AU Solar import export to grid 3 phase balancing circuits- no battery

[exup]

Hi

I have a 10kW solar with 10kW inverter but no battery. So I am consuming solar as its produced and surplus going to the gird. I understand that its more economical to use the solar versus the rebate I get back.

Are my assumptions correct

• If my solar is producing 9kW of power that would be spread evenly across the three phases evenly so 3kW each.
• Surplus power is then feed into the grid via the three phases at varying values due to how much load is being used on each phase in the house

Now if one phase that is connected to one circuit in the house like power points and I started to draw power on that circuit that exceeded the solar supplied on that circuit, am I correct in saying that I would start to draw power from the grid and therefore charged by my utility provider. Even if the other 2 phases were still supplying excess solar into the grid.

Eg L1 is drawing 5Amps but L2 and L3 is supplying 10 Amps each into the grid. Currently I get 12cents/kWh for supply to grid and at peak times charged 48 cents/kWh when drawing.

Watching my utility smart meter I can see the three phases current and if its being drawn or supplied to the grid. There is a little arrow showing supply and draw directions I am assuming for each phase.
As an experiment I load up one circuit in my house with a few heaters and can see when I toggle them off and on that that phase is drawing and supplying in line with the load, the other 2 phases remain supplying.

So after all that does it make sense to ensure I spread the load across each circuit in the house which means I maximise the spread of the loads and reduce the likelihood of one phase drawing power leaving the other supplying power to the grid (which is not as cost effective)

Sorry if that is all confusing

[David_AVD]

Isn't your electricity retailer charging you for the sum of the 3 phases imported / exported?

That is, they don't charge per phase, or even have any idea on the split.

[swingbyte1]

If you have three phase power you should distribute the solar over the three phases.  If you have a single phase inverter onto one phase that is not sinking i.e. solar will be exported, your power bill will reflect that small feed in tarrif rather than offesetting your three phase use.  The power company will charge for the power on the other phases so you will pay more than you offeset

[Someone]

Isn't your electricity retailer charging you for the sum of the 3 phases imported / exported?

That is, they don't charge per phase, or even have any idea on the split.

Its all a bit murky, what's reported to the customer is an accumulated figure of exports and imports. Depending on the meter that can be per phase, per cycle, accumulation of each of those flows, or pre summed over some longer period.

Would need some experimentation while looking at the finest data the retailer will export/provide (likely only 15 minute data). Say disconnecting enough loads so that a reporting period is 100% export, then drawing a significant load on one phase with the inverter disabled/off for a short time in otherwise 100% export.

[Faringdon]

exup i think what you say is correct, because as far as i can tell, your three phase solar inverter has no way of knowing  if the load that it sees on each phase is  in your house, or out on the grid.
To sort this out you would need current measurement devices on the phases coming into your house, and on the solar.
When i worked in a Battery/Inverter place, we needed those current measurement  devices, and a load of software to "zero the customer meter".... ie ensure that as little as possible electricity was exported.

[mzzj]

Isn't your electricity retailer charging you for the sum of the 3 phases imported / exported?

That is, they don't charge per phase, or even have any idea on the split.

Depends on country/area/electrical company.
Here(Finland) measurement has been per phase and ”infinite” resolution.
Start of next year consumer billing is to be based on 1-hour net sum metering over all phases. After that you can have load on one phase and generation on another and net is averaged on 1 hour basis. 

[exup]

Hi, sorry for digging this up but I think this is an issue for 3 phase setups.
 
To recap I have 10KW inverter and the house is three phases (Sydney Australia).
Downloading my data I can see export and import down to 5 min intervals.
In these 5 min intervals I see positive export values at the same time I see demand drawing from the grid.
Eg 10:55AM to 11:00AM 0.2 Kw export and 0.004 KW imported that continues till I see sun went in and export went to zero and import spiked to .5KW per 5 mins.

So the solar production is having an impact. (reducing the overall)
I then put some CT clamps on and see the three phases are all negative (when we have excess solar) but then one phase cant keep up with demand and goes positive.
Therefore is this the issue.

2 phases are supplying excess back into the grid.
1 phase is drawing and I will get charged for this, regardless that the combined Import minus export is negative.

[CatalinaWOW]

After reading all of the threads explaining all of the advantages of three phase domestic power distribution over the single phase system in North America I am grinning smugly about one advantage we have.  None of those problems, though with the various billing/rate schedules it is still plenty complicated here.

[Siwastaja]

After reading all of the threads explaining all of the advantages of three phase domestic power distribution over the single phase system in North America I am grinning smugly about one advantage we have.  None of those problems, though with the various billing/rate schedules it is still plenty complicated here.

Well, it is not related to transmission system, because it is trivial to just calculate the sum of the phases for billing - but it just offers bullshit companies an excuse to charge more, but I'm certain even with "one phase per house" distribution there are plenty of other ways for companies to bill customers.

Here we had approx. 50-50% split of jerk companies vs. sanely billing companies, until summing the three phases for billing was finally mandated by law a few years ago.

Fully free market doesn't work really well with natural monopolies like electrical distribution network, so obviously companies need some regulation - codification of rules that make sense to all. Billing for the sum of three phases is exactly like that, because it averages out quickly even at the level of a single street. Really the only reason not to sum is to extract excess money from the customers without providing anything in return, and it only happens because the politicians allow it to.

The best advantage of your single-phase house delivery is IMO the better availability of peak rating (and less under-utilization of cabling) because there is no issue of balancing loads between the phases. The disadvantage, not being able to run 3-phase motors directly off mains, was never a big issue and nowadays even less because of availability of cheap VFDs. But billing is trivial to handle transparently for a 3-phase system "as if" it was a 1-phase system, which is how it works here.

[CatalinaWOW]

After reading all of the threads explaining all of the advantages of three phase domestic power distribution over the single phase system in North America I am grinning smugly about one advantage we have.  None of those problems, though with the various billing/rate schedules it is still plenty complicated here.

Well, it is not related to transmission system, because it is trivial to just calculate the sum of the phases for billing - but it just offers bullshit companies an excuse to charge more, but I'm certain even with "one phase per house" distribution there are plenty of other ways for companies to bill customers.

Here we had approx. 50-50% split of jerk companies vs. sanely billing companies, until summing the three phases for billing was finally mandated by law a few years ago.

Fully free market doesn't work really well with natural monopolies like electrical distribution network, so obviously companies need some regulation - codification of rules that make sense to all. Billing for the sum of three phases is exactly like that, because it averages out quickly even at the level of a single street. Really the only reason not to sum is to extract excess money from the customers without providing anything in return, and it only happens because the politicians allow it to.

The best advantage of your single-phase house delivery is IMO the better availability of peak rating (and less under-utilization of cabling) because there is no issue of balancing loads between the phases. The disadvantage, not being able to run 3-phase motors directly off mains, was never a big issue and nowadays even less because of availability of cheap VFDs. But billing is trivial to handle transparently for a 3-phase system "as if" it was a 1-phase system, which is how it works here.

We actually agree totally.  You just said it in more words.

[JimboJack]

Yes you need to try and balance as much as possble across the 3phases, splits the heavy appalinces across phases and lights.

It is the same even for a datacentres you need to balance across the supplies, get as close as possible.
 

1. Change your A/C units to 3phase be the biggest draw or split them across phases.
2. If you Electric kitchen setup sames, oven and hob on different phase. ovens about 10-15amps, hobs are +25amps, unless gas
3. multiple fridge freezes,
4. house lights across phases.
5. water heater is the tricky one thats 15-16Amps. unless gas

you may want to colour code your outlets of the phase colours

[indeterminate]

In the old days you could be on a tariff where all 3 phases where added together and you where charged/payed for the total power used or exported.
but that changed to what you are on now and its going to get worse.
in 2025 if you export more power than your assigned limit on one phase you will be charged for the export.

https://www.ausgrid.com.au/Connections/Solar-and-batteries/Solar-tariffs

so balance things out or get a battery and just use the grid as a backup

Australia has a big problem in producing to much power in the middle of the day and not having enough power for the evening peek
the more you can help fix the problem the cheaper power will be for you.

[Siwastaja]

get a battery and just use the grid as a backup

Yeah, with sufficient production + off-grid usage that would work. With grid-tied, be careful. Most inverters on the market can't do different power per phase. Even if they can, do they have working control system? Secondly, most inverters have slow response time in seconds. As a result they work just fine in sane countries, but not with bullshit metering, you would still have simultaneous import/export and battery inverter could actually make it worse. I mean, turn on the coffee maker, and you consume from grid for a few seconds. When it turns off, you export to grid for a few seconds while the inverter ramps down. With temporal netting in billing, this is not a problem as long as the control loop lag/oscillation is symmetric. Without temporal netting, you pay the bill from simultaneous import and export all the time, even from triggered from simple control loop noise!

Australia has a big problem in producing to much power in the middle of the day and not having enough power for the evening peek
the more you can help fix the problem the cheaper power will be for you.

You need a political solution to your political problem. No real incentives are needed, but removal of anti-incentives is a good start.

No netting over phases, and temporal netting period in milliseconds is anti-incentive which blurs real free market mechanisms, because it acts like a pigovian tax on products like grid-tie PV or battery inverters, by causing an extra bill for no real reason whatsoever from "simultaneous" import and export. It is like getting billed in a supermarket for taking a product from the shelf and putting it back ten seconds later.

The other extreme, temporal netting over days, months or even a year is an incentive which blurs real free market mechanisms. Because such long-term energy storage does not exist, billing which resembles an infinite (or huge) "virtual battery" means the money is just extracted from taxpayers, a subsidy which acts as a "thank you" for not investing in storage.

Golden middle road of obvious netting over phases, and netting over temporal period of say from 5 minutes to 1 hour is a sane way to operate and allows people to e.g. use batteries to even out their excess PV production with any grid-tie inverter system, without being ass-raped in billing. But this needs to be in legislation because if the power companies can choose, of course they choose to have an arbitrary source of extra billing.

[exup]

Well I shelled out and bought a shelly 3EM monitor (there is a joke in there...) and hooked it into my Home Assistant. Maybe its not the case if a phase is drawing from the grid whilst the other two are exporting. Looking at the energy Australia meter, I can see the arrows are showing negative P and negative Q. I understand the P is power and +/- is import/export. But what is Q, does that have to be negative as well, sometimes I see -P and +Q (or am I mistaken and that is not possible)

Attached is the utility meter manual showing the display. Plus a screen shot of one phase drawing from Grid. During this time the meter shows -P -Q

In the old days you could be on a tariff where all 3 phases where added together and you where charged/payed for the total power used or exported.
but that changed to what you are on now and its going to get worse.
in 2025 if you export more power than your assigned limit on one phase you will be charged for the export.

https://www.ausgrid.com.au/Connections/Solar-and-batteries/Solar-tariffs

so balance things out or get a battery and just use the grid as a backu

Ouch, i did not realize this was coming next year, so thanks for that.

Footnote: I am not seeing replies to my post, I have ticked Notify me of replies? I see the first reply then it stops.

[Siwastaja]

Q is reactive power. Depending on country / contract, may be billed or may not. Worth checking. It changing sign regularly is a good sign: probably close to 0.

As always revealed in these threads, the problem is getting the information about billing terms. Which is super crazy: you just get bills with no true explanations how it is calculated. Seems to be that way everywhere when it comes to sales of electricity, but won't work that way on any other product or service.

[Poroit]

G'day exup,

Most Electricity Suppliers in Oz do not like Loads that cause Reactive Power with Power Factors less than 0.8 during Peak Periods.

Normally not an issue for Residential but can be in Industry.

3 Phase Watts =¹3 x E x I x PF.......So you can see the effect that low PF has on the Watts they can Bill you for.

[exup]

OK, bare with me as my electrical engineering is limited.

So ideally we should all have a PF of 1 or I think they measure it as a percentage 100% is ideal, but in real world it will flicker +/- that value. So negative PF is 99% and positive is 101% as an example. Hence it would be flickering constantly around the 100% PF value of 1?

Energy companies don't like it as they would have to produce more energy if a PF of 0.7 was seen?
In my case is this normal as it looks to be floating around (during the day) +1 to -1 which I assume is a percentage? Eg 0.90 to 1.1 PF. This should have no impact on billing for me.

I plugged in a cheap watt meter in the Circuit C its currently showing a PF of 100 (247V both in Shelly and multi meter reading.)

[Poroit]

Correct....a PF of 1.0 is what Power Companies prefer.

[Siwastaja]

Plotting a signed power factor is highly confusing. I mean, maybe Shelly uses the sign to denote between leading of lagging power factor. In that case, +0.999 and -0.999 would be both basically the same, nearly perfect. But plotting them on graph they would be on the opposite ends!

For this sort of analysis ("how close I am to perfect power factor?"), it doesn't matter if it's leading or lagging. So you should plot abs(PF) instead, to get rid of that jumping noise on the graph.

And then again, maybe PF is the wrong thing to look at. Power companies are not "interested" in your PF, they might be interested in your reactive power. I mean, if your real power is 10000W and PF is 0.5, that is a disaster; another 10000W of reactive power is flowing and that is the problem. Then again, if you consume 10W of real power, the same PF 0.5 is excellent; only 10W of reactive power is not a problem.

But before diving into the reactive power rabbit hole, it's worth checking if you are billed for it. For example here consumers are never billed for reactive power, limitations/billing only apply to large industrial customers. And reactive power is kept low by legislation forbidding sales of devices with poor power factor; you have similar rules in place there.

[exup]

OK cheers, I think though I have a better understanding and view on how I am using power at home to try and utilise as much solar as we can. Battery option would be ideal, but still not cost effective yet.

thanks all for the comments.

[Siwastaja]

Battery is very hard to make cost-effective, especially if only for PV timeshift. As you say increasing self-use of solar is best bang for buck.