Solar on single phase of 3 phase house

Hedges said:

That works for our split phase, with the assumption that voltage on second leg is equal and opposite (180 degrees apart). You just run the other wire through CT in opposite direction.

It would not work well with 3 phase because L2 and L3 are +/- 120 degrees from L1. It would sum the cosine (sine?) of the currents while subtracting the sine (cosine?).

In the event L2 and L3 currents were identical and in phase with their voltage, because the summed component of the vector is 0.5x its magnitude, you could put each wire through twice and would get the right total. But in general currents aren't identical so wouldn't work. Also wouldn't work if you had a 208 (or 400) volt resistive load between L2 and L3, because wouldn't be in phase.

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Yes, exactly, please disregard my reply on account of it being a Friday afternoon.

Tarquinbob said:

This video shows exactly what I want to achieve, just a shame that the equipment in that video is quite expensive and I'd never get the ROI with my quite small PV setup.

Edit to add, on this video it doesn't show a connection between sunny boy storage and the sunny boy inverter. Does that mean that in theory the sunny boy storage could just be plugged in to any existing solar system. It looks to me that it's behaving as an AC coupled inverter with exactly the feature I was looking for.

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I have that equipment and am playing with it on the bench.
Instead of Sunny Home Manager, I have Wattnode, the 3-phase 120/208Y model. It was shipped with two CT for split-phase but supports a third. SBS 5.0, LG RESU-10H.

At msrp, this equipment makes no financial sense for peak shaving. Maybe for backup (extra hardware required for transfer switch.) Retail price of the battery comes to about $0.50/kWh over its cycle life. I bought them because I got 3x SBS for $2000, and 2x RESU for $3000, about $0.08/kWh.

SBS can work with any GT PV inverter, or just charge from the grid with no PV in the system. If Sunny Boy is connected by Ethernet, then it can command reduced power output to achieve zero export; otherwise it can only store in battery attempting to do that but can't actually prevent export. The SB shown has an antenna; maybe it works over WiFi. I haven't tried SBS <--> SB communications yet.

In my setup it shows instantaneous Wattnode voltages and currents, battery values, SBS inverter values, of course no SB values. It can be set to force charge, force discharge, charge seeking a particular max import from grid, discharge seeking a max export, and I think charge based on SB output. It's software control loop for grid power overshoots and rings for a couple seconds.


For OP, any of the battery or hybrid inverters have adjustable charge rates, and some can discharge in parallel with the grid to support loads. If you can program your Pi or whatever to combine 3 phase meter readings, you can diddle settings on the inverters. One guy here uses a Schneider battery inverter with DC coupled PV + AC coupled Enphase PV inverters. He programs settings to control charging and discharging.

If your utility meter gives no credit for backfeed (hopefully doesn't charge for it), you could implement a continuously variable dump load with a triac "light dimmer" circuit controlling water heater. That makes a nasty waveform with harmonics, but power is adjustable. higher frequency PWM with MOSFET would be better. Or connect through a Variac and motor the shaft to adjust output voltage.

Tarquinbob said:

I live in france and my house is wired as 3 phase. I currently have 4x400W panels connected to a hoymiles 1600W grid tied micro inverter connected on a single phase. In France, for installations of less than 3kW you can inject back in on a single phase and the Linky smart meter is clever enough to sum up the usage on all 3 phases and if the sum is less than what is being produced on a single phase then the net usage is zero and I inject the excess for free to the grid.

I'd like to add a battery to the system as my main power usage is actually at night because as is typical in most French houses my hot water is from an immersion heater running on overnight cheap rate electricity. I've been looking at AC coupled systems, but haven't seen anything that would do what I want it to do. Basically I'd like to find a meter that acts like the smart meter that monitors all 3 phases and only if there's a net export use the surplus to charge a battery.

Does anyone know of something like that that exists and doens't cost a fortune?

The alternative that I've been thinking about is to use another grid tie inverter that's just fed by a battery and get a connect 2 of the panels to a charge controller to charge the battery during the day and then let the battery dishcharge overnight and let my house smart meter handle the phase balancing.

As I live in the south of France and can regularly end up exporting 5-10kWh a day, even on my small install, it seems a shame to waste so much energy. I can't sell the excess because it's a DIY system so I'm just iving it away to the grid for free.

P.S. I know someone is going to say why don't I just convert my house to single phase, but I'd quite like to keep the 3 phase for some woodworking machinery that I have and also for future use for faster charging if I ever get an electric car. Also, siwtching the immersion heater to day wouldn't really work for me either unless I fit significantly more panels which I don't have the space for as the rest of the roof get's too much shade from trees.

Cheers,

Phil

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Thank you Phil!

I also have a house in France with a 3-phase supply (seems to be typical for little country farmhouses) and I've been searching high and low about the implications of feeding in a solar autoconsommation kit into one of the phases. What you say about the Linky summing up usage just blows my mind, its fantastic.

I've been looking at the kits from Sunity - where did you get yours from?

Paul

Hedges said:

It would not work

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Of course, for a moment I was forgetting about the voltage measurement which is needed as well to determine direction and real/apparent power too. A Friday afternoon moment, before a public holiday long weekend!

SeaGal said:

I was just wondering... does anyone know what happens if you could physically fit the 3 live feeds of a 3 phase supply through one single CT clamp? Would the resulting measurement be an accurate sum of the net flow through said clamp?

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CTs measure current going through the hole, no matter if that current is carried by one wire or several... in fact they can do addition and substraction depending on which way the wires go, even multiplication if you loop the wires through the CT several times...

In this case it would measure the sum of currents through the wires, which for three phase would be zero if you don't have neutral, or the opposite of neutral current if you do and the neutral wire doesn't go through the CT. Basically... not useful to measure power.

Simplest way is to use a 3 phase smartmeter like SDM630, nice accurate meter and it can be polled 10 times per second and gives real time data.

Paul JW said:

I also have a house in France with a 3-phase supply (seems to be typical for little country farmhouses) and I've been searching high and low about the implications of feeding in a solar autoconsommation kit into one of the phases. What you say about the Linky summing up usage just blows my mind, its fantastic.

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I also have a house in France with a 3-phase supply too (I'm French) and yes the linky bills the total power you're using no matter how it's split among phases. So if you export on one phase and import on another it cancels out. I'm not sure it's possible to do it any other way and only bill active power. It's quite useful for PV!

Does it make any sense to just add another water heater and use the PV portion to pre-heat water to temp 1, then feed it into the second water heater for the Temperature ( final ) ?

HarryN said:

Does it make any sense to just add another water heater and use the PV portion to pre-heat water to temp 1, then feed it into the second water heater for the Temperature ( final ) ?

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If water does not get to 55-60°C at least once a week and through the entire tank you got a risk of legionella. I don't like preheaters for this reason, because you have to run them through a 60°C cycle once a week, so you end up not saving money. I prefer a big water heater with a water temperature sensor plus house automation. The algo I used was:

1) balance solar and grid according to water temperature: if it gets below 45°C use the grid, otherwise use solar only, on sunny days it will reach max temperature easily
2) If it stayed below 60°C for a week, heat until il reaches 60°C to disinfect

Currently the 1800W heater is switched on/off and I'm relying on the battery to round off the edges. The plan for the next version is to exploit the fact the heating element is three phase (3 resistors) although it is currently wired as single phase. So I will switch the 3 resistors independently, giving 3 power levels, and the battery will have less work to do.

peufeu said:

If water does not get to 55-60°C at least once a week and through the entire tank you got a risk of legionella. I don't like preheaters for this reason, because you have to run them through a 60°C cycle once a week, so you end up not saving money. I prefer a big water heater with a water temperature sensor plus house automation. The algo I used was:

1) balance solar and grid according to water temperature: if it gets below 45°C use the grid, otherwise use solar only, on sunny days it will reach max temperature easily
2) If it stayed below 60°C for a week, heat until il reaches 60°C to disinfect

Currently the 1800W heater is switched on/off and I'm relying on the battery to round off the edges. The plan for the next version is to exploit the fact the heating element is three phase (3 resistors) although it is currently wired as single phase. So I will switch the 3 resistors independently, giving 3 power levels, and the battery will have less work to do.


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Thank you - I had forgotten about the bacteria danger aspect. I appreciate the reminder.

Paul JW said:

Thank you Phil!

I also have a house in France with a 3-phase supply (seems to be typical for little country farmhouses) and I've been searching high and low about the implications of feeding in a solar autoconsommation kit into one of the phases. What you say about the Linky summing up usage just blows my mind, its fantastic.

I've been looking at the kits from Sunity - where did you get yours from?

Paul

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Sorry for the late reply. I didn't buy a kit, I just found someone on le bon coin selling panels cheap (at least as cheap as online sellers, but in stock and could pick them up on the same day) after originally getting lucky with a pricing error on Vevor for micro inverters at €9.99. If you're in the Toulouse area I can give you the contact details of the guy selling cheap panels and mounting kits.