Anyone have first hand experience with large panel or high capacity lfp cell mechanical failures?

[Dzl]

It is often said that smaller panels (~100-150 watt), and lower capacity lfp cells (<200ah) are best for mobile systems, and marine systems, as they are structurally stronger.

This makes sense in theory. But in practice, I'm wondering if anyone has experience with mechanical failures with residential sized solar panels (250-400 watt) or LFP cells greater than 200ah.

All I have come across so far is two cases where one possible cause for failure of an LFP battery bank was mechanical stress on large LFP cells on powerboats.

 

[kernel]

The residential/commercial modules are quite a bit tougher. Mounting tactics will make the best of the situation of flex and shock loads. For some possibilities smaller would have more joints and so more flexibility...... to a point of diminishing returns.

Residential pv modules have better, more rigid frames, better coatings, thicker higher quality glass, tougher junction boxes amd longer pv wire leads with better connectors on them......

Yet, variety is the spice of life!

 

[Dzl]

The residential/commercial modules are quite a bit tougher. Mounting tactics will make the best of the situation of flex and shock loads. For some possibilities smaller would have more joints and so more flexibility...... to a point of diminishing returns.

Residential pv modules have better, more rigid frames, better coatings, thicker higher quality glass, tougher junction boxes amd longer pv wire leads with better connectors on them......

Yet, variety is the spice of life!

Interesting, I hadn't heard this point of view before. Everything I've read up to this point (there isn't a ton to read on the subject) asserted that the surface area to frame ratio of smaller panels made them stronger and better able to handle the forces at play in a mobile or marine system. Do you recall where you learned/heard about the strengths of the residential panels?

I have considered how mounting technique could mitigate the larger surface area of residential panels between frame rails and also potential be used to limit vibration.

 

[kernel]

First ratings..... resi's will have a minimum standard and small modules may meet it...... but how far will they exceed the standard?

2, the modules have similar construction amd as you said about the frame ratio, but the material and types of extrusion are generally of a better engineered strength on serious panels.

Next, my personal observation is that the modules when compared on observation amd inspection and handling have thinner glass, thinner frames with lesser mechanical joinery, and this may make frame ratio moot.

Then again the math might show the difference negligable on the fact that both varieties meet the required strength and durability required.

Again. Commercial panels generally have higher output to area, longer service life amd reduced total components to achieve desired wattages and they are stronger in most every way. My direct observation since 2004... thousands of modules of maybe a couple dozen manufactures.

 

[nosys70]

the problem is with the terminals.
if you have a rigid mount on the terminals (bus bar) and the bottom of the cell is not fixed, you could have each cell moving except at the terminals, that is the worst place to have.
The cure is to make sure all cells are fixed tight together, or forget busbar and use soft cables.

 

[Dzl]

the problem is with the terminals.
if you have a rigid mount on the terminals (bus bar) and the bottom of the cell is not fixed, you could have each cell moving except at the terminals, that is the worst place to have.
The cure is to make sure all cells are fixed tight together, or forget busbar and use soft cables.

This is true, but from what I've heard, a second issue is that the larger the individual cell the weaker the internal structure of the battery. Here is an excerpt from an excellent article from Nordkyn Design on LFP:

Cell Sizes
Single 3.2V prismatic LiFePO4 cells can nowadays be obtained in huge capacity, as high as 10000Ah. Commonly available cells range between 40Ah and maybe 1000Ah. It should be pointed out that the larger sizes are intended for stationary applications where no accelerations, vibrations or shocks are ever experienced.

A sales manager at Sinopoly I was talking to was adamant about using 100Ah or 200Ah cells only for assembling marine battery banks, with 100Ah being preferred and 200Ah acceptable. Large cells simply don’t have the structural strength-to-weight ratio required to be taken to sea on board small crafts and would exhibit shortened life due to internal mechanical damage arising from on-going vessel motion. It is common sense: as a cell becomes larger, its internal weight increases much faster than the rigidity and surface area of the casing and the casing is all what holds the plates together in a prismatic cell.

Failures have been reported on vessels equipped with 700Ah cells following ocean passages: some cells were suddenly found to be losing charge inexplicably, rendering the battery bank completely unmanageable and the matter ended in a complete write-off. All big-brand commercial marine lithium battery packs on the market today are built from cells no larger than 200Ah.

While there certainly are examples of marine DIY systems that were built with large cells in series without issues, closer inspection usually also reveals a houseboat usage or infrequent good weather, sheltered waters sailing. In other words, the data point is null and void if the intent is sailing and designing upon the assumption that the boat won’t be going anywhere would be questionable.

Physical cell dimensions, space availability on board and interconnection topology are the other factors that influence the final choice of cell model. 200Ah cells are usually taller and require more “headroom”.

 

[Dzl]

First ratings..... resi's will have a minimum standard and small modules may meet it...... but how far will they exceed the standard?

2, the modules have similar construction amd as you said about the frame ratio, but the material and types of extrusion are generally of a better engineered strength on serious panels.

Next, my personal observation is that the modules when compared on observation amd inspection and handling have thinner glass, thinner frames with lesser mechanical joinery, and this may make frame ratio moot.

Then again the math might show the difference negligable on the fact that both varieties meet the required strength and durability required.

Again. Commercial panels generally have higher output to area, longer service life amd reduced total components to achieve desired wattages and they are stronger in most every way. My direct observation since 2004... thousands of modules of maybe a couple dozen manufactures.

I'll have to look into this more. I want your observations to be correct and it sounds like you have a lot of first hand experience to base your opinion on, my preference would be to use larger residential panels, they are superior in many ways (including price per watt) so Ideally its what I'd use.

I believe (but am not positive) all solar panels must pass the same minimum standards for wind, hail, etc., and I would imagine there is some variability with large and small panels as to how far they exceed the standards. I also imagine that "strength" is not a singular thing. So a question worth pondering is do the attributes that make a residential/commercial panel strong in a stationary application translate well to a mobile application where vibration, repetitive shocks, and potentially some amount of torsion are factors.

 

[kernel]

Glass is actually amazingly flexible in torsion and bending. Watching the surface of a module as it is being lain, you will see it ripple and bounce like a drum skin. All but baja racers will likely not have an issue with the loads.

A gust of 100mph wind and with the face covered in 2 feet of snow will not break it.... nor the buffeting that occurs.

On maybe some jalopy trailers ive seen there may be cause for concern, but if you have any sort of stout vehicle fit for road travel i shouldnt worry...

 

[kernel]

I have seen exactly one panel broken during installation. A guy on a lift over head pressed a module up onto a large car port type array with his hands in the middle, it was a solarworld.... i still have it and it works.

I would not use module clamps on any vehicle mount. This is the main critical detail. Unless the surface mounted to is sufficiently rigid, just through bolt the module to mounting rail with nylocks or other locking fasteners. Locking flange nuts are workable but will come off if alowed to loosten. I do this even where the warranty is void..... have never used a module warranty and do not expect to need to.

A nylock could loose tension but will not vibrate off the bolt and dislocate that point, which could allow the whole thing to fail on the way.

 

[Dzl]

All but baja racers will likely not have an issue with the loads.

This is not too far from some peoples' use case. Not baja racing obviously but washboards at 30+, overlanding in Baja, etc. In fact the long term effect of washboards is probably my biggest concerns.

On maybe some jalopy trailers ive seen there may be cause for concern, but if you have any sort of stout vehicle fit for road travel i shouldn't worry...

Surprisingly, some very high quality vehicles are built to flex and twist. Overland builders often have to isolate the camper body from the vehicle frame because some vehicles are designed for the frame to twist, but if that force is introduced to the strong but rigid camper body it can fail over time. That said, you are probably right that the flexibility of the actual glass is enough to handle whatever torsion the vehicle can transfer to the panels.
This picture shows a vehicle with an isolated subframe/camper body. You can see (look at the angle of the cab vs the camper body, now imagine if that torsional stress were introduced to the rigid camper body (constructed with fiberglass reinforced panels and VHB adhesive usually, sometimes with an aluminum frame, but usually thats not the main structural element) it could be a big issue.

 

[kernel]

A common truck box or cab or other coachwork is going to be plenty rigid enough, floppy roof racking should be avoided and if you see what i see in the picture....... i would mount on the camper, not the framerails or chassis. Unibody, different story

Jeep cherokee or paris to dakar rally semi truck or unimog, 2-1/2 ton military, etc. will have a suitable mounting surface.

Which brings me to wonder about overland adventure touring with a solar electric budget of 500$??

And 100k$ trail rigs that cost 500$ every couple days to operate. Ok now i see...

 

[Dzl]

A common truck box or cab or other coachwork is going to be plenty rigid enough

Probably yes, overthinking/planning is definitely something I'm often guilty of. That said, its an area that should probably be explored more. We obsess over little electrical details, and theoretically possible modes of electrical failure, and overbuild/overdesign the electrical system, but spend almost no time considering mechanical modes of failure. Thinking about best practices and principles for mobile applications (especially off pavement) seems like a worthwhile endeavor.

and if you see what i see in the picture....... i would mount on the camper, not the framerails or chassis. Unibody, different story

Definitely, but that thing has $20k+ pivoting subframe that isolates the the camper from the frame allowing the frame to twist without transferring that torsion to the camper. This is outside of most of our budgets and design priorities. I was using the picture to show how much twisting occurs (its much easier to see with an isolated body). If I had that vehicle I wouldn't have a worry in the world about mounting solar on the camper, but with a sheet metal vehicle the body is meant to allow some twisting, probably not something to worry too much about, but still worth considering.

Which brings me to wonder about overland adventure touring with a solar electric budget of 500$??

I may be missing your point or your joke, but I don't know where the $500 dollar figure is coming from (edit: connected the dots). The same principles would apply to a large solar budget or a small one, and are probably more applicable to a cheap vehicle than an expensive one like the one pictured (which could spend more on engineering and mitigation).

I think we pretty much agree (though it may not seem like I do) that torsional stress is probably not a factor in all but the most extreme cases. I just believe that (in some contexts like long range marine or overland travel) the same caution and focus on resilience/integrity that many here apply to electrical design should be applied to structural/mechanical design as well.

My main concern is the effect of vibration long term. In the past I've: had my battery box welds fail and the whole battery and box get lodged between the radiator fan and engine, lost a spare tire and rear tire carrier, had two window assemblies fail, had a battery cable connection fail, had numerous screws rattle loose, and had an interior floor crack and splinter (either due to torsion or vibration) all from washboard and/or moderate offroad travel, nothing extreme. Solar panels aren't the most expensive component by any means, but they are an investment, and they are meant to last 20+ years, I just want to be reasonably sure I won't be replacing them every few years because the panel I went with didn't match my application. But if it seems that nobody has had issues using the larger panels off pavement, I would be inclined to buck conventional wisdom and give em a try.

 

[kernel]

Probably yes, overthinking/planning is definitely something I'm often guilty of. That said, its an area that should probably be explored more. We obsess over little electrical details, and theoretically possible modes of electrical failure, and overbuild/overdesign the electrical system, but spend almost no time considering mechanical modes of failure. Thinking about best practices and principles for mobile applications (especially off pavement) seems like a worthwhile endeavor.



Definitely, but that thing has $20k+ pivoting subframe that isolates the the camper from the frame allowing the frame to twist without transferring that torsion to the camper. This is outside of most of our budgets and design priorities. I was using the picture to show how much twisting occurs (its much easier to see with an isolated body). If I had that vehicle I wouldn't have a worry in the world about mounting solar on the camper, but with a sheet metal vehicle the body is meant to allow some twisting, probably not something to worry too much about, but still worth considering.



I may be missing your point or your joke, but I don't know where the $500 dollar figure is coming from (edit: connected the dots). The same principles would apply to a large solar budget or a small one, and are probably more applicable to a cheap vehicle than an expensive one like the one pictured (which could spend more on engineering and mitigation).

I think we pretty much agree (though it may not seem like I do) that torsional stress is probably not a factor in all but the most extreme cases. I just believe that (in some contexts like long range marine or overland travel) the same caution and focus on resilience/integrity that many here apply to electrical design should be applied to structural/mechanical design as well.

My main concern is the effect of vibration long term. In the past I've: had my battery box welds fail and the whole battery and box get lodged between the radiator fan and engine, lost a spare tire and rear tire carrier, had two window assemblies fail, had a battery cable connection fail, had numerous screws rattle loose, and had an interior floor crack and splinter (either due to torsion or vibration) all from washboard and/or moderate offroad travel, nothing extreme. Solar panels aren't the most expensive component by any means, but they are an investment, and they are meant to last 20+ years, I just want to be reasonably sure I won't be replacing them every few years because the panel I went with didn't match my application. But if it seems that nobody has had issues using the larger panels off pavement, I would be inclined to buck conventional wisdom and give em a try.

If that is the case and there is no good way to determine, frameless all plastic laminates would be the obvious choice. Companies also still make butyl backed stick ons like a uni solar module

The uni solar type are available in various lengths and once stuck on will not come off without a heat gun. Will not come off at 160° surface temps on metal roofing though.

The laminates with grometry will be fastenable and unfastenable.

Its the go to where glass and aluminum will not work or you cannot suffer the weight and clearance required for framed modules.

If your truck flexes that much, just use a module that will hapilly flex more.

 

[kernel]

Probably yes, overthinking/planning is definitely something I'm often guilty of. That said, its an area that should probably be explored more. We obsess over little electrical details, and theoretically possible modes of electrical failure, and overbuild/overdesign the electrical system, but spend almost no time considering mechanical modes of failure. Thinking about best practices and principles for mobile applications (especially off pavement) seems like a worthwhile endeavor.



Definitely, but that thing has $20k+ pivoting subframe that isolates the the camper from the frame allowing the frame to twist without transferring that torsion to the camper. This is outside of most of our budgets and design priorities. I was using the picture to show how much twisting occurs (its much easier to see with an isolated body). If I had that vehicle I wouldn't have a worry in the world about mounting solar on the camper, but with a sheet metal vehicle the body is meant to allow some twisting, probably not something to worry too much about, but still worth considering.



I may be missing your point or your joke, but I don't know where the $500 dollar figure is coming from (edit: connected the dots).

I mixed up your post with that of silvanus.... subject material.

We run adventure touring bikes, so i have this picture in mind....

 

[Sgt Raven]

I wonder if using a rubber bushing would help. Where you mount the unit, Use a longer bolt and something like the bushing used on a Pin type shock mount. So the unit sits flush, then the bushing, a large washer, and then the nut. At rest it would sit flat on the mount, but allow a little movement if needed.

 

[Dzl]

I wonder if using a rubber bushing would help. Where you mount the unit, Use a longer bolt and something like the bushing used on a Pin type shock mount. So the unit sits flush, then the bushing, a large washer, and then the nut. At rest it would sit flat on the mount, but allow a little movement if needed.

I was imagining something along these lines. Rubber bushings and/or spring loaded bolts could be used to isolate from torsion or vibration. But the more I think about it, the more I think Kernel is probably right that torsion isn't a big practical concern in most cases, so the bushings would probably be more than enough, and better at handling vibration as well.

 

[Sgt Raven]

I was imagining something along these lines. Rubber bushings and/or spring loaded bolts could be used to isolate from torsion or vibration. But the more I think about it, the more I think Kernel is probably right that torsion isn't a big practical concern in most cases, so the bushings would probably be more than enough, and better at handling vibration as well.

The only question is, put the bushing between the panel and mount, or after the mount, before the nut? The former will isolate it more, the latter is more stable at rest. You could use a thin rubber washer before and a larger bushing after, too. The 3rd way is bushings on both sides like a pin top shock mount uses. In fact, a pair of shock bushings might be the ideal thing to use.

 

[ADM]

I have traveled 50K+ miles with a large Residential 275W panel and no problems what so ever. It has seen extreme washboard, rock crawling, snow, ice, branches, you name it. Installed only with 6 self tap screws directly through frame to angle crossbar. Glued small foam pads in the middle of the long side directly contacting roof in order to absorb excessive flex in the middle. Residential panel frame is much stronger than on smaller 100w panels.

 

[Dzl]

I have traveled 50K+ miles with a large Residential 275W panel and no problems what so ever. It has seen extreme washboard, rock crawling, snow, ice, branches, you name it. Installed only with 6 self tap screws directly through frame to angle crossbar. Glued small foam pads in the middle of the long side directly contacting roof in order to absorb excessive flex in the middle. Residential panel frame is much stronger than on smaller 100w panels.

Now this is exactly the type of first hand feedback I was hoping for!! Thanks for sharing. What brand panels? I'd say 50k miles is a solid long term test. Nice looking van you got.

 

[ADM]

The Panel is an older Chaori Solar 72 cell that I picked up for $50 together with the 23 that I put on my home.
Panel is paired with an Epever 40Amp Mppt and comfortably runs fridge/freezer, max air fan at 100% and chargers the 200Amp AGM battery back up for the evening. Depending on outside temp and wind conditions it puts out approx 250W at noon. Going to be swapping out the AGM setup for Lifepo soon as the AGM are taking a beating (Everything is up and running 365 days a year).

 

[El Jack]

Well that's great news! Planning 3x 350w residential units on the top of a habitation box for overloading as well.

Now how about those larger cell LFP batteries?

 

[Dzl]

Now how about those larger cell LFP batteries?

I'm reluctantly still planning to adhere to the <200Ah recommendation, but the 280Ah cells everyone is buying is certainly tempting me.

A LOT of people are buying the 280Ah LFP cells from Xuba etc, at least some of them are going into vehicles, probably some going into boats too. So one way or another, 2-10 years from now we should have a handful of case studies to learn from.