Max DC voltage <600 with 6400watts?

[Superman_006]

I have been running 9 REC 320w n-cell panels in 1 array for about 2 years. I installed a larger inverter that has 3 MPPT inputs (sunnyboy 5.0 us -41). I finally found more modules. I ended up buying 10 more and was going to put several on my west roof as well as adding to the south… making 3 arrays. Looking at the max specs 10amp and 600v total which you can attach 7100 watts to.

The Voc on these 320w modules are 40.80v and the amps are near the max… how in the world is it possible to attach 7100 watts to this without hitting the max 600v?

I know people say don’t use the STC but people also say oversized the PV arrays by 10-20%… 22 panels are 7,040 watts, then you at 898 volts.

The 7.7-us-41 also has the max volts of 600 with 10amps and says you can attach 10,905w

[solarix]

The 10amp spec is PER input with a max mppt voltage of 480Vdc. So the max recommended power PER input is 4.8kW. If you spread your panels around with a different orientation on each input, you can easily handle 7.1kW without overloading the 5kW inverter.

[Superman_006]

I didn't realize that was per input. It says:
Max PV Power= 7100w
Max DC Voltage= 600v
Rated MPP voltage= 220-480v
MTTP operating voltage range= 100-550v
Min DC Voltage/ Start voltage= 100/125
Max. operating input current per MPPT= 10A
Max. short circuit current per MPPT= 18A
Number of MPPT tracker / string per MPPT tracker= 3/1

So I read the max DC off all the MPPT combined and not per MPPT

Here is the data on my panes
WP=320
MPP-V=34.2v
MPP-A=9.37a
From what I understand you just multiply voltage x amps... and get 34.2x9.37= 320w

Voc=40.8
Short circuit A= 10.18

My current plan as long as im not adding all the MTTPs voltage together
MTTP-1 will have 8 PV on it at 326.4v max VoC (2560W)--- facing south
MTTP-2 will have 8 PV on it at 326.4v max VoC (2560W) --- Facing south
MTTP-3 will have 3PV on it at 122.4v max VoC 9 (960w) ---- Facing west
But some how I also ended up with a REC 365AA PV... its got the 40mm think frames but is a few inches taller. I would like to add this to array #3 and place it portrait above the 3 all in a series but the stats for that panel is
WP=365
MPP-V=37.1v
MPP-A=9.85a
Voc=44v
Short circuit 10.52a

I seen where some people are mix matching PV in this way, I see where some people say it brings that whole array down, but I see where some say it doesn't if they are close... not sure if those are close enough or not.

[oregon_phil]

Go to the sma america website and use the Sunny Design web based program to design your system. And you can download the SMA inverter manual to get the specs and how to interpret them.

One spec above that you quoted above Min DC Voltage/ Start voltage= 100/125 would not be met by your current plan for MPPT-3 input (122.4Vdc max).

[Superman_006]

I assume that the MPPT3 would work in connection with MPPT2 and MPPT1 and this would not be only using 1 MPPT at a time. From how I understand it.. MPPT 1 could be making 2000 watts and MPPT 2 could be making 1500 watts and I would be producing 3500 watts. However it can change the amps/ voltage for the inverter to convert a lot more eff. I haven't really had anyone explain it very well in grid-tied, but in off grid, the MPPT will try to match the voltage of the battery to the voltage coming of the charge controller.

This is why I am not sure about the voltage is for all or one MPPT.. Im kinda reading it as if Mppt 1 is making 80v and mppt was making 95v. 175volts I would be running? But if it works that way... Then obviously its combined voltage of the system. Im not sure how the inverter combines it. If its parallel then its adding the amp, if its series then its adding the voltage. But I think Solarix is saying they are completely independent. I am thinking its more complex and it will kind of do both.

Reading the spec...

If I used the 4th panel I would also be at 166.4v (Voc) I would also think that this system doesn't run on Voc but that actual working voltage? Currently my system still seems to make some sort of wattage up until sunset but it might be that Ive got 9 in a string right now.

[oregon_phil]

I assume that the MPPT3 would work in connection with MPPT2 and MPPT1 and this would not be only using 1 MPPT at a time. From how I understand it.. MPPT 1 could be making 2000 watts and MPPT 2 could be making 1500 watts and I would be producing 3500 watts. However it can change the amps/ voltage for the inverter to convert a lot more eff. I haven't really had anyone explain it very well in grid-tied, but in off grid, the MPPT will try to match the voltage of the battery to the voltage coming of the charge controller.

I have an SMA 7.7 -40 and can tell you that, if wired correctly, you will have three independent MPPT inputs, A, B & C. There is a way to parallel inputs A&B together, but I know you don't want to do that.

The grid tied inverter will run a slightly higher voltage than grid voltage in order to push electrons onto the grid. My grid voltage is not constant and fluctuates up and down due to whatever factors. But in order to push electrons onto the grid, my inverter always runs about 1.5VAC higher than grid voltage.

This is why I am not sure about the voltage is for all or one MPPT.. Im kinda reading it as if Mppt 1 is making 80v and mppt was making 95v. 175volts I would be running? But if it works that way... Then obviously its combined voltage of the system. Im not sure how the inverter combines it. If its parallel then its adding the amp, if its series then its adding the voltage. But I think Solarix is saying they are completely independent. I am thinking its more complex and it will kind of do both.

Your example of MPPT 1 of 80 vdc and MPPT 2 making 95 vdc is the reason for my earlier post. Each MPPT needs at least 125 vdc to start up and 100 vdc to keep running for that MPPT.

If you ran the SMA Sunny Design, it would show you exactly the minimum number of panels required for each MPPT (and the maximum number of panels to stay under 600 vdc with temperature factored in).

If I used the 4th panel I would also be at 166.4v (Voc) I would also think that this system doesn't run on Voc but that actual working voltage? Currently my system still seems to make some sort of wattage up until sunset but it might be that Ive got 9 in a string right now.

There are quite a few articles written about running different panel specs on the same string. Others can chime in on solar panel specs tolerance limits on panels within the same string. Your solar panel attached to an inverter will not be running at Voc because Voc means open circuit. Panel open circuit = zero amps = zero power. Your panel would like to run at maximum power point voltage. Because the 4th panel is the odd ball, most likely it will not be running under optimum conditions.

[Superman_006]

So I did as everyone suggested. I went to the SMA site and made a design. And you all were all correct and the main answer to this question is that the- Max DC voltage = 600v this is per MPPT. Their design software allows me to put 13 modules on each MTTP showing 594/594/594 = 1,782v and the only warning it throws is that my inverter is undersize for the total wattage. It calculate it with the 4/8/8 I get some notes that my "Nominal power ratio is below 87% " which means my inverter is undersized. So, I think I will ditch the extra 365AA module and move one from the south and put on the west.

inverter line.PNG