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

[BKY2003]

18Kpv controls the inverter by shifting the frequency. So it shifts hz higher than 60hz and this causes the grid tie to shut off. Thats why the 6000xp want work, it want respond to the hz shift

 

[BKY2003]

Anyway you probably can call SS and ask them which ones work. I have the Growatt MIN 7600 XH-US. And I can’t say I recommend it, or don’t recommend it. But I can say that if Majicdiver didn’t help me with it I probably would have thrown it in the garbage.

 

[TheFlumph]

18Kpv controls the inverter by shifting the frequency. So it shifts hz higher than 60hz and this causes the grid tie to shut off. Thats why the 6000xp want work, it want respond to the hz shift

The 18kpv manual says:
After the AC couple function is enabled:
When the grid is on, the GEN terminal is connected to the GRID terminal inside the inverter. In this case,
the hybrid inverter will bypass the interactive inverter AC to the GRID and LOAD. Any remaining energy
will be exported to the grid.
When the grid is off, the GEN terminal is connected to the LOAD terminal inside the inverter. In this
case, the hybrid inverter will work as a power source for the grid-interactive inverter to synchronize and
feed power to the micro-grid. The loads will be supplied by solar power first. If solar panels are generat-
ing more power than load consumption, the excess solar power will be stored in the batteries. When
solar power exceeds the sum of load power and max battery charging power (e.g., when the batteries
are nearly full), the inverter will signal the grid interactive inverter to reduce power via the frequency-
shifting, power-reduction mechanism, thus maintaining the balance of generation and consumption of
the micro-grid system.
26
What is frequency-shifting power reduction?
All UL1741SA compliant grid-interactive inverters have the Frequency-Watt feature, which requires the
grid-interactive inverter to reduce power with increasing grid frequency. The power will drop to zero
before the over-frequency trip threshold is reached.
When the grid is down and the hybrid inverter requires an AC Coupled inverter to reduce power,
it simply shifts the output frequency up slightly, and the grid-interactive inverter will limit its output
power accordingly after sensing this frequency shift.
When the grid is up, the frequency is dictated by the grid and the hybrid inverter will reduce exported
power if the frequency goes


It seems to me that it wouldnt matter if the growatt is UL1741sa rated because the 18kpv would just dump it to the load when the grid goes down. But I may be wrong.

 

[BKY2003]

It just has to be a grid tie that will respond to frequency shift. Because when the power goes out and there is no loads and the battery is full. The 18Kpv had to tell the grid tie to shut down. If it doesn’t and the battery BMS does not shut the battery down. We might see an explosion.

 

[BKY2003]

this has a good explanation

 

[BKY2003]

Biggest problem I had with the Growatt was the 18Kpv has 100% derate slope and the Growatt has a 33% derate slope. Both units kept cutting out. Majicdiver recommended I move the Growatt slope up to 100% and they both stop cutting out.

 

[MajicDiver]

The 18Kpv had to tell the grid tie to shut down. If it doesn’t and the battery BMS does not shut the battery down. We might see an explosion.

I would think that as the 18Kpv increases frequency, if the grid tied (ac coupled) inverter does not reduce its generation that the 18Kpv would hit a high frequency trip of some sort. I assume it has high frequency trips - this is one reason it should. Otherwise you are correct, something will certainly “break”

 

[TheFlumph]

Biggest problem I had with the Growatt was the 18Kpv has 100% derate slope and the Growatt has a 33% derate slope. Both units kept cutting out. Majicdiver recommended I move the Growatt slope up to 100% and they both stop cutting out.

I get what you mean after watching the video. those 14 extra panels are getting to be a pain in the ass.

 

[TheFlumph]

It just has to be a grid tie that will respond to frequency shift. Because when the power goes out and there is no loads and the battery is full. The 18Kpv had to tell the grid tie to shut down. If it doesn’t and the battery BMS does not shut the battery down. We might see an explosion.

This newer growatt is UL 1741SA rated and is under $1000. its hard to find affordable grid tie inverters that are SA rated. https://signaturesolar.com/growatt-7-6kw-grid-tie-inverter-min-7600-xh-us/

 

[TheFlumph]

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.

If I did three strings of 11 into parallel on mppt1 I would be under 500v and current would be 29a. Is that what you mean by your last sentence?
this would get me to 55 panels without dealing with ac coupling and buying another inverter. I can just sell the last 5 panels.

 

[Quattrohead]

Why are we concentrating on AC coupling, just use the 6000XP or whatever you find that can do the job to just charge the batteries. I am talking about the 6000XP because it also happens to be a fine inverter and could be used for other AC loads if you ever have them or as an emergency backup to your 18K.
Growatt equipment seems to be temperamental, that's all I can say.

 

[FilterGuy]

If I did three strings of 11 into parallel on mppt1 I would be under 500v and current would be 29a. Is that what you mean by your last sentence?
this would get me to 55 panels

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 (I did not check this)​

18Kpv PV input specs


2 strings of 11 on MPPT:

Voltage at coldest temp: 46.1x11 = 511.5V This is over the 500V top end of the MPPT operation but under the 600V limit. This should be fine. The vast majority of the time it will be well under 500V. In the coldest temps it is still only 511V.
Note: You should never count on it, but Voc is typically lower than the spec. Consequently, there is a good chance the total voltage won't be above 500 even in the coldest conditions)
Impt of the two strings: 18.66A. This is under the 25A usable current of MPPT #1 (There will be no clipping)
Isc of the two strings: 19.54 A. This is well under the 33A Isc limit of MPPT #1.

According to my calculations, 11 panels per string should work fine.

without dealing with ac coupling and buying another inverter.

EG4 Solar Charge Controller MPPT | 500VDC 100A | MPPT100-48HV

Signature Solar provides solar panels, off-grid solar systems, grid-tie, and hybrid systems. Quality solar inverters, bifacial solar panels, complete solar kits, solar batteries. Featuring brands such as EG4 Electronics with their solar battery, LifePower4 and EG4 LLifePower4 and EG4 LL

signaturesolar.com

 

[1201]

Trying to learn, why wouldn't 12 panels work just fine?

Yes voc is close to the limit and above mppt range, but under load will he ever see above 500v? Isn't the vmp the number to use for mppt?

 

[TheFlumph]

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 (I did not check this)​

18Kpv PV input specs
View attachment 191724

2 strings of 11 on MPPT:

Voltage at coldest temp: 46.1x11 = 511.5V This is over the 500V top end of the MPPT operation but under the 600V limit. This should be fine. The vast majority of the time it will be well under 500V. In the coldest temps it is still only 511V.
Note: You should never count on it, but Voc is typically lower than the spec. Consequently, there is a good chance the total voltage won't be above 500 even in the coldest conditions)
Impt of the two strings: 18.66A. This is under the 25A usable current of MPPT #1 (There will be no clipping)
Isc of the two strings: 19.54 A. This is well under the 33A Isc limit of MPPT #1.

According to my calculations, 11 panels per string should work fine.

EG4 Solar Charge Controller MPPT | 500VDC 100A | MPPT100-48HV

Signature Solar provides solar panels, off-grid solar systems, grid-tie, and hybrid systems. Quality solar inverters, bifacial solar panels, complete solar kits, solar batteries. Featuring brands such as EG4 Electronics with their solar battery, LifePower4 and EG4 LLifePower4 and EG4 LL

signaturesolar.com

Thanks for the help.
So the Isc of three strings of 11 being 29a should work too yes? Especially since the voltage is under 500.

 

[FilterGuy]

Trying to learn, why wouldn't 12 panels work just fine?

Yes voc is close to the limit and above mppt range, but under load will he ever see above 500v? Isn't the vmp the number to use for mppt?

When the battery is full and the mppt turns off, it appears as an open circuit to the panels...so they will go to Voc.

 

[FilterGuy]

Thanks for the help.
So the Isc of three strings of 11 being 29a should work too yes? Especially since the voltage is under 500.

With 3 strings the voltage is the same as for 2 strings.... so that is fine
Isc will be 3x9.77=29.31A. That is under the 31A limit... so that is fine.
Imp will be 3 x 9.33 = 27.99A. This is over the usable current of the MPPT, but still within the operational specs. In other words, the MPPT would be slightly over-paneled. This means that if the conditions are such that the panels would produce at full power, the MPPT would not use all the power. However, this is not necessarily a bad thing.

- In winter, when the sun is at a bad angle and the panels are not producing at full power, the system will work without clipping.
- In the morning, the system will ramp up and harvest more power till the current limit is hit.
- On cloudy days the system will harvest more power.

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

 

[1201]

When the battery is full and the mppt turns off, it appears as an open circuit to the panels...so they will go to Voc.

Correct. So when they are above 500v is when the mppt would normally be off anyway, and when the mppt is active they are under 500v so it seems in all cases there is no loss of production due to going over 500v

 

[FilterGuy]

With 3 strings the voltage is the same as for 2 strings.... so that is fine
Isc will be 3x9.77=29.31A. That is under the 31A limit... so that is fine.
Imp will be 3 x 9.33 = 27.99A. This is over the usable current of the MPPT, but still within the operational specs. In other words, the MPPT would be slightly over-paneled. This means that if the conditions are such that the panels would produce at full power, the MPPT would not use all the power. However, this is not necessarily a bad thing.

- In winter, when the sun is at a bad angle and the panels are not producing at full power, the system will work without clipping.
- In the morning, the system will ramp up and harvest more power till the current limit is hit.
- On cloudy days the system will harvest more power.

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

BTW: With 3 strings you will need to fuse the strings.

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

 

[FilterGuy]

Correct. So when they are above 500v is when the mppt would normally be off anyway, and when the mppt is active they are under 500v so it seems in all cases there is no loss of production due to going over 500v

Correct, the Voc limit is about damaging the inverter when the MPPTs turn off. It is not about power production till it gets above 500V during operation. In this case, It is unlikely for Vmp to ever get above 500 when the controller is harvesting power. That is the nice thing about having the extra 100v of 'buffer' beyond the operational range of the MPPT. You can design the system to use the full capability of the MPPT.

The Isc limit is about damaging the MPPT during switching on and off. It is not about power production.

The Imp usable current is about power production but not about damaging the MPPT. As long as the Voc and Isc limits are met, there should be no damage if the array can produce more current than the MPPT will use. However, once it hits the Imp limit, the MPPT will clip and not produce additional energy even though the panels are capable of delivering more energy. (Note: There is a limit to the overpaneling. For the 18Kpv the limit is 21KW total array capacity)

Note: Some people are not fans of overpaneling an MPPT because it means the MPPT will be operating at max capacity. There is a possibility this could shorten the life of the MPPT. Looking at the numbers of this example, my *guess* is the MPPT would not be clipping for very long.
* In the morning and afternoon, the sun will be at a lower angle and the panels will not be operating at full rated capacity.
* Even at the peak part of the day, unless the panels are perfectly aligned, they are not likely to be able to produce at the full rated capacity.

 

[1201]

Correct, the Voc limit is about damaging the inverter when the MPPTs turn off. It is not about power production till it gets above 500V during operation. In this case, It is unlikely for Vmp to ever get above 500 when the controller is harvesting power. That is the nice thing about having the extra 100v of 'buffer' beyond the operational range of the MPPT. You can design the system to use the full capability of the MPPT.

The Isc limit is about damaging the MPPT during switching on and off. It is not about power production.

The Imp usable current is about power production but not about damaging the MPPT. As long as the Voc and Isc limits are met, there should be no damage if the array can produce more current than the MPPT will use. However, once it hits the Imp limit, the MPPT will clip and not produce additional energy even though the panels are capable of delivering more energy. (Note: There is a limit to the overpaneling. For the 18Kpv the limit is 21KW total array capacity)

Note: Some people are not fans of overpaneling an MPPT because it means the MPPT will be operating at max capacity. There is a possibility this could shorten the life of the MPPT. Looking at the numbers of this example, my *guess* is the MPPT would not be clipping for very long.
* In the morning and afternoon, the sun will be at a lower angle and the panels will not be operating at full rated capacity.
* Even at the peak part of the day, unless the panels are perfectly aligned, they are not likely to be able to produce at the full rated capacity.

Thanks, so to make it crystal clear and simple for op and I, there should be no problem with op using 12s strings, correct?