Oversizing a MultiPlus-II 48V 8000VA from 6.3kWp array to 12.6kWp array

DIY
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1

Hi, first post here,

I am self installing a solar system, in the UK near Birmingham, and considering oversizing the panels, so would like a bit of advice on whats possible.

So the system as it stands will be as follows
Victron Energy MultiPlus-II 48V 8000VA Inverter
12 x 525 JA bifacial panels (6.3kWp) three strings of 4 panels
250/85 MPPT
18kWh battery storage to be added later (3 month delivery from China), I may double this up next year to 36kWh

So the original array will be S/W facing roof
The additional array will be on the N/E roof, so obviously will never reach anywhere near peak generation
The roof is approx 30 degrees.

The additional array would be exactly the same size as the existing array 6.3kWp with an additional MPPT giving a total of 12.6kWp, but clearly the system would never get anywhere near this due to the roof orientations.

So my question is, will the inverter handle the oversizing (approx 50% at peak value’s, but clearly less than that in real terms)

So each string of the original array will be 174.92V and 15.21A (4 x 43.73Voc and 15.21A)
The three strings combined will be 174.92v and 45.36A (3 x 15.21A and 174.92Voc)

The additional array will be exactly the same on the N/E roof.

Thanks for any advice

2

Hi. The Multiplus isn’t affected at all by the addition of DC mppts. So what you propose is fine. If you had AC-coupled solar inverters then it would be a different story.

I note that your existing 250/85 is already overpanelled. That might be fine too, but you could check with this… https://mppt.victronenergy.com

3

Thanks for the reply,

i did the MPPT calculator and I only managed to get the original 4 panel 3 string array to work, so will order an additional MPPT just to be on the safe side

4

Also, good to know the multiplus is designed to work with battery, so you cant use it without…

5

Ok, so I wont be able to get generation until I also have a battery installed in the system ?

6

And assuming that it wont run without a battery, is there a cheap option that I can use battery wise, like will a cheap lithiuam battery suffice, or even a car battery ? until I get my battery from china ? any suggestions ?

7

Its a battery based system, so you will need a 48V battery,

minimum for a 8k inverter is about 11kW, but you should be able to get it started with a lower capacity battery as long as it can handle the initial inrush to precharge the capacitors in the multiplus

8

Ok thanks,

I may just bite the bullet and go for a frogstar battery, they do a 16kW kit for 1800 quid, the 18kW battery I ordered from China I can put in a narrow boat I am having built, which I was going to do anyway

9

Did you take a look at the battery compatibilty list?
Frogstar is not on that, that doesnt directly mean it wont work, but can give you headaches

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

I suggest to contact your local victron dealer for system design/battery options

10

Yep I saw that, but I have seen non compatible batteries work perfectly well with victron, I may call Frogstar and ask them direct, at least I will get some comeback if they say it works, but doesnt, I have seen the DIY china batteries work perfectly well with Victron

11

Good info you posted though, will work my way through it, there are always options to exchange the BMS for ones that are more compatable with Victron

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I did just see this on the Frogstar website, so does indicate it will work ok with Victron

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