Over-paneling Victron MPPT controllers.

[Hedges]

FETs, inductor, diode would have a maximum current limit. Excessive heating at higher current.
Switching power supplies can run off a battery (thousands of amps available) drawing just what they need to power the load.
Some have a problem that with low input voltage they draw excessive supply current trying to power the load and burn up.
MPPT charge controllers typically draw all the power available from PV while charging battery in CC mode, then switch to CV mode and draw less from PV.
But, the MPPT algorithm runs PV voltage up and down to see what delivers most power. That's one time where it should be careful in case available power exceeds the input or output current it can handle.
Even if MPPT was settled at some operating point and clouds suddenly cleared, that shouldn't increase current through inductor. That ought to be under algorithm control. Maybe uP decides what "on" time for the transistor my examining current sensor, and there isn't hardware or real-time response monitoring max current?
Some designs are more bullet proof than others.
We put in fuses or breakers, but sized 25% over and they take time to blow. Protection has to be designed into the product.

 

[MrM1]

OK So I was watching YouTube last nite (I know ) and I came across a channel by an installer in TX that installs the Growatts (usually from Sig Solar) in the TX area. So I thought, "what the heck, I'll write him about his experience with Over Paneling the 12kw since he has a video of installing one". So I wrote Solar World LLC on Facebook messenger and got an auto response that said, "Text Me" ... so I did.

And I got a response right back from him. We threw texts back and forth for a few minutes, and he was very responsive to my questions. But the long and short of the discussion was as follows. I asked him about over paneling with 32 370w panels in a 4s4p x 2 configuration and He said ...

"So with the off-grid inverter Growatt 12 KW, The max amperage is 80 amps at 54.5 volts charging at DC voltage. Over paneling the Growatts won't necessarily hurt it by any means it will just help maintain a higher amperage when there are cloudy days.

But the unique thing about the Growatt is the ability to transfer live direct DC energy to AC conversion at a 97 + percent efficiency rate bypassing batteries for on demand power. 12 KW Growatt 12kw worth of solar."

I am really not even sure I am smart enough to interpret all his answers, but here is a fellow that actually installs the units. I thought it might be interesting here.

 

[Hedges]

PV DC to AC is good for efficient production of power used while the sun shines. That's what I get with AC coupled Sunny Boy + Sunny Island. The only conversion from 380VDC to 48VDC is battery charging.
SolArk similarly has a high voltage DC rail, with battery charger (bidirectional to high voltage DC) and AC inverter running off it.
With either Sunny Island or SolArk, added AC coupled PV provides AC power in addition to what comes from batteries. (only if a GT inverter is added to SolArk.)

So he's saying his 12k Growatt can only charge 4kW to battery, but with 12kW of PV it can put out 8kW AC at the same time. (Same as SolArk)
<edit: Data sheet doesn't seem to support that>
That should mean it has 12kW of MPPT. But maybe not? 4kW of MPPT deciding how much power to put in battery to maximize power drawn from PV, but at the same time inverter draws as much as it wants? I guess that works. Inverter converts whatever DC voltage is available to AC with its switcher, and MPPT just sees that PV + inverter source and load on DC rail (which has capacitors), and it runs charge current up & down to find what is maximum power.

 

[MrM1]

? So I'm still like "install all 32 370w panels in a 4s4p x 2 into pv 1 and pv 2 with the array pointing south? "

Or

Drop 2 4s groups (8 panels)

Or

Or point 1 4s group east, one west, we every thing else aimed south.

Just don't want to fry the mppt but we do want the larger array for clouds, winter and morning /evening

 

[RobertGreen]

So he's saying his 12k Growatt can only charge 4kW to battery, but with 12kW of PV it can put out 8kW AC at the same time. (Same as SolArk)
That should mean it has 12kW of MPPT. But maybe not?

Wouldn't that mean that the unit was capable of running the AC inverter from the high voltage DC input bus? In other words, that the inverter was bypassing the MPPT? This seems unlikely to me with the growatt-- look at their spare parts, I believe I have seen that the separate MPPT and AC inverter boards do not have a high current connection between each other except for that between them and the 48v/dc output. If you're feeling frisky, would you consider posting some pictures of the internals so that we might try and decipher this? (edit: upon re-reading, I have misunderstood-- for some reason I thought you had one of these units in hand. My bad.)
If it had 12kw of MPPT, it seems like it would be capable of providing that as charging power 12kw... what would be the reason why not?

 

[MrDan]

Is that documented? Maybe it is, but I did find this:

"Maximum PV Array Power"

It's listed under the charger section, but that's the only place where I can find a mention of PV power: https://www.growatt.es/upload/file/contents/2021/01/5ff923130f7e6.pdf.

I would consider it to be a selling point of being able to do both full DC charging and provide the rest of the power at the nameplate value through the AC inverter, so I'd be surprised if they didn't put that in the documentation somewhere...and maybe it is.

 

[MrM1]

Thank you @FilterGuy . I did not mean to hijack this thread, but merely contribute to your desire to update the Over Panel guide.

I can start my own thread on this topic, and we have bantered around several thoughts here, But at the end of the day, would you Over Panel the Growatt SPF 12kw DVM 250vdc? By how much? Some have said no more than 30%. We at this point have to point all the panels in the same direction. We have 32 370w panels. But maybe that is too much? We can always limit that number, but by how much?

I also read in the undated Over Panel guide that some of the Growatt hi frequency inverts listed in the guide have a hard limit to the array size. I wonder if this lo frequency Growatt 12kw also has such a hard limit.

What is the final analysis from all our discussion?

 

[Bluedog225]

Subscribed

 

[Zwy]

Got a little more anecdotal info about the Growatt 12kw 250 and the idea of over paneling from Watts247.

"You can overpanel, however this can be a waste when an sc48120 (dual mppt charge controller - same as what's in this unit is just a few hundred bucks) port your extra panels into a new charge controller."

So this is saying that the Growatt's internal Mppt SCC is the same unit as the sc48120 mpv? Still not much info out there on it.

Ian says that if you want to overpanel the unit but want to harvest as much PV as possible, it would make more sense to just add another SCC. Makes sense, the inverter is large enough for needs but the SCC is limited on input to 7Kw total. With adding a SC48120 MPV, you add another 6.6Kw at 250V.

Most likely this is the route I'll be taking on my residential system, one GW 48V 12000T MPV with an SC48120 due to over 8Kw of panels. You have to keep under PV 150V max and with larger panels around 50VOC it can make it complicated to keep amps per string down. The GW 48V 12000T MPV I believe is 250V total but each SCC is limited to 145VOC. Ian has 4S listed on 40VOC panels but I think that might exceed to rated MaxVDC says 150V. If you look at the SC48120 MPV, it lists 145V max. My guess is the SCC in both units is the same, with dual inputs.

If you run 4x47V panels in series as he indicates, there might be smoke. I'd surely want to know if it's true or not.

 

[MrM1]

Odd it would be called a 250vdc SCC but be limited to 150vDC. Not sayin your wrong, and (if I recall) Ian wrote me that it was the same SCC as the stand alone SC48120.

If this is the case, makes install even more confusing.

 

[MrM1]

The GW 48V 12000T MPV I believe is 250V total but each SCC is limited to 145VOC. Ian has 4S listed on 40VOC panels but I think that might exceed to rated MaxVDC says 150V. If you look at the SC48120 MPV, it lists 145V max. My guess is the SCC in both units is the same, with dual inputs.

Yeah not actually sure how you come up with the SCC of the 12kw inverter being only 150 vdc each PV input. If that is true seems like there'd be a lot of smoked inverters as the manuals only instruction on installing pv is as follows.

 

[MrM1]

I'm now trying to find the manual for the SC48120 MPV- 120A 250vdc and it seems all I can find is the one that is for the 150vDC. This might be part of the the confusion. The picture of the 250vdc on Watts247 is different from the manual.

 

[Zwy]

Odd it would be called a 250vdc SCC but be limited to 150vDC. Not sayin your wrong, and (if I recall) Ian wrote me that it was the same SCC as the stand alone SC48120.

If this is the case, makes install even more confusing.

I agree and I did look thru the manual after posting. There is not a clear explanation in the manual either. As there are 2 PV ports, it could easily be 150VDC input max on PV. The brochures on Wats247 show 150VDC input. But then where does 250VDC come in?

Right now, I'm looking for an answer as it sure makes a huge difference. At this point, I'm actually leaning more towards a high freq pure sine in parallel, and adding the SC48120 MPV- 120A 250VDC to take full advantage of the PV array.

 

[Zwy]

Yeah not actually sure how you come up with the SCC of the 12kw inverter being only 150 vdc each PV input. If that is true seems like there'd be a lot of smoked inverters as the manuals only instruction on installing pv is as follows.

View attachment 71980

Found this link in your thread, it appears Ian may have the wrong spec sheet listed. https://www.growatt-america.com/show-42-642.html

 

[Zwy]

I'm now trying to find the manual for the SC48120 MPV- 120A 250vdc and it seems all I can find is the one that is for the 150vDC. This might be part of the the confusion. The picture of the 250vdc on Watts247 is different from the manual.

Page 17

 

[MrM1]

Yeah seen those spec sheete. It seems even growatt might be behind in publishing specs for their newer 250vdc SCC and 12kw inverter.

 

[MrM1]

I did write Ian again yesterday and he confirmed 250vdc on each input of the 12kw 250vdc, and said he saw no problem over paneling even up to my designed 11840w all in the same direction, just broken down into two 4s4p arrays and not exceeding 250vdc on each input (which is my plan). And that I might want to go into the menu and limit charging out put down from 120A to 80-100 amps.

 

[Zwy]

I did write Ian again yesterday and he confirmed 250vdc on each input of the 12kw 250vdc, and said he saw no problem over paneling even up to my designed 11840w all in the same direction, just broken down into two 4s4p arrays and not exceeding 250vdc on each input (which is my plan). And that I might want to go into the menu and limit charging out put down from 120A to 80-100 amps.

Sounds good, I'm currently leaning back towards the low freq inverter in the GW 12000T DVM. I ordered 16 panels today, San Tan has a 530w panel in stock and MT Solar was able to make a pole mount that worked with it. I have a VOC of 49.65, ISC 13.43 so it looks like 4S4P for me and adding a SC48120 MPV- 120A 250vdc as amps will exceed 120a for 4S4P. Are you splitting your arrays to face different directions to get around the 120a?

Thanks for the update from Ian, I would have contacted him but you beat me to it.

 

[MrM1]

All same direction unfortunately (design constraints). Two 4s4p arrays, one in to PV1, the other into PV2. 370w panels: voc 47.46 (4s = 190vdc) / isc 11.07 (4p = 44.28).

I wish you would write Ian. I'd be curious to hear his response to your query.

 

[MrM1]

If you've got 16, why not 4s2p in 2 home runs back to the inverter /SCC and go one each into pv1 and pv2? Couldn't u then skip the extra SCC?