Please check my string calculations. EG4 18kpv, 60 300w panels.

[TheFlumph]

I've got 60 300w panels I'm trying to fit in my 18kpv. This is the best I could come up with. This is my first system, I would appreciate some double checking. Im mainly concerned about my plan for mppt1. 2 and 3 look plenty good I think.
Thanks!

string plan for 60 panels and EG4 18kpv

Panel Specs
Hyundai Hia-S300hg
300w
Voc 39.25v
Isc 9.77a
Vmpp 32.15v
Impp 9.33a
Temp coef of Pmax -0.417
Temp coef of Voc -0.306
Temp coef of Isc +.046

Coldest temps in my area -35C
max panel voltage at lowest temp- 46.5


MPPT 1 -25 amp limit
string 1
12 panels in series-
557v
9.77a

string 2
12 panels in series-
557v
9.77a

string 3
12 panels in series-
557v
9.77a
-three strings into parallel at combiner box equaling-
557v and 29.3a which is under the 600v limit and over amps by 1.2x

MPPT 2 -15 amp limit
string 4
12 panels in series -
557v
9.77a

MPPT 3 -15 amp limit
string 5
12 panels in series-
557v
9.77a

 

[Danke]

I've got 60 300w panels I'm trying to fit in my 18kpv. This is the best I could come up with. This is my first system, I would appreciate some double checking. Im mainly concerned about my plan for mppt1. 2 and 3 look plenty good I think.
Thanks!

string plan for 60 panels and EG4 18kpv

Panel Specs
Hyundai Hia-S300hg
300w
Voc 39.25v
Isc 9.77a
Vmpp 32.15v
Impp 9.33a
Temp coef of Pmax -0.417
Temp coef of Voc -0.306
Temp coef of Isc +.046

Coldest temps in my area -35C
max panel voltage at lowest temp- 46.5


MPPT 1 -25 amp limit
string 1
12 panels in series-
557v
9.77a

string 2
12 panels in series-
557v
9.77a

string 3
12 panels in series-
557v
9.77a
-three strings into parallel at combiner box equaling-
557v and 29.3a which is under the 600v limit and over amps by 1.2.

MPPT 2 -15 amp limit
string 4
12 panels in series -
557v
9.77a

MPPT 3 -15 amp limit
string 5
12 panels in series-
557v
9.77a

“…and 29.3a which is under the 600v limit and over amps by 1.2.”

29.3 -25 = ?

MPPT 1 has two inputs, maybe split one string off for the second input?

 

[TheFlumph]

“…and 29.3a which is under the 600v limit and over amps by 1.2.”

29.3 -25 = ?

yes. Ive read that going over amps a bit is fine, but over voltage is not. Is this incorrect?

oh I think I see what you mean. by 1.2x not 1.2 amps. sorry. I will edit to make it clear.

 

[Danke]

yes. Ive read that going over amps a bit is fine, but over voltage is not. Is this incorrect?

I was checking your math, did you mean 1.2 over? 120% over?

Anyway, you can clip… how long do you want your inverter to last?

 

[BKY2003]

one thing to consider is the full power MPPT range. 230-500 VDC

 

[TheFlumph]

one thing to consider is the full power MPPT range. 230-500 VDC

I had a hard time finding out if I needed to stay under 500v for the mppts or 600v for the inverter limit. many places here said just stay under 600.

 

[TheFlumph]

This post from @FilterGuy says my calculations should be within limits. Thats what I was going by.

Limit Specifications:
For the 18K pv there are a few limits to what the MPPTs can be exposed to:

• Isc (31/19/19A)
• Voc (600/600/600V)
• Total array PV power for all three MPPTs. (21KW).

The solar array(s) must not exceed any of these limits or the unit can be damaged. Conversely, as long as the solar arrays do not exceed these specs, you are good to go.


Capability Specifications:
For the 18Kpv there are several capability specifications:

• Usable IMP current: (25/15/15A)
  The Imp current spec tells you how much current the MPPT will use but does not specify a limit on the solar array. Even if the solar array is capable of producing a higher Imp, the MPPT will not use it.
• Usable PV power of all three MPPTs: (18kw)
  This spec tells you the total power the 3 MPPTs can generate. Even though the the PV arrays might be able to generate more power, the system will not use it. If the total generated power reaches this limit, the MPPTs will start limiting the amount of power they will harvest from the array.
• Full power MPPT Operating Range: (230V - 500V).
  This tells you that the MPPT will do power point tracking in this range. However, the system can still work below and above that range (up to the 600V Voc limit).

EG4 18kPV - String Calculations

I searched for Ioc limit on this forum but this posting and another looking for specs on PV panels are the only ones that mention it. I am not aware of the term Ioc limit, so would like to know more! Sorry. Ioc was a typo. It should have said Isc and I corrected it above. Note: Ioc would...

diysolarforum.com

 

[Quattrohead]

Electrically what you are proposing will work and not blow anything up but I think it is not optimal.
I would prefer 10 or 11 panels in series. Two of these strings in parallel on mppt one and a single set on mppt's two and three is the maximum you can do without clipping. If you went beyond that you would have to see how much clipping you get but ideally I think you're looking at another mppt device to get the absolute maximum out of your 60 panels.

 

[TheFlumph]

Electrically what you are proposing will work and not blow anything up but I think it is not optimal.
I would prefer 10 or 11 panels in series. Two of these strings in parallel on mppt one and a single set on mppt's two and three is the maximum you can do without clipping. If you went beyond that you would have to see how much clipping you get but ideally I think you're looking at another mppt device to get the absolute maximum out of your 60 panels.

Thanks for the advice. That cuts my panels from 60 to 40. Thats pretty significant. A bit less than a third less because of clipping.

Is it not optimal because of stress on the inverter? If EG4 says 31 amps like filterguy said in his post, I wonder if there would be a warranty issue.

 

[BKY2003]

You could try it and see if it works. And if it doesn’t turn out efficient just move some of the panels over onto a Grid tie inverter and AC couple them with the 18Kpv.

 

[FilterGuy]

This post from @FilterGuy says my calculations should be within limits. Thats what I was going by.

EG4 18kPV - String Calculations

I searched for Ioc limit on this forum but this posting and another looking for specs on PV panels are the only ones that mention it. I am not aware of the term Ioc limit, so would like to know more! Sorry. Ioc was a typo. It should have said Isc and I corrected it above. Note: Ioc would...

diysolarforum.com

I have since learned a little more about what the 18Kpv does if the PV input voltage goes above 500V. Apparently, above 500V, the MPPT starts ramping down the allowed input current. Apparently, there is also a ramp down of the power output of the MPPT as the voltage gets higher. (This came from a translation from Chinese so it may not be 100% accurate. )

However, this is not all bad. Where the input voltage becomes problematic is in cold weather. Design the system such that even with the 'typical' cold weather it stays under 500V and you still have plenty of headroom for the rare super-cold event.

 

[glandpuck]

I'm running the Lux version of the inverter. IMO you should place in series 11 panels on PV1 a +/-, 11 panels on PV1b +/-, 11 panels on PV 2 +/- and 11 on PV3 +/-.

This will provide close to the maximum specs. I know it is 44 panels and you bought 60, but that is how the cookie crumbles in this case.

I would suggest you connect your series string to this breaker from Midnite solar or equivalent:

MNEPV15-600-2PP

I also suggest you use a 20 amp solar fuse in a din rail holder, one for the + and one for the - from the array. Look at Littlefuse and UL listed DIN rail holder.

Lastly, make certain that your DC disconnect box/switch is rated for 500-600 volts DC. Many are rated for only 250 volts. If the fuses are DIN rail near the breaker, then you don't need them in the DC disconnect. The disconnect switch can be single pole safely when using the double pole breakers and fuses.

 

[TheFlumph]

Ok,I have reworked this. Thanks to @glandpuck for the 11 panel advice. Thanks @BKY2003 for the AC couple suggestion. @FilterGuy Does this look better to you? The strings are barely above 500v, but only during record low temps. And honestly, its much milder here in the last decade due to climate change.
Thanks to everyone else who steered me away from maxing this thing out.

string plan for 60 panels and EG4 18kpv
Panel Specs
Hyundai Hia-S300hg
300w
Voc 39.25v
Isc 9.77a
Vmpp 32.15v
Impp 9.33a
Temp coef of Pmax -0.417
Temp coef of Voc -0.306
Temp coef of Isc +.046
Coldest temps in my area -35C
max voltage at lowest temp- 46.5


MPPT 1 -25 amp limit
string 1
11 panels -
432v
511v @-35c
9.77a
string 2
11 panels -
432v
511v @-35c
9.77a
2 strings into parallel at combiner box equaling-
511v and 19.5a which is under the 600v limit, wont go over 500v mppt limit unless its record cold temps and under 25a limit.

MPPT 2 -15 amp limit
string 3
11 panels -
432v
511v @-35c
9.77a

MPPT 3 -15 amp limit
string 4
11 panels -
432v
511v @-35c
9.77a

15 Panels remain for AC coupling.
Growatt min 3000TL-X grid tie inverter
4200w max input (14 panels @300w =4200)
500v max input
12.5a max input per mppt

String 5
mppt1
7 panels-
274v
325v@-35c
9.77a

String 6
mppt1
7 panels-
274v
325v@-35c
9.77a
Growatt AC out coupled to the gen inputs on the 18kpv.
One panel left over to mount on my sawmill shed for lights.

 

[Quattrohead]

Can you swing the extra few hundred bucks to get a 6000XP instead of the Growatt ?
You could still AC couple it or charge the batteries direct.

 

[BKY2003]

Can you swing the extra few hundred bucks to get a 6000XP instead of the Growatt ?
You could still AC couple it or charge the batteries direct.

I wish but the 6000XP want work. It does not frequency shift.

 

[TheFlumph]

I wish but the 6000XP want work. It does not frequency shift.

Its over double the price of the growatt too. under $500 is worth it for me to hook those 14 panels, but $1200 really isnt. Im trying to budget for the 15kva transformer the electric company is making me buy them.

 

[BKY2003]

It’s over double the price of the growatt too. under $500 is worth it for me to hook those 14 panels, but $1200 really isnt. Im trying to budget for the 15kva transformer the electric company is making me buy them.

where did you find the Growatt for $500

 

[TheFlumph]

where did you find the Growatt for $500

https://signaturesolar.com/growatt-240v-3kw-grid-tie-inverter/ $426

oh thats the mic version not min version. only has 1 mppt. damn let me find the min

I can find the min 5000 but not the 3000. oh well. its $683 https://signaturesolar.com/growatt-120-240v-5kw-grid-tie-inverter/
and the 6000 is only $30 more.

 

[BKY2003]

For some reason I thought the grid tie inverter had to be UL174SA. Some please correct me.

 

[TheFlumph]

I have Covid with a massive headache. So my thinking is not the best. For some reason I thought the grid tie inverter had to be UL174SA. Some please correct me.

Would that matter if its plugged in to the gen input on the 18kpv? Wouldnt the 18kpv controlling the grid connection be good enough? If the electric company made a stink, I could just use it to charge batteries through the 18kpv gen input.

Sorry for your illness. Hope you get better soon.