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neilsmith avatar image
neilsmith asked

Rule of 1 Islanding & mutiple Multiplus II Minimum Batteries

Hi everyone, I'm VE & battery system newbie, so could I ask for some help on understanding the VE Rule of 1 & the minimum battery sizing rules?

I currently have 11kW PV system (35x315w panels & 2xABB Powerone Inverters, a 5kW & a 6kW) plus my enitre house runs off electric, including the water supply. Therefore I'm looking to add a battery system to improve my self consumption plus backup due to electric prices and grid brownouts.

Unfortunately due to the grid going into our separate garage plus the PV located on our house; I need battery system which supports PV generation on the micro island output. I know VE Multiplus II & Quattro II support this but:

Question 1: Do I need:

- 3 x 5000VA Multiplus/Quattro II to support my 11kW PV generation based on the Rule of 1 webpage OR;

- Could I get away with 2 5000VA Multiplus/Quattro II, taking I only export 9.5-10kW to the grid, due to PV genration efficiencies & loads?

Question 2: Assuming I need 3 x 5000VA Multiplus/Quattro II & I have 11kW PV, will I need:

- 7/8 PylonTech UC2000 battery modules based on minimum battery capacity from AC-coupling webpage OR;

- 12 PylonTech UC2000 battery modules based on Multiplus/Quattro/PylonTech webpage OR;

- Can this be reduced below 7/8 PylonTech UC2000 battery modules?

https://www.victronenergy.com/live/ac_coupling:start#:~:text=In%20both%20grid%2Dconnected%20and,3.000%20Wp%20installed%20solar%20power.

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom

Basically, do I need 3 x 5000VA Multiplus/Quattro II plus 12 PylonTech UC2000 battery modules due to my 11kW PV generation or can this be done cheaper?

Thank for your help in advance.

Cheers

Neil

MultiPlus Quattro Inverter ChargerLithium Battery
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1 Answer
Alexandra avatar image
Alexandra answered ·

@NeilSmith

If you are wanting a system whose sole purpose is to export to grid put the AC PV inverter before the inverters, then 1:1 can be ignored. And the inefficiency of it all.

If you need it to be supported in the case of grid faliure for own consumption then the bank needs to be large enough to handle the full current sink of the PV and the full surge rating of the inverter setup you choose.

11kwh on a 48v system is 229A, the system would need to be able to take that current. For us2000 that is 9 units as they are 25A each nominal. 10 units if you want to be kind to the batteries.

If you choose 2 or 3 5kva inverters now will also change the sizing again. But it is better to use one bigger unit sich as a 10kVa quattro (unless you are using three phase) rather than a parallel system to meet the minimum inverter sizing. It is less complicated to set up and get right and way more efficient.

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neilsmith avatar image neilsmith commented ·

@Alexandra thank you for the reply.

Unfortunately due to the location of the grid, loads & PV inverters on my electric distribution, putting the 11kW PV on the grid side isn't a option; unless I start plastering / digging for 50A/40+m rated cable, which is a pain - with hindsight, I should have taken the PV output back to the grid distribution board when I built the house.

Do you think the 10kVA Quattro or Multiplus would be ok with the 11kW PV generation? That would save a good amount of cash.

I can live with the 10 US2000, as it will help over the winter with off peak charging.

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Alexandra avatar image Alexandra ♦ neilsmith commented ·
@NeilSmith

How confident are you that the PV will be able to do 11kW continuously? I have found in practice it is usually ok to be slightly over as there are losses anyway.

For the temps where we are in Africa and irradiance we do slightly over size/ panel our PV so end up producing less than installed anyway.


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neilsmith avatar image neilsmith Alexandra ♦ commented ·

I'm very confident it's below 11kW, but I don't know how much. I've infrequently seen 10.1kW export via my smart meter at the peak time of day, when majority of the loads are off.

What would happen to the battery system if the rare event of being off-grid and seeing 10+kW generation occured? I'm assuming it would alarm/shutdown/self-protect? If so, I could accept that, taking it's very very unlikelky & I could manage it when the power cut occurs (automatically turn on a few heavy loads during peak points in the day, aka immersion heaters).

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Alexandra avatar image Alexandra ♦ neilsmith commented ·

If you are not running your batteries near the BMS cut off voltages you should be fine. It will only alarm and shut down if there is overshoot mostly. And running the inverter hard will mean it gets pretty warm. And possibly terminals. So really those are the main concerns.

Particularly if you have no DC pv for charging, you will likely see temperature warnings and possibly alarms, depending on how your cooling or environment controls are set up.

If the batteries shut off before the current of the overshoot is sunk other components can go bang. So not really a scenario you want to repeat.

Have you considered using DC PV like the rs 450/100 units?

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