Have 2 dwellings and 2 inversters. A single eskom supply provides the property.

The one inverter is a 8kva with 2 hubble batteries and an array of solar panels. Used as backup power to the main house

The other inverter is a 5kva with no batteries and an array of solar panels. Used as a grid tied solution with no export to reduce power consumption.

 

Challenge: when power goes off, grid tied solution dies.

 

Want to know: Can I connect the 8kva aux to the grid from the 5kva for it to leverage power from the main house till batteries are depleted till 60%. Settings I am thinking will do the trick

8kva - zero export, priority load, aux, 60%, batt config (CT coil next to the main inlet of the house allowing it to bleed over to the internal property to feed excess power)

5kva - zero export, priority load, gen (not connected, no battery (CT coil at the DB before it feeds back to the main house or inverter as indicated)

 

attached diagram for info

I believe you will need another battery for this to work.

10 minutes ago, P1000 said:

I believe you will need another battery for this to work.

Hi there

SunSynk apparently supports grid tied that you don't need a batt. Whilst connected to Eskom and the sun is out, it uses less power from grid when pulling from panels. So want to make the aux the grid feed. 

 

It is for an office at home that will only operate during the day time. Want to ensure that the inverter doesn't go off during loadshedding and I enjoy the benefits of the sun powering the lights, chargers, equipment. 

 

Don't know if this falls in their micro inverter setup perhaps to powerultiple? Also asked sunsynk support and will feedback to forum if any responses. 

 

Happy to get another battery, but an expense that is not needed in this setup for the intended purpose. 

38 minutes ago, francoisj1 said:

Also asked sunsynk support and will feedback to forum if any responses. 

That would be good. There is a slight chance that it might support that, but it's unlikely. The control algorithm to do that with the Sunsynk topology would be quite challenging. With a low frequency inverter it is easier.

5 minutes ago, P1000 said:

That would be good. There is a slight chance that it might support that, but it's unlikely. The control algorithm to do that with the Sunsynk topology would be quite challenging. With a low frequency inverter it is easier.

Thanks a mil for the help and guidance. 

 

Currently they running from grid individually with said setup. Reason for 2nd inverter is that the home office runs fridges, some heat loads at winter and a bunch of electrical equipment. 

 

Just looking to "save" the bucks to not spend it for another battery or to replace the current 2nd inverter from 5kva with a 8kva to parralel them up. 

 

Seems i am in for a pretty penny either way if this can't work ;(

 

 

 

5 minutes ago, francoisj1 said:

Seems i am in for a pretty penny either way if this can't work ;(

I think the way your drawing is laid out and your needs as described, I would think it should work, either way, if I were in your shoes, I would just try it, disconnect the 5k from the grid and run a connection to the AUX on the 8k unit and set the 8k unit with the relevant parameters. If its a daytime outage, then the 5k should keep on going with, mostly its solar providing the power and the 8k providing the frequency and Voltage that the 5k should utilise on its output and possibly a bit of power as well, assuming the 5k units' solar isn't enough for the load, either way, I would think it should work and see no reason why it should not.

So, I was thinking about this exact thing in another scenario.

My non-professional understanding is that for a grid tie to work it needs a reference frequency to sync to, that can be provided by the grid, a generator or even another inverter. 

Couldn't you just connect the 5k on the load side of the 8k and then it will use the 8k's frequency for reference (in either island or grid attached mode)? You would need to ensure that the 5k's CT clamp is connected to the load side of the 8k inverter so that it can't back feed into the8k, but the 5k could then offset all the loads, not just the ones in the 2nd dwelling. 🙂  

1 hour ago, francoisj1 said:

SunSynk apparently supports grid tied that you don't need a batt. Whilst connected to Eskom and the sun is out, it uses less power from grid when pulling from panels. So want to make the aux the grid feed. 

Definitely supports grid-tied, have a friend running in grid tied mode and generating close to 70kw/hr a day on his 8k, no batteries. 

Search around, I recall seeing a YT video from Keith from Sunksynk where he did this: use a second Sunsynk inverter as the "micro-inverter," AC-coupling it to the AUX port of a first inverter. Must just be careful not to exceed input size. Try it.

23 minutes ago, Kalahari Meerkat said:

I think the way your drawing is laid out and your needs as described, I would think it should work, either way, if I were in your shoes, I would just try it, disconnect the 5k from the grid and run a connection to the AUX on the 8k unit and set the 8k unit with the relevant parameters. If its a daytime outage, then the 5k should keep on going with, mostly its solar providing the power and the 8k providing the frequency and Voltage that the 5k should utilise on its output and possibly a bit of power as well, assuming the 5k units' solar isn't enough for the load, either way, I would think it should work and see no reason why it should not.

 

Thanks for response. 

 

Info omitted from my drawing that will aid in discussion

 

8kva has 12x 550w (6600w) strung up 6 x 6

5kva has 12x 450w (5400w) strung up 6 x 6

 

 

22 minutes ago, francoisj1 said:

Info omitted from my drawing that will aid in discussion

 

8kva has 12x 550w (6600w) strung up 6 x 6

5kva has 12x 450w (5400w) strung up 6 x 6

you mean 6S + 6S 🙂 in both cases... this is less relevant to the whole scenario you did state that both inverters had solar panels and that's the important part, I'm guessing your grid feed per month is pretty low, since the 8k inverter can probably peak around 6kW in solar production and let's say average 5kWh times 8 hours, then it should be potentially generating 40kW for the day and the 5kW unit lets say around 4k5Wh times 8 hours, potentially 36kW power produced for the day, presumably a lot of the power is actually not used and thus not produced, but my guess is that, depending on the clouds/weather, you probably aren't using very much from the grid at all, except after hours/very cloudy days...

Running the 5kW, on the load/output side of the 8kW would be of no real benefit, since then you can't cut it off at a predetermined battery level, either way it won't be able to feed power back, since the Aux port is either power in or power out on the 8k and not both at the same time and the output side on the inverters do not expect to have power shoved in either, so whatever excess power the 5k might be able to produce during sunlight hours will be going to waste... time to look at where else you can feed power form the 5k's Aux port or output side, when the sun is blessing us with free electrons...

1 hour ago, Sc00bs said:

My non-professional understanding is that for a grid tie to work it needs a reference frequency to sync to, that can be provided by the grid, a generator or even another inverter. 

It's not quite that simple - as the grid tied is by law required to only generate power at a power factor of 1 (with a little bit of margin). This means that all of the reactive power gets offloaded to the upstream inverter. This might work 99% of the time if both inverters are loaded, but could potentially result in an expensive paperweight or 2. That is why it is a good idea to check with the manufacturer first.

50 minutes ago, Kalahari Meerkat said:

you mean 6S + 6S 🙂 in both cases... this is less relevant to the whole scenario you did state that both inverters had solar panels and that's the important part, I'm guessing your grid feed per month is pretty low, since the 8k inverter can probably peak around 6kW in solar production and let's say average 5kWh times 8 hours, then it should be potentially generating 40kW for the day and the 5kW unit lets say around 4k5Wh times 8 hours, potentially 36kW power produced for the day, presumably a lot of the power is actually not used and thus not produced, but my guess is that, depending on the clouds/weather, you probably aren't using very much from the grid at all, except after hours/very cloudy days...

Running the 5kW, on the load/output side of the 8kW would be of no real benefit, since then you can't cut it off at a predetermined battery level, either way it won't be able to feed power back, since the Aux port is either power in or power out on the 8k and not both at the same time and the output side on the inverters do not expect to have power shoved in either, so whatever excess power the 5k might be able to produce during sunlight hours will be going to waste... time to look at where else you can feed power form the 5k's Aux port or output side, when the sun is blessing us with free electrons...

 

Good insight thanks. And thanks for the highlight in the panels 6s + 6s is correct. And all your assumptions on the power generation from panels are correct too. Little power from the grid is used as I only use power at night. I leave the battery to float at 85% to make sure there is minimal use and for it to be preserved for power outages. 

Right now the only usage from Eskom is at night. 

 

The power will be "dumped" that cannot be used as I don't want to push back to the grid by principle. Whatever is not stored in the battery on the 8kva is surpluses that the 8kva and 5kva will then use what is needed and purge the rest. 

Power will travel ine way from Eskom to 8kva, then one way from 8kva to 5kva, the rest will purge, the aux on 5kva will be voided unless I get another battery, then I will connect the gen to it and change parameters to charge the batt at night when it depletes to keep that setup always on (in compliment with the feed from the 8kva when aux is above 60%)

 

As a backup, there is a change over switch in generator too that disconnects the system into an island to run the 6500w generator only to supply office. 

5 hours ago, GreenFields said:

Search around, I recall seeing a YT video from Keith from Sunksynk where he did this: use a second Sunsynk inverter as the "micro-inverter," AC-coupling it to the AUX If port of a first inverter. Must just be careful not to exceed input size. Try it.

I understand that if you want the Sunsynk to be able to control production on the Grid Tie then it has to be connected to the Aux port. 

But if you have a CT to stop back feeding into the Sunsynk 8kw then can't you just connect it downstream of the Sunsynk 8k and it will control itself? 

7 minutes ago, Sc00bs said:

I understand that if you want the Sunsynk to be able to control production on the Grid Tie then it has to be connected to the Aux port. 

But if you have a CT to stop back feeding into the Sunsynk 8kw then can't you just connect it downstream of the Sunsynk 8k and it will control itself? 

 

Hi Sc00bs, 

 

That's the idea and the thought, been getting good feedback on the forum. Seems exactly as you described is possible. 

 

If I think about it, the AUX is just another "GRID" feed where my 8kva will act as "Eskom"

 

Regards 

13 minutes ago, francoisj1 said:

where my 8kva will act as "Eskom"

exactly, *including* "load shedding" at the appropriate battery charge level, to be set by you...

4 hours ago, Kalahari Meerkat said:

Running the 5kW, on the load/output side of the 8kW would be of no real benefit, since then you can't cut it off at a predetermined battery level, either way it won't be able to feed power back, since the Aux port is either power in or power out on the 8k and not both at the same time and the output side on the inverters do not expect to have power shoved in either, so whatever excess power the 5k might be able to produce during sunlight hours will be going to waste... time to look at where else you can feed power form the 5k's Aux port or output side, when the sun is blessing us with free electrons...

I disagree, enabling the 5kw to power loads in the 8kw Inverters house allowing the 8kw inverter to put more of it's PV power into it's batteries instead of powering load. Maybe not a big deal on high production days, but when you have lower production days it would mean better utilisation of your available resources. 

12 minutes ago, Kalahari Meerkat said:

exactly, *including* "load shedding" at the appropriate battery charge level, to be set by you...

You would need to connect the 5kw onto the essential side on the 8kw, only thing then is that the 2nd dwelling will be running of the 8kw batteries if there is no sun as well. 

Maybe  perhaps have a smart switch to disconnect the load when there is load shedding at night? Not sure how smart switches would feel about power going through them the wrong way, anyone? 

@francoisj1 Would speak to Sunsynk locally first to find out how they feel about setting it up like that before I would do it just to make sure you don't have any fire/smoke 🙂 

1 hour ago, Sc00bs said:

I disagree, enabling the 5kw to power loads in the 8kw Inverters house allowing the 8kw inverter to put more of it's PV power into it's batteries instead of powering load.

You can disagree all you like, but if you think about it, then the CT for the 5kW would have to sit at the output of the 8kW unit, I suspect cabling wise that this will be a distance/cabling issue that may be less than a cinch to overcome.

 

1 hour ago, Sc00bs said:

You would need to connect the 5kw onto the essential side on the 8kw

Nope, onto the Aux side of the 8kW

 

16 minutes ago, Kalahari Meerkat said:

You can disagree all you like, but if you think about it, then the CT for the 5kW would have to sit at the output of the 8kW unit, I suspect cabling wise that this will be a distance/cabling issue that may be less than a cinch to overcome.

 

Nope, onto the Aux side of the 8kW

 

 

Current thoughts and conclusions from the discussion comments. 

 

Over and above the fact that I need to check this with local Sunsynk support to avoid an expensive fireworks show... 

 

Cabling wise, I will terminate 5kva connected CT at the mains feed at the office to ensure there is no feedback to the 8kva. This is a very short cable run from inverter tot the DB next to it.

 

I feel the mains feed on the 5kva will need to be supplied by the Aux from 8kva so I can manage battery levels on low productivity days and "loadshed" the office from the 8kva feed. 

 

Make sense? 

 

1 hour ago, Kalahari Meerkat said:

You can disagree all you like, but if you think about it, then the CT for the 5kW would have to sit at the output of the 8kW unit, I suspect cabling wise that this will be a distance/cabling issue that may be less than a cinch to overcome.

 

Nope, onto the Aux side of the 8kW

 

@francoisj1 How far apart are the residences? 

@Kalahari Meerkat you are 100% correct regarding the CT coil position for the 5kw inverter if you want it to run loads from both residences.  I have however heard of CT Coil cable length being up to 20mtr's without an issue so not sure what the site looks like but might be an option and not sure what the cable length limits are using twisted pair cabling. Otherwise you could have the CT Coil on the power coming into the second residence from the essential side of the 8kw. You will then be able to have power in the 2nd residence during load shedding and being offset during the day with power from the 5kw grid-tied inverter. 

Regarding the option of connecting the 5kw to the Aux port on the 8kw, I would assume that would mean you would have to put in another power cable to the 2nd residence to take the power back from the 8kw to the house? Also you would be limited to a max power of 3.5kw-4kw from the 5kw inverter if you are using the Aux port according to Sunsynk. 

 

1 hour ago, francoisj1 said:

I feel the mains feed on the 5kva will need to be supplied by the Aux from 8kva so I can manage battery levels on low productivity days and "loadshed" the office from the 8kva feed. 

 

Make sense? 

Hmmmm not really - If you are going to use the Aux port as a non-essential output port then your grid tie will not work when there is load shedding as the non-essential side is disconnected when there is load shedding.

If you are going to use the Aux port as an input port you are going to need to run another cable from the 8kw essential load to the 2nd residence as I don't think the cable can be input and output.  Not sure ❓ You will also be limited to 3.5-4kw input from your grid-tie.

Other option is to feed your 5kw from the essential load side of the 8kw. Connect your 8kw to Home Assistant and using a smart switch you can "load shed" the 2nd residence when conditions dictate i.e. low solar production, Battery SOC, Time of Day etc using automations in Home Assistant.  

3 hours ago, francoisj1 said:

Make sense? 

Yes perfectly...

1 hour ago, Sc00bs said:

Hmmmm not really - If you are going to use the Aux port as a non-essential output port then your grid tie will not work when there is load shedding as the non-essential side is disconnected when there is load shedding.

really? I'm not using my Aux port, but did initially test it and without grid feed power did come out of the Aux port... has this changed in newer firmware? My 5kSS we put in, in July 2020...