Solar Power for a 2-Phase House in a Single/Three Phase World....

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Bewildered

87 posts

Master Geek

#298735 12-Jul-2022 07:22

Hi,

I'm exploring the possibility of installing solar panels etc but am banging my head on the wall trying to figure out how to deal with the fact that I have a two phase power supply. The phase consumption is reasonably balanced if you look across a week, but obviously not balanced moment-to-moment. In Australia you can get two phase inverters (Fronius does one) but I can't see any here....it seems the only options single or three phase.....or microinverters. You can also get 'balancing' inverters that compensate for load on a phase to that they level the 'export' not the output per phase - for for example it might output 1kW, 2.5Kw, and 1.7kW across the three phases to respond to the specific load on each different phases....ultimately the export to the grid (solar generation - load) would come out as 1kW per phase; this ensures that self consumption is maximise and that there is not need to balance the load as the generation is matched instead. Again, not much to see about that here in NZ....I might be a little jaded but it always seems that in NZ we get half the value for 3 times the price versus our overseas counterparts.... :-(

Has anyone got any experience with two phases?

Thanks!

Scott3

3340 posts

Uber Geek

Lifetime subscriber

#2940931 12-Jul-2022 10:25

Family members have two phase.

When their solar setup was installed a single phase solar setup was installed, and all their loads moved to a single phase. They have a tesla powerwall, which is a single phase product, meaning this was the only really viable decision in their case.

If you want to spread the solar over two phases, I think either two independent setups (two single phase inverters), or micro inverters will be your main options.

It's a pity that balancing inverters as you describe aren't common.

Note that with some power plans now, the benefits of self consuming your solar is not what it was historically.

As an example, Octopus energy. Screenshot below is for their central Auckland rates. On a standard user plan, one would actually be better to sell power at 17c/kWh, and to buy it back at 14.29c/kWh "Off-peak" rate, and much better off to sell power to the grid in the middle of the day at 17c, and set timers (Hot water cylinder, dishwater, dryer, EV charging etc) to use night rate power at 11.6c/kWh.

On a low user plan, night rate is similar to the solar buy back rate.

(note, my understanding is that octopus energy only offers a credit for solar buy back, so you can't cash out money for solar power you generate if your production $ exceeds you consumption $)

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eonsim

261 posts

Ultimate Geek

#2941119 12-Jul-2022 13:22

I think the typical solution is two single-phase inverters with the panels split between them. It does have the advantage you can position the panels differently as two single-phase inverters may give you 4 MPPT between them, allowing you to have upto 4 different orientations or angles of panels. That might allow you to have two north-facing arrays at different angles (optimised for summer and winter) as well as east and west facing arrays optimised for maximum solar hours to spread your solar generation out into the peak periods of 7-9 and 5-7. Generation in peak hours certainly helps maxmise the value of your investment if your own a time of use power plan.

You could also potentially place the secondary inverter on a separate building such as a standalone garage or granny flat if you have one and they're on the second phase.

CrazyM

72 posts

Master Geek

ID Verified

#2941136 12-Jul-2022 14:06

Depending on the size of your phases Of you can put all your loads onto a single phase and have a single phase inverter then that is the simplest and easiest solution. Otherwise as others have said you can do 2 inverters. But I’d only be heading down that route if you were going to have a fairly large system 2x 5kW or so

It might be worth checking and seeing if you actually have 3 phase run to your switchboard. It’s not too uncommon to have 3 phase run from the pole, and then only 2 phases connected to the house

Bewildered

87 posts

Master Geek

#2941153 12-Jul-2022 14:30

Nice! We definitely only have two phase as I pulled the replacement cable to the street myself. Kind of wishing I'd done three phase now....!

Unless I can find a local two phase inverter I think the micro-inverter approach might be best - it is more expensive that an inverter, but likely cheaper than two single phase inverters....it will clip the output, but only at the peak of production which is only for an hour or two in the middle of winter - the rest of the time the panel output should be under the microinverter limit (assuming I get the biggest microinverter). I am asking for multiple quotes as I want to see what the cost difference is between a 'normal' system and what it would be if I went for something larger...it might not be super economic but sometimes you've got to spend some money to feel better about the state of the planet.

As for Octopus - yes! We've already switch to Octopus as have many of the people I talked to about the new option. With their rates it actually makes sense to export everything and load shift into the night rate time period and then buying back the power at a lower rate. You can clear 5 - 7c per kWh that way.....where I am the Octopus off peak rate is lower that the buy back rate too. Those rates may not last but will make hay while the going is good! If nothing else it makes batteries pointless as you will never get a return storing power at 17c per unit to use it when you could buy for 10c. Plus, in the future we will no doubt end up with an EV and then by the time that is charged there'd be little left for the storage battery. As such I can't see any future for $20k battery systems unless you need to be able to ride through a black out (in which case it would be great!).

I might do more digging to see if I can't get a two phase inverter from somewhere....sometimes I think it might be worth just importing everything directly but the challenge then is finding someone to install it.

eonsim

261 posts

Ultimate Geek

#2941333 12-Jul-2022 20:53

Bewildered:

Unless I can find a local two phase inverter I think the micro-inverter approach might be best - it is more expensive that an inverter, but likely cheaper than two single phase inverters....it will clip the output, but only at the peak of production which is only for an hour or two in the middle of winter - the rest of the time the panel output should be under the microinverter limit (assuming I get the biggest microinverter). I am asking for multiple quotes as I want to see what the cost difference is between a 'normal' system and what it would be if I went for something larger...it might not be super economic but sometimes you've got to spend some money to feel better about the state of the planet.

I suspect it's worth checking with a local installer or two, with the micro inverters they'll be more expensive individually and you'll probably need to double up some of the hardware (combiners etc) for each phase. In which case it may be much the same or possibly cheaper to get two smaller quality inverters such as the Fronius ones. The newer Fronius inverters (Gen24) also have a dedicated backup/PV only socket you can run a few of kW of load off (via extension cable and assuming enough sun) even when the power is out, without requiring a full battery based self isolating system.

pipe60

119 posts

Master Geek

#2943823 19-Jul-2022 14:23

just starting installing solar on my place i have 3 phase to house with 2 phases uncontrolled and the other phase for HW on the controlled rate.

I am going with 2 separate inverters(5Kw) and catch power relays to dump surplus back in to the HW(850L) so can maximize self consumption.