1 EG418KPV: supplying it's multiple mppt inputs from a large SINGLE solar array?

[sun_of_a...]

Hi, thanks for help. I'm looking at getting a EG4 18KPV Hybrid Inverter and making one solar array of 55 panels: each string w/ 11 panels in series, w/ the 5 strings paralleled. Array: 20kw / 41 amps / 487 volts. (Panels are REC 365AAs). One pair properly-sized positive and negative DC cables 350 feet long from array to the EG418KPV (DC Input Voltage Range 100–600 VDC and Maximum Solar Input 21kW.)

From the EG418KPV manual: "The inverter has three MPPT PV charging circuits. MPPT #1 will use up to 25 amps which means two strings can be paralleled for any modules having less than a 12.5 A (Imp) rating. MPPT #2 and MPPT #3 will use up to 15 Amps each so they are usually limited to one string."

This question is supplying 2 or all 3 of the EG418KPV's 3 mppt input circuits with the single pair of properly-sized 350 foot positive and negative wires bringing DC at 20kw and 41 amps and 487 volts (of course with some voltage drop). Can I simply split/splice the 350ft cable pair into 2 or 3 pairs to supply 2 or 3 of the unit's 3 mppt inputs? I would think not, but the following sentence from the EG418KPV manual makes me wonder:

"The array can have a higher Imp than the 25A/15A specified, but the MPPTs will not make full use of the extra current. Having an array that can produce more current than the MPPTs will bring in is useful for increasing morning, winter or cloudy day solar production."

Also note, "The inverter will limit the total MPPT current to 25 A for MPPT #1 and to 15 Amps for MPPT #2 and 15Amps for MPPT #3."

Let's just assume properly-sized wire for now please. Would this work, and (leaving amp drop due to distance aside) would it utilize the full 41 amps of the big solar array naturally?

Thank you so much!

Stu

edit, added :
PV Input Data
Number of MPPTs 3
Inputs per MPPT 2/1/1Max. Usable Input Current 25/15/15AMax.
Short Circuit Input Current 31/19/19A
DC Input Voltage Range 100–600 VDC
Unit Startup Voltage 100 VDC
Load Output Minimum Voltage >140 VDCMPP
Operating Voltage Range 120–500 VDC
Full Power MPPT Voltage Range 230–500 VDC
Nominal MPPT Voltage 360 VDC
Maximum Utilized Solar Power 18kW
Recommended Maximum Solar Input 21kW

 

[FilterGuy]

his question is supplying 2 or all 3 of the EG418KPV's 3 mppt input circuits with the single pair of properly-sized 350 foot positive and negative wires bringing DC at 20kw and 41 amps and 487 volts (of course with some voltage drop). Can I simply split/splice the 350ft cable pair into 2 or 3 pairs to supply 2 or 3 of the unit's 3 mppt inputs? I would think not, but the following sentence from the EG418KPV manual makes me wonder:

I don't think that will work very well. Each mppt will probably do the MPPT scan at different times and mess everything up. The other issue may be the Isc limit. I suspect the MPPTs will operate out of sync with each other and a single MPPT could see the full array Isc at the time it can't handle it..

 

[Danke]

What are your goals? do you want to get the maximum amount of power out of your panels? Is this grid tied? Does it have to be UL listed equipment? Etc.

 

[timselectric]

No, it won't work like that.
Each MPPT needs its own separate array.
Otherwise, they will fight for control over the circuit. And none of them will perform well.

 

[MajicDiver]

Some inverters, such as the Growatt MIN-xxxxx-TL-XH-US, have a setting to make all of the mppt inputs (3 or 4 depending on model) function as a single mppt. I doubt that the EG4 inverters do, but you might ask, it might prompt them to consider adding the feature

 

[sun_of_a...]

Okay, thank you all. Maybe the EG418KPV is not the right choice for me . Can i further ask, if I did go w/ the EG418KPV and set up 3 separate solar arrays meeting the amp limits as described:

"The inverter has three MPPT PV charging circuits. MPPT #1 will use up to 25 amps which means two strings can be paralleled for any modules having less than a 12.5 A (Imp) rating. MPPT #2 and MPPT #3 will use up to 15 Amps each so they are usually limited to one string."

If I meet the kw, volt, and amp limits, can I have multiple strings of panels in series and parallel for each mppt input? Is there some limit on the number of strings? Say 3 or 4 strings paralleled for #1 mppt input , 2 strings in parallel for #2 mppt input, etc, as long as I meet the reqs/limits for the EG418KPV ?

 

[Danke]

Okay, thank you all. Maybe the EG418KPV is not the right choice for me . Can i further ask, if I did go w/ the EG418KPV and set up 3 separate solar arrays meeting the amp limits as described:

"The inverter has three MPPT PV charging circuits. MPPT #1 will use up to 25 amps which means two strings can be paralleled for any modules having less than a 12.5 A (Imp) rating. MPPT #2 and MPPT #3 will use up to 15 Amps each so they are usually limited to one string."

If I meet the kw, volt, and amp limits, can I have multiple strings of panels in series and parallel for each mppt input? Is there some limit on the number of strings? Say 3 or 4 strings paralleled for #1 mppt input , 2 strings in parallel for #2 mppt input, etc, as long as I meet the reqs/limits for the EG418KPV ?

Are Any of the strings different orientations?

 

[zanydroid]

For a pull of that distance you probably want to pull extra wires to give the option for reconfiguring in the future and broader MPPT compatibility.

There is an overpaneling guide/threads on this forum. Does EG4 publish a max Isc limit? If not +50% and +100% is probably within what some forum members are happy with. These levels will probably clip though if oriented in the same direction. The safe current also depends on whether you care about reverse polarity protection, usually you can go higher if you accept that reverse polarity will kill the MPPT above that level

 

[sun_of_a...]

What are your goals? do you want to get the maximum amount of power out of your panels? Is this grid tide? Does it have to be UL listed equipment? Etc.

Thanks. I want to keep my grid connection for when needed, but don't want to feed power back to grid.

Are Any of the strings different orientations?

No, i suppose they could be. This is a new concept for me. Thanks.

 

[zanydroid]

Thanks. I want to keep my grid connection for when needed, but don't want to feed power back to grid.

That doesn’t really answer the question of whether you need listed equipment. If you export you will need it. If you zero export to allow the grid to supply surge current you will need it legally speaking but you can choose also to operate as a renegade ?‍

And then there is the matter of your solar panels being reported by utility workers at your property, after which you may need to prove that they are off grid. If this requires supplying single line diagram as approved by AHJ then that requires using listed equipment. Then you need to determine whether UL1741 is sufficient, or UL9540 is required, in your state

IMO the first step for a balanced approach to solar is to find out what the interconnection rules and solar incentives (if any) are in an area.

 

[timselectric]

Is there some limit on the number of strings?

No
But if you have 3 or more strings in parallel. Each string must be fused.

 

[sun_of_a...]

For a pull of that distance you probably want to pull extra wires to give the option for reconfiguring in the future and broader MPPT compatibility.

There is an overpaneling guide/threads on this forum. Does EG4 publish a max Isc limit? If not +50% and +100% is probably within what some forum members are happy with. These levels will probably clip though if oriented in the same direction. The safe current also depends on whether you care about reverse polarity protection, usually you can go higher if you accept that reverse polarity will kill the MPPT above that level

"Clipping" in this context is new to me. Is "clipping" and same "orientation" why there may be a limit on the number of strings per mppt input circuit?

When i saw "MPPT #1 will use up to 25 amps which means two strings can be paralleled," I thought to myself, "they are certainly not going to tie my hands by LIMITING me to two strings to get to 25 amps and my desired voltage and kw." With my panels, I need three strings (11 panels in series) paralleled to get to just under 25 amps at sufficient voltage to travel the distance nicely. I see large solar arrays far away from the house and charge controller all the time. And I thought dc current at 487 volts would travel such distance better/easier/cheaper than alternating current. But I'm ignorant of many things, I accept, and welcome and desire the help of the forum. Thank you!

 

[sun_of_a...]

That doesn’t really answer the question of whether you need listed equipment. If you export you will need it. If you zero export to allow the grid to supply surge current you will need it legally speaking but you can choose also to operate as a renegade ?‍

And then there is the matter of your solar panels being reported by utility workers at your property, after which you may need to prove that they are off grid. If this requires supplying single line diagram as approved by AHJ then that requires using listed equipment. Then you need to determine whether UL1741 is sufficient, or UL9540 is required, in your state

IMO the first step for a balanced approach to solar is to find out what the interconnection rules and solar incentives (if any) are in an area.

I appreciate the advice and I agree with you about avoiding taking on the utility. It's a small cooperative and there are no incentives.

 

[zanydroid]

"Clipping" in this context is new to me. Is "clipping" and same "orientation" why there may be a limit on the number of strings per mppt input circuit?

Clipping means the available DC power exceeds the AC rating, so it will plateau (literally looks like this in the graph) and you lose the production.

Orienting multiple parallel strings in different directions causes them to have peak output at different times of the day, which helps with clipping a lot.

Then there is the electrical safety limit. Max Isc and power levels where reverse polarity protection limit breaks

Yes, sending DC is absolutely better than AC from a power loss angle, and you also likely do not want to put your batteries at the array which is what is needed if you send AC. The inverters also need current sensors in some situations, and those need to be placed close to the load.

OTOH at some point AC becomes easier to mix together than DC, you see a bit of that here in how you can’t connect multiple MPPT to the same array unless they can be locked together.

I would say most AIO and hybrid MPPT would be designed for #8 and #10’s ampacity limit. Standalone MPPT likely go higher.

 

[zanydroid]

So they do publish a do not exceed ISC, the 31/19/19. You might ask around here whether that is OK to exceed if no reverse polarity protection is needed. There’s also the possibility that it will void warranty as a blanket policy ? .

 

[timselectric]

A fuse or breaker is the simple solution to avoiding going over ISC.

 

[sun_of_a...]

Clipping means the available DC power exceeds the AC rating, so it will plateau (literally looks like this in the graph) and you lose the production.

Orienting multiple parallel strings in different directions causes them to have peak output at different times of the day, which helps with clipping a lot.

Then there is the electrical safety limit. Max Isc and power levels where reverse polarity protection limit breaks

Yes, sending DC is absolutely better than AC from a power loss angle, and you also likely do not want to put your batteries at the array which is what is needed if you send AC. The inverters also need current sensors in some situations, and those need to be placed close to the load.

OTOH at some point AC becomes easier to mix together than DC, you see a bit of that here in how you can’t connect multiple MPPT to the same array unless they can be locked together.

I would say most AIO and hybrid MPPT would be designed for #8 and #10’s ampacity limit. Standalone MPPT likely go higher.

Great explanation on clipping and orientation, I understand now.

"would say most AIO and hybrid MPPT would be designed for #8 and #10’s ampacity limit. Standalone MPPT likely go higher."

you're talking wire gauge right?

"OTOH at some point AC becomes easier to mix together than DC, you see a bit of that here in how you can’t connect multiple MPPT to the same array unless they can be locked together".

Yes, I have a 36 ft cargo trailer and 40 ft 5th wheel I want to put solar panels on top of each with batteries and controller/inverter inside each. They can be parked near the house in the small sunny spot and could send ac power to the EG418KPV or other house controller/inverter, single or stacked/paralleled multiple inverters. With the grid input and generator input on the EG418KPV, or other single or paralleled units, there's lots of ways to give it ac power from the trailers. That's cool.

reverse polarity protection

I need to learn about this and so much. Ultimately I'll get hands-on trustworthy help with this project, but only after I've attempted to understand it best I can myself. I sure hope you all will help. Very lucky and grateful to be able to learn and make this dream come true.

 

[sun_of_a...]

A fuse or breaker is the simple solution to avoiding going over ISC.

I would like to learn and understand where every fuse/breaker should go in this system, as well as all the other component eventually.

 

[zanydroid]

A fuse or breaker is the simple solution to avoiding going over ISC.

I've thought about this before, but if it's this easy, why isn't the overpaneling guide much shorter?

you're talking wire gauge right?

"OTOH at some point AC becomes easier to mix together than DC, you see a bit of that here in how you can’t connect multiple MPPT to the same array unless they can be locked together".

Yes, I have a 36 ft cargo trailer and 40 ft 5th wheel I want to put solar panels on top of each with batteries and controller/inverter inside each. They can be parked near the house in the small sunny spot and could send ac power to the EG418KPV or other house controller/inverter, single or stacked/paralleled multiple inverters. With the grid input and generator input on the EG418KPV, or other single or paralleled units, there's lots of ways to give it ac power from the trailers. That's cool.

Yes, wire gauge.

I think it's easier to do plug/unplug on AC vs DC. Switches and breakers/fuses for AC are a little cheaper/easier to find, also you can just use standard plugs/receptacles.

 

[timselectric]

I've thought about this before, but if it's this easy, why isn't the overpaneling guide much shorter?

No idea.