one multiplus 10kVA or two multiplus 5kVA - pros and cons

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bladerunnervf asked Jan 28, '24

one multiplus 10kVA or two multiplus 5kVA - pros and cons

Hi, hopefully someone else has had this puzzle too and may be able offer comment please, I looked but didn't see a previous question quite like this in the forum

1x Multiplus II 48/10000/140-100 (8000W) is around £2500 +VAT

1x Quattro 48/10000/140-100/100 VE.bus (8000W) is around £2600 - £2900 +VAT

1x Multiplus II 48/5000 70-50 GX (4000W) is around £950 +VAT

So would it be better to have two 48/5000's or one 48/10000 ? Two 48/5000's would save around £500 on parts? What are the pro's and con's ?

Pro's

- 2x 48/5000 is £600 cheaper

- 2x 48/5000 gives redundancy in case of a failure

Con's

- 2x 48/5000 take up more space and take longer to fit, but not £500 more?

- 2x 48/5000 need to communicate? Guess some 1st, 2nd priority arrangement - easy/difficult?

- each 48/5000 needs own dedicated battery??

Thanks for taking a look

Multiplus-II quattro 10kva

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Answer 1 · 2024-01-28T16:48:54Z

ejrossouw answered · Jan 28 at 04:48 PM

I will advise on a single 10kVA to keep things simple and the no of potential pofs down. Also, it will avoid the added complexity and some level of inefficiency a parallel system brings. A topic worth a search on the forum. Parallel systems only offers redundancy with reconfiguration. You will use a single battery bank for parallel systems. The AC and DC cabling and switch etc. sizing should also not be overlooked if it is very much cost driven. Don't forget the installation space required and ventilation as a fair amount of heat can be produced. Finally, the 8 & 10kVA MP units cannot be run in parallel at this time if you were considering expansion in the future.

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bladerunnervf commented · Jan 31 at 03:22 PM

@ejrossouw

Thanks for the tips. Especially regarding redundancy only with reconfiguration, single battery bank.

I had been thinking of starting with 10 or 15kWh of rack battery, potentially increasing to 30kWh later. I had wondered if it made sense to assign batteries equally to 1st and 2nd inverters, having East-West roof configuration.

Will do a search on parallel and inefficiency as you suggest to learn more

My absolute max which I could, theoretically but not monetarily for now, expand to in the future would be a South-East-West+shed system, around 4 to 5 kWp each for East & West, then about 2-3kWp South wall and 1kWp shed roof.

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Answer 2 · 2024-01-28T18:57:27Z

nickdb answered · Jan 28 at 06:57 PM

In some cases it was required when certification was lacking on larger units.

It is less efficient, as mentioned, but if you are happy to manually reconfig, then we can get the system running again after failure. I have had to do this myself.

Given a choice now, I would just use one, larger system, it is simpler.

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bladerunnervf commented · Jan 31 at 04:00 PM

@nickdb

Thanks nickdB

By manually reconfig, did you mean re-route cables etc or just menu settings?

Yes the 8 and 10kVA multiplus were only added to the ENA list in the UK in Oct2023,

Given theoretical max of 2x5+3+1 = 14kWp has me suddenly wondering if I should just go for the biggest Quattro from the start (ignoring budget)!

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Answer 3 · 2024-01-31T17:38:43Z

bartrs answered · Jan 31 at 05:38 PM

From a € point of view I started off with a single Multi 48/5000, 30 panels, SmartSolar 450/200RS, Cerbo, Lynx and a single DIY 14kWh battery. I then discovered that I needed more power and added another 14kWh battery and a second Multi 48/5000 (which feeds the first Multi in case of higher loads).
Does it work? Yes, perfectly.

If I had to do it over again, would I go for a bigger Multi? Maybe.

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the-doon commented · Jan 31 at 08:55 PM

I tried this as I had trouble starting my lathe on a single 48/3000. I connected 2 in parallel and it worked but I saw a big imbalance in loads between the 2 units. So changed it and connected in series, they weren’t quick enough to support the inrush current. I had to put everything back to parallel again. Have since changed to a 48/10000.

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bartrs the-doon commented · Feb 01 at 07:12 PM

I don't have a lathe so don't know about the load.

The 2nd Multi is constantly on standby and will deliver when the loads are higher than 3kW for 1 second, it will stop when under 2kW for 30 seconds. Been running for over a year and never failed.

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bladerunnervf commented · Jan 31 at 08:59 PM

Thanks for your thoughts bartrs, your system sounds very close to one option I had been thinking of.

The 450/200 has 4xMPPT inputs IIRC?

If you don't mind me asking, how many kWp do you have on each MPPT, and was the extra inverter and kWh of battery for more peak discharge rate into house to power appliances or more hours of supply from battery?

Thanks

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bartrs bladerunnervf commented · Feb 01 at 07:07 PM

Yes the 450/200 has 4 MPPT's, my 4 strings: 8x395wp East, 8x395wp West, 6x395wp West and 8x 450wp South.

I measured the roof sizes and spend a couple hours to find out which panels fitted best, I then used the Victron MPPT calculator.

The system can easily take 200A in summer, which I don't need/want, I bought more panels to have a decent kWh harvest throughout the whole year.

The extra inverter was for peak loads, but now that I have the extra power I started to buy more loads (a boiler for example to save on expensive gas).

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Answer 4 · 2024-02-01T20:17:47Z

daniel-feist answered · Feb 01 at 08:17 PM

You don't need two batteries if you use two Multiplus's. The communication between the two units and programming is trivial once you know how to do it. (training is free online). I don't think you'd get automatic redundency TBH, but your other pros/cons are correct. I would add these though:

Cons of using two:
- Bit more labour
- Need busbar (which might not needed otherwise if you don't have MPPT only only have single battery) and additional isolators etc.
- From a regs perspective 10kVA is rated 8kW, but the 2 x 5kVA are rated 8.8kW (so you are actually applying for more inverter power with two).

Pros of using two:
- You can use G99 fast-track (if you limit feed-in to 32A). 10kVA requires full G99 application.

G99 fast-track doesn't typically take much more than 1 week, G99 takes longer.

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