Solar panel connection

[Roelf]

I bought 9 Axpert MKS 5kva 48 volt inverters with following detail

Inverter mode related power 500v/a/5000, DC input  48 vdc 117 A, Ac output 230 vac 50hz 22 A

Ac charger mode: Ac input 230Vac 50hz 35 A, DC output 54 vd, max60A default 30 A, Ac output 230ac 50hz 22 Amp

Solar charger mode:rated current 80Amp, system voltage 48 vdc, min solar voltage 40vdc, maxsolar voltage (voc) 145 Vdc

Panels: 325 W, Power sorting 0,499w, voltage at pmax 37.4v, current at pmax8,7A, OCV45. 8V, short circuit urgent 9.16Amp

BATTERIES: SS202 - 5 LITIUM ION 51.2 V, 144 Ah/7372 wh and max discharg 100A, 3 cabinets with 3 batteries each for each phase

How many panels could I connect to inverters and how many strings. 141 panels available. Want to use 3 inverters in line and 3 rows  for 3 phase 

[Arandoza]

For the panels typically, 3 in series and 4 strings per array, per inverter.

mppt VOC 145 v 

panel pmax 37.4v. X 3 = 112.2v 

just bear in mind to consider the pmax is at 25 deg c and in cold conditions the 112.2v will increase - refer to the spec sheet for the panels, if very cold and clear sky’s and pushing the inverter hard, it maybe possible that the panels per string get close to the 145voc of the mppt.

 

Also a consideration maybe the discharge rate of the battery packs, each pack with 3 inverters that could potentially pull 12kva, will the packs be able to discharge at a fast enough rate if full 12kva being used? I see the maximum discharge rate is 100a for the lithium ions you mention above, which would equate to 4800 watts max, probably a bit less due to losses, per battery pack and. Inverter set of 3. This maybe an issue in cloudy weather, as clouds pass by and if the inverters are running hard over 5000 watt per inverter set of 3? 

Sounds like you have a monster of a system planned   It’s going to take a bit of wall space for the 9 inverters

Good Luck and I expect some of the experts of the forum will be able to give really good advice.

 

[Dex_]

7 hours ago, Arandoza said:

For the panels typically, 3 in series and 4 strings per array, per inverter.

mppt VOC 145 v 

panel pmax 37.4v. X 3 = 112.2v 

just bear in mind to consider the pmax is at 25 deg c and in cold conditions the 112.2v will increase - refer to the spec sheet for the panels, if very cold and clear sky’s and pushing the inverter hard, it maybe possible that the panels per string get close to the 145voc of the mppt.

 

Also a consideration maybe the discharge rate of the battery packs, each pack with 3 inverters that could potentially pull 12kva, will the packs be able to discharge at a fast enough rate if full 12kva being used? I see the maximum discharge rate is 100a for the lithium ions you mention above, which would equate to 4800 watts max, probably a bit less due to losses, per battery pack and. Inverter set of 3. This maybe an issue in cloudy weather, as clouds pass by and if the inverters are running hard over 5000 watt per inverter set of 3? 

Sounds like you have a monster of a system planned   It’s going to take a bit of wall space for the 9 inverters

Good Luck and I expect some of the experts of the forum will be able to give really good advice.

 

shouldn't you work on the open circuit voltage? i personally would put them in 2's

 

i would go with 12 per inverter, giving you a total of 108 panels

Edited October 4, 2019 by Dex_

[Roelf]

Thanks for the feedback.  I have 60 x 340 watt panels spare, could I use it only for charging the batteries during the day. 3 x 4 strings with MPPT 80 Amp charge controller from JSM power. Use 75 % of my power from 9 till  6 in the afternoon.  What should I do if I do not want to use combiner boxes between panels and inverters. Could I use dc breakers in normal db and then to the inverters.

[Dex_]

5 hours ago, Roelf said:

Thanks for the feedback.  I have 60 x 340 watt panels spare, could I use it only for charging the batteries during the day. 3 x 4 strings with MPPT 80 Amp charge controller from JSM power. Use 75 % of my power from 9 till  6 in the afternoon.  What should I do if I do not want to use combiner boxes between panels and inverters. Could I use dc breakers in normal db and then to the inverters.

combiner boxes normally contain your fuses and surge protection. inline fuses are better than nothing but imo you still want proper type 1 or 2 protection

[Roelf]

I received my second batch panels today but the specs differ a little bit, pmax 340W, vmp 39.09V , lmp 8.70V,  Voc 46.94V , mx system voltage dc 1000  VDC and maximum series fuse rating 15A,  could I still use them 3 x 4 strings for the inverters. First batch 325 Watt and connect them 2 strings of 3 (54 panels)  6 per inverter and want to add new panels 2 x 3 strings for each inverter.

[Dex_]

I would personally keep them separate since you should more easily be able to than people adding to a single system.

I would still only put them in 2's.

3 in series is going to be >15A? even 2 will be? where does the 1000VDC and 15A come from?

[Coulomb]

4 hours ago, Dex_ said:

3 in series is going to be >15A?

? All panels in a series string carry the same current. So that's 9.16 A max.

Quote

even 2 will be?

Two in series will also be 9.16 A max (per string).

Quote

where does the 1000VDC come from?

That's the system voltage. It will all be under 145 V, since that's the max for the Solar Charge Controller. So that's not a problem.

Quote

and 15A come from?

That's the maximum fuse size. You need a fuse per string, so that's not a problem.

4 hours ago, Dex_ said:

I would still only put them in 2's.

I agree with you there (see next post).

[Coulomb]

15 hours ago, Roelf said:

I received my second batch panels today but the specs differ a little bit, pmax 340W, vmp 39.09V , lmp 8.70V,  Voc 46.94V

The Voc of 46.94 V is likely too high for 3S. Anything over 45.0 V is likely to be.

46.94 x 3 = 140.8 V @ 25°C. I generally use a factor of 1.07 for panels at 0°C; you should check the temperature coefficient for your actual panels to be completely sure. So using my rough guess, that's 140.8 x 1.07 = 150.7 V @ 0°C. That's way too high; it could damage your Solar Charge Controller.

So with those panels, you should configure them for 2S. Nearly all the modern panels require the 2S configuration for a 145 V SCC. 60 cell panels are becoming much less common.

[Roelf]

On the label at the back of panel.

[Dex_]

54 minutes ago, Coulomb said:

? All panels in a series string carry the same current. So that's 9.16 A max.

Two in series will also be 9.16 A max (per string).

That's the system voltage. It will all be under 145 V, since that's the max for the Solar Charge Controller. So that's not a problem.

That's the maximum fuse size. You need a fuse per string, so that's not a problem.

I agree with you there (see next post).

of course... my bad xD

[Dex_]

50 minutes ago, Coulomb said:

The Voc of 46.94 V is likely too high for 3S. Anything over 45.0 V is likely to be.

46.94 x 3 = 140.8 V @ 25°C. I generally use a factor of 1.07 for panels at 0°C; you should check the temperature coefficient for your actual panels to be completely sure. So using my rough guess, that's 140.8 x 1.07 = 150.7 V @ 0°C. That's way too high; it could damage your Solar Charge Controller.

So with those panels, you should configure them for 2S. Nearly all the modern panels require the 2S configuration for a 145 V SCC. 60 cell panels are becoming much less common.

yeah, I am very happy i went in 2's rather. sure the cost is a bit more on the cabling and combiner but why stress the inverter to its limits, you save now you pay later....

Edited October 7, 2019 by Dex_

[Roelf]

Just to confirm,  I connect 6 strings of 2 panels to each combiner box and total of 12 panels for each inverter.

[Coulomb]

3 hours ago, Roelf said:

Just to confirm,  I connect 6 strings of 2 panels to each combiner box and total of 12 panels for each inverter.

Ah. So that's two panels in series for each string, 6 strings per inverter, i.e. 2S6P. That sounds fine.

All that multiplied by 9 for 3 rows of 3-phase inverters? (In other words, 3 inverters paralleled, times 3 phases.) So 9 x 12 = 108 panels. About 36 kW of panels. An impressive system.

BTW, my understanding is that all batteries for the 9 inverters have to be paralleled; you can't separate the batteries for the three phases. That's how the parallel guide shows all examples. My apologies if that's what you intended, and I misunderstood.

Edited October 7, 2019 by Coulomb

[Roelf]

Each cabinet of 3 batteries in parallel  for each row inverters, it is single phase inverters 3 rows of 3 in parallel. Each row supply power for 1 phase and the the main supply are balance that each phase use more or less the same power.  For each set of 3 batteries additional mppt charger with 12 panels 3S4P for additional charging during the day. That is my planning but could change according to expert advice. My concern is , could one inverter handle 6S2P according to the specs. I could use less panels with inverters.

[Coulomb]

The inverters will handle 2S6P (you wrote 6S2P). I assume that the 3S4P you mention is for MPPTs separate from the inverters, because 108 panels isn't enough.

My understanding is still that every battery has to be paralleled, on two giant bus bars, and all 9 inverters use that same pair of busbars. Not 3 islands of batteries and inverters. Else you'll get errors. But I'm no expert in 3 phase systems.

[Roelf]

Yes, inverters 2S6P (total 12 panels) and 60 panels for MPPTs 3S4P total of 5 MPPTs only for charging the batteries. The total watt for 12 panels is 4000 Watt and that will be fine. (6 x 325 plus 6 x 340) On the batteries you are correct. I did use our local solar installer, for the first setup, but was not satisfy and decided to figure it out myself to do it correct and use expert advise to guide me.

[Roelf]

Is it possible to draw a diagram how I should connect the  9 batteries , 9 inverters and 5 charge controllers, 108 panels for inverters and 60 panels for charge controllers.

[DeepBass9]

Are you sure you shouldn't employ an elecrician to wire up such a large installation?