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

QrizB

JC_Derby said:

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.

From the opening post:

The application was for 5kW inverter and AC coupled battery also with 5kW inverter.

JC_Derby

ta

However the point is still valid. why not DC coupled

QrizB

JC_Derby said:

However the point is still valid. why not DC coupled

A valid point indeed, and (in light of recommendations made on this thread) something that the OP should be discussing with their installer.

Qyburn

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.

QrizB

I think @Reed_Richards has a GoodWe(?) hybrid inverter that provides EPS (ie. backup) plus solar generation during power cuts. There are probably other makes which do the same.

This won't help with your desire for 10kW.of output, but exactly how often do you think you will need that much?

Reed_Richards

QrizB said:

I think @Reed_Richards has a GoodWe(?) hybrid inverter that provides EPS (ie. backup) plus solar generation during power cuts. 

That's true and it is a Goodwe inverter.  It's nice when there is a power cut and the light flicker but come back on as the switchover happens.  And it was a big boon during Storm Arwen when we lost mains power for 24 hours.  But I don't have whole house backup, that wouldn't make sense unless I had a much bigger battery than my 6.5 kWh one.  When Storm Arwen hit my battery was by no means fully charged and I would have run out of power if the following day had not been sunny.  And that was just running the fridge, freezer and router.  

Qyburn

It's true the 10kW (inverter plus battery) may not often be needed. Or in fact not always available.

"Whole house" backup is desirable because our important loads, fridge freezer, energiser and water supply, are in different buildings. Running addditional separate cabling to these locations wouldn't really be practical. So a system with a separate backup outlet would mean a bodge of running extension leads in and out of the house and across the yards. And wouldn't give "nice to haves" like lights an Internet without further badges. In the original proposal the battery would last us around three days if we were careful, maybe even more, and would get some charge if there was enough sun.

That's all water under the bridge as we now know we can't have any of these benefits. But just to say that our original design was actually chosen for a reason.

Qyburn

Reed_Richards said:

QrizB said:

I think @Reed_Richards has a GoodWe(?) hybrid inverter that provides EPS (ie. backup) plus solar generation during power cuts. 

That's true and it is a Goodwe inverter.  It's nice when there is a power cut and the light flicker but come back on as the switchover happens.  

How does that changeover work? The systems we were offered (other than Tesla) had a separate emergency power outlet which would then need to be manually connected when needed.

Reed_Richards

Before we moved in in 2018 we commissioned an electrical safety check which found that two circuits had been cross-wired.  On the strength of that, and given that the wiring was about 40 years old, we got some money knocked off the house price to fund rewiring.  This was done gradually over several months and I had solar panels installed before it was finished.  Now the main "consumer unit" has a circuit that feeds a secondary unit with the circuit breakers for the two lighting circuits and a ring circuit that covers the sockets for the fridge, freezer and router (all doubles, so six outlets in total).  My oil boiler was also covered, when I had one.  I live in a bungalow, all the wiring is in the loft, so this was relatively easy.  Although my inverter may have been able to manage the backup alone, my electrician fitted a separate changeover unit, a "GCDQCN Double Power Auto Transfer Switch" according to the label.  It all works very well (except once when the backup feature was accidentally turned off, possible a consequence of a software update).

And see https://support.goodwe.com/portal/en/kb/articles/back-up-function-of-the-inverter for what the inverter. does          

QrizB

Further to RR's post above, there's a current eBay listing that shows the essential components of an EPS transfer box:

https://www.ebay.co.uk/itm/266390313267

And here's the same sort of thing from Solax (theirs uses two separate contactors, per the description):

https://batteryfactory.co.uk/products/solax-x1-eps-emergency-power-supply-box-uk

Here's a photo of typical internals (taken from the eBay listing):

This one is meant for a Sofar ME3000SP (which is why I'm watching it) but the basic principle is the same for all of them. (Also note the contactor in the photo is only rated at 9 amps.)

Per the diagram in the photo:

Grid power comes in from the right, loops through the contactor (the CHiNT box) and then feeds the inverter. The EPS output from the inverter connects to the other set ofcontactor inputs. The contactor outputs at the bottom of the diagram via the big red switch and powers the protected circuits.

Normally, the grid holds the contactor in position "A", allowing the essential circuits to be powered by the grid. If the grid fails, the contactor releases and switches to position "B", switching the essential circuits over to the EPS output of the inverter.

I know RR had his whole house rewired. While effective, you probably don't need to go that far; if there are specific circuits that you want supported by your EPS, you can move them out of the main consumer unit to a secondary consumer unit, and connect that CU to the EPS-protected supply.

I should probably add that you don't have to use an automatic changeover; you can do it manually if you prefer, although I'm not sure why you would. Here's an example :

https://theecosupermarket.co.uk/product/solax-power-eps-changeover-switch/