Help understanding panel sizing capacity for Conext MPPT 100-600

[scuba_pr]

After some research and help from members of this forum I've decided to start with a 6k Grid-Tie system and expand to 12kWh within 12-18 months. For the inverter I'll be choosing the Schneider Conext XW 6848 with the full Conext PDP as I plan to expand. Battery size will be 20-30kWh but still haven't decide on brand (SOK, Trophy or KiloVault HAB V4 7.5 because UL listing).

Problem now is that I don't know how to properly calculate the panel sizing / connection to the Conext MPPT 100-600. For panels I'm looking into some Q CELLS 480 Bifacial as I have a flat concrete roof with a very reflective white surface. I estimated 13-14 Q CELLS 480 panels needed for 6.2-6.7kWh production. But 14 panels in series @ Voc: 53.39V will be 747.46V far exceeding the MPPT 600V max PV.

After some reading about parallel/series MPPT connections I calculated:

• String 1 (series): 7 PV @ 53.39V = 373.73V @ 11.12A
• String 2 (series): 7 PV @ 53.39V = 373.73V @ 11.12A
• String 1 + String 2 (parallel) = 373.73V @ 22.24A

Did I understand this correctly or do I need 2 MPPT? Any advice?

*Note: I'm in warm weather never less than 70 and usually in highs 80-90's. Right now is 79F

Thanks!

Bellow are the specs for the QCell 480 & MPPT 100-600.

Q CELLS 480 Watts (525W with bifacial gain):

• Vmp: 45.33V
• Imp: 10.59A
• Voc: 53.39V
• Isc: 11.12A
• Maximum System Voltage: 1500V
• Maximum Series Fuse Rating: 20A

MPPT 100-600 (As I understand the unit has 3 PV inputs):

• Nominal battery voltage: 24 and 48 VDC
• PV array operating voltage: 195 to 550 VDC
• MPPT voltage range: 195 to 510 VDC
• Max. PV array open circuit voltage: 600V
• Battery voltage operating range: 16 to 67 VDC
• Max. array short circuit current at STC: 35A
• Max. charge current: 100A
• Max. and Min. PV wire size in conduit: #6 AWG to #14 AWG
• Max. output power: 6000 W (nominal 48V systems)

 

[FilterGuy]

After some reading about parallel/series MPPT connections I calculated:

• String 1 (series): 7 PV @ 53.39V = 373.73V @ 11.12A
• String 2 (series): 7 PV @ 53.39V = 373.73V @ 11.12A
• String 1 + String 2 (parallel) = 373.73V @ 22.24A

Did I understand this correctly or do I need 2 MPPT? Any advice?

You have it correct. You do not need an additional MPPT unless you have shading issues or the two strings are at different angles..... Even then you may not need a 2nd MPPT.

You may want to review this as well:

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

*Note: I'm in warm weather never less than 70 and usually in highs 80-90's. Right now is 79F

Wow. That sounds pretty nice. Where are you?

 

[scuba_pr]

You have it correct. You do not need an additional MPPT unless you have shading issues or the two strings are at different angles..... Even then you may not need a 2nd MPPT.

So technically the max panels I could have on one MPPT 100-600 will be:

• String 1 (series): 11 PV @ 53.39V = 587.29V @ 11.12A
  • 8 x "String 1" (parallel) = 88 @ Q CELLS 480 PV's = 587.29V @ 88.96A

Is that correct? Although I know it will be around 42.2kWh exceeding the 6848kWh limit of the Conext XW Pro. But something does not feels right with the above.

Fortunately, I don't have shading issues in my roof and I'll try my best to have them all at the same angle/orientation.

You may want to review this as well:

Fusing & Wire Sizing guidelines for solar panels

To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...

diysolarforum.com

Will do!

It's amazing how much I have learned on this forum since I started considering a PV system. Without this planing and research I could easily have ended up with a system that was not going to be able to be certified (UL) for grid-tie/sell use. Definitely planing is the most important part.

Thank you very much for your knowledge sharing!

Wow. That sounds pretty nice. Where are you?

It is! (less politicians & power grid)
Caribbean / Puerto Rico. You are all welcome to visit!

 

[FilterGuy]

So technically the max panels I could have on one MPPT 100-600 will be:

• String 1 (series): 11 PV @ 53.39V = 587.29V @ 11.12A

Is that correct?

No. The 587.29V would exceed the 550V max voltage input of your MPPT controller.

• 8 x "String 1" (parallel) = 88 @ Q CELLS 480 PV's = 587.29V @ 88.96A

Is that correct?

No. The max Isc for the array that the controller can handle is 35A. That means you could not do more than 3 strings. (3 x 11.12 = 33.36)
(The spec that says "Max. charge current: 100A" is referring to the current going into the battery. Not the PV current.)

 

[scuba_pr]

I was told today, by a Schneider System Installer, that for the MPPT 100-600 I'll have to be aware of not to exceed any of these 3 parameters:

• PV array operating voltage: 550 VDC
• Max. array short circuit current at STC: 35A
• Max. output power: 6000 W (nominal 48V systems)

So in my planed scenario of a 14 PV array of Q-Cell480 Watts (525W with bifacial gain):

• String 1 (series): 7 PV @ 53.39V = 373.73V @ 11.12A
• String 2 (series): 7 PV @ 53.39V = 373.73V @ 11.12A
• String 1 + String 2 (parallel) = 14 PV = 373.73V @ 22.24A

The combined 14 PV (6,700W @ 480W) or (7,350 @ 525W with bifacial gain) will exceed the max output power 6,000 W of the MPPT 100-600 reducing it's life / warranty. So he recommended getting two smaller MPPT 60-150 with max 3,500W ea for a total of 7,000W to allow for each series into an individual MPPT 60-150. Price wise, the 2 MPPT 60-150 will basically cost the same as 1 MPPT 100-600. But he is still worried of the possible 7,350W @ 525W (with bifacial gain) exceeding the 7,000W max of 2 @ MPPT 60-150.

Does that make sense or it's just a selling tactic?

Thanks.

 

[FilterGuy]

Does that make sense or it's just a selling tactic?

It mostly makes sense.

* The array Voc limit is true with nearly all controllers.
* The array Isc limit is a spec on some other controllers (such as Victron)
* An array Wattage limit is a spec on some other controllers......

However, I have never seen a controller that has a limit on Isc AND wattage. In fact, a wattage limit is a bit of a strange limit in my opinion. As an example, I could have a large array facing east and a second large array facing west, both on the same controller. However, there would never be a time when both are at full production at the same time so the controller would never see that combined wattage of both.

Having said that, it the cost of the two smaller controllers is the same as the one large controller.... I would go for it.

 

[Prince Of Darkness]

scuba,

The Conext SCC (MPPT 60-150) has a max Isc rating of 48 Amps, and an absolute max Voc of 145 Volts.

So you are limited to strings of two of those PVs. And, then Isc needs to be heeded.

IMO, POD

 

[FilterGuy]

The Conext SCC (MPPT 60-150) has a max Isc rating of 48 Amps, and an absolute max Voc of 145 Volts.

How did I miss that??!!

With VOC of 53 volts, he would have to keep it down to two in series on each string
With an Isc of limit 48A, he could do 4 strings of two on each controller. Consequently, he could have up to 8 panels per controller for 4200W....oops too high for the controller limit of 3500W

Dropping down to 3 strings of two we get 3150W. This is under the array wattage limit but is 2 panels shy of the desired total 14 panels.
(Also note that when you go above 2 strings per controller, the fusing requirements get a lot more complicated)

Now that I am looking at the numbers closely, I realize the wattage limit on the controllers is already significantly higher than what you will get out of the controllers. If the 100-600 limits the battery current to 100A, then most of the time there will only be 51.2V x 100A = 5120W going into the battery. Even at the end of the charge cycle when the battery voltage is higher you will only get 57.6V x 100A = 5760W going into the battery. For the 60-150, the controller will typically only put 60A x 51.2 = 3072W into the controller and up to 57.6V x 60A = 3456W at the end of the charge cycle.

Note: There is still value in having more panel wattage on the controller than what the controller will put through. By over paneling, there will be more charging in the morning and late afternoon. There will also be more charging on cloudy days. However, if you want to get the full power of the panels, larger controllers will be needed.

If you want to know more about over-paneling, you may want to review this:

Overview of Over-paneling an MPPT controller

To get to the paper, click on the orange button at the top of the screen. There is a misconception that putting more panels on an MPPT controller than the controller is able to use will damage the controller. However, in almost all cases it is...

diysolarforum.com

 

[pvdude]

I started with a single Schneider MPPT 100-600.
Three strings of REC365AA, (Imp=9.85A, Voc=44v), over paneled
for about 8760 watts.
16 facing South, 8 facing West.
At peak, the single controller would clip @ 5300 watts.
Added a second MPPT 100-600, now peak is about 6500watts from the panels.
Am adding more panels, if any REC ever become available again.
(The Schneider software combines the hardware that is duplicated, so as to display a single image. There are two MPPT 100-600, two inverters)

 

[scuba_pr]

If you want to know more about over-paneling, you may want to review this:

Overview of Over-paneling an MPPT controller

To get to the paper, click on the orange button at the top of the screen. There is a misconception that putting more panels on an MPPT controller than the controller is able to use will damage the controller. However, in almost all cases it is...

diysolarforum.com

Thank for the link.

I'm not sure, but I think the issue brought by the installer is exactly about over paneling. As I understood it is that I should not have a production greater than 6,000W max on that MPPT 100-600 as it will significantly reduce the life of the controller.

He pointed out that although my planed 14 PV Array of 2 strings in parallel (373.73V @ 22.24A) is well under the 550V @ 35A. The production for those panels at full irradiance could be 6,700W-7,350W far exceeding the MPPT 100-600 6,000W max. Also told me that he had to service a burned MPPT 100-600 after just 2yr because a user was placing over 8,000W PV even under the 35A / 550V config limit.

I was searching couldn't find much info on the the MPPT 100-600 documentation papers. I originally thought that the 6,000W was the maximum output that could go into the battery (if charging is needed) and that the excess will go into the inverter for a maximum use of 6,848W continuous, 8,500W @ 30min or 12,000W @ 60sec. Any additional PV production excess after that would just go into the grid.

I started with a single Schneider MPPT 100-600.
Three strings of REC365AA, (Imp=9.85A, Voc=44v), over paneled
for about 8760 watts.
16 facing South, 8 facing West.
At peak, the single controller would clip @ 5300 watts.

That clipping was on a cold day/month? Or basically with the 8,760W over paneled only 5,300W was usable? Any issues during the time you had this configuration?

Thanks

 

[pvdude]

8760W is the total of 365W x 24 panels.
But losses from heat, cabling, conversion, etc. results in 6500 actual watts of output.
5300W was all that the single controller could put out, 100A @ 53VDC.
The single controller was at maximum capacity at that point, even though there was more PV power available, the controller clipped it's input automatically when the limit was reached.
Adding the second controller, and moving one 8S string to controller #2 allowed each controller to operate well below capacity.
Temperature does not change much here, most of the year it is hot.
In the couple of months that the weather cools, the Sun is also in a position that reduces insolation.
The maximum voltage each controller sees is about 350, well below the limit.
Schneider HW is very good, I have not had any issues.

 

[Prince Of Darkness]

Just my opinion:
Manufacturers of power hardware, generally know the capabilities and limitations of their products.

If a manufacturer of a solar charger has limitations stated for Isc and/or STC power, etc, then, generally it is probably a very good idea to observe and follow this guidance.

It has been said, that SCCs that have specs of Isc maximums, generally might well have fairly slow output current limiting. So that limit on Isc helps limit the stress on the SCC, while it is getting around to limiting output current.

When an MPPT SCC is limiting output current (Clipping), the PVs are more lightly-loaded, which raises the Vin, to the SCC. This usually raises its operating temperature, reduces efficiency (at least a bit), and can increase the risk of some failure in the SCC, especially, in warm ambient environments.

Just sayin', am a newbie here, POD

 

[scuba_pr]

Just found this on Schneider website for the MPPT 100 600. Based on their own site info, over paneling shouldn't be a problem.

So technically my planed configuration of 14 PV array of Q-Cell480 Watts (525W with bifacial gain) producing (6,700W @ 480W) or (7,350W @ 525W with bifacial gain) shouldn't be a problem as it's 373.73V @ 22.24A well below their 550V @ 35A limit.

Still I'll try to contact Schneider on this. I want to be 100% sure before committing into this setup.

 

[FilterGuy]

Here is the spec sheet

The installer was probably referring to the highlighted section. However, I do not read "Maximum Charging Power" as meaning "Maximum allowed Array Power" The websight the OP found from Schnider reinforces the idea that the array power can be higher.

It is true that when the MPPT is 'clipping' the power it is running at its maximum. It is also true that this is the most stressful operating point. If this were a lower-quality brand there would be a reason for concern but Schnider has a pretty solid reputation. If you are within the limits laid out by the spec sheet it is reasonable to assume it will work well. (but pay close attention to any ventilation requirements on the charger)

BTW: Notice the 6000W spec is at a battery voltage of 60V. I would never set a charger to that voltage for LiFePO4. 56.8V (3.55V/Cell) is as high as I would ever go, and that is only if I was pushing the batteries hard. At 56.8V the wattage going to the battery will max out at 5680W. At a more conservative 55.2V (3.45V/cell) the wattage would max out at 5520W). Also, note that these wattages will only be seen at the very end of the charge cycle. When the battery is in the flat part of the charge curve the voltage will be closer to 52v (3.25V/cell) and the wattage will be 5200W. When the battery is almost fully depleted (48V), the controller can only produce 4800W. (It is a cruel twist of physics that when the battery is low and you need the power the most is when the controller will produce the least amount of power).

As mentioned in a previous post... there is still value in over-paneling.



Edit: Added the following:
The above diagram shows the concept but it is a bit of a simplification. The 'controller power limit' is shown as a constant, but it will vary as the battery voltage varies. As the battery charges, the available power for charging will go up. Once the charge controller hits the target charge voltage, the current into the battery will rapidly start declining so the power going into the battery will also rapidly decline. Once the battery is fully charged to the target voltage, the current into the battery will stop and the charging power will be zero.

 

[scuba_pr]

The above diagram shows the concept but it is a bit of a simplification. The 'controller power limit' is shown as a constant, but it will vary as the battery voltage varies. As the battery charges, the available power for charging will go up. Once the charge controller hits the target charge voltage, the current into the battery will rapidly start declining so the power going into the battery will also rapidly decline. Once the battery is fully charged to the target voltage, the current into the battery will stop and the charging power will be zero.

Thank you very much for the provided info. I read the PDF and was very helpful.

I really don't want to stress the equipment. But at the same time, if the equipment is advertised as capable of 7-8kWh of PV input, then I suppose it should be safe. I do prefer to over-panel to get the all the benefits as the graphs simply explained.

One question, If the battery is 100% and full sunny day. Do the inverter will see the full PV Wattage 7kWh+, the 6.848k or just 6k limit available for home use?

Thanks!!!!

 

[FilterGuy]

The MPPT controller will limit its output to 100Amps. The controller does not know or care where that 100A is going. If the inverter is taking the full 100A, the controller will happily provide it.... but the controller will not let the current go above 100A and will not let the voltage go above the configured charge voltage.

So, no. The inverter will not get more than the 6K limit..... In fact, since the voltage will always be lower than 60V for reasonable LiFePO4 settings, the inverter will not even get the full 6K.

Note that over-paneling is only practical due to the low cost of panels. Back when panels were multiple times more expensive, no one would have purposely over-paneled. They would have gotten more or larger controllers so they could squeeze out every electron possible from the expensive panels. Overpaneling just lets you get more from the expensive controller at the cost of some unrealized capacity of the low-cost panels.

 

[pvdude]

The way I have mine configured, the PV runs the loads directly, through the inverters.
The batteries are FLA, and so not designed to be heavily cycled, they are in "standby" service.

No sell back to the grid, I want all the power.
Grid assist is enabled in the inverters, so that when the clouds/night the loads can still receive power.
The sequence is: Full Sun, loads run from PV.
As clouds move in, the inverters briefly take some energy from the batteries, then shift to taking energy from the grid.
When the clouds pass, the batteries are topped off by the charge controllers, and the PV supports the loads.
Here is an example of the load needing 9kW, PV can only provide 6.2, so the inverters "borrow" from the grid.
When I add more PV in the future, I expect the full load to be supported from the PV, much less grid use.

I don't think many others do it this way, as if you have lots of kW of Lithium, you can really cycle them heavily, avoiding substantial grid support.

I did not go with Lithium because this is my first attempt at a large solar project, had no idea what I was doing.
Lithium was too confusing as to sourcing, technologies, accessories (BMS is still a mystery to me).
And there was a Rolls FLA battery dealer within driving distance, so I could pick them up.

 

[FilterGuy]

The way I have mine configured, the PV runs the loads directly, through the inverters.
The batteries are FLA, and so not designed to be heavily cycled, they are in "standby" service.

No sell back to the grid, I want all the power.
Grid assist is enabled in the inverters, so that when the clouds/night the loads can still receive power.
The sequence is: Full Sun, loads run from PV.
As clouds move in, the inverters briefly take some energy from the batteries, then shift to taking energy from the grid.
When the clouds pass, the batteries are topped off by the charge controllers, and the PV supports the loads.
Here is an example of the load needing 9kW, PV can only provide 6.2, so the inverters "borrow" from the grid.
When I add more PV in the future, I expect the full load to be supported from the PV, much less grid use.

I don't think many others do it this way, as if you have lots of kW of Lithium, you can really cycle them heavily, avoiding substantial grid support.

I did not go with Lithium because this is my first attempt at a large solar project, had no idea what I was doing.
Lithium was too confusing as to sourcing, technologies, accessories (BMS is still a mystery to me).
And there was a Rolls FLA battery dealer within driving distance, so I could pick them up.

View attachment 102827

Yup. Lead acid certainly encourages a different strategy than LiFePO4. Keeping LA fully charged is a lot more important.

 

[scuba_pr]

scuba,

The Conext SCC (MPPT 60-150) has a max Isc rating of 48 Amps, and an absolute max Voc of 145 Volts.

So you are limited to strings of two of those PVs. And, then Isc needs to be heeded.

IMO, POD

Thanks for the pointer POD. You are correct! I was assuming 150V @ 60A based on some specs I found online.

With the correct specs, I still could do 16 PV instead of 14 PV for:

• 4 series of 2 PV of 53.39V = 106.78V @ 11.12A = 960W connected in parallel which will bring the total array to 8 PV = 106.78V @ 44.48A = 3,840W / 4,200W (with bi gain).
• With 2 MPPT 60-150 in the same configuration I could get a total of 7,680W-8,400W (with bi gain). without exceeding the Max PV array rating of 5,250 W for each MPPT.

That will give me the full XW 6,848k and between 832W-1,552W (with bi gain) for over panel.

Looking at the Pro/Cons for going into 2-4 smaller MPPT 60 150 instead of 1-2 larger MPPT 100 600 I found:

• Power consumption, night time: 2.5 W vs < 1 W
• Supported battery types: (Flooded, GEL, AGM, Custom) vs (Flooded, GEL, AGM, Lithium-ion, Custom)

After all considerations, I think I'll setup around the MPPT 100 600. Found another SE Technical document detailing that the 100/600 can go up to 8.5kWh in over panneling:

 

[scuba_pr]

@pvdude and @FilterGuy. Thanks for the previous pointers and detailed explanations. I'm getting a better grasping of of this PV world everyday. Hope someday I could help others the same way I received help here. Thanks!!!!

Now I'm going for the semi-final step. Deciding the battery setup/brand. Will probably go with 20-30kWh of LiFePO4.

Right now I'm considering:

• 6 @ SOK Battery | 100Ah 48v | 5.12 kWh = 30.72 kWh
• 3 @ Trophy | 48V220E-1 48/51.2 Volts, 220 Amp | 11.26 kWh = 33.78 kWh
• 3-4 @ KiloVault HAB V4 7.5kWh | 48V/150A | 7.5kWh = 22.5 kWh - 30 kWh *Most expensive but closed loop

I don't think I'm ready for the maintenance and setup of FLA, Flooded, GEL, AGM. Was considering EG4, but some users reported compatibility issues with the XW.