lbs) -2427.6
Leeward drag force (lbs) -1260.4
Leeward lift force (lbs) -1899.9
If there are 6 supports (3 in front and 3 in the rear), do the center supports carry 1/2 the load and the outer two carry 1/4 the load?
ASCE 7-10 Velocity Pressure q = 0.00256*Kz*Kzt*Kd*(V^2) = 17.740 psf
ASCE 7-16 Velocity Pressure qh = 0.00256*Kz*Kzt*Kd*Ke*(V^2) = 15.775 psf
ASCE 7-16 velocity pressure has one more term Ke which compensates for the density of air at elevation.
ASCE 7-16 also differs in calculating the design wind pressure (p). p = qh*G*CN where G is a gust factor (usually 0.85) and CN is a net pressure coefficient which varies by wind direction. There is a CN coefficient for the panel Windward side (CNW) and another for the Leeward side (CNL). ASCE 7-16 also uses two load cases (A & B) but I'm not sure how they differ. From what I understand we are to use the worst of the cases. In my example, with a North wind, I have a worst case windward panel force of -30.8 psf and a worst case leeward panel force of -24.1 psf. The negative number means it is a lifting force.
I believe ASCE 7-16 is the best fit for ground mount solar panel modeling. Now I'm undecided how best to characterize the requirements of the ballast. Initial estimates using lift and drag coefficients give me:
Windward drag force (lbs) -1610.5
Windward lift force (lbs) -2427.6
Leeward drag force (lbs) -1260.4
Leeward lift force (lbs) -1899.9
If there are 6 supports (3 in front and 3 in the rear), do the center supports carry 1/2 the load and the outer two carry 1/4 the load?
OffGridForGood
Catch, make or grow everything you can.
Depends on the spacing, and if the outside supports are flush with the ends of the array or inset. Do you have a sketch/dimesions?
LOL, that makes sense, no need to have the end supports clear at the end! I would prefer to have the load balanced equally across all 3 ballasts so that they are all the same size. I put together a sketch to show the rough design (attached). The concrete ballasts, as drawn, should come up to about 1250 lbs each. These are what I want to make sure stay put in a freak wind event! Thanks again for your feedback!
OffGridForGood
Catch, make or grow everything you can.
you have the spacing equalized. each balast block will support 2.67 panels x 3 = 8.
double check the horizontal members (cantilevers) under worst case snow/wind load also.
For the freak wind events, always take the calculated result and add some margin for safety, typically x 1.5.
Thanks for the reply!
How would you go about determining if the ballast was sufficient to not tip over?
In ASCE 7-16, velocity pressure (qh) is first calculated and then they apply a net pressure coefficient that is based on the wind direction, roof angle, and clear or obstructed wind flow. In the case of the windward pressure it goes from qh=15.8psf to p=30.8psf and they call this (p) the design wind pressure and I'm not sure if a safety factor is already built into it? This is 1.74 times higher pressure on the windward side than ASCE 7-10 comes up with.
Plum Crazy Rob
Solar Enthusiast
Engineering Alert!!! 
Following, Enjoying. Have the EG4s and thinking about possibly running the calcs with additional supports on front and see where that leaves me on lift-off force. My county modified the IRC table R301 to reduce wind speed required to 90mph...
Saw somewhere that greenlancer.com may be available to PE stamp your design for a reasonable amount $300 or such??
Following, Enjoying. Have the EG4s and thinking about possibly running the calcs with additional supports on front and see where that leaves me on lift-off force. My county modified the IRC table R301 to reduce wind speed required to 90mph...
Saw somewhere that greenlancer.com may be available to PE stamp your design for a reasonable amount $300 or such??
OffGridForGood
Catch, make or grow everything you can.
With very high wind speeds like 98mph you are going to see large forces applied. (the forces are ralated exponentially to wind speed)
The wind speed and forces are unfactored.
A back of the envelope calculation using your sketch and typical safety factor nets the concrete blocks at 3,526 lbs each for 98mph wind and reasonable safetly margin. You can apply exposure and drag coefficients and move the numbers around all day long, but ultimately you have to settle on a max load per sqft, and how much margin you want to add to this, and then see what mother nature sends. Seems like weather is getting less predictable statistically, time will tell.
Based on blocks of 1250 lbs, you may be safe to resist wind forces of up to 11psf, keeping a typical margin for safety.
As Plum Crazy noted, you may want to reach out to PE with local knowledge. You mentioned earlier you are EE, maybe you work with some structural guys locally that would take a look for you. You start to see why some tie-downs into rock become a simple solution to the overturning. Building a big sail raised up on posts, with only gravity to resist overturning quickly turns into heavy construction.
@Plum Crazy Rob I looked at our county site again and it looks like I'm right on the edge of a special wind area and the AHJ would need to make the call between 98 mph and 110 mph. I'm guessing they would say 110! Good luck on your EG4 project!
@OffGridForGood I guess it may come down to economics in the end. How much does concrete cost vs dealing with rock to get something in the ground. A slab pour would even be nice as it would keep the weeds out from under the panels! Thanks for the envelope calcs and I took your advice and reached out to my engineering manager who happens to be a mechanical PE and oddly enough he has done similar calcs a few years back.
Also found this video interesting and the software tool may prove to be a useful cross check.
Video that uses Ftool to analyze solar panel frame.
Civil Engineering software site for Ftool https://www.cesdb.com/ftool.html
@OffGridForGood I guess it may come down to economics in the end. How much does concrete cost vs dealing with rock to get something in the ground. A slab pour would even be nice as it would keep the weeds out from under the panels! Thanks for the envelope calcs and I took your advice and reached out to my engineering manager who happens to be a mechanical PE and oddly enough he has done similar calcs a few years back.
Also found this video interesting and the software tool may prove to be a useful cross check.
Video that uses Ftool to analyze solar panel frame.
Civil Engineering software site for Ftool https://www.cesdb.com/ftool.html
MTM98290
Solar Enthusiast
- Joined
- Dec 24, 2022
- Messages
- 312
Platt platt.com is a great place to do business with. They have all sorts of mounting hardware and materials in stock, mostly warehoused in Portland from my experience.
They can order things to your local branch where you can pick orders up without paying for shipping. Take a look at their catalog and you may find what you need.
Well, this has been a fun exercise and the solution for me is not quite what I was expecting. I'm still going with a ballast mount but the shape of the ballast is now a concrete slab rather than individual ballasts. This has advantages for me of better weed control, grass fire abatement, reduced frame stress with frost heaves, and bonus semi-sheltered storage for non-flammables. The size of the "structure" is below 200 sqft and less than 10ft tall so my county does not require a permit. They typically are not overly concerned with on-grade slabs in the first place. Any way, the engineers that have looked at the calcs seem to feel that ASCE 7-16 includes risk category's and coefficients sufficient for design and probably no need for additional safety factors. The attached are my calculations and a sketch the ballast slab. Hopefully the forum allows attaching spreadsheets (zipped). Perhaps this will help others out. If I can get the slabs poured before winter, I can get the install going!
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