Exceeding PV max input spec on MPP 2424LV-MSD

[Scoob-SanDiego]

I recently purchased a MPP 2424LV-MSD
Lovely starter unit... Now I wish I had gotten a more capable EG4 3K LOL. Live and learn!

The unit has a restricted VOC of 150V. and operating voltage of 30-80V... limiting me to setting my (used) 240W Trina panels
in strings of 2 panels (about 60V output). I have a total of 4 regular strings for a total of 1920W max.
And I have an extra 4 panels (2 strings) that I can turn on/off with a separate DC isolator.

Works great to crank up the juice when the sun is not hot enough... but today with the extra panels my
PV input was around 1950W.

QUESTIONS:

• What happens if the PV input exceeds the 2000W maximum specification for that model?
• And by that, I mean exceeds by 100-200W and for short period (say, less than 5 minutes).
• Is the MPP unit protected from over input PV current or will it just smoke / get damaged / catch fire?
• Is it a hard 2000W input or is there some wiggle room for a short period (ex. up to 2200W for 4min)

I am thinking of creating a little RPI circuit to drive a DC relay that can read the output of my solarAssistant
through MQTT either with a python library or possibly using Node-Red.

• https://solar-assistant.io/help/integration/mqtt
• https://solar-assistant.io/help/integration/node-red

A simple algorithm along the lines of: IF PV power < 1400 or 1500W, then turn on extra panels.
And if PV power exceeds 1900 (or 1950W), then disconnect extra panels.

I could easily increase the granularity of the booster panels by adding 2 DC relays and add a single string at a time.

Any input, suggestions, shared experience with going over the rated PV limit of the inverter is welcome!

- Christian

 

[sunshine_eggo]

MPPT pull from panels. Panels don't push.

You've over-paneled your MPPT. It's pretty common to do.

Based on my calculation, you have a 2880W array on a MPPT capable of ~2000W. You're not over 150Voc and you're not exceeding the OUTPUT current on the PV input.

The worst part I see is turning the 4 panels on and off. Just leave them on unless you don't need them at all.

These are generalities. Wouldn't hurt to ask your supplier.

 

[Scoob-SanDiego]

MPPT pull from panels. Panels don't push.

You've over-paneled your MPPT. It's pretty common to do.

Based on my calculation, you have a 2880W array on a MPPT capable of ~2000W. You're not over 150Voc and you're not exceeding the OUTPUT current on the PV input.

The worst part I see is turning the 4 panels on and off. Just leave them on unless you don't need them at all.

These are generalities. Wouldn't hurt to ask your supplier.

Yes, I effectively have 6 parallel strings of 2 panels (62V per string), coming into a PV bus bar. Each string is 15A fused.
I also sent an email to MPP (as well as Victron and Eg4 to how their systems respond to over paneling).
I took advantage of SanTan Solar's holiday sales onused panels ($20 each... plus another $250 freight to San Diego)... still under $500 for 12x 240W panels... not bad!

I will post a summary of the responses I got from each vendor.

 

[zanydroid]

I think you already got your answer about overpaneling being the meta.

Just wanted to point out that you might need some monster DC relays to safely switch under load, above certain voltages. Because DC arcs are pretty metal (err I mean not self extinguishing)

 

[crossy]

I think you already got your answer about overpaneling being the meta.

Just wanted to point out that you might need some monster DC relays to safely switch under load, above certain voltages. Because DC arcs are pretty metal (err I mean not self extinguishing)

Yeah, I'm using solid-state relays to switch panels off and putting up with the few watts of losses.

 

[zanydroid]

Yeah, I'm using solid-state relays to switch panels off and putting up with the few watts of losses.

SSRs felt like they would hold up better. What is the voltage and amps rating on those?

Are there any pitfalls with interrupting under load? I assume if voltage and current is ok, then the arc won’t be a thing because it is SS, but I want to understand the best practice vs semi educated guessing

 

[crossy]

You need to ensure you have "DD" (DC control, DC output) relays.

IIRC the ones I have are 3-30V DC control and 220V 20A DC output side.

Bigger / higher voltage ones are available, all will need some form of heatsink.

EDIT have a look at units from Fotek https://www.fotek.com.tw/en-gb/product-category/144

 

[zanydroid]

What are the other kinds of relays and what kind of bad stuff can happen?

I assume you have to do VOC adjustment for the ratings on SSR as well?

 

[crossy]

The main types of SSR are DD and DA.

DA ones are for controlling AC they won't turn off on DC - not what we want.

The rated voltage must be greater than the Voc of the string, just like your charge controller.

 

[littleharbor2]

That's a very low MPPT range but I think I would have still wired at 3s. In your neck of the woods your actual Vmp. of those older panels will likely be under 30 volts at actual operating cell temps. If the 2s config. is working for you then really not worth the effort to rewire your array.

 

[sunshine_eggo]

Yes, I effectively have 6 parallel strings of 2 panels (62V per string), coming into a PV bus bar. Each string is 15A fused.
I also sent an email to MPP (as well as Victron and Eg4 to how their systems respond to over paneling).
I took advantage of SanTan Solar's holiday sales onused panels ($20 each... plus another $250 freight to San Diego)... still under $500 for 12x 240W panels... not bad!

I will post a summary of the responses I got from each vendor.

Victron publishes their over-paneling criteria:

1) Never exceed Voc
2) Never exceed published input current (Isc) limit.

And they elaborate about it on their community form.

#2 is flexible. The PV input current limit is the maximum short circuit current that the MPPT can protect itself against connecting the panels in reverse polarity. However, if you do not connect the panels in reverse polarity, there is no meaningful limit.

Using their RS450/200 as the uber example, it's limited to about 11kW of output at 48V across 4 independent MPPT.

You could install a Vmp 306V and Isc 30A array ON EACH MPPT. That's about 8300W PER MPPT, or 33,200W with about 11kW actually usable.

My 250/100 MPPT can have about 11kW on it even though it can only output 5800W @ 48V.

 

[zanydroid]

I'm not 100% convinced #2 means, "raise Isc to whatever level as long as you have correct polarity". +50% or +100% is probably OK, but +1000% would not feel right. There's probably some thresholds where a black swan failure mode, that they haven't analyzed, will end in tears. IOW the reverse polarity thing feels like a failure mode they did anticipate and analyze, and probably it's on the list most likely to occur/types of failures they could imagine.

Did OP ever post where 3S's Vmpp lands in the operating range?

Is there a formula for how much you lose if Vmpp goes over operating range but Voc is still OK?

(I thought the operating range is designed so that the typicall Vmpp will drop into that range, assuming Voc was picked c orrectly)

 

[Scoob-SanDiego]

I head back from the MPP folks who btw have been SUPER helpful and fast to respond.... We are talking 3 email responses from them in 1.5 hours, the first withing 15 min of my initial inquiry!

They essentially say the same thing as Sunshine_Ego: If you respect the VOC and lsc, then you're good. I did just write back to MPP asking them WHAT the lsc of the LV2424-MSD unit was as I can't see any hint of that value anywhere in the spec sheets.
From MPP:

To clarify, the PIP2424LV-MSD has a maximum rated PV power input of 2000W. If you were to set up a system with 3000W of panels, the inverter would only utilize the maximum rated input of 2000W. The extra 1000W would not be loss.

It's important to note that the inverter is designed to handle inputs within its specified range, and exceeding this range could lead to inefficiencies in power production. However, the inverter itself is built with safety features, and it should not be damaged if the PV input slightly exceeds the rated value.

In your scenario with 3000W of panels, as long as the Voc (open-circuit voltage) and Isc (short-circuit current) values of the panels fall within the acceptable range of the inverter, it should function safely.

It is interesting to note that 50% over-paneling falls withing the "acceptable" range. With that thought in mind, I completely dropped any idea of having a dynamic panel on/off system as it is pointless. From now on, all my panels are on all the time.

My panels are 12 used Trina 240W panels with the following specs:

• Voc: 37.2
• Vmp: 30.4V
• lsc: 8.37A
• lmp: 7.89A

• 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

It has been humming between 1240 and 1260W all morning.
My setup is just to run my office equipment / computers and soon a small freezer and the TV on the other side of the wall.
As of 11:30am my batteries were full so I decided to experiment a little.
I ran a thick extension cord and am now running/heating my hot tub with the excess solar (it's. small softTub with no heating elements... the water is heated from circulating around the pump... Consumes about 1Kw when running. It DID cause an error code and a freeze on my MPP on first try. But the second try worked like a charm and now it's humming along
A quick thermal scan reveals that everything is cool as a cucumber!

Here are some photos of my system. It's still an experiment and needs a little tidying up. The panels are currently just propped up. I am building wooden angle frames to incline them to the sun (44deg in winter, 12 deg in summer, almost due south (in San Diego, CA)).

 

[zanydroid]

I am building wooden angle frames to incline them to the sun (44deg in winter, 12 deg in summer, almost due south (in San Diego, CA)).

You’re going to incur extra structural scrutiny to get angled roof mounts approved in California. It’s doable, I have exactly one neighbor (out of 50 with solar) that has bothered.

You have enough space there to get the same generation by spamming panels parallel to roof (which has little scrutiny if you use approved hardware & standard rafter framing). That is what the other 49 neighbors did.

 

[Scoob-SanDiego]

You’re going to incur extra structural scrutiny to get angled roof mounts approved in California. It’s doable, I have exactly one neighbor (out of 50 with solar) that has bothered.

You have enough space there to get the same generation by spamming panels parallel to roof (which has little scrutiny if you use approved hardware & standard rafter framing). That is what the other 49 neighbors did.

Good point... the higher profile DOES get a lot of attention. No permits. This is totally OFF grid. And when something is not PERMANENTLY attached, they have stupid rules where they don't regulate it LOL.... 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.

The cool thing about home made triangle structure is that I can just pull the bottom bolt to lower the panel to 12deg in the summer (or pull the panel to the roof in case of high wind, which we just had a week ago).

But your point is well made. I am still experimenting to get numbers on how much more juice I get with the proper inclination of my panels and how many more panels would I need if I set them flat on the roof... I kick myself for not having ordered 24 panels instead of just 12 when they were $20 a pop LOL.

 

[Scoob-SanDiego]

I head back from the MPP folks who btw have been SUPER helpful and fast to respond.... We are talking 3 email responses from them in 1.5 hours, the first withing 15 min of my initial inquiry!

They essentially say the same thing as Sunshine_Ego: If you respect the VOC and lsc, then you're good. I did just write back to MPP asking them WHAT the lsc of the LV2424-MSD unit was as I can't see any hint of that value anywhere in the spec sheets.
From MPP:

It is interesting to note that 50% over-paneling falls withing the "acceptable" range. With that thought in mind, I completely dropped any idea of having a dynamic panel on/off system as it is pointless. From now on, all my panels are on all the time.

My panels are 12 used Trina 240W panels with the following specs:

• Voc: 37.2
• Vmp: 30.4V
• lsc: 8.37A
• lmp: 7.89A

• 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

I heard by from MPP (they are REALLY good at responding to email fast!).

I asked them what the short-circuit current limit (ISC) was on the LV2414 and they said:

For low PV input (145V) models like the PIP2424LV-MSD, the maximum charging current is 80A, which corresponds to the short-circuit current limit (ISC).

With my configuration (see above), I currently have an ISC of 50.22A (with 6 strings in parallel).
With the 80Amp headroom, I could add an extra 3 strings (80 - 50.22) / 8.37 = 3.4 strings (so up to additional 3 strings)

 

[Scoob-SanDiego]

I heard by from MPP (they are REALLY good at responding to email fast!).

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:

The inverters will clip a bit of PV wattage that goes over the limit but if you go far enough overt the limit it will sound alarms and very possibly get damaged. If nothing shuts down during PV overvoltage or current then there is the possibility of a fire though it is very very rare. I would recommend configuring the PV to fit the inverter PV specs.

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).

 

[zanydroid]

I wouldn't necessarily trust MPP to answer correctly. I'd recommend putting a fuse after the combining. The output current and input current are also decoupled with an MPPT due to the voltage conversion.

For any of these vendors, I don't think you can expect the same service as, say, a dedicated application engineer responding to an existing big account. That said, I know some people that have had success talking to the vendors this way.

 

[sunshine_eggo]

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!)

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.):

For low PV input (145V) models like the PIP2424LV-MSD, the maximum charging current is 80A, which corresponds to the short-circuit current limit (ISC).

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

Based on my calculation, you have a 2880W array on a MPPT capable of ~2000W. You're not over 150Voc and you're not exceeding the OUTPUT current on the PV input.

The same criteria they gave you.

 

[darknet]

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.