Hi all,

I m new member here and just installed a solar system in my house, everything is functioning correctly except "SUB" where it draws electricity from utility at the same time as my panels even though i have enough power on panels to power the whole house and then some. 

My system is : Voltronic max 2 8kw inverter, 15 590w panels in 2 strings ( 7 + 8 ) , 8 250Ah 12v batteries ( 2 x 4 ) .

 

 If I use SBU it works correctly and only draw power from the battery when its cloudy and there i not enough power form solar, also in SUB the utility doesnt charge batteries unless there is zero solar power and i have solar and utility set to recharge batteries at the same time. I m not sure if thats how SUB should work or there are some settings i m not aware off.

 

Ive been reading a lot and learning about all this, the only solution i found is to use SBU and put a timer on it where it switched to SUB when its night time, my goal is to not use utility power at all when i have enough from solar to power the house and charge the batteries, only use it in the night time or extreemly cloudy days.

 

Thank you

Edited January 26, 20223 yr by Tnaik

Welcome you have a good system with a good size battery bank for a lead acid bank.

250ah x 48 volts= 12000watthours

50% of that should last you most of the night.

 

My suggestion would be to leave it on sbu but set the back to ac setting to what the battery manufacturer says corresponds with 50% dod.

1 hour ago, Buyeye said:

Welcome you have a good system with a good size battery bank for a lead acid bank.

250ah x 48 volts= 12000watthours

50% of that should last you most of the night.

 

My suggestion would be to leave it on sbu but set the back to ac setting to what the battery manufacturer says corresponds with 50% dod.

Thank you for the reply.

In my country we have around 8-9 hours power outage a day although not straight, so i m trying to keep the batteries ready for that time.

Ive been noticing that a lot of inverters struggle with correct SUB implementation, i ll try ur suggestion but probably set the back to ac a little higher to keep more juice in the batteries when power outage happens.

But ideally if SUB just works it would be the best solution.

Edited January 26, 20223 yr by Tnaik

11 hours ago, Tnaik said:

If I use SBU it works correctly and only draw power from the battery when its cloudy and there i not enough power form solar, also in SUB the utility doesnt charge batteries unless there is zero solar power and i have solar and utility set to recharge batteries at the same time. I m not sure if thats how SUB should work or there are some settings i m not aware off.

Hi Tnaik,

you can achieve this with setting 16 to CSO (charge source priority: solar first). No need to switch to SUB, remain in SBU.

On 2022/01/27 at 8:57 AM, Beat said:

Hi Tnaik,

you can achieve this with setting 16 to CSO (charge source priority: solar first). No need to switch to SUB, remain in SBU.

I have it set to solar+utility but utility never charges batteries unless there is zero power from solar, if i use USB than utility  charges batteries at the same time as solar, why not with SUB though? 

The whole SUB mode isnt working as i was thinking it should work.

1 hour ago, Tnaik said:

I have it set to solar+utility but utility never charges batteries unless there is zero power from solar, if i use USB than utility  charges batteries at the same time as solar, why not with SUB though? 

You will have to decide what you really want. Perhaps setting 16 to SNU (solar and utility will charge at the same time) could satisfy your thoughts.

Edited January 29, 20223 yr by Beat

On 2022/01/29 at 10:22 AM, Beat said:

You will have to decide what you really want. Perhaps setting 16 to SNU (solar and utility will charge at the same time) could satisfy your thoughts.

What i really want is for SUB to work correctly, Solar to be 1st priority and utility to be 2nd priority to be used ONLY when there isnt enough solar.

My whole issue is even when there is enough solar power to power the whole house and charge the batteries, the utility is still providing power to the house at the same time as the solar, SUB should achieve this on paper but its not.

 

As for setting 16, its not a big issue for me but i have it set up as SNU,  yet only Solar charges the battery. I have to set power output priority to USB for both to charge battery at same time.

 

English isnt my main language so hope i m getting my message through clearly.

 

Thank you

Edited January 30, 20223 yr by Tnaik

9 hours ago, Tnaik said:

What i really want is for SUB to work correctly, Solar to be 1st priority and utility to be 2nd priority to be used ONLY when there isnt enough solar.

My whole issue is even when there is enough solar power to power the whole house and charge the batteries, the utility is still providing power to the house at the same time as the solar, SUB should achieve this on paper but its not.

 

As for setting 16, its not a big issue for me but i have it set up as SNU,  yet only Solar charges the battery. I have to set power output priority to USB for both to charge battery at same time.

 

English isnt my main language so hope i m getting my message through clearly.

 

Thank you

I can understand your frustration with SUB not working as it should. This mode is one of the great changes that was introduced for the MKS 111 and on the King and Max versions. It should actually use all the solar the panels produce and just add from the grid to make up the whole load. 

For your use you are correct that you need to ensure your batteries are kept full for the 8 hour a day power cuts. 

Perhaps you need the inverter checked why SUB is not working. I think some people got this mode working after updating software. 

In the mean time set the back to utility as high as you can. On my inverter it is setting 12.

So how much power does it draw from utility when in SUB output source priority? If it's just a few hundred watts, that could be a buffer against pushing power towards the utility when loads suddenly decrease. 

Could it be the problem identified in other topics where under some conditions the MPPT algorithm gets stuck at a PV voltage well below the actual maximum power point? To help with this, can you report your PV voltage and power when it's using too much utility power, and then when you switch to SBU priority with a similar load? 

I've been quiet on this because you have an 8kW model, and there is no 8kW firmware to read. I do have several 7.2kW firmwares to read, but they likely won't work in your model. 

Also, is yours one of the newer models with the fixed display and the RGB LED ring around the display? These likely require different firmware to models with the removable display.

I have an idea for possibly fixing or working around the MPPT bug, but I can't patch 8kW firmware as I don't have a firmware update file for them. 

5 hours ago, Scorp007 said:

I can understand your frustration with SUB not working as it should. This mode is one of the great changes that was introduced for the MKS 111 and on the King and Max versions. It should actually use all the solar the panels produce and just add from the grid to make up the whole load. 

For your use you are correct that you need to ensure your batteries are kept full for the 8 hour a day power cuts. 

Perhaps you need the inverter checked why SUB is not working. I think some people got this mode working after updating software. 

In the mean time set the back to utility as high as you can. On my inverter it is setting 12.

Thank you for the reply.

I m thinking of getting an electrician just to measure how much power the utility is drawing when there is enough solar power.

My inverter the the max II so it should be the latest version, not familiar much where i can find the latest firmware for my model.

But like u said, setting It to SBU and setting back to utility a little high would probably solve the whole thing, its just would be preferable with SUB if it works as it should.

I ll take couple of pics of the inverter screen once we have a sunny day just so i can show how SUB is functioning on mine.

 

Thank you.

Edited January 30, 20223 yr by Tnaik

2 hours ago, Coulomb said:

So how much power does it draw from utility when in SUB output source priority? If it's just a few hundred watts, that could be a buffer against pushing power towards the utility when loads suddenly decrease. 

Could it be the problem identified in other topics where under some conditions the MPPT algorithm gets stuck at a PV voltage well below the actual maximum power point? To help with this, can you report your PV voltage and power when it's using too much utility power, and then when you switch to SBU priority with a similar load? 

I've been quiet on this because you have an 8kW model, and there is no 8kW firmware to read. I do have several 7.2kW firmwares to read, but they likely won't work in your model. 

Also, is yours one of the newer models with the fixed display and the RGB LED ring around the display? These likely require different firmware to models with the removable display.

I have an idea for possibly fixing or working around the MPPT bug, but I can't patch 8kW firmware as I don't have a firmware update file for them. 

I m going to get an electrician to measure the utility power since it doesnt show on the main screen, it only shows voltage ( around 230v ) and 50 hz.

Yes mine is the new model with RGB LED ring around the touch screen. I ll attach a picture of the one i have.

If its drawing insignificant amount than thats no problem at all, i m just worried that it might be drawing a lot more and it ll increase my electricity bill for no reason.

As for the PV voltage, i dont recall ever seeing fluctuating massively wether there is utility or not, i have PV1 and PV2, each read on the screen between 220v and 280v when there is a pretty good amount of power (3000+w from each PV) and cold weather.

one thing i can confirm is when i use for example 5000w load from my home in a good weather, i can see more then 5000w split between PV1 and PV2 on the inverter screen while still having enough to charge the batteries but utilty still show the 2nd priority arrow indicating its providing power, it might be like u said few hundred watts and thats totally fine, thats what confusing me at the moment. 

 

Edited January 31, 20223 yr by Tnaik

1 hour ago, Tnaik said:

I m going to get an electrician to measure the utility power since it doesnt show on the main screen, it only shows voltage ( around 230v ) and 50 hz.

I guess I'm spoiled with my home made monitoring software. I assume that it must calculate the input power (it's been a while since I looked at that, and a colleague wrote most of it).

If you have an AC clamp meter, even a cheap one would do, you could clamp that over one (not both) of the AC-in wires.

Or just figure it out from other power figures, using an assumed efficiency of 97% (probably optimistic) and an idle load of 75 W (wild guess).

9 minutes ago, Coulomb said:

I guess I'm spoiled with my home made monitoring software. I assume that it must calculate the input power (it's been a while since I looked at that, and a colleague wrote most of it).

If you have an AC clamp meter, even a cheap one would do, you could clamp that over one (not both) of the AC-in wires.

Or just figure it out from other power figures, using an assumed efficiency of 97% (probably optimistic) and an idle load of 75 W (wild guess).

I ll get one tomorrow to measure it myself and see what kind of power i m drawing fron utility and will let u know.

 

Thank a lot for the much appreciated help.

On 2022/01/31 at 5:19 AM, Coulomb said:

I guess I'm spoiled with my home made monitoring software. I assume that it must calculate the input power (it's been a while since I looked at that, and a colleague wrote most of it).

If you have an AC clamp meter, even a cheap one would do, you could clamp that over one (not both) of the AC-in wires.

Or just figure it out from other power figures, using an assumed efficiency of 97% (probably optimistic) and an idle load of 75 W (wild guess).

I did some quick testing while we had like 30min of good weather, I took some pictures of the inverter screen along the way. 

When i m using SUB and even when there is enough power from solar i m always drawing around 1100-1200w from utility ( the overall power draw was around 5000w)

So majority is from Solar i just dont know why i keep drawing 1100-1200w from utility, keep in mind utlity isnt charging batteries.

When i switch to SBU, utility power draw drops to 0 and full power is drawn from Solar, although i noticed sometimes when i m drawing alot of power, it takes some time to completely switch from SUB to SBU, it does switch but it keep using utilty even as third priority arrow is shown whilr bypassing batteries.

I ll show some pics so u can see better what i m talking about.

PS: i saw couple of quick times where voltage on PV1 and PV2 dropped below 100v.

 

here are some pics in SUB.

Edited February 1, 20223 yr by Tnaik

And here are some pics while in SBU.

In first picture u can see how even in SBU it was using utility still without even using the batteries, usually when I switch from SUB to SBU i can hear a clique, i didnt this time and couple other time and i can clearly see third priority arrow is displayed on utility now, i think though that is happening when i have a big load,  once its lowered it function properly but it needs more testing. 

 

Thank you

On 2022/01/30 at 10:53 AM, Tnaik said:

My whole issue is even when there is enough solar power to power the whole house and charge the batteries, the utility is still providing power to the house at the same time as the solar, SUB should achieve this on paper but its not.

That doesn't make sense to me. Why would you want utility to provide power to the system while solar is delivering enough? Well, I'm thinking in terms of my off grid system. It is either completely cut off from grid (normal operation) or in case of low battery SOC connected to it. Then the battery will be charged from grid at nighttime, but from solar during the day while the load is covered from grid.

6 hours ago, Beat said:

That doesn't make sense to me. Why would you want utility to provide power to the system while solar is delivering enough? Well, I'm thinking in terms of my off grid system. It is either completely cut off from grid (normal operation) or in case of low battery SOC connected to it. Then the battery will be charged from grid at nighttime, but from solar during the day while the load is covered from grid.

Thats the issue i m talking about, i dont want utility to provide power when solar is delivering enough, thats how the system is acting and  i m trying to find a solution for that...

37 minutes ago, Tnaik said:

Thats the issue i m talking about, i dont want utility to provide power when solar is delivering enough, thats how the system is acting and  i m trying to find a solution for that...

Are you still on the old batteries or on the new lithiums?

1 hour ago, Scorp007 said:

Are you still on the old batteries or on the new lithiums?

My whole system is two weeks old, i m using 8 250ah 12v batteries, acid batteries if  i m not mistaken

On 2022/02/01 at 11:41 AM, Beat said:

That doesn't make sense to me. Why would you want utility to provide power to the system while solar is delivering enough? Well, I'm thinking in terms of my off grid system. It is either completely cut off from grid (normal operation) or in case of low battery SOC connected to it. Then the battery will be charged from grid at nighttime, but from solar during the day while the load is covered from grid.

It seems to be an inherent design, both my Axpert VM 3 and max does it in SUB. Although at low power draw say 500 watt the utility will supply about 400 w, however once runing at say 2kw, the utility supply will drop of to almost nothing. I have never seen the extreme  Thaink is refering to of 1kW from the utility if theres enought solar.

On 2022/02/11 at 10:57 AM, Deon Zeelie said:

It seems to be an inherent design, both my Axpert VM 3 and max does it in SUB.

I understand now that this is a problem inherent to grid tied inverters. Off grid inverters don't have the SUB option. By choosing off grid inverters on advice of the seller I apparently avoided many problems and costs. My aim is as much as possible independence from grid in view of load shedding and rising tarif.

The local municipality makes it anyway rather discouraging with complicated administrative procedure and a monthly fee for allowing to feed back. How many kWh would one have to deliver only to offset that fee?

@Beat  For some people the units with SUB are indeed a better option. When you want to have the maximum battery power for LS you would not want to use battery power each time you have thick cloud and your PV reduces. That's why one would rather use the grid to supply combined with the little PV for the actual load.

It all boils down to your configuration. Bear in mind the units with SUB also have the SBU setting so they offer an option that the older units do not have.

Edited February 12, 20223 yr by Scorp007

On 2022/02/13 at 1:47 AM, Scorp007 said:

@Beat  For some people the units with SUB are indeed a better option. When you want to have the maximum battery power for LS you would not want to use battery power each time you have thick cloud and your PV reduces. That's why one would rather use the grid to supply combined with the little PV for the actual load.

It all boils down to your configuration. Bear in mind the units with SUB also have the SBU setting so they offer an option that the older units do not have.

Indeed,  i have my batteries saved for power outage during the night time.

What I did to solve my issue is to just set a timer on my inverter to have SBU on the whole daytime and SUB on at night, glad i had this setting available, the only thing is i have to change it in the summer time since day time will become longer.

Now if SUB functions as advertised it wouldve been better but thats still a pretty good solution. 

On 2022/02/11 at 10:57 AM, Deon Zeelie said:

It seems to be an inherent design, both my Axpert VM 3 and max does it in SUB. Although at low power draw say 500 watt the utility will supply about 400 w, however once runing at say 2kw, the utility supply will drop of to almost nothing. I have never seen the extreme  Thaink is refering to of 1kW from the utility if theres enought solar.

The thing is when i switch to SBU it takes zero power from batteries or utility if there is enough solar power, only in SUB it still draw around 1kw from utility regardless. 

But like i said above, setting timers for each is a good workaround, but wouldve been better if SUB just worked like it should.

22 minutes ago, Tnaik said:

The thing is when i switch to SBU it takes zero power from batteries or utility if there is enough solar power, only in SUB it still draw around 1kw from utility regardless. 

But like i said above, setting timers for each is a good workaround, but wouldve been better if SUB just worked like it should.

Thanks for pointing out that the SUB does not only use PV when there is enough PV to cover the load.  As said that is not what one would have believed.