My home solar system is old, is just solar to three phase SMA grid-tied inverter and then on one phase in my DB I have a battery inverter that carries those loads during loadshed.   I do export and I do get credit for it, but a weakness (besides being off in loadshed) is that the way the SMA works in my understanding is that it will only export at the lowest nett kW of the three phases.    So if solar is 4+4+4 and loads are 3+1+1 across phases, then it will export 1+1+1.

reason for unbalanced is mainly because when we put the loadshed on one phase, we split things like aircons, stove, pool pump across the unprotected phases and all the lights and plugs are on the protected phase.    So at times we could have aircons and pool pump running hard, while the protected phase is idling along.   And also after loadshed that loadshed inverter draws a lot recharging battery on protected phase in addition to the loads on that phase running.

I got my hands on two 15kWh batteries and am considering (1) increasing solar and (2) replacing the SMA with a hybrid of 20-25 kW.   (I am on a 30A council three phase connection).

So question is with hybrid inverter, would it sort the solar + battery source better?    I imagine that at minimum if loads are unbalanced and battery is not yet full, it will satisfy the 3+1+1 loads and take the 1+3+3 first to battery.    Then when battery full, will it still export at lowest nett or would it be able to export 12-5 =7kw =2.33kW per phase?

Loaded question but which is the “best” hybrid in that size class - must have a phone/browser app for remote settings and monitoring?

Edited February 24, 20251 yr by macafrican
clarify

31 minutes ago, macafrican said:

replacing the SMA with a hybrid of 20-25 kW.

Why not consider, let's say 3 X 8kW inverters in 3 phase connection (1 inverter per phase) and them sharing your batteries?

11 hours ago, Kalahari Meerkat said:

Why not consider, let's say 3 X 8kW inverters in 3 phase connection (1 inverter per phase) and them sharing your batteries?

I doubt that is legal in terms of NRS rules.    NRS097 specifies unity export? 

20 hours ago, macafrican said:

I do export and I do get credit for it, but a weakness (besides being off in loadshed) is that the way the SMA works in my understanding is that it will only export at the lowest nett kW of the three phases.    So if solar is 4+4+4 and loads are 3+1+1 across phases, then it will export 1+1+1.

If this is the case, there has to be a meter or CTs at your main breaker. If you move this to the circuit of the SMA, you should "export" maximum.

You only have to install a hybrid inverter for your critical loads but I assume you have 48V batteries. You could install a 3 phase 12kW Sunsynk/Deye and connect the SMA to the Aux configured for micro inverter.

9 hours ago, macafrican said:

I doubt that is legal in terms of NRS rules.    NRS097 specifies unity export? 

Which section is that?

3 hours ago, Kalahari Meerkat said:

Which section is that?

I’d have to go look probably in NRS097 under shared LV connection.     Pretty sure the council SSEG rules also requires unity.

3 minutes ago, macafrican said:

Pretty sure the council SSEG rules also requires unity.

for home users that is difficult to do, I'd say. I looked at https://www.sseg.org.za/wp-content/uploads/2024/02/NRS-097-2-1-Published-2024.pdf briefly and can't see a unity rule. Unity would make sense if you ran a 3 phase alternator, but nor really for an inverter, never mind if its 3 units making up a 3 phase source, or a single 3 phase inverter, its like saying you have a 3 phase supply, now ensure your load is split 100% over the 3 phases, with a single or multiple 3 phase motors, no problem, but with other single phase consumers in the home, it isn't very likely to ever achieve balanced consumption...

4 hours ago, frivan said:

If this is the case, there has to be a meter or CTs at your main breaker. If you move this to the circuit of the SMA, you should "export" maximum.

You only have to install a hybrid inverter for your critical loads but I assume you have 48V batteries. You could install a 3 phase 12kW Sunsynk/Deye and connect the SMA to the Aux configured for micro inverter.

I am going to look at adding solar so thought may as well move all the solar onto the new 3p hybrid inverter.     There are CT on the council 3p incomer and the SMA has its internal current meters.

Part of my thinking is I keep my loads split as they are, and keep the smaller existing lifepo4 as backup on the protected phase since it is there already.     So essentially just add solar, add storage available for all three phases and for optimising how much solar I self-consume by allowing thee 3p storage to draw down before taking council when there is no loadshedding.   If my timing is bad and solar is bad and there is loadshedding, I would still be able to continue on the protected phase.

Because of my sometimes unbalanced loads, was just wondering about how hybrids handle this.    If there is no grid they can handle unbalanced phase loads, so was hoping they can also then juggle that if solar is 4+4+4 and battery is full and loads are 4+1+1, it exports 2+2+2 rather than how 3p SMA grid tied does 0+0+0.

1 minute ago, Kalahari Meerkat said:

for home users that is difficult to do, I'd say. I looked at https://www.sseg.org.za/wp-content/uploads/2024/02/NRS-097-2-1-Published-2024.pdf briefly and can't see a unity rule. Unity would make sense if you ran a 3 phase alternator, but nor really for an inverter, never mind if its 3 units making up a 3 phase source, or a single 3 phase inverter, its like saying you have a 3 phase supply, now ensure your load is split 100% over the 3 phases, with a single or multiple 3 phase motors, no problem, but with other single phase consumers in the home, it isn't very likely to ever achieve balanced consumption...

Getting loads per phase balanced by juggling which breaker is on which phase would be very tough mainly because the reason for unbalance varies so much.    Is the oven on, is the pool pump running, which rooms’ aircons are on, is the backup system recharging after loadshed, etc.

I am fairly certain my council does outright not allow having an inverter per phase.

did some more reading and all I can find under export unity is one may export active power only, voltage at allowable higher V than grid side for the current to go that direction and obv same frequency.

So I might have it wrong that the old SMA grid-tied inverter would at times export 0+0+0 if zero is what’s available on any one of the three phases.    That is how the installers described to me and one of their bosses helped write the first NRS097 way back when.

at moment what is the “best” three phase inverter?

8 hours ago, macafrican said:

Because of my sometimes unbalanced loads, was just wondering about how hybrids handle this.

To my knowledge the 12kW Deye can do 6kW on one phase (unbalanced). 

 

8 hours ago, macafrican said:

I am fairly certain my council does outright not allow having an inverter per phase

Whether they allow it or not, if most of your load is on one phase, it could be to your advantage to install a large single phase inverter on that phase. They should measure your consumption on each phase for usage.

7 hours ago, macafrican said:

export active power only

This is unity power factor. 

 

7 hours ago, macafrican said:

“best” three phase inverter

Probably high voltage Sunsynk or Deye (not 48V).

8 hours ago, macafrican said:

I am fairly certain my council does outright not allow having an inverter per phase.

well, if you do a bit of research you will find, that if you set up, for instance, 3 X 8kW Deye or Sunsynk inverters in 3 phase mode, one per phase, then you will find that this acts like a 24kW 3phase inverter, since there will be one master and 2 slaves and the output between them will be 120degrees apart, whether commercial power is there, or not...

1 hour ago, Kalahari Meerkat said:

well, if you do a bit of research you will find, that if you set up, for instance, 3 X 8kW Deye or Sunsynk inverters in 3 phase mode, one per phase, then you will find that this acts like a 24kW 3phase inverter, since there will be one master and 2 slaves and the output between them will be 120degrees apart, whether commercial power is there, or not...

Thanks Meerkat,

to date I only have experience of old days (2015) grid tied residential on LV feeder no storage and very large (over 1MW own transformer) with big storage.    This middle ground seems to be a minefield.

if this was your own house, would you go one 3p hybrid onto one large battery or do three single phase?    I do relay cancel my one 3p load already if eskom is off.

2 hours ago, frivan said:

To my knowledge the 12kW Deye can do 6kW on one phase (unbalanced). 

 

Whether they allow it or not, if most of your load is on one phase, it could be to your advantage to install a large single phase inverter on that phase. They should measure your consumption on each phase for usage.

This is unity power factor. 

 

Probably high voltage Sunsynk or Deye (not 48V).

Thanks, Sunsynk and Deye are what shows up best rated, if one can go by ratings 😕

I reckon one 3p that can jump and side step in software is better than three single phase trying to connect to one solar array and also at same time run three unbalanced loads with ability to export.   KISS

13 hours ago, macafrican said:

if this was your own house, would you go one 3p hybrid onto one large battery or do three single phase?

We were single phase here, so stayed that way, however, we run a pump at the canal for water, this might have been nice if 3 phase had been available, a physically smaller pump... but our daily consumption here is around 30kWh/day and climbing, so not huge and I have no 3 phase consumers here, so single phase it is...

If you have a lathe (3 phase) or pumps that are 3 phase, then you may want to stick to it, but, if you only have single phase consumers, then maybe its time to convert to single phase, from the Eksdom/Commercial power providers end it may save a bit of the fixed fees, only problem may be, what is the cable size per phase and capable of carrying, you'd probably want 60 to 80A for that single phase feed from the commercial side.

As for single 3 phase unit vs one unit per phase... if you were looking at 20 to 25kW, which you stated, you could get 2 X 12kW 3 phase units in parallel to give you 24kW in total, or 3 X 8kW units in 3 phase configuration to also give you 24kW in total, I suspect the 3 X 8kW units would be less expensive than the 2 X 12kW 3 phase units, but I haven't checked... if you were to convert to single phase down the line, the 3 X 8kW units would just parallel up and give you 24kW single phase... the 2 X 3 phase units however... will not likely do that and will always be 3 phases...

Also consider the amount of MPPTs

Sunsynk 8 kWhas 2 MPPTs

So three of them would give you 6

The 12 kW three phase has 2 MPPTs

One of the MPPTs has about twice the capacity of the other one 

So in total for two of these inverters, you have 4 MPPTs

 

So if you need multiple strings at different angles, then the three 8 kW will be better 

Also you need to look at maximum pass through capacity 50 Amp for the 8 kW and maximum inverter capacity of around 35 Amps 

 

With two 12 kW three phase in parallel each has maximum pass through capacity of of one is 40 Amps per phase, so that gives you 80 Amp for the two . The inverter capacity is up to around 26 Amps max on a single phase 

So the two 12 kW will be the same as the  three 8 kW units on inverter capacity 

 

 

Edited February 26, 20251 yr by James 1