Site Export Limit - Additional Solar

[Deleted User]

I have solar panels spread across 2 buildings with 2 orientations: facing 140 and 230 degrees. My 6.35kWp of panels are controlled by a single SolarEdge inverter capped at 5kW. There is also a Powerwall 2. My site export limit is 11kVA.

I thought that I would look at whether it is possible/financially sensible to put a separate array on the NW-facing side of my roof. One supplier has come up with a very competitive quote for 16 panels (6.56kWp) with a predicted annual output of 4300kWh/year again with an inverter limit of 5kW.

Negotiations have stalled after I asked ‘what do you think the DNO will say about the site export limit’? I pointed out that my present array and battery have a potential maximum output of 10kW.  I say ‘potential’ as Tesla has never allowed export on a UK Powerwall 2 outwith the now defunct Tesla Energy Plan.

Looking at my present set up, they are only a few days a year when the 5kW inverter limit is reached - and then only for a couple hours each day. The new array would be back-to-back with the main roof array. It follows as the sun moves around, power from the main array will reduce as power from the new array increases. 

My guess is that the present site limit will never be exceeded. My proposed installer would just like me to sign the order and then see what the DNO has to say.

I would be interested to hear about the experiences of others who have added additional PV. 

ispookie666

Following with keen interest. I'm in a similar ⛵. 

 My export is capped at 8.8KVA and thinking of adding a smaller array on the garage roof.
 I suspect DNO are going to stick to the original limit and would want me to have Zero export for the new array. Hopefully they will say, OK for fast track application.  But, I will Likely  need new grid profile for the new micro inverters and I have no idea if you can have different grid profiles in the same setup! 

70sbudgie

Has your DNO told you why your export is limited? If not, it might be worth seeing if you can talk to an engineer to understand the reason. It could be the equipment supplying your house, in which case money could increase the limit - though it is likely to be in the tens of thousands.

Or it could be shared equipment further upstream, in which case ask if the cost will change after the 1st April. (There are lots of changes being implemented).

The other question is how is your export limited now? The DNO will only be concerned with the export at the meter point and the total inverter capacity.

If your Tesla scheme has come to an end, I'm wondering whether installing the new inverter as a hybrid with your existing batteries could be an option?

Martyn1981

Hiya Dolor, the following are all guesses:

I'm assuming you have a 3phase supply, given the 11kVA limit?
So, what were the terms of the DNO notification for the Powerwall, did it include export?
Will the new array also be 3phase, so sharing out the total 10kW inverter limit evenly?
If any of that makes sense, then could you apply for the second array, and at the same time notify the DNO that the battery storage will be set to not export, and is thus a zero export application?

Pulling all those guess together, then you'd have 10kW of capped PV output, within the 11.04kW limit, and the storage wouldn't interfere?

As I say, all guesses, as I'm not 100% sure how this would all work. Also, whilst the PV would sit within the limits for post notification to the DNO(?), your circumstances are more complicated, hence arranging it all as a package.

Apologies if this is all a steaming pile of carp!

[Deleted User]

Martyn1981 said:

Hiya Dolor, the following are all guesses:

I'm assuming you have a 3phase supply, given the 11kVA limit?
So, what were the terms of the DNO notification for the Powerwall, did it include export?
Will the new array also be 3phase, so sharing out the total 10kW inverter limit evenly?
If any of that makes sense, then could you apply for the second array, and at the same time notify the DNO that the battery storage will be set to not export, and is thus a zero export application?

Pulling all those guess together, then you'd have 10kW of capped PV output, within the 11.04kW limit, and the storage wouldn't interfere?

As I say, all guesses, as I'm not 100% sure how this would all work. Also, whilst the PV would sit within the limits for post notification to the DNO(?), your circumstances are more complicated, hence arranging it all as a package.

Apologies if this is all a steaming pile of carp!

Actually, I have a 100 amp single phase supply. The proposed new array would also be single phase. My installer has also suggested a DC battery. I confess that I have no idea how 2 separate solar systems: one with an AC battery and the other with a DC battery work together.

For the moment, I have kicked the suggestion of a second battery into the long grass and I have emailed my DNO asking for a ‘quick look’ opinion based on my present 11kVA site limit. As my Powerwall 2 is ‘locked down’ and it cannot export to the Grid, I have gently suggested that 2 by 5kW inverters should not be an issue. The orientations of the panels give me confidence that a 10kW output will never be achieved.

I have to confess that the 3 installers that I have spoken to seem to take the view that installing a second array is nothing different to a new installation and if the DNO gets difficult they will just limit the inverter to 3.86kW. I don’t share their confidence.

Martyn1981

Hmmm. Are you sure you have been given an export limit of 11kVA / 11kW? That seems very high for single phase. Presumably you have been granted at least 5kW, given the current inverter, so a DNO application to exceed 3.68kW was made? Was the Powerwall II application part of it / made at the same time / made under a zero export (battery) application?

I'm thinking that theoretically you could export 12kW (briefly) between the PV and Powerwall II (7kW 10seconds, 5kW sustained), so the DNO would have detailed the permissions and export limit at some point?

Have to be honest, I'm pretty confused at this point, but that's not at all unusual. 

ABrass

If you have a G99 system and want to increase the size there's a variation of the G99 process to follow for the second system. You won't be able to just bolt on another G98 application

[Deleted User]

Martyn1981 said:

Hmmm. Are you sure you have been given an export limit of 11kVA / 11kW? That seems very high for single phase. Presumably you have been granted at least 5kW, given the current inverter, so a DNO application to exceed 3.68kW was made? Was the Powerwall II application part of it / made at the same time / made under a zero export (battery) application?

I'm thinking that theoretically you could export 12kW (briefly) between the PV and Powerwall II (7kW 10seconds, 5kW sustained), so the DNO would have detailed the permissions and export limit at some point?

Have to be honest, I'm pretty confused at this point, but that's not at all unusual. 

Maximum Power Station Capacity - 11 kVA

Maximum Export Capacity - 11kVA

 Comprising of solar and battery - one/one

Manufacturers: SolarEdge and Tesla

I have emailed my DNO for advice. 

[Deleted User]

The DNO’s advice is ‘submit a G99 application’!