Which kind of installation is more efficyent?

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elixsaltoki asked Mar 31, '22

Which kind of installation is more efficyent?

Hi! I'm new here on Victron Community. I look forward to doing my bit!

I need to do a new installation for my home and I don't know which kind of equipments would be better. I've two variants, and for both, I've some questions.

System Description:

Installation type 1 (AC Coupling):

In this case, the energy produced by the 20 kW SMA or Fronius inverter, will be distributed between the "secondary" loads and the critical loads. On the other hand, to feed the critical load, I would use a Fronius inverter of 15 kW which, in turn, I would use it to do "AC Coupling" and take advantage of the surplus to charge the batteries.

To do this, I have used the Factor 1.0 rule. For every 1.5 kWp, 4.8 kWh of battery. As the inverter is 15 kW, I must install at least 48 kWh of battery.

For this case, I have the following doubts:

- Will the 20 kW inverter charge the batteries in any way? I think that if it is located where it is, it will not.

- Is it possible to put smaller batteries?

- Would it be necessary to put some other equipment apart from the Color Control?

Installation type 2 (MPPT Regulator):

In this case, as in the previous one, the 20 kW will be distributed between both loads and the charge regulator will be charging the batteries, which in this case I wanted to give it an autonomy of about 2h-3h, in case there was a cut in the network.

Here I have many doubts:

- While the 9 kWp photovoltaic field is delivering energy to the regulator, this energy produced will only serve to charge the batteries or, on the contrary, it will send it to the Victron to reverse the energy and deliver it to the loads instantly as a primary function and charge batteries as a secondary function.

- If the batteries are fully charged, where will that 9 kWp go?

- If the batteries are fully discharged, where will that 9 kWp go?

- If the batteries are at 60-70-80 % of their capacity, where will those 9 kWp go?

- If the secondary loads consume 10 kW, how will the remaining 10 kW from the inverter be consumed?

- If the secondary loads consume 20 kW and the batteries are discharged, how will the critical loads be fed?

- Would it be necessary to put some other equipment apart from the Color Control?

Thanks to everyone!!

Elias Gil.

Multiplus-II MPPT Controllers CCGX Color Control

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Answer 1 · 2022-03-31T15:48:18Z

shaneyake answered · Mar 31, 2022 at 03:48 PM

First thing I would recommend is you a Cerbo not Color Control GX as it is getting close to end of life and the GX has more software support.

Installation type 1 (AC Coupling):

The meter should be before the inverter. Like Grid -> Meter -> PV inverter. Then the system would use the extra PV power to charge the batteries.

I don't understand what you mean by "For every 1.5 kWp, 4.8 kWh of battery".
You need to size your battery for the power, MIN SOC and runtime you want. BYD LVS has pretty low power output so will need bigger pack. You could use FreedomWon Pack that will deliver 10kw for every 10kwh. So in your setup you could go with a 15kwh pack or 20kwh to be safe. Pylontech you would need around 28kwh. It all depends on the battery you choose.

Grid Meter and Cerbo GX is all that is needed.

Installation type 2 (MPPT Regulator):

If the batteries are fully charged, where will that 9 kWp go?

It will go to loads or be exported depending on settings.

- If the batteries are fully discharged, where will that 9 kWp go?

To charge batteries + any excess from the 20kw inverter.

- If the batteries are at 60-70-80 % of their capacity, where will those 9 kWp go?
Cover loads and rest charges battery

- If the secondary loads consume 10 kW, how will the remaining 10 kW from the inverter be consumed?

- If the secondary loads consume 20 kW and the batteries are discharged, how will the critical loads be fed?
The way ESS works is that it will try keep the grid meter at 0W or whatever you set it to but lets say 0W.
If you have 20kw of solar (Both MPPT and AC coupled combined) the system will work to keep the grid 0W, so
if you have 20kw of solar and 20kw of load then all solar will go to loads,
If you have 10kw of solar and 20kw of loads then 10kw will come from battery,
If you have 20kw of solaar and 10kw of loads then 10kw will charge battery.

If you have 20kw of solaar and 10kw of loads and battery full the extra power will be exported.

Critical and Normal loads are in the same "loads" when grid is present.
When grid is lost then only Critical is provided with power.

- Would it be necessary to put some other equipment apart from the Color Control?
Grid Meter and Cerbo GX is all that is needed. Cables to MPPT

My recommendations is actually a combination of AC and DC coupling.

I would install 15kw of solar AC coupled to the output of inverter and I would then put the other 15kw on a Victron 450/200 MPPT for a total of 30kw of PV.
If you have 48kwh of battery, you could expand the DC PV to like 20 or 25kw. If you want more autonomy on cloudy days.
It is best to have both AC and DC pv so you can do a no grid startup which you can't do if you only have AC PV. It is also better to have all PV attached to Victron Inverter so that in a grid outage all that PV will still work to keep system running and not be just turned off.

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elixsaltoki commented · Mar 31, 2022 at 05:32 PM

Hi shaneyake and thank you so much for you quick response!

You've cleared almost all my doubts.

Regarding the 1.0 factor rule, I've found it on this Victron Energy post: https://www.victronenergy.com/live/ac_coupling:start?_ga=2.25794751.369544734.1648571061-1937129544.1647876268

Most concretly:

So, after this I thought that is a must to install 4,8 kWh of battery per each 1,5 kWp PV installed to prevent failures on the system.

In the other hand, I really apreciate your recomendation and it was a really nice installation type. To do it, I would need 3 x Victron Quattro 10.000 VA or 15.000 VA, depending on the finall PV power installed. That's right?

Thank you!

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shaneyake elixsaltoki commented · Apr 01, 2022 at 03:39 AM

I am actually not sure. What they are trying to say in this battery sizing section, it could be related to Victron batteries. As long as the Battery is able to handle the power in both directions it will be fine. EG. 3x 5kva would be mean the battery will need to handle a charge and discharge rate of at least 15kw continuous and you will not have any problems.

The inverter size will only need bigger or equal to the PV on it's output. So if you want 15kva of PV inverter on the output you will need 15kva of Victron inverter. The DC or MPPT connected PV has nothing to do with the inverter size. Obviously you don't want crazy mounts of DC pv that can't be exported.

So inverter size should be based on load and how much AC PV you would like have coupled to it. If the PV is on the input size the inverter it also doesn't matter as this is only a factor when there is no grid. Also 6x or 9x Mutilplus-II might be cheaper than 10 or 15kva Quattro's depends on install but if you don't have a generator then no need for Quattro.

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