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

Ectophile

My system has a DC coupled battery, wired into the inverter.

If there's a power cut, I have to crawl into the meter cupboard and operate a big rotary switch.  Position 1 means the main house consumer unit is connected to the mains.  Position 2 is "islanded" mode, with the whole house running off the inverter.

In islanded mode, it's up to me to judge what to turn on.  If I go over the inverter's limit of 3.6kW, I expect the whole lot will shut off.  And at that power, it would run my little 3.3kWh battery flat very quickly.

The advantage of this approach is that you don't have to rewire the curcuit with separate sockets for important things.

Reed_Richards

QrizB said:

I know RR had his whole house rewired. While effective, you probably don't need to go that far; if there are 

No indeed!  It just made it convenient because I had an electrician I could call on who was intimately familiar with the house wiring.  

Qyburn

Thanks, it was just for interest really. There's no real possibility of moving our essential loads onto a separate set of circuits as they're scattered over different buildings. Manual backup would be fine, so I'm trying to work out if I could convert a discrete EPS output into a manual whole house backup. Kind of similar to what we have to do with the generator at the moment. 

Reed_Richards

You will need a very big battery to back-up you whole "house" "scattered over different buildings" for any length of time.  

Qyburn

Reed_Richards said:

You will need a very big battery to back-up you whole "house" "scattered over different buildings" for any length of time.  

Not really if we don't switch on non-essentials. The essentials don't draw more power just because they're fed from garage or one of the barns rather than directly from the house.

Reed_Richards

Yes, I guess that's true.  In which case you want a manual switchover so you can turn off all the non-essentials first to ensure you don't demand a greater power output than your battery is capable of, if it's dark at the time so you have no solar power.  Of course you'll have to do that with the aid or a torch or a candle.  Or maybe you light you way to the consumer unit, switch off all circuits except the lights, throw the manual switchover to give yourself light, wander round and disconnect anything that might draw high power when it comes back on, then re-enable the power circuits.

I don't rate my chances of persuading my wife not to boil the electric kettle if she could, she regards that as an essential
  

QrizB

Of course you'll have to do that with the aid or a torch or a candle.

I've got a non-maintained emergency light that I'm planning to fit above my consumer unit. It will let me see what I'm doing during an outage.

JC_Derby

you could just use a torch?

JC_Derby

Qyburn said:

Of the options I was offered, the AC coupled battery was the only one that offered whole house backup and solar generation during power cuts. The other advantage was that battery and solar together could supply our loads, whereas DC coupled means the battery output is limited by the inverter.

BUT the DNO constraints mean all this needs to be reassessed. It looks like we won't get what we want, so need to decide how to make the best of it.

I've also had a closer look at the transformer and it looks like this retapping may not be possible. The data plate gives settings for +5%, Normal, and -5%. But it also says 250V at Normal, so it looks to me as if we're already tapped at -5%.  I sent photos to SSEN but they've not responded so I guess they want their £2,000 to even look at it.

generally Transformers have 5 tap settings in 2.5% stages.
Please bear in mind QYburn they are basing their (likely software based analysis) on a system voltage - do you know what your actual voltage is at your property.
mgiht also be worth at some point if you are getting nowhere asking what there losses strategy is on undersized transformers? I'm presuming you are the only customer connected to your transformer as its 16kva...
Regarding the DC coupled battery - that would change the way that your generation is analysed - likely not cumulatively as it is (when AC coupled).

Reed_Richards

JC_Derby said:

Regarding the DC coupled battery - that would change the way that your generation is analysed - likely not cumulatively as it is (when AC coupled).

My generation meter measures the AC output from the inverter as export, import and the default reading is the difference between the two.  This difference is what I have actually generated, except for any losses that result from charging and discharging the battery.  So my generation is possibly measured as being slightly less than if I didn't have a DC-coupled battery, but it's not something I worry about.