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Axpert MKS II SUB (Solar-Utility-Battery) mode


Denarius
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It's popular knowledge that the Axpert MKS switches over to grid completely if the load is too much for solar and optional battery.  It doesn't supplement it's solar with grid.  This video describes what I'm referring to: https://www.youtube.com/watch?v=n6DVS8lLgjw

 

However, with the latest MKS II the marketing material of the various companies that white label the product mention this:  google search phrase below

Quote

This Mark II version is designed to run without batteries, thus being able to supliment usage during the day,

This makes me expect that there is a "SUB" mode as described in the very similar Axpert King manual (shown below).  However I don't see it in the MKS II manual.

https://portal.segensolar.co.za/reseller/docs/Axpert-KING-manual-NEW.pdf

image.png.30fd87ee5225354c6f30df522a787b4e.png

Does anyone know anything about this new mode referred to in the marketing material?

Edited by pierre.
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This has been available for some time in the Axpert VM III model. It looks like they might be introducing it to some other models, or it might also have been available in the Axpert MKS II model all along (the II is the model with the 450V MPPT). [ Edit: this page, seemingly from 2015, says PIP-5048MG models (Axpert MKS IIs) can operate "battery optional". ] [ Edit May 2020: the page appears to have been updated in March 2020, and no archive exists in archive.org at present. ]

The batteryless operation has always seemed gimmicky to me. I imagine that with clouds and load changes, the unit could be constantly switching between PV and utility power to supply the load. Can actual Axpert VM III users operating without a battery (at least for some time) comment one way or the other (i.e. works well, or useless, just connect a battery), please?

Edited by Coulomb
Keyboard went crazy again. Sigh.
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It sounds like your expectation is that it switches between PV and Utility instead of using both at the same time like hybrid or grid tie inverters.  If that is the case then I agree it isn't very useful.  They do however mention the words "at the same time" in the manual, the same words they use to describe how solar and battery works together.

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11 hours ago, pierre. said:

It sounds like your expectation is that it switches between PV and Utility instead of using both at the same time like hybrid or grid tie inverters. 

My understanding, without ever owning one, is that these models with the 450 V max MPPT are more like hybrid inverters, and do in some circumstances blend PV and grid power. SUB mode may encourage more of this. As far as I know, models without the 450 V max MPPT don't have the SUB option.

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So I was about to post the same question as you Pierre - there has definitely been a change in the manuals for the Axpert type inverters since that famous Youtube video was made. I'm about to install my first solar/backup system and am looking at the VMiii axpert. I have spent weeks agonising if I should just bite the bullet and stretch quite a lot further for a "proper" grid tie system, but when looking at the manual found this in the operation mode section:

image.png.389cb5e795adbd9ef5298340157e6dd8.pngVMiii

Compared to the V series
image.png.104c04c44df5a5a0cbdbf131bd09caa4.pngV

And compare this with the King series which has been confirmed to combine AC and PV

image.png.4e3b8a9781c9d4248323bb2bb03db16b.pngKing

 

I'd love it if anyone with a VMiii or MKS II could confirm the mix of PV and AC for powering the inverter output.

image.png

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So the disadvantage of this over a "proper" grid tie system is that solar is only available for essential loads within the 3kw/5kw of the inverter. My plan to improve this is to basically have as much as possible on the essentials line and combine that with good family training and an inverter bypass switch when I have to use more than 3kw.

Sorry to hijack a bit Pierre... but here is my proposed system:

Axpert VMiii 3kw
JAsolar 340w x 4 (One string in series)
US2500 (2.4kwh) - Was basically given to me which is what started this whole crazy process...
Mounting kit for the panels
DC disconnect
125A battery disconnect
20A in-line DC fuse
AC inverter change over and breaker

I've got an electrician friend who is going to help me do all the DB side stuff. The PVWatts website indicates I could expect around 6.5kwh a day from the panels (1360W), so if I can use 2kwh to charge the batteries and 4.5kwh for day time loads I can theoretically pay back the system in 9 years... But I can avoid loadshedding (mostly) and upgrade latter and add more solar via grid tie if needed.

If anyone has any comments on this system, feel free to leave them.

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On 2020/02/21 at 3:22 AM, JaseZA said:

So the disadvantage of this over a "proper" grid tie system is that solar is only available for essential loads within the 3kw/5kw of the inverter.

I would just point out that the supposed Axpert MKS II (edit: probably actually an Axpert VM II) in the kettle example was in line mode, so the inverter proper (the DC-AC power converter) was not in use. [ Edit: except for PV load powering [ edit2: was "charging" ], see next several posts. ] So the name plate rating of the inverter doesn't come into play; apparent power output is then limited by the rating of the transfer relay. In the case of the 5 kW models (and quite possibly the 3 kW models as well, I don't know), that's 40 A, so the AC-out could handle over 9 kVA of apparent power (and over 9 kW of real power if it's a purely resistive load).

Granted, you can't power any "non-essential" loads that aren't connected to AC-out. However, I strongly suspect that the Axpert MKS II and other models with this blending feature will try to not export power (into the AC-in port, from the inverter's point of view) under any circumstances. So you'd never be able to power those non-essential loads (any not connected to the inverter's AC-out terminals) from PV with this sort of inverter.

Edited by Coulomb
Also added "into the AC-in port"
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4 hours ago, Coulomb said:

the Axpert II in the kettle example was in line mode, so the inverter proper (the DC-AC power converter) was not in use.

I'm not sure I understand this - would the DC-AC converter not be required when converting the Solar DC to AC for the output to the kettle? Or is there a different inverter for the Solar vs battery? Or is this maybe to do with how the inverter blends these two sources - I read on the King inverter that it inverts grid AC to DC, then combines with Solar DC, and finally inverts this combo back to AC to drive the output load?

4 hours ago, Coulomb said:

I strongly suspect that the Axpert MKS II and other models with this blending feature will try to not export power (from the inverter's point of view) under any circumstances. So you'd never be able to power those non-essential loads

I agree, I think that would be beyond the capabilities of this inverter. That's why I'm going to try and have as much as reasonable on the essential side of the inverter, and then just manage my loads well to stay within 3kw and not run the batteries down too quickly when Grid AC is off.

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May I propose that maybe Coulomb or anyone else that has the intricate knowledge of the Voltronic/Axpert  draws up a small test case for the MK II so we can put this topic to rest.

Early last year I fried my inverter while experimenting 😝, my replacement unit was the MK II, so I have pretty much played by the book since then.

Obviously nothing that might endanger the integrity of the system and nothing thing that will involve opening the until and measuring inside.

I would be willing to conduct the test and provide feedback.

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1 hour ago, LMthethwa said:

I would be willing to conduct the test and provide feedback.

Thanks for offering to test for us! Obviously Coulomb will be better equipped to devise the best test, but a simple one would just be to look and the display during the day, and force a load that's bigger than the available solar (run a kettle for example) - then see if it stops drawing power from solar and only uses the grid, or if it combines the two. Not having a unit in front of me, I'm not exactly sure which screen would be the easiest to see this on. Or if you'd need to plug in with a computer and use the power monitoring software to see. If you had a clamp meter you could also just check if there is a drop in solar current to the inverter, or a smaller increase in current from the grid.

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On 2020/02/21 at 3:06 PM, JaseZA said:

I'm not sure I understand this - would the DC-AC converter not be required when converting the Solar DC to AC for the output to the kettle?

You're quite correct; my bad. Here is my block diagram to cover most of the Axpert models:

1282960311_Presumedblockdiagram.png.fc546b6bb67759ecf6560f6681b82bab.png

Ignore the red part (for Axpert King only) and the blue lettering and line (for 145 V max MPPT only). But since the max PV is say 4 kW and the inverter can handle 5 kW, the inverter isn't in a place where it will be the bottleneck.

Let's say there is a 6 kW load, and 2 kW of PV. The inverter is rated at 5 kW, so it is forced into line mode, so the top switch is closed. So power can flow from the AC-in to the AC-out. But in SUB mode, the other switch would also be on, so that PV power can flow to the load as well. The inverter can't handle all the load, but it doesn't have to; the AC-in is there to supply part of the load. So 4 kW will come from AC-in, blending with 2 kW from the PV, to provide 6 kW to the load. The inverter only carries the PV-supplied portion of the load.

It's possible for part of the PV power to charge the battery, via the bidirectional DC-DC converter (at right). In that case, less power supports the load, obviously.

Edited by Coulomb
Updated image to include "max" after "450 V" and "145 V"
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I run 2 of these Axpert MKS VII in parallel with the ICC control module.  It seems like the PV can't be blended with grid if you have batteries connected.  Under "operating modes" the manual also specifically states "and battery is not connected":

image.png.b14d84a16823d33329e29a7bd1cc30d0.png

This effectively means that it is not possible to achieve a SUB (Solar Utility Battery) mode or setting.

Edited by pierre.
duplicate image
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On 2020/02/21 at 12:35 PM, Coulomb said:

You're quite correct; my bad. Here is my block diagram to cover most of the Axpert models:

2020421383_Presumedblockdiagram.png.dd51e86157cd9ac2538e9da1843f26f4.png

Ignore the red part (for Axpert King only) and the blue lettering and line (for 145 V max MPPT only). But since the max PV is say 4 kW and the inverter can handle 5 kW, the inverter isn't in a place where it will be the bottleneck.

Let's say there is a 6 kW load, and 2 kW of PV. The inverter is rated at 5 kW, so it is forced into line mode, so the top switch is closed. So power can flow from the AC-in to the AC-out. But in SUB mode, the other switch would also be on, so that PV power can flow to the load as well. The inverter can't handle all the load, but it doesn't have to; the AC-in is there to supply part of the load. So 4 kW will come from AC-in, blending with 2 kW from the PV, to provide 6 kW to the load. The inverter only carries the PV-supplied portion of the load.

It's possible for part of the PV power to charge the battery, via the bidirectional DC-DC converter (at right). In that case, less power supports the load, obviously.

As far as I understand only one of the AC switches to the Loads can be closed at any time. The King can blend power from the grid, but only once it's on the DC bus. If the load goes above 5kW it will switch over to grid only.

Edited by gooseberry
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5 hours ago, gooseberry said:

As far as I understand only one of the AC switches to the Loads can be closed at any time.

That's how it is for all the 145 V max MPPT models, including the Axpert King.

Quote

The King can blend power from the grid, but only once it's on the DC bus. If the load goes above 5kW it will switch over to grid only.

Yes. But for the models with 450 V max MPPT, and as I suspected and @pierre. has confirmed, only when the battery is disconnected, they seemingly can blend AC-in and PV. The only way to do that is with both switches on.

Of course, with both switches connected, that implies the capability to push power into AC-in, especially when the load drops suddenly. I suspect that they keep this quiet because such operation should have regulatory approval, and that's expensive, so they want to avoid that for "off-grid" models.

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@pierre. @Coulomb

Wow this thread really clarifies a lot with regards to how and why the the Axpert models operate. Thank you!

I'm looking at installing 2 x Axpert MKS II 5K in parallel as my demand is greater than 5KW and often reaches 10kW plus... obviously the aim is to try and keep it below 10KW.

Please confirm or correct me with the following:
-I'll have +-4KW solar input on each Axpert MKS II and a total of 14kWh storage - 4 x pylontech 3.5kwh (to begin)

If my output priority is set to SOL:
1) lets say my load is 6kW and there is sufficient solar - solar solely provides to load.
    - if the available solar drops less than my 6kW demand, or my demand/load increases to more than my available solar (but still less than 10KW) - Solar + battery will provide to load. 
    - But now if battery levels drop to low set point, will it switch to utility ONLY ?? Or will it use the available solar and supplement with utility ?
2) As far as i understand, If my load now increases beyond 10KW, only utility will provide to the load. But the available solar energy will only be able to charge the batteries. Otherwise wasted!


Again please correct me if my wrong. (The manual isn't so clear here), If I parallel two Axpert Kings instead .. Such that in SUB mode the available solar will provide any load less than 10KW with the utility supplementing? 
And then if the load increases over 10KW only utility will provide?

I need to make a decision on which inverters to buy  :) please advise .. 

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1 hour ago, RAYRAY said:

Please confirm or correct me with the following:

I believe that you are correct on all points. (Apart from using upper case "K" for "kilo" occasionally 😀). But thanks for not getting kW and kWh confused; it makes for much more peaceful reading. Weber wrote an excellent post on this, in case you are interested.

1 hour ago, RAYRAY said:

2) As far as i understand, If my load now increases beyond 10KW, only utility will provide to the load. But the available solar energy will only be able to charge the batteries. Otherwise wasted!

Yes. Axperts other than the King work better when the load doesn't exceed rated power, and there is adequate battery capacity installed. Under those conditions, utility power is rarely used, and PV power blends with a little battery power as needed.

In a situation like yours, true hybrids like a Goodwe ES (or two or three) work better. But the hassle with the Goodwe ES is that you can't parallel the essential loads, so you have to split those up. Then you can have one overloaded and the other loafing.

Edited by Coulomb
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Just a few notes on how my thoughts on this confusing issue have evolved.

2 hours ago, RAYRAY said:

If my output priority is set to SOL:1) lets say my load is 6kW and there is sufficient solar - solar solely provides to load.
    - if the available solar drops less than my 6kW demand, or my demand/load increases to more than my available solar (but still less than 10KW) - Solar + battery will provide to load. 

I've been thinking of the Axpert MKS II as the same as an Axpert MKS, except for the high voltage MPPT. That's how it's grouped on the Voltronic Power web page. But now that I re-read the appropriate manuals, I see that this is not the case.

For an Axpert MKS (with a 145 V MPPT whose output connects directly to the battery), you get the "pure bypass" behaviour, i.e. the inverter switches to line mode, BYPASS is shown on the LC Display, and there is no path from PV to load.

But for an Axpert MKS II in SOL mode (only, it seems), if there is solar power available, line mode appears to be different. The word BYPASS doesn't appear, and there are two paths shown to the load, one from AC-in, and one from the inverter-proper powered from PV. Confusingly, the battery is shown as not connected in the examples in the manual. For some time, I assumed that this meant that the behaviour described only happens if the battery is detected as not present. But now I think it happens whether the battery is present or not. [ Edit: Sigh. @Pierre's post contradicts this. ] In fact, maybe it's implying that in this mode, the battery to bus DC-DC converter is not operating, so that the battery won't ever get used in this situation. (I suspect that the battery still supplies the idle power of some 50 W for a 5 kVA model).

Edited by Coulomb
Several chops and changes as I confused myself. Sigh.
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15 minutes ago, Coulomb said:

But now I think it happens whether the battery is present or not.

@Coulomb thank you for the reply.

But this is what is confusing me !! It clearly states when the battery is not connected - solar energy and the utility will provide the loads! 

I really would prefer using 2 x MKS II over the Kings because of the high MPPT range.. 

MKS II snip.png

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5 minutes ago, RAYRAY said:

But this is what is confusing me !! It clearly states when the battery is not connected - solar energy and the utility will provide the loads! 

Sigh again. It's 2am here; I shouldn't be posting about tricky things.

OK: so the manual doesn't say what happens, and in fact Pierre's post does NOT confirm blending of AC-in and PV with a battery present (I even acknowledge this in a reply. In my defence, I read and respond to a lot of posts, so I easily forget the "flow" of any particular post.)

So: can anyone using an Axpert MKS II confirm or deny blending of AC-in and PV power when a battery IS present?

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haha i was just trying to work out what time it is there.. Again i appreciate your reply.

So according to @pierre. previous posts, blending is not possible with batteries connected!

So basically if that is the case, i should max my solar panel input on each MKS II , say 4500W each. And have a large battery storage - in order to utilize the system correctly without the need of using power from the utility ?  

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6 hours ago, RAYRAY said:

haha i was just trying to work out what time it is there..

Since you so sensibly don't use daylight "savings", just add 8 hours to your time for AEDT (Australian Eastern Standard Time), observed all year round in Queensland where I live.

Quote

So according to @pierre. previous posts, blending is not possible with batteries connected!

The word "seems" in his post suggests that there is some room for doubt.

Quote

So basically if that is the case, i should max my solar panel input on each MKS II , say 4500W each. And have a large battery storage - in order to utilize the system correctly without the need of using power from the utility ?  

Yes. Of course, not everyone is in a position to pay for large PV arrays and a large battery. [ Edit: and not everyone has the same aversion for using some utility power. ]

Edited by Coulomb
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10 hours ago, Coulomb said:

Yes. Of course, not everyone is in a position to pay for large PV arrays and a large battery.

This is also true. But my logic is more along the lines of seeing a return and utilizing the system efficiently. I don't want to spend money for just a "back-up" system. I might as well spend more and depend on the utility much less to none! That way I will actually see a return in a couple years :) 

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