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ewalderasmus avatar image
ewalderasmus asked

Excess (DC-Coupled) Solar exporting without loosing Power Assist Feature

Good afternoon all.

I have a question that I cannot seem to read bout in the user manual. I already have an 8kVA Quattro and Pylontech system coupled with a generator, it has been working flawlessly for a few years now, but I would like to add solar now. As I have it I have two options AC coupled or DC coupled.

At the moment I use the Victron Power Assist feature daily, so implementing an ESS is not an option (unless my information is old and one can implement an ESS with Power Assist?)

My question. If I implement DC-coupled PV, what happens if the battery is full? Will it automatically export the excess energy to the load? is there any way to retain the power assist feature and have DC-coupled PV pushing back to the grid/load?

MultiPlus Quattro Inverter Charger
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2 Answers
Alistair Warburton avatar image
Alistair Warburton answered ·

OK... I have a 48/5000 Multi but the setup is the same as far as I know...

1. You only have one AC/DC converter and it can either charge the battery or draw from the battery, making AC but cant do both. (even if it could it wouldn't make any sense to do both.)

2. Think of your system like a 'T' shape grid on the left, the inverter/charger on the vertical and AC out on the right.

3. With the grid, or a genny, feeding the AC your loads and the AC side of inverter charger are all connected together. If your loads exceed the AC in limit the inverter will 'assist' the AC Out. when AC Out is less than the AC In limit the system will charge the battery, assuming it isn't full.

4. DC solar charges the battery directly, without using the inverter/charger. If the battery is full charging stops, if not then the battery/DC bus receives DC from the solar charger which either charges the battery or contributes to the DC requirement of the inverter. So yes solar will help to run loads when the battery is full, because the voltage will dip, provided the grid is not connected or grid charging is disabled.

5. AC coupled solar is managed by small changes to the frequency, which backs out the chargers, or by dumping excess charge to the grid/loads. With the grid connected the frequency can not be changed so exporting is required, as far as I know, to manage the voltage. You would need an export licence, G99 because its would be over the 16A/3.68kW G100 limit.

Going with DC coupled solar is less messing about because you can keep your export disabled. There are several control/configuration options using assistants or Node Red to get your system to do exactly what you want. I can't comment on ESS & Assist compatibility but you could implement an ESS Esq strategy with Node Red.

What battery do you have? are you using DVCC to integrate a BMS based battery system?
I am asking because direct control of DC charging current can be achieved with the DVCC system if you are not already using it. I know because I do it.

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ewalderasmus avatar image ewalderasmus commented ·

Hi @Alistair thanks so much for your detailed response.


I am using Pylontech US2000 batteries, so yes I am using DVCC.

I just want to confirm, your setup, are you using your batteries as an ESS? or are you primarily grid-connected and only use it as a backup?

If you are using it as a backup, what happens when the battery is 100% with utility present and full sunshine? Also what state does your VE.Bus go into when this happens? Power assist?


I am using my setup as a backup only, therefore the batteries will remain charged 99% of the time. The only time there is any discharge is:

  1. When the utility drops and the generator is signaled to start (roughly a minute or two).
  2. When the load is larger than the AC input limit (ie the inverter is assisting).


Because the battery is charged 99% of the time, if I implement DC coupled solar and the solar output is throttled by the SOC, then I am wasting solar potential, and implementing the solar via an AC-coupled inverter is my only option.


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nickdb avatar image
nickdb answered ·

Are you off-grid? You mention a generator. ESS isn't for off-grid, or generally, generator-based systems.

Power assist is superfluous in an ESS anyway, as everything runs from battery or solar, and only shortfalls come from grid.

When there is no grid to lean on, your batteries have to be able to supply or sink transients as loads come and go, so they need to be sized correctly to accommodate this, else you may end up with some undesirable issues.


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