DNO limited export - inverter size?

[Conor]

I'm installing a 5.2pkW array - but split 50/50 from a south facing roof and a west facing roof. So most I'll generate at one time is going to be closer to 3.5-4kW.

 

Edit: I may be adding another couple pkW in the future once we have our garage installed - should I future proof now?

 

My supplier has specced a 5kW inverter. Is this correct or should I be using one limited to 4kw? I've not confirmed with my DNO yet, but I'm assuming I'll be limited to the usual 3.68kW export as I'm on a single cable shared with several properties.

Edited December 7, 2020 by Conor

[ProDave]

On a good day you will see the peak 5.2kW at mid day.  I have a nominal 4kWp split E/W and I definitely see the inverter limit of 3.68kW on a sunny day.

 

You need to first ask your DNO.  This seems to be a lottery, SSE for instance wanted to charge me money to do a survey before they would even tell me how much I was allowed but I got the distinct impression they were going to want to upgrade the network for anything more than 3.68kW

 

Up to 3.68kW output you can install without prior permission and notify afterwards.  If going that route you need to get an inverter with limited output but you will need to confirm that it can handle that many panels, it might fail on over voltage for instance.

[Conor]

Thanks @ProDave. Seems my DNO won't confirm whether they will go above 3.68kW until after my system is commissioned... cart before the horse!!

[joth]

20 minutes ago, Conor said:

Seems my DNO won't confirm whether they will go above 3.68kW until after my system is commissioned

Hmm It would be illegal to commission the > 3.68kW system without approval in advance from the DNO, so no idea how you proceed there!
The DNO application will need to know exact design, schematic and BOM for the install in order to approve, but you have most of that already. 

 

FWIW my original G99 went in for 7.36kW (i.e. 2x 3.68kW inverters) and that took months to approve (in parallel to the PP for it), but when we swapped to the newer 8kW single phase inverter (SE-8000H) then it was a couple weeks to get the existing approval updated.

I'm not sure there's any downside in over-specing the inverter now and not installing all the panels to it until a later date; if I thought I might expand the system in future I expect that's what I would try to do.

 

 

 

[Conor]

1 hour ago, joth said:

 

I'm not sure there's any downside in over-specing the inverter now and not installing all the panels to it until a later date; if I thought I might expand the system in future I expect that's what I would try to do.

 

 

That's a good call. There's not much cost difference between inverters so I may as well go big. I can install the GSE mounts and even the panels and just not connect up the four west ones once I've approval for more. 

Edited December 7, 2020 by Conor

[Conor]

Update. Supplier has said the solar edge can be configured to output at a lower limit. So I'll go for the 5kW inverter for now, and If I go for more panels in the future it can handle up to 7.5kW anyway.

Edited December 7, 2020 by Conor

[markharro]

I asked some questions about DNO approval on another thread and this has opened up more questions. We want to install about 18kW. My understanding is that I can do this and fit an invertor that maximises self-consumption eg electric car and ASHP and as long as it automatically throttles export at the 3.68kw limit then there is no need for DNO approval? 

 

Is this correct as I don't want to and cant afford to pay £100s just to be told that I cant install so many panels even with throttling or I need to use a much lower capacity inverter for example? All this stuff just seems a total nightmare to understand when you move above the standard 4kW array size.

[ProDave]

5 minutes ago, markharro said:

I asked some questions about DNO approval on another thread and this has opened up more questions. We want to install about 18kW. My understanding is that I can do this and fit an invertor that maximises self-consumption eg electric car and ASHP and as long as it automatically throttles export at the 3.68kw limit then there is no need for DNO approval? 

 

Is this correct as I don't want to and cant afford to pay £100s just to be told that I cant install so many panels even with throttling or I need to use a much lower capacity inverter for example? All this stuff just seems a total nightmare to understand when you move above the standard 4kW array size.

They will ask the simple question, is the inverter G98?  and what is it's model number.

 

[markharro]

Thanks Dave but thats begs the question can a G98 inverter service an 18kW array allowing you to self-consume as much as possible and only throttle when export is going to run over the 3.68 limit? This is what I don't understand. Is a G98 inverter simply one that has the throttling function built in to it?