Going 240V AC!

[venquessa]

Been a while in the making but I have all the ducks lined up now and nothing stopping me but getting it done and done right.

DNO stipulations. I can run the battery/inverter system without notification under G98/NI if I do not hardwire connect it in anyway to my "private LV network". If it runs on a normal consumer plug socket, they don't care. I am free to use the Multiplus in "off grid RV style" and use the grid as "shore power".

The next hurdle was earthing the island. However both DNO and my spark are happy a local earth rod will provide adequate protection for the inverted circuit.

So, the next bit of work I plan, unless you guys or the spark has any objections, is...

AC-In. Straight out of a 13A 3 pin plug socket with a consumer RCD on it as a JIC.
16A 3 core flex from that to the inverter AC-In. For isolation switch I can use the socket switch, which leaves the earth and neutral attached or I can pull the plug out of the socket

AC-Out. Off board by a bit of 16A flex to a AC consumer unit board. A "Garage consumer unit" with a 40A main isolator, 16A MCB, 6A MCB and a 10mA RCD. The 16A can run a local utility plug socket on that board and the 6A ....

The 6A connects to the existing 3 core 6mm outdoor cable running to the office which currently carries 24VDC. It will be terminated with a standard double 13A socket. It will be correctly labled with some yellow warning stickers about it being an island phase.

The earth rod will be installed as deep as it will go and I'll leave the impedence testing up to the spark.

The earth circuit will include: the panel frame to the earth rod direct, a 6mm earth tail from the ground rod terminating on the inverter chassis, the MPPT chassis, the island AC consumer unit earth block.

So RCD both sides of the inverter. The inverter has a LOM transfer switch AND an island PNE bond relay. Since I have provided an earth reference that should keep things in "same potential" land even in a grid fault.

Again this is open to review by my spark. If he disapproves, he can do what he thinks is best.

What are your guys thoughts?

I missed some numbers:
Multiplus 24/800/16-16.
2.6kWh 24V LFP battery - 100A cabled/fuse/MCB to bus bar, current limited to 40A continuous by BMS.
16A DP isolator for the panel. 40A DP isolator for MPPT. 40A DP isolator for the Multiplus DC.
330W Solar, single panel
Gird is 240VAC @50Hz. Inverter output is 230V @50Hz, unless the battery charger is engaged or the load overloads the inverter, when it's 240VAC passthrough.

Near term upgrade options: Increase to 3x330W panels, possibly due to shading with individual MPPTs. Double the battery capacity or go even higher with bigger cells.

 

[Ampster]

What are your guys thoughts?

Hard to read with all the abbreviations. If you want to share useable information with the broadest cross section of international readers, explain the acronyms.
In summary one 330 Watt solar panel, 2.6 kWh battery and an 800 Watt inverter. What are your daily loads?

 

[Hedges]

The next hurdle was earthing the island. However both DNO and my spark are happy a local earth rod will provide adequate protection for the inverted circuit.

In the US under NEC, we have to tie all grounds within a building together. We also bond gas pipe, water pipe, foundation steel to same ground network. So I would have grounded island system to the ground wires/rod of existing grid-tied system.

Most of the time that wouldn't make a difference. Perhaps it would if:
1) Current flowing through the earth from outside source (lightning, downed power line) made island system's ground rod and utility system ground rod different voltages.
2) Your island system connected to a water pipe or similar, and due to a fault put AC on that pipe, with no wires bonding pipe to island system's ground.

So, the next bit of work I plan, unless you guys or the spark has any objections, is...

AC-In. Straight out of a 13A 3 pin plug socket with a consumer RCD on it as a JIC.
16A 3 core flex from that to the inverter AC-In. For isolation switch I can use the socket switch, which leaves the earth and neutral attached or I can pull the plug out of the socket

Do you mean plug bonds neutral to ground, unplugging floats it? Why would you not want it bonded?

 

[venquessa]

In the UK we have funky earthing. In short our earth often arrives already broken out of the PNE (protective neutral/earth) conductor from the utility. So 2 conductors to the house, splits into 3.

This guy explains.

He has other more specific (to generators, ESS and EVs), but the main fault of concern is... losing the grid "neutral" makes all 3 conductors float at full 240VAC.

Do you mean plug bonds neutral to ground, unplugging floats it? Why would you not want it bonded?

No, I mean the socket has a switch to turn the inverter power off. That switch is a single pole switch, it breaks phase only.

Obviously if I remove the plug from the socket then it isolates everything.

 

[venquessa]

In summary one 330 Watt solar panel, 2.6 kWh battery and an 800 Watt inverter. What are your daily loads?

I missed this sorry.

I hope to run an extension socket in the office. So it will be running about 200W of monitors, laptops, the usual office stuff. Anything which can be switched off freely, runs from a single plug socket. It's that socket which I want to make "occasionally" solar. If power is available.

The multiplus does cover me in the event I don't notice the battery drop during an office day as otherwise I will switch the socket entirely back to grid.

I don't think I can run the 200W (ish) load for the full 16 hour day. (3.2kWh), but there are expansion options for the panels and the battery to about 3 times it's current values. 1kW panel, 6-8kWh battery.

This setup will replace the existing 24V DC currently going to the office and running whatever I can get to run on raw DC. Currently I have 30-50W of DC usage 24/7. Those 24/7 loads will move back to the grid. The 16/7 loads will go on the 240V inverter for a number of hours - as per battery and solar status.

 

[Ampster]

So it will be running about 200W of monitors, laptops, the usual office stuff.

That is a start on answering the question of load. Now the next step is calculating kWhs by determining how long those kW loads will run. That way you will know how much battery capacity (kWhs) you will need. That in turn will determine how much solar (kWs) is needed to replace the energy drawn from the batteries. Or you can charge from the grid but that won't save any money. If I understand your loads correctly, your inverter is probably sufficient.
It really doesn't matter whether you run an extension or hardwire the devices. Those details distract from the bigger picture of understanding what your loads are