Does this actually work?
I would like to do this. But I don't see this documented anywhere.
Neither in grid boss manual nor in flex boss manual.
I heard the same YouTube. But haven't seen this option documented anywhere.
Flexboss21 and Gridboss
- Thread starter jwy224
- Start date
Does this actually work?
I would like to do this. But I don't see this documented anywhere.
Neither in grid boss manual nor in flex boss manual.
I heard the same YouTube. But haven't seen this option documented anywhere.
Usernameinuse
New Member
I bet it would work, but when it fries something don't call support:
However, since I posted my problems earlier, they have updated the manual, and its starting to make a lot more sense:
Still doesn't explain the blackouts, but the inconstant settings at least make more sense now.
However, my testing disagrees with this statement:
"start" seems to work only when the value is below. Maybe I am dumb, but that doesn't make sense.
However, since I posted my problems earlier, they have updated the manual, and its starting to make a lot more sense:
Still doesn't explain the blackouts, but the inconstant settings at least make more sense now.
However, my testing disagrees with this statement:
"start" seems to work only when the value is below. Maybe I am dumb, but that doesn't make sense.
skimandan
New guy
I don't have AC coupled solar but I saw EG4 had a new white paper on connecting it to the load port of the Flexboss21 here:
EG4® FlexBOSS21 - EG4 Electronics
EG4 FlexBOSS21: A powerful 21kW hybrid inverter, ideal for scalable solar setups, offering 16kW AC with solar gain & 90A grid feed-through.
eg4electronics.com
Usernameinuse
New Member
oh, great find, that wasn't there when I set mine up. I will have to try it out.
Usernameinuse
New Member
Ok, I re-wired it my AC coupled solar to the load port on the Flexboss. You now lose any measurement of AC coupled solar power:
See me charging my batteries at 6677w and exporting 232w magically? before you would see it coming in on a smart port.
Additionally, I got a total blackout after 7 minutes running off grid. Hey, at least it is getting faster and easier to troubleshoot.
The AC couple guide also gives no advice on settings, and there are no settings to configure. You can't change anything about the load port.
See me charging my batteries at 6677w and exporting 232w magically? before you would see it coming in on a smart port.
Additionally, I got a total blackout after 7 minutes running off grid. Hey, at least it is getting faster and easier to troubleshoot.
The AC couple guide also gives no advice on settings, and there are no settings to configure. You can't change anything about the load port.
CaySol
Solar apprentice
Check the settings page on the mobile app for the inverters.
skimandan
New guy
I don’t have a dog in this fight but I’d be pretty upset if ac coupling didn’t work as advertised. Does EG4 specifically market ac coupling working off grid?
Usernameinuse
New Member
It works, sort of. I feel like there is just a firmware bug or something that it panics when something happens, and shuts down.
jwy224
New Member
I think @EG4TechSolutionsTeam might need to jump in here and help you out.
Usernameinuse
New Member
Grid up, AC coupled solar on smart port works very well.
Grid goes down (by me flipping breaker from meter), settings are strange. "Start" feels weird since the value must be below it. AC coupling turns on and feeds batteries/loads.
After some time between 5-120 minutes, total blackout of gridboss and flexboss21. Only turning back on breaker restores anything.
A new whitepaper came out explaining you can do exactly what I am attempting, and it should work:
I re-wired it to be on the load port of the Flexboss21, and same issue, but failed even faster after about 7 minutes.
Oh, that's no good. I guess I will be testing out my midnite AIO for ac coupling as well. Just can't assume these things work when you most need it!
How about grid down and batteries are at say more than 30% capacity? Does AC coupling work without an issue in this scenario?
There is no point in installing a battery system if it would go down few minutes without the grid.
Is there a way to make AC coupling work without the grid? Does this work if I just go with just flex boss or 18KPV or 12KPV? Does this work flawlessly if the AC coupling is connected to the smart ports?
If this is not possible, I don't think I will consider EG4. I already have AC coupled Solar and is trying to add batteries. AC coupling without grid is a primary requirement for me.
I just assumed AC coupling without grid is something that would work seamlessly, and black start is the only missing feature. I somehow assumed AC coupling without grid will do the following.
1. Produce at max capacity while home load + battery charging < max production
2. Limit production by adjusting frequency while home load + battery charging < adjusted production
3. Stop AC coupling when batteries are full, and home load is less than lowest adjusted production.
4. Even if it is stopped, AC coupling will start again once conditions 1 or 2 are met.
I understand AC coupling will not work without batteries or grid. But if there are issues with AC coupling while batteries have capacity to provide whole home back up, I will not even consider it.
Usernameinuse
New Member
I have never been less than 50% when it is a blackout. I doubt it is SOC issue.
If I had to guess it is too much power. AC coupled solar is just dumping a lot (up to about 12KW in my case) power into the system. I am not consuming even close to that. When coupled at the smart port, I would see it take the excess and put it on the batteries, so for a time (1 hour or so) it works beautify, just as you describe.
And come to think of it, with the new re-wiring I did to the load port on the Flexboss, how can it cut off the AC coupled solar? Is there a relay on that connection? How else can it kill it as described in your #3? We know there is on the smart port.
Just did another test today, and at least I am getting consistent. about 5 minutes after flipping grid breaker, blackout.
I bet it is not a coincidence that is exactly how long it takes the AC Coupled solar to wake back up.
The fact that it works when wired into a smart port still makes me believe it will work longterm, just need a software fix. I don't mind being a bleeding edge user, but I think EG4 does need to figure this out. Think of the millions of existing AC coupled solar systems. Huge market for them.
EG4TechSolutionsTeam
Online Support for EG4 Electronics
It will keep operating. It can handle up to 600V. However, it will only use up to 440V and the rest would be essentially wasted.
skimandan
New guy
@EG4TechSolutionsTeam
I am considering a bit of reconfiguring the 36 ZNShine 455 panels I installed in January to make room on the inverter for 10 more panels.
The 10 new panels will be 5 east facing and 5 west facing. I have not chosen the panels yet, but I will lean towards a higher Vmp lower Isc panel than the ZNShines.
While entering the data into the EG4 String Sizer Tool I noticed a "Max Allowed Watts per MPPT" that my new strings would exceed. This spec is nowhere in the Flexboss21 specs or manual. Note I am not concerned about the slight clipping that might occur due to the 26.16 Imp.
1. What happens if the Max Allowed Watts per MPPT is exceeded? Math says 440V*26A=11,440. String Sizer says 9,360. What does the FlexBoss21 do when 360V*26A=9,360W is exceeded?
I also noticed that EG4 is still marketing "MPPT Voltage Low 120" which is part of what put me into this reconfiguration mess to begin with.
Can EG4 please "Fix" the string sizer "MPPT Voltage Low" to the real value of 140V, per your CEO's declaration that the FlexBoss21 will not support 120V. Oops!
I am considering a bit of reconfiguring the 36 ZNShine 455 panels I installed in January to make room on the inverter for 10 more panels.
The 10 new panels will be 5 east facing and 5 west facing. I have not chosen the panels yet, but I will lean towards a higher Vmp lower Isc panel than the ZNShines.
While entering the data into the EG4 String Sizer Tool I noticed a "Max Allowed Watts per MPPT" that my new strings would exceed. This spec is nowhere in the Flexboss21 specs or manual. Note I am not concerned about the slight clipping that might occur due to the 26.16 Imp.
1. What happens if the Max Allowed Watts per MPPT is exceeded? Math says 440V*26A=11,440. String Sizer says 9,360. What does the FlexBoss21 do when 360V*26A=9,360W is exceeded?
I also noticed that EG4 is still marketing "MPPT Voltage Low 120" which is part of what put me into this reconfiguration mess to begin with.
Can EG4 please "Fix" the string sizer "MPPT Voltage Low" to the real value of 140V, per your CEO's declaration that the FlexBoss21 will not support 120V. Oops!
CaySol
Solar apprentice
Someone more knowledgeable can correct me or elaborate, but I’m guessing there is a good reason that Wmax is less than Vmax x Amax.
Last edited:
This is how I understand it, feel free to correct.
If the string can achieve 26A@360V, MPPT will reduce the current in order to keep the power at 9360W. I'm still not exactly sure how it operates above 440V, because MPPT needs to continue reducing the current, but I don't know how it can do it if it stops tracking.
Power isn't always linear. When the weather is cold, the string's idle voltage will be high even without the optimal irradiation, but the current it can supply will be lower. The practical losses from oversubscribing the inverter won't be high. Enphase has a white paper on the clipping losses https://enphase.com/download/pv-module-and-inverter-ratings-iq8-series-tech-brief
TL;DR- you can oversubsribe by 30-40% with minimal losses.
Granted, it is a bit more complex with FlexBoss, as it will spend more time generating more than 16KW. This excess power can only be used to charge batteries, so its usefulness would depend on your battery size and willingness to do daily cycles.
skimandan
New guy
I’d like to know if there is an actual mppt limitation at 9,360W or just erroneous info in the string sizer tool.
I’d prefer not to speculate.
If the Flexboss 21 behaves the same way as an 18k PV does,
The string should still work at reduced efficiency when it gets past mppt range.
skimandan
New guy
If, Should Maybe? I'll wait for a definitive answer to how it behaves within its mppt range but outside of the String Sizer Tool wattage limit spec.
Quattrohead
Emperor Of Solar
If I remember rightly it was showing 16 watts over per string, it will be fine.
skimandan
New guy
My new string would be 1,600W over. I agree it’s probably fine, but I guess only EG4 knows why the string sizer tool limits to 9,360 per string.
The optimal large string voltage is 360V, the max current is 26A 360x26=9360
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