Increasing PV panels on a single phase grid connection

[Dave Edwards]

Someone is connected to the grid with single phase supply and they have a 4kW PV array directly connected. They want to increase their PV generation, and add another 4kW.
I keep reading that if you generate more than 4kW you need a "3 phase inverter to split the load".
But I can't find out whether you can only have a "3 phase inverter" connected to a 3 phase grid supply, or if the 3 phase inverter would somehow work with a single phase grid connection.

Can anyone answer this???

 

[Dave Edwards]

(PS I also know that you'd need to meet the G83 standards too.)

 

[littlespark]

Is it a domestic installation? I believe these are limited to 4Kw if you register for FIT payments.

 

[Dave Edwards]

Domestic installations aren't limited to 4kW. The best fits rate is paid upto 4kW, plus questions like the one I'm asking, arise once you go above 4kW....
I'd still like to know if anyone knows whether or not a 3 phase inverter can be connected to a single phase grid supply?

 

[shaun1]

If it has a 3phase output then this would not be possible. I suppose you might be able to connect one phase to the grid but i doubt the inverter would work without all 3 connected. But it isnt the solution you are looking for.

 

[Dave Edwards]

That makes sense...
I'm just baffled that in the discussions I've seen about this, everyone seems to assume that all grid connections are 3 phase.
They're not!
An awful lot of domestic connections (If not most??) are single or split phase.
So to say that if you go above 4kW you need a 3 phase inverter without also saying you need to have a 3 phase grid connection, seems really weird to me! I still think I might be missing something here!

 

[Dave Edwards]

This is one of the articles I've read:
Don't limit your solar PV system to 4kWp - http://www.yougen.co.uk/blog-entry/2106/Don%2727t+limit+your+solar+PV+system+to+4kWp/

 

[Octopus]

^^ that's over 5 years old ...............

 

[solarsavings]

You can in theory go well above 4kw on a single phase system. I have fitted a 17kw system on a single phase supply.
But you will need permission from the DNO. And that is more often than not refused.
The thre phase inverter bit is nonsense.

 

[littlespark]

I'm not a PV installer, so don't know the ins and outs of it all but I have a PV system and when that was installed several years ago now, I was told I couldn't have more than a 4kW, so that's what I was going by.
Logically, I would think if you had a 3 phase invertor, you would need a 3 phase supply from the grid to match it into.
Although on 3 phase systems, don't they just use 3 single phase invertors and connect one to each phase?
If the system is permitted to be added to, then there is the associated works with a new invertor (3 phase, or bigger capacity single phase) and increase the size of the cable from the invertor to the supply position.
Biggest system I've seen was 200 panels on one roof. 50kW across 4 inventors, all on same phase.

 

[Captain Black]

Seems like if you go over 4kw then G59 rules kick in...

https://www.ukpowernetworks.co.uk/i...+distribution+network+G59-3+50kW+or+less+.pdf

 

[dmxtothemax]

I would first of all ask DNO if you can go above the 4kw,
I believe you can, if they say it's ok first
So ask them

 

[Dave Edwards]

....
Biggest system I've seen was 200 panels on one roof. 50kW across 4 inventors, all on same phase.

It's the last bit of what you said (Littlespark) that interests me...
How could 4 inverters all connect to one phase? And if they CAN, then surely three can too?
All the stuff I read was saying that the load needs breaking down to smaller amounts rather than one large amount.
Is this the same as 3 phase?
Isn't what you're suggesting '4 phase' (I know there's no such thing)
D.

 

[littlespark]

No. It was only 4 invertors because there wasn't one single invertor could cope with 200 panels. I believe it was down to cost of 4, and the fact if one failed, there was still some power being produced.
The building only had a 1 phase supply.
Maybe someone with more knowledge can answer this:
Does the PV invertor give a full ac sine wave like a regular supply? If so, does it get synchronised somehow to the main supply?
With that thought, 3 separate invertors would all synchronise together onto the one supply phase.
Does a "3 phase" invertor knock the 2nd and 3rd phases a third of a cycle out (and 2/3 respectively)

 

[Dave Edwards]

I'm grateful to everyone replying to this. Thank you all.
I am hearing people who are telling me to just ask my DNO.
I don't yet have a 100% certain plan, so there's no point in asking them yet as they will want precise details of what I'm asking to do.

That's why I came here to ask what is possible and what isn't.
It has shown so far that you certainly can generate more than 4kW when only attached to a single phase supply, and that you don't have to have a 3 phase inverter when generating more than 4kW.

So, it seems some of the regulations around this are simply at the whim of the DNO and not dictated by what is scientifically and physically possible.

Thanks for all your help, it will allow me to feel more confident when I do decide my next move.

Cheers.