Parallel single phase inverters on two-phase installation

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Parallel single phase inverters on two-phase installation

Postby Singlepot » Sun Mar 19, 2017 2:25 pm

Hi folks, I am from Brisbane, an ageing ex-sparky, ex-electrical contractor and still-working professional electrical engineer. I was recently asked to look at a very good solar resource for some old friends - they have a nice home with great north-facing roof. The Energex incoming electrical supply is split over 2 phases (not 3). 2-phase connections to large homes were once pretty common due to the maximum demand exceeding a certain amount, so 2-phase is nothing unusual in older large homes. This means they have two Tariff 11 meters and one Tariff 31 (off peak) meter.

Before becoming aware of the 2-phase supply, they received one solar quote which was for a single single-phase inverter, so I imagine they were expected to pick the phase/meter that has the most daytime loads.

They are also interested in installing a battery-ready Solar system, and that got me thinking about the best configuration for the 2-phase supply. I now think the best configuration is a single DC side (series and parallel PV panels and in due course, parallel batteries) feeding to two single phase inverters (one per phase), probably about 3kVA each. In this way any battery added can provide DC to either inverter as needed.

Any suggestions gladly taken on board.
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Re: Parallel single phase inverters on two-phase installatio

Postby Gordon-Loomberah » Mon Mar 20, 2017 10:30 am

Welcome to the Energy Matters Forums Singlepot :)

Singlepot wrote: I now think the best configuration is a single DC side (series and parallel PV panels and in due course, parallel batteries) feeding to two single phase inverters (one per phase), probably about 3kVA each. In this way any battery added can provide DC to either inverter as needed.


I'm sure you can't run 2 grid-connected inverters from a single PV array, and also the battery doesn't go in between the array and a string inverter, it is generally attached to the inverter independently of the PV array, and the inverter either does the charging, or manages another add-on charger to do the job.
If you want to run 2 inverters, then you will need 2 PV arrays.

Facing the panels all to the north is not necessarily the best idea when on a net FiT, it is best to match generation to loads as much as possible, and arranging the panels as a Virtual Tracker is the best way to do that. See: solar-wind-gear/topic5064.html
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Re: Parallel single phase inverters on two-phase installatio

Postby davidg » Mon Mar 20, 2017 9:52 pm

Singlepot wrote:I was recently asked to look at a very good solar resource for some old friends - they have a nice home with great north-facing roof. The Energex incoming electrical supply is split over 2 phases (not 3).


Is it actually 2 phase or is it really "split phase", if it's single HV line to a transformer and it's tapped for 460V/480V and then centre tapped neutral for 230/240 then it is in fact split phase. ie the 2 halves are actually 180 degrees out phase to each other rather than the STD 120 degrees for 2 phase.

This is far more common compared to 2 phase, ie based on a SWER line. I have to ask because I've seen it mistaken often, I'm not saying its not 2 phase trying to ensure it really is 2 phase and not "split" phase.
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Re: Parallel single phase inverters on two-phase installatio

Postby Singlepot » Tue Mar 21, 2017 6:15 am

Thanks very much for the replies. The first one gave me much-needed boost in current PV array/Inverter/battery configuration.Thank you.I needed to know whether the battery could be common to two inverters and it seems not.

The second post about "Is it really 2-phase" the answer is most definitely yes. It is 2 phases brought in from a normal street 3-phase 415V distribution system. Included angle of voltage displacement 120 degrees

It is definitely not a SWER center-tap split phase supply

So common batteries across two inverters are out - that is the main thing I needed to know, and I thank you for that information.
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Re: Parallel single phase inverters on two-phase installatio

Postby davidg » Thu Mar 23, 2017 10:13 am

Singlepot wrote:So common batteries across two inverters are out - that is the main thing I needed to know, and I thank you for that information.

Well thats not correct at all, you most certainly can use common battery pack, but it would require two, lets say Selectronic Sp-Pro Battery inverters for instance and if required by the distributor to balance the Solar as well then two lets say fronius inverters as well although there are also Solar DC options or ABB inverters another option. None of this is cheap, works well and 2 phase is a no brainer using SP-pro's, I don't know about, other brands as I've not used other brands for this sort of work, however I would guess there would be other brands could do it, Selectronic SP-pro definitely will though just need more than one.
Hybrid & Off-grid Systems - You could store Sun to use later- I Do!
SELECTRONIC SPMC-482 7.5kW, 7.2kW's of Arrays

with AC-Coupled Grid-Connected Inverters,
1100Ah 48V Bank

Auto Backup Genset
PVOutput Stats

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Re: Parallel single phase inverters on two-phase installatio

Postby Gordon-Loomberah » Thu Mar 23, 2017 10:20 am

The 3phase Fronius inverters operate from a single battery, and I think they now have firmware to operate as back-up when the grid goes down.
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