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3 phase supply but no 415v connections

Posted: Thu, 29 Aug 2019, 12:26
by T1 Terry
I have had an inquiry about setting up a house off grid, but they want to remain with grid back up for 12 mths just to certain they have enough solar and battery capacity.
The switch board appears as though 3 phase power is supplied to the premises, it has a 3 phase back to grid inverter that unfortunately does not have a connection for battery back up. Yet there are no 3 phase appliances, just 3 separate single phase supplies.
I can fit 3 inverters, but do I need to fit the 3 phase linking part if there is no actual 3 phase appliances?
I expect I could get the local sparky to wire the three single phases into one single phase supply point, but if I was to use one phase from the 3 phase supply to power the mains side of the inverter would that cause problems?
The mains will only be there as a "just in case" thing rather than a generator so the owners can get a better idea of how much power they actually use/need.
The buy in power is 38 cents kWh and the feed in is 10 cents, so a real rip off there, but the real issue is power failures, 8 at least in the 8 mths they have owned the place. Their options are either a back up generator or battery/inverter and use the solar they are paid 10c for to supply the grid power that costs them 38c + GST. In the end they hope to ditch the grid completely and save the $1 per day supply charge and other associated tacked on charges and the 10% GST added to the whole lot.

T1 Terry

Re: 3 phase supply but no 415v connections

Posted: Thu, 29 Aug 2019, 12:35
by jonescg
The vast majority of three phase off-grid places use three separate inverters, one for each phase, and a data link for synchronisation between all three. The link between them usually comes standard, and would be totally worth doing given the low additional cost.

That said, if they have no three phase appliances, and aren't likely to in the future, you might be better off setting them up with a single phase inverter and using one of the three phases on the grid side as a back-up. Depends on their power needs of course.

Re: 3 phase supply but no 415v connections

Posted: Thu, 29 Aug 2019, 13:20
by T1 Terry
The benefit of using 3 x single phase inverters is each would have an idle shut down capability where it wouldn't if they were linked to product 3 phase or paralleled to increase the capacity, so possibly not as much loss on standby.
The down side is the need for 3 inverters rather than 1 or 2 inverters paralleled depending on the peak load. The inverter can produce 5kva continuous and 10kVa for 5 secs for any big start up loads. This means 2 in parallel would have a continuous 10kVa and a 20kVa peak for 5 secs. I would imagine that would be plenty for their needs, so a continuous 15kVa spread across 3 phases would probably be overkill and an addition expense that wasn't really needed.

Of course, the 3 inverters, one for each phase would be the easiest to integrate into the system without a heap of rewiring. I could then split the solar into 3 parallel series groups, one for each inverter.

T1 Terry

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 14:19
by T1 Terry
OK, I've found yet another option, the 3 phase MPI hybrid 10kW inverter/charger/solar controller/grid tie unit all thrown into one box. One of these things https://www.mppsolar.com/v3/mpi-hybrid-series-2/ They say these units can be paralleled, but a house that required more than 10kW continuous and 16kW if the grid was available is rather unlikely isn't it?
Now, has anyone had any bad reports about these units? They are from the same people who are selling the various PIP inverters mentioned in other threads.

T1 Terry

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 14:26
by jonescg
Terry - that was the inverter I was quite seriously considering for my home. As long as it can be installed inside and/or under cover it looks OK. AS4777 approved, but might take some convincing of the utility that it's OK to install.

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 15:38
by T1 Terry
It would be replacing the grid tie 3 phase inverter that is already there. I think as long as the system remains at 5kW of solar and the battery does not try to feed back into the grid, there shouldn't be a problem. Would we even have to tell them?
Now I'm back into the area I know bugger about, 3 phase load sharing. This 3 phase inverter is 10kW, is that a 3333w per phase limit, or can it shift output from one phase to another as required to a max of 10kW?

T1 Terry

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 16:00
by jonescg
It depends on the setting, but you can choose zero export, or at the very least, maximise self consumption. It would take solar energy and meet immediate loads, then with whatever spare power is left it will charge the battery. When the battery is full, it will divert solar to the grid. If will do this down all three phases, shared amongst them.

I've not played with one, just my interpretation of the users manual...

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 17:34
by brendon_m
T1 Terry wrote:
Fri, 30 Aug 2019, 15:38
Would we even have to tell them?
In WA, Western power want to know the serial number of the inverter so if you change it technically you're meant tell them(and they may refuse the unit). But it's not like they are going to come round and check the number as long as you don't start exporting at midnight which might raise questions.

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 20:09
by coulomb
T1 Terry wrote:
Fri, 30 Aug 2019, 15:38
This 3 phase inverter is 10kW, is that a 3333w per phase limit, or can it shift output from one phase to another as required to a max of 10kW?
It's 3.33 kW per phase, so no one phase can be transferring more than 3.33 kW at any one time (with allowance for short term overloads).

However, within those limits, I speculate that it could balance things out a bit. Suppose phase one had the most load, and phase 3 happened to have the most solar at the moment. It could direct phase 3 to charge the battery more, and phase one to take from the battery the same amount, effectively transferring power from one phase to another without wearing out the battery (the battery is more or less a 50 V bus for transferring power in this case). The utility sees a nicely balanced load, so your neutral cable sees low current, and you're not pushing any of the cables in street (all the way back up the distribution system) more than the others, so you're a model citizen, despite your loads actually being quite unbalanced.

Whether I've got the above right, and if I have whether it actually bothers to do this, I don't know. It's a lot of juggling to do, but it seems to me that it has the ability to do it.

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 21:30
by antiscab
brendon_m wrote:
Fri, 30 Aug 2019, 17:34
T1 Terry wrote:
Fri, 30 Aug 2019, 15:38
Would we even have to tell them?
In WA, Western power want to know the serial number of the inverter so if you change it technically you're meant tell them(and they may refuse the unit). But it's not like they are going to come round and check the number as long as you don't start exporting at midnight which might raise questions.
our meters here in WA are fairly dumb - I haven't even heard of one that's not still manually read

on my meter, export volumes are metered in specific time bands (I'm on the old smart power, so 9pm - 7am is off peak, 7am - 9pm weekends is cheap, and the rest swaps between being cheap and expensive depending on the season)

in summer I regularly export off peak, mainly between 5am and 7am, when the sun starts to hit my south facing array.
Western power has know means to know if I'm actually exporting at midnight instead, they just know I've exported something between 9pm and 5am on at least one day in the billing cycle.

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 21:39
by brendon_m
I have a mate who works at Western power and even he didn't think the readings where more granular then peak, shoulder, off peak but If I log onto the synergy website I can look at power usage in 30min increments. I believe it's still manually read but they obviously download logs.
I don't know if all the smart meters can do this or only the newest.

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 21:44
by antiscab
holy moly
what sort of meter do you have?
would you mind posting a picture (feel free to block out your NMI)

Re: 3 phase supply but no 415v connections

Posted: Fri, 30 Aug 2019, 21:48
by brendon_m
Scrap that, I have maximum dardiness. I can look at power usage up to yesterday, so unless I was just read and they're super efficient (doubtful), my meter must phone home constantly
Screenshot_2019-08-30-21-45-20-446_com.android.chrome.png
Screenshot_2019-08-30-21-45-20-446_com.android.chrome.png (125.53 KiB) Viewed 614 times

Re: 3 phase supply but no 415v connections

Posted: Sat, 31 Aug 2019, 05:47
by 4Springs
brendon_m wrote:
Fri, 30 Aug 2019, 21:48
Scrap that, I have maximum dardiness.
Screenshot at 2019-08-31 07-45-22.png
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Re: 3 phase supply but no 415v connections

Posted: Sat, 31 Aug 2019, 11:54
by T1 Terry
Hmmm..... that 3 phase hybrid inverter won't do the job if it can only provide 3.3kW because there is a single phase monster ducted air con unit that can suck a peak 26.4 amps according to the specs label. 3.3kW is barely enough to feed a 15 amp supply single phase.

The next option seems to be this unit https://www.ebay.com.au/itm/MG-5000w-48 ... Sw8b9bmylX with a parallel kit and the 3 phases on the house returned to a single phase. This way the inverters has a peak load capacity of 20kW and continuous of 10kW and a power factor of 1.

T1 Terry

Re: 3 phase supply but no 415v connections

Posted: Sat, 31 Aug 2019, 12:13
by coulomb
T1 Terry wrote:
Sat, 31 Aug 2019, 11:54
Hmmm..... that 3 phase hybrid inverter won't do the job if it can only provide 3.3kW because there is a single phase monster ducted air con unit that can suck a peak 26.4 amps...
That's OK, just don't put it on the essential loads output. Because it's a hybrid, the grid will supply some of it and solar will try to direct power to the phase with the largest load to minimise imported power. But it can only support that phase to a maximum of 3.3 kW. So if the monster is drawing 6.3 kW (26.4 A × 240 V, ignoring power factor for simplicity), you'll be drawing at least 3 kW from the grid. Yes, it's far from ideal, when you have two other 3.3 kW phase inverters at probably well under full capacity, but it is possible.

You also can't run the monster air conditioner when the grid is down, even if your battery and/or solar could supply enough energy and power.

Re: 3 phase supply but no 415v connections

Posted: Sat, 31 Aug 2019, 19:59
by brendon_m
IMG_20190831_195206.jpg
IMG_20190831_195206.jpg (752.34 KiB) Viewed 582 times
Pic of the trendy meter as requested


Edit to fix picture

Re: 3 phase supply but no 415v connections

Posted: Sat, 31 Aug 2019, 21:18
by jonescg
brendon_m wrote:
Sat, 31 Aug 2019, 19:59
IMG_20190831_195618.jpg
Pic of the trendy meter as requested
I'll take your word for it ;)

Re: 3 phase supply but no 415v connections

Posted: Sat, 31 Aug 2019, 21:28
by brendon_m
Fixed (I hope)

Re: 3 phase supply but no 415v connections

Posted: Sun, 01 Sep 2019, 00:08
by antiscab
I wonder if it's one of the ones that had a zigbee installed as part of the solar homes trial

Re: 3 phase supply but no 415v connections

Posted: Sun, 01 Sep 2019, 10:44
by T1 Terry
coulomb wrote:
Sat, 31 Aug 2019, 12:13
T1 Terry wrote:
Sat, 31 Aug 2019, 11:54
Hmmm..... that 3 phase hybrid inverter won't do the job if it can only provide 3.3kW because there is a single phase monster ducted air con unit that can suck a peak 26.4 amps...
That's OK, just don't put it on the essential loads output. Because it's a hybrid, the grid will supply some of it and solar will try to direct power to the phase with the largest load to minimise imported power. But it can only support that phase to a maximum of 3.3 kW. So if the monster is drawing 6.3 kW (26.4 A × 240 V, ignoring power factor for simplicity), you'll be drawing at least 3 kW from the grid. Yes, it's far from ideal, when you have two other 3.3 kW phase inverters at probably well under full capacity, but it is possible.

You also can't run the monster air conditioner when the grid is down, even if your battery and/or solar could supply enough energy and power.
The people are looking at staying on grid for 12 mths to get an idea just how grid dependant they are, if the feed in tariff will cover the connection fee etc and if they want to add to the solar and or battery pack to go fully off grid.
If we use the hybrid 3 phase inverter it would need a second unit in parallel to feed the single phase air conditioners for an off grid set up, but if we go with the PIP-5048MG we can parallel 2 of them and converter the house to single phase.
With a bit of jiggery-pokery we can also have the excess solar still feeding into the grid tie 3 phase inverter while they are still on the grid. The grid tie inverter has 2 separate solar arrays wired in, each 2500w at 438vdc open circuit according to the plaque attached to both the grid tie inverter and power board, that doesn't match up with the solar panel specs of 36.1v x 10 panels in series for each array, but still within the voltage range that each PIP-5048 inverter can accept. By switching each 2500w array between the MG inverter and the grid tie inverter, once the battery reaches the programmed voltage, the dry contact in the MG can switch the solar to the grid tie inverter. If I stagger the switching voltages between the 2 MG inverters, one 2500w array can still be finishing off the battery recharge while the other array is feeding back to the grid. Still have to read through the manual to see if the staggered relay switching is possible, being linked it might simply program as master/slave so the master would switch both dry relay contacts at the same time. Not a deal breaker if the staggered switching isn't possible, but it would be nice to be able to do that.
I can only tie one phase of the 3 phase supply to the 2 MG inverters to supply the grid back up function, so I guess the phase the monster air con was on would be the best choice as it should already be set up to handle the 26.4 amp load.

T1 Terry