Inverter single or 3 phase?

[ashthekid]

Hi,

 

This may seem like a silly question but would I be correct in thinking my inverter phase must match the phase coming into my property?

 

I have 3 phase coming in but I've just noticed in my solar summary report that it's planned to have a SolarEdge HD Wave single phase inverter. Does that sound right?

Does it make a difference?

[ProDave]

Why did you get 3 phase?  Expecting a big load or have some 3 phase equipment?

 

If you have a single phase inverter, then you want to put as much as you can in the way of other loads on that phase to maximise the chance of self using all that you generate.  You only really need a 3 phase inverter if having a large array, 3 times the max power before you need to seek prior approval from your DNO.

[ashthekid]

3 phase was already existing at the property when I purchased it and all electricians have said it's great that we have it so decided to keep it.

 

We only have an array of 11 panels running at just under 4kW with SolarEdge optimisers.

 

3 phase or single inverter now you know that?

[SteamyTea]

Are you thinking of getting an EV and a 3 phase charger for it?

And only charge your EV between 10 AM and 2 PM.

And fit another 16A per phase.

[Mr Blobby]

We're going to install a 3 phase inverter in our new build to balance the phases. 

 

Why are you installing only 4kW pv when you are not restriced by a single phase connection?  Sounds like your quote is for a single phase installation.

 

Maybe think about dual MPPT 3 phase inverter without optimisers over two PV arrays?

 

 

Edited December 14, 2021 by Mr Blobby
speeling

[Thorfun]

we have a new 3 phase connection (it was about £20 more for 3-phase so was a no-brainer really) but the whole house will be run on a single phase so we are having a single phase inverter for our 10.5kWp array. just seemed to make sense to me.

[ashthekid]

I must admit I don't totally understand. I suppose i just assumed it was always best to match the 3 phase with a 3 phase inverter.

 

I am planning on future-proofing the property and having an EV charging point but don't have an electric car to use it yet.

 

The 11 panels and optimisers are already installed. The installer is planning to come back when the rest of the project is finished or at least the 1st fix electrics are in.

I'm in a strict conservation area so 11 was all I could fit on a particular roof within the planning criteria.

 

At some point when battery costs come down i am planning on adding some sort of battery storage onto the setup.

And have plans on installing an air source heat pump for UFH and hot water. Am hoping this PV array go some way to helping with that.

 

Just need to make sure i have the correct inverter though before it's too late.

[joth]

12 hours ago, ProDave said:

Why did you get 3 phase?  Expecting a big load or have some 3 phase equipment?

 

If you have a single phase inverter, then you want to put as much as you can in the way of other loads on that phase to maximise the chance of self using all that you generate.  You only really need a 3 phase inverter if having a large array, 3 times the max power before you need to seek prior approval from your DNO.

 

This should not be necessary.

 

We've discussed it many  times already, but 3 phase meters should not require you to put generation on the same phase you draw from. They employ net metering across the phases. This is true for  smart meters, and should be for legacy meters too you just might have to get the supplier out to configure it correctly as they don't always set them up right if it was installed before energy export became common.

 

I can point out the SMETSv2 spec if needed. 

 

Do you already have a smart meter?

 

[ashthekid]

No smart meter, just a standard 3 phase meter.

[ashthekid]

What model SolarEdge inverter would be best suited to have my 11x array with Optimisers run most efficiently?

 

So I know what to ask for. I don’t want my installer to install something that’s more convenient for him over what should be put in. 

[SteamyTea]

24 minutes ago, ashthekid said:

with Optimisers

Do you need these, how bad is your shading?

[joth]

4 hours ago, ashthekid said:

No smart meter, just a standard 3 phase meter.

Any sort of idea on age? Is it digital or analogue? If you can get the model number of it you might be able to google.  Unless you're happy to do research/testing, dealing with the supplier, and/or just upgrade to a smart meter, then you do risk it billing you for import even when you are net exporting.

Note that even if you get a 3phase inverter, it's not plain sailing as you'd still likely be putting 2/3 of generation onto unused phases and "wasting" it.

 

Are you planning on doing MCS registration and getting pair exports? If so a smart meter maybe simplest path anyway.

 

Alternatively, you could ask to have the meter replaces with single phase and cap the others phases off, but you may regret that when you come to add EV charger(s).

 

 

20 minutes ago, ashthekid said:

What model SolarEdge inverter would be best suited to have my 11x array with Optimisers run most efficiently?

 

 

One that is correctly sized for you array and HD-Wave enabled. keep it 3.68kWp or less, to avoid G99 paperwork

e.g. SE3680H  https://midsummerwholesale.co.uk/buy/SolarEdge/solaredge-3680-screenless

 

The 3 phase inverters are all >4kW so will require G99 application, even if you only connect <4kW of panels.

 

[joth]

1 minute ago, SteamyTea said:

Do you need these, how bad is your shading?

Sounds moot as he' already installed them, but FWIW they have a couple other benefits besides handling shading:

- smaller, cheaper, cooler running and more reliable inverter (as it doesn't have any MPTT built in)

- per-panel lifetime performance tracking

 

[SteamyTea]

5 minutes ago, joth said:

Sounds moot as he' already installed them, but FWIW they have a couple other benefits besides handling shading:

- smaller, cheaper, cooler running and more reliable inverter (as it doesn't have any MPTT built in)

- per-panel lifetime performance tracking

 

May be better off with just microinverters, rather than a main inverter and optimisers then.

[joth]

1 minute ago, SteamyTea said:

May be better off with just microinverters, rather than a main inverter and optimisers then.

Even after factoring in the cost of climbing back on the roof, removing the optimizers and installing microinverters and new AC cabling (and possible new roof penetrations), and disposing of the optimizers and DC cabling?

 

[SteamyTea]

4 minutes ago, joth said:

Even after factoring in the cost of climbing back on the roof, removing the optimizers and installing microinverters and new AC cabling (and possible new roof penetrations), and disposing of the optimizers and DC cabling?

No, but that will have to be done with optimisers as well.

More interested to find out what the shading is like, installers are very happy to spend others money.

[joth]

16 minutes ago, SteamyTea said:

No, but that will have to be done with optimisers as well.

 

No - they said the optimisers are already up there:

 

16 hours ago, ashthekid said:

The 11 panels and optimisers are already installed.

 

[joth]

34 minutes ago, joth said:

Sounds moot as he' already installed them, but FWIW they have a couple other benefits besides handling shading:

- smaller, cheaper, cooler running and more reliable inverter (as it doesn't have any MPTT built in)

- per-panel lifetime performance tracking

 

+ they have safety cut out to 1V when the DC cable is not connected

 

[SteamyTea]

16 hours ago, ashthekid said:

The 11 panels and optimisers are already installed.

Whoops, missed that.

[ashthekid]

Yes already installed with optimisers with the cable hanging down inside ready for the inverter etc.

 

@joth analogue meter. Wasn't planning MCS as I am planning to keep all generated electricity. I think the little i'll have left over won't generate much back from the grid in terms of payback so i didn't think it was worth it. I'm planning on adding a myEddi to my water cylinder to use up any excess.

 

I've not heard of any G99 paperwork before. Will I need to consider that even if I'm not feeding back to the grid?

 

Array is 3.960 kW.

 

I've just paid to have a service alteration to move the 3 phase coming in, I've been strongly advised to keep the 3 phase because of the potential loads of the property so i won't be changing that.

[joth]

11 hours ago, ashthekid said:

 

I've not heard of any G99 paperwork before. Will I need to consider that even if I'm not feeding back to the grid?

 

Array is 3.960 kW.

 

G99 only needed if you want to connect an inverter > 3.68kW (regardless of how much if any you expect to export).

 

Your array is slightly larger than that but fine to use on the SE3680 and you won't lose anything in practice, so I'd keep life simple and go for that inverter and less paperwork.

 

11 hours ago, ashthekid said:

I've just paid to have a service alteration to move the 3 phase coming in, I've been strongly advised to keep the 3 phase because of the potential loads of the property so i won't be changing that.

 

In this case you'll also need to pay your supplier to move the meter (as well as the dno to move the cutout), and I'd use that opportunity to get onto a digital meter that can handle net metering of generation correctly, even if you're not planning on being paid for any export.

Asking for a SMETSv2 smart meter is *probably* easiest, but there maybe a wait time for you. Ask your supplier.

 

 

[Nickfromwales]

12 hours ago, ashthekid said:

I've just paid to have a service alteration to move the 3 phase coming in, I've been strongly advised to keep the 3 phase because of the potential loads of the property so i won't be changing that.

Then a 3-ph inverter is a no-brainer. 
Have you sat down yet with a bit of paper, and drawn out your CU with the 3 phases and actually worked out how you are going to practically and safely ( and economically ) divide / allocate the loads of the dwelling over the 3 phases? What will go on which etc? All of the issues with ‘economical’ go away in an instant with a 3-ph inverter, so why would you not get one?

Fronius is what we’ve just specified and installed ( my bonafide PV associates and I ( to save any of the previously received pedantic comments )) to alleviate such issues. This has left me much more flexibility to allocate phases throughout the domestic dwelling to maximise safety, practicality and above all safety for the clients.
3 story residence, so power and lighting most likely going on a phase per floor, kitchen ring on the same phase as the sockets in the open plan dining / living space ( as it’s immediately off the kitchen ), but appliances on fixed wiring will be ok to go over the other 2 phases.
I’ve designed the electrical system to maximise divisibility / balance of the power available from each phase of the inverter, for best utilisation of the PV productivity + the output of the DC battery system, eg so the clients will not have to remain constantly mindful of how / when / which way to optimise this discipline ‘manually’ on a daily basis.

The other downside of the single phase inverter is the max throughput. Even if your max PV generation doesn’t get close to the stated throughput threshold of the 3-ph inverter, you’ll still be guaranteed to be using every ounce of the PV you produce on a bright sunny day. 
Question here is of economics; 11 panel / ~4kWp array could be manageable by such ‘manual’ intervention, particularly if fortified with a diversion controller to scoff up any excess linear to it being produced, so it’s down to some maths to estimate the possible savings and how that overlays on the ROI eg when will it offset the uplift in capital expenditure.

Next point would be, why go 3-ph CU at this time? Who’s idea was that? 
Why not go 2-ph, with the main domestic CU ( DB1 ) on ph-1 and then the remaining ph-2 ( DB2 in a garage for eg ) made off strategically to adopt an EV charger or 2 later down the line? You won’t have that much excess to harvest in an EV IMO, certainly not enough to warrant going 3-ph throughout with associated costs, 3-ph inverter so time for a reality check on the proposed 3-ph install IMO. 
Even with a 3-ph head + meter and initially just using the 2-ph setup, you can still retrospectively add a 3-ph compact CU for a 3-ph EV charger if you ever needed one.

 

There would need to be a very good reason to go 3-ph in the house in this particular instance, and I’m not hearing one yet? Is there something significant you intend running off electricity that were not aware of atm?

[joth]

@Nickfromwales you also seem to be under the impression that net metering across phases does not work, and the house needs to equally divide its usage across all phases and supply generation equally across all phases to maximize self consumption? Why do you think this? 

 We solved the "net metering" question 2 years ago (for SMETSv2 meters..), and I've still not found any counter-evidence that this doesn't work:

 

Why not just ensure the meter works correctly (i.e. with net metering) and then you can do whatever you want with the phases (up to the statutory limits)

 

47 minutes ago, Nickfromwales said:

Then a 3-ph inverter is a no-brainer. 

Well, aside from the extra cost and needless effort on a G99 application, sure, no brain needed.

 

47 minutes ago, Nickfromwales said:

Next point would be, why go 3-ph CU at this time? Who’s idea was that? 

 

(Who mentioned anything about a 3-ph CU?)

 

 

Personally (i.e. for my house) for such a small array, I'd sling the single phase inverter and single phase house CU on one phase (just to minimize the standing voltage rise/drop on that line), and use other phases for "outdoor" things like garage/ashp/EV charger(s). But it depends a lot on the building size and layout as to what makes sense, and I don't know any of that info.

 

Edited December 16, 2021 by joth

[Nickfromwales]

1 hour ago, joth said:

 

(Who mentioned anything about a 3-ph CU?)

It’s obvious from the first few posts that the OP is being sent in that direction. Any mention of a 3-ph inverter would obviously require a 3-ph CU. 

[Nickfromwales]

1 hour ago, joth said:

you also seem to be under the impression that net metering across phases does not work, and the house needs to equally divide its usage across all phases and supply generation equally across all phases to maximize self consumption? Why do you think this? 

Err, if a single phase inverter feeds into one of there phases, how would the PV generation get to ph-2 and ph-3 without that methodology?