G99 knocked back by DNO - trying understand proposed "reinforcemen"

Ectophile

The voltage limits in the UK are 230V +10%/-6%.  That's about 216 to 253V.

The problem is that drawing the full 16kW will make the voltage drop, but exporting 5kW will make it rise.  They might struggle to keep the voltage in range if you export anything.

Qyburn

Ectophile said:

The voltage limits in the UK are 230V +10%/-6%.  That's about 216 to 253V.

They seem to require it tighter than that. We're supplied at 240V, as stated by SSEN and confirmed by my measurements. They state their G100 max voltage rise as 2.3%, which would take it to 245.52V. They may be including an allowance for variation in their supply voltage, but thats just a wild guess. If they won't grant permission for anything above their stated maximum voltage rise, I'm not sure I'll change their mind by quoting some other tolerance.

QrizB

The G100 spec is published and available to freely download. You can check if you want.

(I'm in a notspot with only my phone and a sporadic data connection, otherwise I'd check it myself.)

Qyburn

Some more clarification from SSEN this morning. Not surprising l did misunderstand. Their G99 export limit is 1.3% voltage rise, which they assess can be met with export limited to 4kW.  The 2.3% that they quoted is for total installed capacity irrespective of export limit. I suppose what they're saying is that if the limiting mechanism failed, the unrestricted export mustn't exceed 2.3% voltage rise.

Reworking my voltage drop calculations that's 3.12V rise/drop at 16.67A. After recapping the low voltage limit will be 223.5V which would be reached at roughly 12kVA. 

I'm not sure how much this helps. I'm not sure I'm comfortable reducing nominal voltage and therefore supply capacity at all. What happens if we later want an EV charger, or (heaven help us) a heat pump?

Chris_Type_R

OP have you looked at the G98 Sunsynk 3.6kW hybrid inverter ? It's a bi-directional charger which supports 7kW of  PV, so you can notionally charge at, use and export  > 3.6kW while remaining within the G98 limit. That's my understanding anyway. It might be worth looking at, as I think it addresses your concerns of using battery and solar simultaneously.

Qyburn

Thanks, I'll look into that.  I guess my ideal would be a 7kW hybrid inverter, with 4kW export limit. With battery on the DC side to mop up excess solar for use for export later. Realistically with that total power limit (7kW) an AC battery isn't on the cards as it would either be a stupidly small battery, or stupidly small inverter. The suggestion of 2kW inverter and Tesla Powerwall doesn't seem that great.

But over riding all this, it needs to be a system that someone round here is actually prepared to recommend, install, and support.

Chris_Type_R

Qyburn said:

Thanks, I'll look into that.  

Here's the one I'm referring to, and a description of its bi-directional ability - https://www.youtube.com/watch?v=XGlOKQHVgww&ab_channel=Sunsynk

It's pretty easy to get hold of in the UK - it's available from City Plumbing. It's a popular for DIY installs - with a large user base in South Africa, where there are very strict controls (bans) on feeding in/back to the grid. I've installed mine myself, as well as a 5.3kWh battery. 

They're actively trying to improve the software to work with Octopus. 

Qyburn

Chris_Type_R said:

It's pretty easy to get hold of in the UK - it's available from City Plumbing. It's a popular for DIY installs - with a large user base in South Africa, where there are very strict controls (bans) on feeding in/back to the grid. I've installed mine myself, as well as a 5.3kWh battery. 

They're actively trying to improve the software to work with Octopus. 

Cheers. Did you get your DIY install approved for export MPAN, and G99?

Chris_Type_R

Qyburn said:

Chris_Type_R said:

It's pretty easy to get hold of in the UK - it's available from City Plumbing. It's a popular for DIY installs - with a large user base in South Africa, where there are very strict controls (bans) on feeding in/back to the grid. I've installed mine myself, as well as a 5.3kWh battery. 

They're actively trying to improve the software to work with Octopus. 

Cheers. Did you get your DIY install approved for export MPAN, and G99?

I have submitted a G99 application as we have an pre-existing 2kWp installation. The two combined push me into G99 territory. I've only test/temporarily fitted it, pending approval..... but, the nature of how it's installed with a CT clamp means that the aggregated production is constrained to G98 level. In terms of export, the plan is to sign up with Octopus in a years time, as I'm currently on a 3 year fixed rate contract until then (at Aug 2021 prices).

Between now and then the plan is to get my spark in to install a new CU, and a distribution board so that I can make use of the UPS function for PCs, fridges, lighting, etc and the AUX port in winter to drive space heaters. The existing CU is dated, so ultimately I want RCBOs, intumescent protection, etc. This exercise should remove the DIY 'smell' of the installation. 

JC_Derby

ABrass said:

Why not a DC coupled battery on a 5kW inverter?

Qyburn - This is quite an important point... I've not seen you mention this at all (only skimmed) how are your installer proposing to connect the battery storage - Ac side of inverter or DC coupled.