Reply to DNO Question?

[kla456]

I recently submitted the attached schematic for a revised G99 following a new 3-phase connection.
DNO has raised the following question:
I note on your G99 form that the existing 6kW of PV is installed on 1 phase and the additional 10kW will be spread over three phases. Can I ask for an update SLD to show how the total of 16kW is to be split over the three phases?

DNO's figures relate to inverter power, not PV
Any input to help draft my reply will be gratefully received

[Oldgreybeard]

They will be looking for an assurance that the phase balance will be maintained (i.e. near-equal export on all three phases) or the split of export from the additional 10kW. My guess is that they would prefer the new 10kW to be split 5kW per phase over the two phases that are not being used for the existing single phase 6kW system.

The infuriating thing that I found when dealing with our DNO was that they never offered anything, they played a silly game where they expected me to ask them for something and they would then say yes or no. It was infuriating, and I only got a straight answer when I found who our local manager was and called him directly. He was great, within ten minutes he'd given me chapter and verse on what they could offer, the best way to proceed with laying the new cables, how to get the job done at the least cost, etc.

[kla456]

They will be looking for an assurance that the phase balance will be maintained (i.e. near-equal export on all three phases) or the split of export from the additional 10kW. My guess is that they would prefer the new 10kW to be split 5kW per phase over the two phases that are not being used for the existing single phase 6kW system.

Yes, that was my first thought also. But I'm not exactly sure what she is getting at or looking for. Currently have approved export limit of 7.4 kW for the single phase so 22.2 kW should be ok for the extended system.

[Oldgreybeard]

I think they will want to know if the new 10kW system is going to be split across all three phases equally (so about 3.33kWp per phase), which would give a big phase imbalance. There would be 7.4kWp for the existing system, plus another 3.3kW, so 10.73kWp on one phase, and only 3.33kWp on the other two phases.

My guess is that they would prefer to see the phase loading be as even as possible, so if there is 7.4kW on one phase, then perhaps arrange the new installation to just use two phases, split 5kWp each. That gives a phase balance of 7.4kWp on one, and 5kWp on the other two, so not a massive imbalance. They would probably prefer it if both systems were connected to all three phases, giving about 5.8kWp per phase, but that would mean altering the existing system.

You can't assume they would allow 7.4kWp on every phase, that depends on the existing phase loading, and there may already be a degree of imbalance from other consumers.

[kla456]

I've put a call through to them. I will ask if that's ok (6kW,5kW,5kW).