Having offgrid solar installation installed in outbuilding to supply house switchboard but also with grid infeed at house. (Australia)

[craka]

Note this is in Australia, and I'm trying ascertain whether what I would like to do is reasonable/acceptable within Australian wiring rules.
I have a rural property where the existing switchboard with incoming grid power is located at the house, but I am planning on having offgrid solar setup with grid supply only as backup.
I am building a shed which will be orientated with roof orientated North for solar panel installation and will house inverter and battery, planning on using 2x Growatt SPF 5000 ES and a SEPLOS battery. My queries are about whether it is okay to run the grid power across from its current location at the house to the inverter at the shed and than back to supply the load circuits in the house which is the same switchboard location. I've tried mocking up a pretty average diagram in paint. On a side note what to other use to draw there diagrams up that are free to use?

 

[wattmatters]

I pretty much have done this with the exception that my kit is located near the main circuit board.

The thing I have is a transfer switch so that I can flip the house back to run from the grid if needed.

My queries are about whether it is okay to run the grid power across from its current location at the house to the inverter at the shed and than back to supply the load circuits in the house which is the same switchboard location.

There is nothing inherently wrong with it, you just need to make sure the wire is of a sufficient gauge to not experience much voltage drop.

Can use this as a guide:

Cable Size Calculator AS/NZS 3008

Cable size calculator for current rating, voltage drop, loop impedance, earth cable and short circuit, based on Australia and New Zealand standard AS/NZS 3008.

www.jcalc.net

 

[craka]

I pretty much have done this with the exception that my kit is located near the main circuit board.

The thing I have is a transfer switch so that I can flip the house back to run from the grid if needed.


There is nothing inherently wrong with it, you just need to make sure the wire is of a sufficient gauge to not experience much voltage drop.

Can use this as a guide:

Cable Size Calculator AS/NZS 3008

Cable size calculator for current rating, voltage drop, loop impedance, earth cable and short circuit, based on Australia and New Zealand standard AS/NZS 3008.

www.jcalc.net

Thanks Wattmatters, cheers, I just hadn't been sure about shooting out of the house switchboard across to shed and than back to the same switchboard at house. The inverter I plan on using, the growatt spf 5000 es is offgrid in that it can only supply AC out on the load side and not export back to the grid so I don't think the transfer switch is necessary and the inverter is on the CEC approval list.

Though I'd like to know if the neutral from the AC input side of the inverter has continuity though to the AC output side and remains so in all modes. If does not is it acceptable to bond the neutral from input to output to assure that neutral is not disconnected to maintain bond back to MEN?

 

[wattmatters]

The inverter I plan on using, the growatt spf 5000 es is offgrid in that it can only supply AC out on the load side and not export back to the grid so I don't think the transfer switch is necessary

With the transfer switch I have supplying the house essential loads panel, the two inputs to the transfer switch are the grid supply and the off-grid supply (AC output from the off-grid inverter).

That way if the off-grid supply goes down (e.g. it has a problem or you want to do some work on it) then you can flip the home over to operate directly from the grid supply. The grid is the backup.

If your only option for using grid power means it has to pass it through the off-grid inverter then you have a single point of failure (and a power throughput limit) I would not be comfortable with.

Also, I have some loads which are not supplied by the off-grid inverter because their power draw is a little high. Ducted aircon, oven, induction stove and water heater for instance. The inverter could manage them individually but my system is supplying two dwellings and one large outbuilding so I can't risk the reasonable possibility they may be needed at the same time.

So I have an essential loads panel the transfer switch supplies, and the "non-essential" circuits are powered by grid supply only, including the AC input to the off-grid inverter.

Though I'd like to know if the neutral from the AC input side of the inverter has continuity though to the AC output side and remains so in all modes. If does not is it acceptable to bond the neutral from input to output to assure that neutral is not disconnected to maintain bond back to MEN?

Not my gig really so I would not give advice on that. One for a licensed sparky.

 

[craka]

With the transfer switch I have supplying the house essential loads panel, the two inputs to the transfer switch are the grid supply and the off-grid supply (AC output from the off-grid inverter).

That way if the off-grid supply goes down (e.g. it has a problem or you want to do some work on it) then you can flip the home over to operate directly from the grid supply. The grid is the backup.

If your only option for using grid power means it has to pass it through the off-grid inverter then you have a single point of failure (and a power throughput limit) I would not be comfortable with.

Also, I have some loads which are not supplied by the off-grid inverter because their power draw is a little high. Ducted aircon, oven, induction stove and water heater for instance. The inverter could manage them individually but my system is supplying two dwellings and one large outbuilding so I can't risk the reasonable possibility they may be needed at the same time.

So I have an essential loads panel the transfer switch supplies, and the "non-essential" circuits are powered by grid supply only, including the AC input to the off-grid inverter.


Not my gig really so I would not give advice on that. One for a licensed sparky.

True, I'll have all loads run from installation, hence will be using 2 inverters to increase power output. Will have just one split A/C , and induction cooktop as heavy loads, will be using standalone water heater and wood heater for heating. But I do see your point about using a transfer switch pretty much as a bypass switch from the inverter to connect loads direct back to grid.

 

[wattmatters]

But I do see your point about using a transfer switch pretty much as a bypass switch from the inverter to connect loads direct back to grid.

Yeah, I'd be giving that some serious consideration. Treat the grid as an enormous backup generator. Being single phase it's not all that complicated for a sparky to wire up. Mine is a 3-phase supply so the wiring is pretty tricky.

 

[Ghosty]

Hi,
I am no expert, and this is not legal advice. I am going through this at the moment. I have two points of comment.
1. There needs to be segregation between the Grid Supply and the inverter supplied appliances in the switchboard. Most metal DB's (distribution Board) on the front of the home don't really allow enough space for this in Aus( 2 x rows of 9 poles, so if its 3 phase you get 3 breakers and the row is full). I have had to put a second DB on the other side of the wall. All circuits fed from the Inverter go into this second DB. The changeover switch also goes in this second DB. So the Grid is in one DB (main DB or switch Board) and all inverter or alternative grid supply is in the second....But you may have space in your DB, make sure its well labeled.

2. MEN, My inverter has a Neutral Earth Relay(Dont know about the growatt, ask there help line possibly or in the docs?). Typically the N/E passes through the inverter when the AC is connected, should the power disconnect / loose the grid. The inverter opens an internal double pole relay to the grid, and then closes the internal MEN or neutral earth realy creating the MEN for the system being held up by the inverter. You are not allowed to multiple MEN's is my understanding. So with that said I would expect that you can not tie the grid Neutral to the Output neutral of the Inverter. I think even AS/NZS4777 says something along the lines of all active conductors must be disconnected. The neutral counts as an active conductor.

Hope this clears the muddy water....

 

[wattmatters]

1. There needs to be segregation between the Grid Supply and the inverter supplied appliances in the switchboard. Most metal DB's (distribution Board) on the front of the home don't really allow enough space for this in Aus( 2 x rows of 9 poles, so if its 3 phase you get 3 breakers and the row is full).

I put in (well my sparky did) a separate "essential loads" panel under the existing MCB:



The transfer switch is inside the MCB. There is also one other sub-main supplied by the off-grid which is still inside the MCB. All the circuits are all labelled accordingly.

We used links to group the circuits so that it would be easy to add or change which circuits were on the off-grid side or which were grid-only. Else there are too many wires to fit inside the transfer switch terminals.