Exceeding PV max input spec on MPP 2424LV-MSD

[darknet]

• I have 6 strings of 2 panels connected in series: Voc: 74.4v. Vmp: 60.8V. lsc: 8.37A, lmp: 7.89A
• Each string is fused with an inline 15A fuse
• The 6 strings are then connected in parallel: Voc: 74.4v. Vmp: 60.8V. lsc: 50.22A, lmp: 47.34A

Also, I suspect your PV wire is not rated for 50A, you likely need 6 awg depending on distance

 

[sunshine_eggo]

I can tell you exactly what will happen... I recently changed out some Growatts with MPP LV6048s which had the same "Max VOC" rating, but the MPPs could not handle the 125V that my 3S4P 4KW layout was doing that the Growatts handled fine. I had to restring to 2S6P which is now working great. I generally get 3.2 to 3.5 KW on a good day, but during the "overpanel" situation it was restricting it to just over 2KW. See the attached picture.

Yeah, that peak MPPT operating voltage is pretty surprising. That pretty much limits your voc to 100V-ish. IIRC most are around 115V peak MPPT voltage.

 

[Scoob-SanDiego]

Also, I suspect your PV wire is not rated for 50A, you likely need 6 awg depending on distance

Yes. I have each string fused (15Amp), going into a "Y" connector so only 2 strings go along a 10AWG solar cable... so 3 sets of solar cables come into an aggregator box and comes out in 8AWG cable. It's all well and meeting the correct power rating / AWG.

 

[Scoob-SanDiego]

You're asking for 10 year old information readily available online, and Victron regularly demonstrates that support of DIY end users is not their model, especially when you're not a customer:

Matching solar modules to MPPT charge controllers - Victron Energy

Life used to be so simple; in a 12V battery system you took a ‘12V’ solar module, watched carefully that the maximum PV current would not exceed the charge controller maximum current and the system would work. Unfortunately due to the fact, that with PWM controllers the PV module is not feeding...

www.victronenergy.com

Limits to Oversizing a PV array

How to determine by how much you can oversize a PV array? This can be done with help from the spreadsheet tool. Here though is the manual explanation of how it is done.

There are two limits, when determining the maximum array size that can be connected to an MPPT:

1. The Maximum PV open circuit voltage (Voc at STC)
2. The Maximum PV short circuit current (Isc at STC)

Both values are specified in the datasheets of all our MPPT Solar Charge Controllers. Those two ratings of the PV array must not exceed these MPPT limits.

For the Voltrinics units (MPP Solar, Growatt, etc.):



This has been the "conventional wisdom" on this forum for a few years, hence my post:



The same criteria they gave you.

Thanks for putting the Victron and MPP information linked in one post.
In short: Rexpect max VOC and max Isc on your Solar Controller. Victron publishes their max lsc. For MPP I had to ask.
I just heard back from Signature Signature solar and they clarified that EG4 already publishes specs related to the 6000XP for Max PV power used (8000W, 4000W per mppt string) and Max recommended PV input: 10,000W. so about 25%.

 

[Scoob-SanDiego]

I also emailed Victron, Eg4, Signature Solar (asked about EG4 3K and 6000XP) and Current Connected (asked about EG4 6000XP and Victron).
I heard back. from

• Victron: Please talk to a reseller (not impressed!)
• EG4: Haven't heard back yet
• CurrentConnected: Haven't heard back yet
• Signature Solar (in 2 days) saying:

My comments: This is a technical question that goes beyond the common installation questions that a retailer / installer would answer. It is a legitimate question for the manufacturer / product design team. Victron punting me down the line w/o answering is not to my liking. Presumably a sales flunky that doesn't understand the question and I was fed a canned redirection w/o any consideration to the nature of the question.

The answer from Signature Solar is also overly "hand waving" and not entirely to my liking. If you go far enough it will alarm and possibly get damaged. IF nothing shuts down it might catch fire.... well, this is a piece of electronic equipment... it is DETERMINISTIC!!!! It WILL or it WILL NOT give an alarm. It WILL or it WILL NOT get damaged. It WILL or it WILL NOT catch fire!. So my impression is that someone over there pulled an answer out of the hat from a gut feeling.... NOT from hard engineering inquiry. (I wrote back asking for a more specific answer and gave the MPP feedback as an example of what I was looking for. Hopefully they will be able to get some more specific engineering data from EG4. I will report back here with my findings).

To that extent, the responses form MPP were more helpful. Your inverter is rated for 2000W. You suggest plugging 3000W of panels on it, that should be fine! As long as you don't go beyong VOC and ISC you're good and safe.

Frankly I am so far disappointed with the responses I got from the sources other than MPP. Fingers crossed that EG4 directly and CurrentConnected will do due diligence and give me an explicit and accurate answer (if somewhat tardy).

And after *6* weeks, I finally heard back from EG4 directly. Essentially what they say "don't overpanel your system".
However, if you read the specs for their inverters, they give you a Max Utilized PV input power AND a Max Recommended PV input Power.
For instance, for the 6000xp:
Max utilized PV power: 8000W (4000W per MPPT),
Max recommended PV input: 10,000W (5K/MPPT)

Here is the answer verbatim:

On all 3 of the units you mentioned, having amperage or wattage over the listed specification runs the risk of seeing over current/wattage errors on all units, and given the right scenario you also run the risk of blowing the MPPT on all 3 units.

The maximum DC current, voltage, and wattage that each of those units can handle is as follows:

3000EHV-48 - 500VDC, 18A, 5000W
6000XP - 480VDC, 25A, 5000W (all specs per MPPT)
18K PV - PV input 1 - 600VDC, 31A, 7000W, PV inputs 2 & 3 - 600VDC, 19A, 7000W

Once again, we do not recommend intentionally over sizing your PV array as the maximum specifications are in place because this is what our testing has shown what these units can handle. Oversizing your PV array can destroy your unit.

 

[Norwasian]

Mine are not attached AT ALL
I DID comment that these were my Gypsy panels . They weigh 42lb a pop plus the 2x4 structure so a solid 50+lb per set. I will add an eye loop at the bottom of each and run a long fake rock climbing rope (the ones you find at home depot for 20/100' and are 1/2" diameter.... I will connect to the bottom of each triangle structure and anchor on the side of the house at each end. If things go really bad (i.e. hurricane winds), then the tripod might topple on the roof but no 50lb panel will go flying off the roof.

I'm not sure what material your climbing rope is made of, but if it has any kind of polyester fiber, which most of the cheap ropes do, I would highly discourage this plan. The ropes will work fine for a few months. After this, the polyester will have deteriorated enough in the sunlight to weaken it, making it no longer safe. After a couple years or so, depending on its thickness, it may just blow away in the wind on its own. Most types of plastic are vulnerable to sunlight. A steel cable would be more secure, and it would probably be more aesthetic, too (less noticeable).

Note that this perspective is shared from Thailand where the sun is more intense and perhaps the quality of products is less--so your mileage may vary--but I have seen ropes destroyed by sunshine here.

 

[Scoob-SanDiego]

I'm not sure what material your climbing rope is made of, but if it has any kind of polyester fiber, which most of the cheap ropes do, I would highly discourage this plan. The ropes will work fine for a few months. After this, the polyester will have deteriorated enough in the sunlight to weaken it, making it no longer safe. After a couple years or so, depending on its thickness, it may just blow away in the wind on its own. Most types of plastic are vulnerable to sunlight. A steel cable would be more secure, and it would probably be more aesthetic, too (less noticeable).

Note that this perspective is shared from Thailand where the sun is more intense and perhaps the quality of products is less--so your mileage may vary--but I have seen ropes destroyed by sunshine here.

Thanks, I appreciate the feedback and agree with you.
I am using #6 AWG for grounding all my panels so I will simply tie in to that. No amount of sun wind and rain will rip a #6 AWG copper wire

 

[OffGridForGood]

Thanks, I appreciate the feedback and agree with you.
I am using #6 AWG for grounding all my panels so I will simply tie in to that. No amount of sun wind and rain will rip a #6 AWG copper wire

Copper as a PV restraint. wow.
Perhaps a deliberate attempt at humour.
Be sure your insurance is up to date.

 

[Scoob-SanDiego]

Copper as a PV restraint. wow.
Perhaps a deliberate attempt at humour.
Be sure your insurance is up to date.

I hope this little bit of sarcasm helped you feel better somehow. But I'm afraid it did not provide any value to this conversation. Perhaps you would have some valuable insight to share that would help us understand the folly of our tentative plans and save us from some unforeseen catastrophe?

 

[OffGridForGood]

Not sarcasm, bitter reality.
Sure, valuable insight is appropriate.
A copper ground wire is a poor choice for a restraint for roof top loose laid PV panels, meets no code requirements (structural or electrical), and since you plan to attach the cable only at the ends of the roof, the hold-down effectiveness for the centre area will be nearly zero; hold-down force will be a function of the wire tension and the angle between the tie-down point and the PV panel so flat laid cable no matter the tension will provide very low/no hold down vector. It's math.
From your photos it appears your located in a municipality and building codes, electrical codes, insurance, neighbours are components of the decision process. We have see others on the forum report fines they paid for non-compliant loose panels on a roof, perhaps you will be next. If not, and wind produces conditions resulting in damage to a neighbour's propertery you may be culpable - ie "be sure your insurance is up to date" was the advice.

Roof top solar panels need to be secured to the roof structure. In many areas this will mean a submission to the local AHJ for review and approval proir to construction. Many commercially available PV restraint systems are available for various types of roofing.

 

[Norwasian]

My chief concern with copper cables would be that copper is quite malleable, and might stretch and/or have insufficient tensile strength in the moment when it was needed. Steel cables would hold firmly, and if strung from one eave, over the ridge, and down to the opposite eave (which is what I was imagining when I suggested them), I think it should hold well enough, provided it was suitably attached to the panel's base, and provided each end of the cable was well anchored, not just screwed to the external fascia board. Mathematically, you would be holding from two different vectors, and if the cable were tight, there should not be much wiggle room.

Running a plank on either side of the bases with multiple attach points on each one (at least two, if using sturdy lag bolts, more if resorting to deck screws) to prevent the bases from even flipping over would be another way of sturdifying the assembly, and again, without needing to puncture the roofing and risk leakage. The cables would still be necessary to hold the assembly down, but this would greatly restrict movement and by tying it all together, the weight would be increased in order to budge even one part of it (all or none). Of course, winds are more powerful than many understand, and with the panels' exposure, the potential force is substantial. (If I've done the math correctly, with a conservative estimate of each solar panel being about two feet by three feet in dimension, i.e. 6 sq. ft. total, each panel would have a force of around 55 pounds of wind load in a 60 mph wind. But increase the wind to 80 mph and the wind load is nearly 100 pounds per panel. With the angle of the panels, some of that will be a lifting force, like for an airplane wing--which would reduce the resistance to movement based on traction with the roof shingles. Lots of physics to consider.)

One thing's for sure: I would not fancy carrying a piece of plywood (okay, 32 sq. ft. of surface area) on that roof with even a 15 mph breeze! I think I'd be a nose-diving kite!