question

@Dr Mobeus

FYI 6 x US 3000 is not enough for an 15kVa inverter, I would have used 8 min (DC wired in pairs, the lynx makes this convenient), since you will need to use the Pylon provided cable system, 10 & I would be more comfortable with the set up.

A lot of the questions you are asking actually have regulations related to them, so they are best addressed to the DNO or electrician for your area.

Yes to a system bypass eve if it is not a requirement. But for self knowledge purposes ... what is the main incoming on your service? Plan to use that gauge wire. the inverter can pass through 100A but you are not likely going to have that high a consumer connection, and will be limited by that factor.

10 x 405w = 4050w so at least an 85A mppt or higher. with 10 (check the VOC of your panels) you are likely going to use a 250V (or higher) mppt. since it will be 2 strings of 5. Otherwise 10 is an awkward number. gauge can be a low as 4mm if you are running two separate strings to a combiner, which should have all the protective gear in it. needs to be able to be isolated/protected from both ends as well.

Thanks for the response,

So for the batteries, I would be best using 8 x usc3000 wired in 4 pairs each pair connected to the lynx? What's the best way to calculate the battery requirements? The manual for the multiplus I had downloaded only list up to the 48/10000/140 which suggests 250-1000ah is recommended. I had seen that the USC is rated for 74ah so 6x74ah=444 but have seen further ratings that suggests that it also has a charge/discharge rate of 37ah, is this the number I should be using? It sounds like the minimum I should be aiming for is around 300ah of battery storage?

The mains incoming service is on 25mm2 tails which feed into the consumer unit and this is why I was going for that. There is a 100amp mains fuse so was under the impression that up to that could be utilised through the consumer unit here in the UK so would that be a limiting factor?

Would 8 be a less awkward number for the solar panels and MPPT? VOC on those panels is 37.2. I had put in the plan a 150/100 so from an amp point of view this should be ok what are my options on the voltage? 2 strings of 4 panels so 37 x4 which is 148 would that be the correct way to get a rough calculation?

Cheers for the help

Nice schematics! I have learnt from the schematics that there are simple changeover switches. The changeover switch is useful when the solar system fails, during maintenance, and when using temporarily consumers that should not run on the battery, e.g. the welding machine.

Thanks! After reading around on this forum at the best option for making one I went with Visio and images I found on the internet, hopefully it clearly shows what I am trying to achieve and allows someone to point out any glaringly obvious issues.

In regard to your statement about running welders through inverters, is this not advised?

looking back at the research I did on battery sizing I had found this https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom previously. It refers to the US2000C which suggests its 50Ah, 25Ah continuous compared to the US3000C which is 74 Ah and 37Ah continuous (taken from https://www.wattuneed.com/en/lithium-batteries-/20563-pylontech-lithium-battery-us3000c74-36-kwh-0768563816987.html). For a 15000kva Quattro the page recommends 10 x US2000C.

US2000C 10 x 50 = 500Ah, 10 x 25=250Ah

USC3000C 6 x 74 = 444Ah, 6 x 37 = 222Ah

a little under the recommended

Where as if I went with 8 instead

USC3000C 8 x 74 = 592Ah, 8 x 37 = 296Ah

Which is quite a lot more, can I go for an odd number and go for 7?

What will be the outcome if it's slightly under the recommended using just 6, looking at these numbers it is only just over 10% under the recommended?

I have 8 x 405W Longi panels (2 x 4) with a 250/60 MPPT, all within spec, slightly overpanelled but that is quite usual, the MPPT will limit the output v. slightly on summer days when there is plenty of generation anyway. AFAIR it could also have been 2 x 5 on a 250/70 but you would need to check with the calculator as @Alexandra advises.

Lots of discussion on this thread which you have probably read as it is quite recent.

You will need to think about earthing i.a.w. IET code of practice. And make provision for an EV charger while you are at it even if you have not got an EV yet, there are specific earthing requirements for that too and like the Multi it should not share an RCD with anything else.

Main question, what kind of a property do you have that would require a 15kVA inverter (unless you really are planning to run a welding set from it)? This is driving you to have a really expensive battery. Also check whether the DNO will impose constraints. E.g. mine (WPD) restricts inverter power to 3.7 kW (16A) - even though it can be set up not to export - so pointless having anything bigger than 5kVA in this scenario. But the 50A passthrough is quite sufficient even with an electric cooker and the wiring all in 10mm^2 is much easier.

Some specific answers: yes, install your isolator at (a), this will make it much easier for later modifications. You won't need any more downstream as the main switches in the two CUs will be fine. You do need the ET112 at (b) since the internal current sensor can't see the heavy loads as you say.

Recommend you also look at the Pylontec 3.55 kWh Force-L2 units, the packaging is less agricultural, they are not necessarily more expensive and much easier to install. I have 10.5 kWh of them (3 modules) which is fine for a large-ish house. It gives >2 hours endurance which is a good rule of thumb. You can have up to 4 in a stack with one BMS. It also has its own isolator with overcurrent protection so you can wire directly to the terminals on the Multi with the cables provided.

"I am wanting to go for a Multiplus 15000/48/200 "

Currently not on the ENA type register in the UK, however the Quattro is and compliant worth talking to your DNO before you buy anything.

https://www.ena-eng.org/gen-ttr/

Thanks sharpener for pointing out that post, I had spotted its title in the list and thought it looked worth a read but had not just had a chance to check it out until today and will go through it again to get my head around it all but it does sound like really useful and relevant stuff.

So the Multiplus needs its A/C in connected through its own individually protected RCD/MCB or RCBO? and earthing needs to be correctly configured, I will look at amending that properly to my plan. Thinking about an EV charger at this stage does make absolute sense, is it ok to do this on the UPS out of the Multiplus powered by the batteries thus allowing charging from pv generated stored energy even when there is no grid connection available?

Quite a large house and that's a yes on the welding, additionally, I have IT equipment, servers and have a smallish crypto mining and ai processing infrastructure which can all draw quite a lot of power hence wanting to be able to make use of cheaper power stored in batteries and PV. Rather than ever exporting any additional power I will just use it up providing cpu/gpu processing power. I would also like to be able to move over to using A/C units for heating and cooling to reduce gas consumption and potentialy electrical heated hot water

In these situations where you never ever want to feed in but instead just take power to charge your batteries it seems like you still need the equipment to be certified and signed off by the DNO even though you configure the device to not even provide that function, is that correct? You would think that as long as a setup like this is safety checked by an electrician and therefore meets building regs that you should be fine, its your own internal setup and separated from feeding the grid so what impact will it have on them and why do they get involved - I obviously completely understand if it is back feeding and the risk it has when there is a power outage and the danger it can be for people performing repairs.

So if I understand correctly and what I am currently proposing would need the equipment to be certified (which with what I am proposing currently is a no by the sound of it) and the DNO notified and signed off (which from reading around they may not want to do for inverters over 8000kva or 10000kva) what can I do to avoid this if I never ever want to feed in? Can I install the Victron Energy Anti-Islanding Relay UFR1001E or is there another solution I am missing?

Thanks for the heads-up on the L2 batteries although being agricultural is not necessarily a problem, they would be stored in the garage and I am well used to servers in racks due to working in IT and the standard Pylontech gear looks very similar to that.

@Dr Mobeus "Thinking about an EV charger at this stage does make absolute sense, is it ok to do this on the UPS out of the Multiplus powered by the batteries thus allowing charging from pv generated stored energy even when there is no grid connection available? "

Well it is only of value if your EV is not at home to accept charge when the sun is out, and many people would not do that because of the round-trip losses, but with such a massive system you might not care.

As @awalkerinuk says, best to talk to your DNO soonish because if you have an ordinary domestic supply I think what you propose will be well outside their comfort zone. I don't think an anti-islanding relay will help, usually they are happy with the internal provision, the problem is the capacity for export even if only in error. There is a consultancy called G59 which may help, for a fee.