Adding to my current system and need help clarifying terms

[EVH5150]

I currently have a sonnenBatterie hybrid 9.53 with 8 x 385W Trina solar panels on one PV/MPP input and plan to add panels to that bank and then another smaller bank on the other MPP input. I've searched through the forums and haven't yet found an answer to my question which is; Is the Max. input voltage the total of both the MPP inputs? e.g. If I have one bank with 500v then one with 250v, then I'm up against the 750v max input voltage? I have the choice of two different brands of 415w panels. Brand A has a higher Voc of 50.1v and a lower Maximum Power Current-IMPP (A) of 9.86a while Brand B is 38.45v & 13.1A. If I max out the space available on my roof with brand A and my existing panels I get 766.4v total with both banks but less current. Brand B gets me 668v but the higher current. Any advice on which to run with?
Thanks.

The specs for the PV input side of things are as follows:

 

[OffGridForGood]

8 x 385W Trina solar panels on one PV/MPP input and plan to add panels to that bank and then another smaller bank on the other MPP input. I've searched through the forums and haven't yet found an answer to my question which is; Is the Max. input voltage the total of both the MPP inputs? e.g. If I have one bank with 500v then one with 250v, then I'm up against the 750v max input voltage?

No the two separate MPP input voltages do not add together.
if the max input voltage is "X" and you stay below "X" on each, you are okay.

750v max input voltage

Max is Max. It is not a suggestion.

with brand A and my existing panels I get 766.4v total

766.4 > 750 - if you put 766.4 volts into an MPP on this inverter, you should expect it to fail, and then you will be looking for a new inverter, hopefully not also looking for a new home.

Brand B gets me 668v but the higher current.

9.86a

I assume the pv is all in series 668<750 = Not blow it up, but your spec sheet shows MPP range to be 75v-600v so you need to reduce the number of panels until your string voltage is less than 600v.
I have seen this in my own system, too high voltage string and the MPP can't do it's search for the maximum power point.

668 x 9.86A = 6586W 6586 > 6500 you could expect some clipping back to 6500. However, since the voltage is too high, you will be reducing the PV string to get under 600v
so 600v x 9.86 = 5916 no clipping

 

[EVH5150]

No the two separate MPP input voltages do not add together.
if the max input voltage is "X" and you stay below "X" on each, you are okay.


Max is Max. It is not a suggestion.


766.4 > 750 - if you put 766.4 volts into an MPP on this inverter, you should expect it to fail, and then you will be looking for a new inverter, hopefully not also looking for a new home.



I assume the pv is all in series 668<750 = Not blow it up, but your spec sheet shows MPP range to be 75v-600v so you need to reduce the number of panels until your string voltage is less than 600v.
I have seen this in my own system, too high voltage string and the MPP can't do it's search for the maximum power point.

668 x 9.86A = 6586W 6586 > 6500 you could expect some clipping back to 6500. However, since the voltage is too high, you will be reducing the PV string to get under 600v
so 600v x 9.86 = 5916 no clipping

Thanks for the info. I've done a lot more research since I posted that and it all makes sense now.

If I add two more panels that are rated at 13a to my current string that run at 11.46a, they will run at the lowest current in the string and reduce rated output of 415w to 365w. A bit of a reduction, but Im ok with that for only two extra panels.

On another string I can run 6 more of the 415w panels. The total voltage will fall under the 750v (s1 438v & s2 255v) allowing for min temerature. From what I understand, the panels that run at 13.08A wont damage the inverter which says max input current 13a, the critical number is the 750v and 600v for the mpp range.

Max output of the two strings would be 6300w but since one will be facing north and one west, I wont see that at any one time I assume.

 

[OffGridForGood]

Max voltage is max voltage - do not exceed
Max amperage - if you exceed most equipment will just clip off the extra (lost potential) but no damage. Current is "pulled", not "pushed".
{Your main panel doesn't explode and send sparks all over if you draw less amperage than the panel is capable of supplying.}

 

[MisterSandals]

If I add two more panels that are rated at 13a to my current string that run at 11.46a, they will run at the lowest current in the string and reduce rated output of 415w to 365w. A bit of a reduction, but Im ok with that for only two extra panels.

I'd check the output before you add those 2 panels. I wouldn't be shocked if your array without the 2 with a different current doesn't allow your MPPT to produce more.

Have you done the math, particularly in regards to the MPPT range that @OffGridForGood is talking about? It sounds like you think more is always better, pay attention to the output numbers (and please report the results here!) and use that as your guide. Mixing panels to fiddle like you are considering just sounds wrong (but i'd have to see all the numbers to be able to predict the results).

 

[EVH5150]

I'd check the output before you add those 2 panels. I wouldn't be shocked if your array without the 2 with a different current doesn't allow your MPPT to produce more.

Have you done the math, particularly in regards to the MPPT range that @OffGridForGood is talking about? It sounds like you think more is always better, pay attention to the output numbers (and please report the results here!) and use that as your guide. Mixing panels to fiddle like you are considering just sounds wrong (but i'd have to see all the numbers to be able to predict the results).

Attached are the data sheets of the panels. My current panels are the Trina 385's and the ones I'm looking at purchasing are the DA Solar 415w.

My calcs are as follows:

String one. 8 Trina 385's - Voc 40.6v, Temperature Coecient of VOC -0.25%, coldest daytime temp on record 0 degrees C = 345.1v
If I add 2 more Das 415 panels to this - Voc 38.45v, Temperature Coecient of VOC -0.25%, coldest daytime temp on record 0 degrees C = 81.7v

String 1 total = 426.8

String two. 6 Das 415 panels = 245.1v

Total combined Voc = 671.9

Both strings well inside the MPP voltage range and under the 750v max of the inverter.

Does this look about right?

 

[MisterSandals]

String one. 8 Trina 385's - Voc 40.6v, Temperature Coecient of VOC -0.25%, coldest daytime temp on record 0 degrees C = 345.1v

8 x 40.6V x .0025 x 25 deg C = 20.3V rise at 0C

324.8V x 11.46A = 3722W

If I add 2 more Das 415 panels to this - Voc 38.45v, Temperature Coecient of VOC -0.25%, coldest daytime temp on record 0 degrees C = 81.7v

2 x 38.5V x .0025 x 25 deg C = 4.8V rise

(77V x 13.1A = 1009W)

4731W individually

Vmp 11.46A (lower of the 2)
(324.8V + 77V) x 11.46A = 4605W combined mixed (on paper) looks good!

 

[EVH5150]

Thanks for double checking MisterSandals. I appreciate your time and expertise.

 

[EVH5150]

No the two separate MPP input voltages do not add together.
if the max input voltage is "X" and you stay below "X" on each, you are okay.


Max is Max. It is not a suggestion.


766.4 > 750 - if you put 766.4 volts into an MPP on this inverter, you should expect it to fail, and then you will be looking for a new inverter, hopefully not also looking for a new home.



I assume the pv is all in series 668<750 = Not blow it up, but your spec sheet shows MPP range to be 75v-600v so you need to reduce the number of panels until your string voltage is less than 600v.
I have seen this in my own system, too high voltage string and the MPP can't do it's search for the maximum power point.

668 x 9.86A = 6586W 6586 > 6500 you could expect some clipping back to 6500. However, since the voltage is too high, you will be reducing the PV string to get under 600v
so 600v x 9.86 = 5916 no clipping

One more question if I may... Should the max input power (6500w) in my inverters case be calculated with the mppV or Voc compensated for the min temperature? You mentioned above there would be some clipping if it went above. In calcs ive kept all voltages under the maxs, but can get the power output over 6500.

 

[DougfromdaUP]

String 1 total = 426.8

String two. 6 Das 415 panels = 245.1v

Total combined Voc = 671.9

Why are you adding the voltage of two separate strings together? These are different MPPTs, right? If so, the voltage limit is 750 for each MPPT. Don’t add voltages going to different devices.

If these go to different inputs on the same MPPT the lower voltage string will contribute nothing to the power produced.

 

[OffGridForGood]

Max output of the two strings would be 6300w but since one will be facing north and one west, I wont see that at any one time I assume.

Note to anyone following along - OP is in southern Hemisphere - ie North array is pointing directly towards the sun,
As to the question: with two arrays pointing 90-degrees difference they will both get sun but at reduced efficiency at a point in the sun's arc across the sky. Say sunset is normally 7:00pm and noon = solarnoon, then at 3:30 the sun is halfway and you may have 70% of each array's normal max at the same time.

Should the max input power (6500w) in my inverters case be calculated with the mppV or Voc compensated for the min temperature? You mentioned above there would be some clipping if it went above. In calcs ive kept all voltages under the maxs, but can get the power output over 6500.

Calculate the max power based on the panel max output - ie 400W panel x #of panels = max output.
In practice we seldom see max Panel output it seems, generally I see 80-90% per panel unless there is snow on the ground here.
The exess should be just clipped off by the inverter typically.

 

[EVH5150]

Note to anyone following along - OP is in southern Hemisphere - ie North array is pointing directly towards the sun,
As to the question: with two arrays pointing 90-degrees difference they will both get sun but at reduced efficiency at a point in the sun's arc across the sky. Say sunset is normally 7:00pm and noon = solarnoon, then at 3:30 the sun is halfway and you may have 70% of each array's normal max at the same time.

Calculate the max power based on the panel max output - ie 400W panel x #of panels = max output.
In practice we seldom see max Panel output it seems, generally I see 80-90% per panel unless there is snow on the ground here.
The exess should be just clipped off by the inverter typically.

Thanks mate. That's what I was after. Cheers.