Cable confusing + AC setup on Multiplus II 48/5000GX

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Rasmus Mikkelsen asked Mar 10, '22

Cable confusing + AC setup on Multiplus II 48/5000GX

Hi all

I'm writing here because my electrician and me are having a bit of a trouble figuring out a few things. It might be a stupid question, but we are unsure about it so here goes. He tells me every solar inverter he's setup only has 1 cable running to it, I believe him.

I have build a insulated small house behind my PV array, it is quite a long distance up to my AC distributor box, we figured we need 4G10mm2 cables to connect it to support the 4kw+ load.

1. Our main trouble is figuring out if we only need 1 x 4G10mm2 cable down to my small house/Multiplus II, or actually need 2 x 4G10mm2 cables coming from AC distributor box to inverter.

If we are looking at this pdf - https://www.victronenergy.dk/upload/documents/Datasheet-MultiPlus-II-GX-inverter-charger-EN.pdf

The one called Grid parallel topology with MPPT solar charge controller looks like my system. I have 20x310w panels with the 250/100 MPPT, and 22kwh of 48v Lithium storage. With this setup if grid goes out my house goes out, I obviously don't want to backfeed during a blackout, to protect workers. And I dont mind my house being without power if grid goes out, its really rare here in Denmark anyways.

According to the diagram there, there's the grid coming in from left, then theres a dot which means 1 cable running down to inverter? And then there's Loads to the right, which would illustrate my house wiring, yes?

2. So with this setup I will be able to back feed overproduction from PV to grid from inverter while my standby usage is covered (with one cable to inverter). I will also be able to charge my batteries if the electricity is cheap, if no solar and low battery?

Is there anything I should keep in mind here?

I'm not sure what no break loads means in this case? Is it like critical loads, the multi wont shut down that load and will keep it isolated from the rest if grid outage.

Thank you

Regards from Rasmus

Multiplus-II

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Answer 1 · 2022-03-10T21:53:31Z

Any "grid-tied" system relies on presence of the grid to function. If the grid goes away, the battery powered inverter or a PV inverter must shut down to avoid back feeding voltage into the inactive grid. Many solar systems utilize grid-tied PV inverters to add power from the solar array to the system. These will power loads and feed excess production to the grid if allowed.

Normally, you would connect the loads to the OUTPUT of the Multi. That is labeled "No break loads" in the drawings from your link. These loads would be powered by thebattery and PV array connected to the battery if the grid is not present.

Many drawings include two load boxes. One is labeled "no break loads" or "critical loads" or something similar. The other is labeled "non-critical loads" or simply "loads". The non-critical loads are powered only when the grid is available even with a PV inverter or charger connected to the system.

So, you would need an AC connection from your house to the Multi and another running back to the load distribution panel.

You may be better off locating the Multi, its battery bank and the solar charge controller close too the AC grid source and load distribution panel. You'd then need long cables from the PV array to the solar charge controller.

If you are planning an Energy Storage System and selling power back to the grid, you will also need a GX device (Cerbo, CCGX, etc.) to control the system. The Multi would need the ESS assistant installed (a software plug-in). You may also need additional components between the Multi and the grid connection. This would be based on your grid provider's requirements.

Answer 2 · 2022-03-11T07:41:51Z

Rasmus Mikkelsen answered · Mar 11, 2022 at 07:41 AM

Hi, thanks @Kevin Windrem for replying much appreciated.

To summarize what you are saying (sorry I'm still a bit confused)

1. Loads connected to "No break loads" or " Critical loads" is powered by battery and PV if no grid is available. In this case need to run two AC cables?

2. If connecting house to "Loads" or "Non-critical loads" then I loose power if grid failure / power outage, but when the grid available 99.99% of the time, house is powered by PV and batteries. This scenario only needs one cable from house to multi? Or will I be missing out on crucial functions then.

Maybe it is not that simple, and like you say will need 2 cables to and from Multi like the first scenario.

I wanted to avoid running two big AC cables (230v) but will do it if required.

I don't mind my house looses power duing a power outage that is fine with me.

My plan was to be self sufficient with electricity, and sell the rest to grid If I produce too much. I also drive an EV, so it makes sense to me.

Is there anywhere I can read up on what parts I need to order, I find it very confusing as to what I need inorder for the system to function.

Thanks for your time, and have a great weekend

From Rasmus

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Answer 3 · 2022-03-11T16:12:52Z

Kevin Windrem answered · Mar 11, 2022 at 04:12 PM

I would hire a local professional that has experience with Victron systems and ESS systems. They will know the rules for connecting to the grid and the politics of feeding energy to the grid. They will also be able to asses your situation and provide the best alternative to system design.

I don't know of any Victron documentation that describes a system that does not have any critical loads.

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