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Nicolas Verrier avatar image
Nicolas Verrier asked

Config 3 Quattro and 12 Smart solar

Good day,


For a complete OFF-grid system we want to have the following configuration:


a) 3 * Quattro 48V 15kva in parallel

b) on the DC battery side 12 Smart Solar MPPT 250/100 each connected to 5.5kW of panels each (total of 66.6kW of DC power on the pv side)

c) LiFePO4 batteries, 100kWh, 52V, Max cont. charge and discharge current: 2 000 Amps

d) 3 phases 60kva genset on AC 1 of the Quattro (with dynamic current limiter activated)

e) everything controlled by a Venus GX, use the two outputs to start/stop the genset and disconnect some non critical loads in case of low battery level


Three questions:

- is it at first feasible? I indeed saw so far a max of 8 MPPT connected to the DC side, will it then be possible to configure the entire solution with Victron's softwares?

- will the fact that DC charging power on the MPPT side is higher than the charging power on the quattro side be a problem?

- can i couple all quattro and MPPT on the same DC bus (each equipment will be fused protected of course prior reaching the bus) was thinking about a standard bus bar, otherwise having 4 Victron Lynx Distributor + lynx shunt + lynx Power In, but then i am limited to 1000 Amps on the bus bar (where we can potentially reach 1200)



Alternative would be to remove 3 MPPT250/100 and add 3 Fronius 5kva on each phases or 1 Fronius 20kva three phases (we might then have issues with the balancing of the phases except if the 3 quattro can correct this).



Thank you

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Hi @Nicolas Verrier

about the MPPT's: please choose the CANbus (VE.Can) connected versions, the maximum limit with these is 25 units.

https://www.victronenergy.com/solar-charge-controllers/smartsolar%20mppt%20ve.can

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Nicolas Verrier avatar image Nicolas Verrier Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Hi Daniël,

So the MPPT 250/100 with Can bus do exist! I though only the 150 was available!

It is not yet in the catalog of our distributor here in SA (not sure whether i can mention the name here or not but they are an international company).

That is noted, thanks a lot, will simplify the installation and most probably the configuration!


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petajoule answered ·

First off, looks like a big installation. Feasible? Yes. Trivial? No. So be careful.


Where is the installation located? If it's somewhere with enough solar irradiation all over the year ... the MPPT/PV dimensioning is acceptable. If you have big changes between summer and winter, you should use way less MPPTs.

You would need another busbar than Lynx (selfmade, custom probably) - 1000A limit is not feasible for such an installation.

You would be better off using a https://www.victronenergy.de/panel-systems-remote-monitoring/octo-gx instead of a Venus GX for such an installation.

You talk about using 3 15kVA Quattros in parallel, later on you refer to a 3p installation. Which one is it?

I heavily favor the "AC arm" with the Fronius Inverter(s) because it's also more efficient for ad hoc self-consumption, but without more information about the usage characteristics of this off-grid system it's hard to make recommendations for sure.


- will the fact that DC charging power on the MPPT side is higher than the charging power on the quattro side be a problem?

No.




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Nicolas Verrier avatar image Nicolas Verrier commented ·

Thank you very much for your answer!

We designed the system as three phases, not in parallel sorry*, there is no three phase requirement as such (no three phase load) however for such power we were thinking of splitting the site on three different phases, as well we started the design thinking of three phase AC coupled PV inverter.

The site is:

- loacted in DRC,

- powering a frontier post from 6 to 18, after that only some lights will stay on and few small equipment. Max estimated consumption (with 20% extra: 36 kva), average daily consumption (still with 20% extra): 186 kva. Biggest loads are the aircons. I am waiting for our elec engineer about inductive loads on this small config and his recommendation.

With Helioscope we are quite stable ranging from 7.8 to 9.5 MW per month along the entire year, chosing a 5deg tilt South-facing. Pic monthly production? ... in winter :) However we can have days from 35kWh (during rainy season) up to 480, but any system would have the same issue there.

Your comment regarding the bus bar is noted, that was also my opinion, we will go custom made.

Regarding the use of the Octo GX, 100% with you, our issue was actually the 10 VE Direct ports only. That would mean we would need to connect two extra MPPT using a VE direct to USB adaptor, then a USB hub and connect to the Octo. Victron said they would have released a version of the MPPT with VE Can by end of last year but it is still not yet available from what i see, this would have allowed to connect up to 25 equipment on the bus.Moreover the Octo has only on output available. Any recommandation on the complete connexion here is more than appreciated.

For the AC arm of the PV generation that would be so much simpler as we could then consider 3 Fronius 20 kVA on the AC side and maybe a few MPPT on the DC side to increase the charging capacity, however we would then have issues with phase balancing on the PV inverter side here as aircons might give us headache by switching on and off not in sync, if you have any recommandation?

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Nicolas Verrier avatar image
Nicolas Verrier answered ·

Thank you very much for your answer!

We designed the system as three phases, not in parallel sorry*, there is no three phase requirement as such (no three phase load) however for such power we were thinking of splitting the site on three different phases, as well we started the design thinking of three phase AC coupled PV inverter.

The site is:

- loacted in DRC,

- powering a frontier post from 6 to 18, after that only some lights will stay on and few small equipment. Max estimated consumption (with 20% extra: 36 kva), average daily consumption (still with 20% extra): 186 kva. Biggest loads are the aircons. I am waiting for our elec engineer about inductive loads on this small config and his recommendation.

With Helioscope we are quite stable ranging from 7.8 to 9.5 MW per month along the entire year, chosing a 5deg tilt South-facing. Pic monthly production? ... in winter :) However we can have days from 35kWh (during rainy season) up to 480, but any system would have the same issue there.

Your comment regarding the bus bar is noted, that was also my opinion, we will go custom made.

Regarding the use of the Octo GX, 100% with you, our issue was actually the 10 VE Direct ports only. That would mean we would need to connect two extra MPPT using a VE direct to USB adaptor, then a USB hub and connect to the Octo. Victron said they would have released a version of the MPPT with VE Can by end of last year but it is still not yet available from what i see, this would have allowed to connect up to 25 equipment on the bus. Any recommandation on the complete connexion here is more than appreciated.

For the AC arm of the PV generation that would be so much simpler as we could then consider 3 Fronius 20 kVA on the AC side and maybe a few MPPT on the DC side to increase the charging capacity, however we would then have issues with phase balancing on the PV inverter side here as aircons might give us headache by switching on and off not in sync, if you have any recommendation?

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petajoule avatar image petajoule commented ·

Ok, I'm interpreting DRC as "Democratic Republic of Congo". So let's forget about the word "winter". ;-)

I had a look at the global solar atlas for conservative estimate for global tilted irradiation at optimum angle etc. and still: if you meant "5.5kWp panels each MPPT" - that would mean you dimension the panels to the max output of the MPPTs (5800W).

But you should be aware, that - especially for off-grid systems - it may make sense to overdimension the PV array, as you want high output for as long as possible throughout the day and for various and less optimal sunlight conditions.

See also https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/

Especially the part about "Oversizing the PV array". If you have the PV area and you know PV panels are one of the cheapest components in this game, you should put like 7kWp per MPPT. Just make sure the max. input current does not go over 70A and the max input volage does not go over 250V (so there is a theoretical maximum of 17,5kWp PV array per 250/100 MPPT).

If you put 7kW on one MPPT, you can use just 10 of them, OcotGX is sufficient. Usually, in off-grid systems we go for 30-50% oversizing the PV array for both DC and AC arms.

(Fronius allows for 100%.)

If your biggest loads are aircons, you definitely

a) want 3-phase systems and the aircons 3-phase as the startup current draw of 1-phase aircons is worse than 3p

b) definitely want an AC arm for immediate self consumption. You can also use more than 1 Fronius.

It's much more efficient if the Fronius helps driving the ACs than if the MPPTs deliver DC to the Quattros and these invert it to AC. Means also you need less MPPTs and have less strain on the Quattro inverters.

3 x 15kVA Quattros can "drive" 2 x Fronius Symo-20


Nice installation. If you need the right batteries for that - let me know. ;-)

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Nicolas Verrier avatar image Nicolas Verrier petajoule commented ·

Thanks a lot for the detailled answer again.

I think i am going to change the conf to the following one then:

a) 3 * Quattro 48V 15kva in parallel

b) on the DC battery side max 4 Smart Solar MPPT 250/100 each connected to about 6.5kW of panels, will see how much i can add within the 250V and 70Amps limits (lucky we don't have very cold days in Africa :)

b*) on the AC side two Fronius Symo 20kva 3 ph

c) LiFePO4 batteries, 100kWh, 52V, Max cont. charge and discharge current: 2 000 Amps

d) 3 phases 60kva genset on AC 1 of the Quattro (with dynamic current limiter activated)

e) everything controlled to a GX (Venus if only 2 MPPT, Octo if 4).

Thank you very much for the valuable explanations :)

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petajoule avatar image petajoule Nicolas Verrier commented ·

Yes. (Quattros in 3p config ;-) )

You can plan also roughly 25-27 (depends on the panels used) kWp on the Fronius inverters.

Everything sounds about right. Not sure how much Storm & Lightning you encounter at the place of installation, but if you do, make sure you equip your installation with the right amount and dimensioning of fuses and SPDs.

Victron offers a nice portfolio of devices and people are tempted to "simply connect them to each other". While this works in principle, you do not want to have a induced power surge (lightning -> PV) frying your MPPTs or Fronius inverters.

Citel, Dehn etc. are the companies that come to mind for the relevant products.

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