180W consumption of 2x Sunsynk 5kW while running on grid ???

[wolfandy]

Hi all

I know that the question regarding the self-consumption of the Sunsynk has been posted here a number of times - and I myself have reported it at 45W. This is what my SolarAssistant is reporting for each inverter:

However, the other night I noticed something different (and quite confusing to me). I had depleted my batteries to my changeover point and the inverters had switched over to running on grid. I was expecting a draw from my batteries of around 90W for my 2x inverters - however, my consumption was around 180W:

 

Does anyone have a similar experience? And/or an explanation? 180W for self-consumption seems high to me

[Scubadude]

1676+182+1-1744 = 115W. Sounds about right for two inverters I'd say. 

[wolfandy]

4 hours ago, Scubadude said:

1676+182+1-1744 = 115W. Sounds about right for two inverters I'd say. 

Thanks - but I have to admit that I still do not understand the high draw from the batteries. I could understand the difference between the reported 2x45W and the 115W through conversion factors, inaccuracies, etc. But even from the 115W to the 180W is still a sizeable gap. Does that mean that the Sunsunk still draws from battery for load usage even though it is running on grid?

[Antonio de Sa]

5 minutes ago, wolfandy said:

Thanks - but I have to admit that I still do not understand the high draw from the batteries. I could understand the difference between the reported 2x45W and the 115W through conversion factors, inaccuracies, etc. But even from the 115W to the 180W is still a sizeable gap. Does that mean that the Sunsunk still draws from battery for load usage even though it is running on grid?

I have two Growatt inverters and they do exactly the same, they continually pull +_ 90w each from the battery.  ( no load loss )

 

[Coulomb]

14 hours ago, wolfandy said:

And/or an explanation? 180W for self-consumption seems high to me

Not an explanation, but a guess / speculation: this seems like a missed target to me. The inverters (as in the DC-AC converters) are presumably running, ready to take over in an instant if the grid falls away. So the inverter is pushing against the grid, which is connected to the load, and it's presumably aiming for zero power output. But it's missed that zero target a little, pulling a little from the battery. That's why the load is 1744 while only 1676 comes in from the grid. The difference is 68 W, out of 1744, 4%. I'll assume that the 1W from solar is a measurement error. The battery sees a load of 182 W, so 182 - 68 = 114 W of that is losses. Most of that is idle power, but a tiny bit is I²R losses on the 68 W transfer from battery to load. Call it 4 W at a wild guess, then you have 110 W from each inverter as idle load/loss, or 55 W per inverter. Granted, that's still 25% more than you expect. It's likely that the reported 4 significant digits of power isn't as accurate as that implies. Also, loads are fluctuating all the time. I wonder if they calculate the power factor accurately too. I know that the Axperts actually do an RMS power calculation.

If I'm right, then at least the mystery has been reduced from 68 W to 20 W.

I wonder if they somehow deliberately aim to "miss the zero target". And/or whether improved firmware could improve on this.

 

[Antonio de Sa]

46 minutes ago, Coulomb said:

Not an explanation, but a guess / speculation: this seems like a missed target to me. The inverters (as in the DC-AC converters) are presumably running, ready to take over in an instant if the grid falls away. So the inverter is pushing against the grid, which is connected to the load, and it's presumably aiming for zero power output. But it's missed that zero target a little, pulling a little from the battery. That's why the load is 1744 while only 1676 comes in from the grid. The difference is 68 W, out of 1744, 4%. I'll assume that the 1W from solar is a measurement error. The battery sees a load of 182 W, so 182 - 68 = 114 W of that is losses. Most of that is idle power, but a tiny bit is I²R losses on the 68 W transfer from battery to load. Call it 4 W at a wild guess, then you have 110 W from each inverter as idle load/loss, or 55 W per inverter. Granted, that's still 25% more than you expect. It's likely that the reported 4 significant digits of power isn't as accurate as that implies. Also, loads are fluctuating all the time. I wonder if they calculate the power factor accurately too. I know that the Axperts actually do an RMS power calculation.

If I'm right, then at least the mystery has been reduced from 68 W to 20 W.

I wonder if they somehow deliberately aim to "miss the zero target". And/or whether improved firmware could improve on this.

 

@Coulomb Thanks for the explanation, so what you say if I select my inverter to utility that will not happen. Because on SUB I can clearly see pulling about 2 Amps from the battery. see attached at 21:40 I switched the inverters to SUB and from there onwards the load is supplied by the grid

[system32]

I have a single SunSynk 8k with the full house connected to essential.
The SunSynk is set to trickle feed 20W from grid to prevent meter reversal.
I have a separate meter which records that grid directly (before SunSynk) and it shows ~65W.

65W-20W = 45W - seems to match what Solar-Assistant shows.

[wolfandy]

2 hours ago, Antonio de Sa said:

Because on SUB I can clearly see pulling about 2 Amps from the battery. see attached at 21:40 I switched the inverters to SUB and from there onwards the load is supplied by the grid

Thanks. Happy to see that I am not the only one experiencing this

1 hour ago, system32 said:

The SunSynk is set to trickle feed 20W from grid to prevent meter reversal.
I have a separate meter which records that grid directly (before SunSynk) and it shows ~65W.

65W-20W = 45W - seems to match what Solar-Assistant shows.

Thanks. Agree to the trickle feed. But that should not be necessary when the inverter is running on fully on grid, or?

And in your case, is the 45W taken from grid?

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To make things even weirder, I just noticed this in my charts:

So in the first window that the inverter was running on grid, it pulled the +/- 180W from the batteries. Then it reached my next setpoint and ran on batteries again for a while before again switching back to grid (next setpoint). But the 2nd time running on grid, it pulled between 0W and 5W from the batteries.

Any thoughts on this inconsistent behavior?