More about AC coupled vs DC coupled system

[Bob Smith]

To fill the gaps left in the conversation here


Here and there, especially from manufacturers I read that DC Coupled system with batteries can only be done:
1) with hybrid inverters
2) The hybrid inverters must be compatible (kind of only works with the same brand). I don't believe this.

I see from Victron ESS training this diagram



Apart from the PV inverter on the right (with the critical loads) the rest is exactly what I want to do. I have a grid tied inverter since 2016 and I want to add more panels (3 times the current kWp I have 4kWp and will add 12kWp), so I think DC coupled will be better (originally I thought that I will have to have ac coupled (I was told so last year by some installers and I stuck with it) but now I realize I will lose a fair bit. DC->AC->DC->AC means between 10 to 15% loss from what I read in several places. Due to the fact my new panels are expected to generate at least twice as much energy as my existing panels (the orientation won t be as good as my existing panels but there will have higher efficiency and Wp). I think it is better to connect the battery as per the Victron's diagram.

The guy from Victron from the video below. clearly explains that the MultiPlus will always manage the "PV on DC", the "PV on AC Input" and the battery to ensure the import from the grid is 0 as much as possible.

Therefore, I don't understand why they talk about hybrid inverters. In the Victron scenario, there is a MPPT charge controller and an inverter. That is.


Furthermore, can batteries such as the fogstar rack 48V be used in a DC coupled system?

Victron video (first 6 minutes are the most interesting)


Thank you

 

[binky]

Ok nothing converts DC from the panels to AC and back again to charge the batteries. When we talk of AC batteries, what we are actually talking about is a battery with no solar connection, just linked to the AC grid supply. Hybrid inverters are just standard inverters with the extra bit that allows them to charge batteries, and discharge batteries to provide power in demand.

As it happens most AC inverters are hybrids, that could have panels connected, but have been designed to work without them. There are a few which are pure battery chargers. All batteries are DC. So with an AC system, it converts AC to DC, and back again. If you have a hybrid inverter, it charges the batteries direct from the DC from the panels after stepping down the voltage to around 50v, but, as has been discussed many times, you can also set times to charge from the grid aswell

 

[Bob Smith]

Thanks Blinky.

just to be clear.
Here are two design proposal. One I consider the AC coupled batteries (the one with the Lux, HanchuESS, the Enphase. The other one DC coupled (with Victron and Fogstar).

Are you saying as far as the current transformation/conversion is concerned, it does not make any differences?
In other words, which design will generate less loss (from PV generation to home consumption)?









I actually have a 3rd option with SolarEdge







Sometimes I wonder, if life would not be easier without so many questions!

 

[Ronski]

DC coupled batteries are more efficient, therefore less loses. In a DC system such as the Victron system, current flows from the panels through the MPPT to the batteries, apart from the MPPT dropping the voltage down there is no conversion, so it is more efficient.

The batteries are normally connected to a busbars, the MPPT controlers connect to the same busbars, and the inverter connects to the same busbars as well.

My system has a SolarEdge inverter as well, because I have whole house backup the Victron inverter has to be able to control the SE inverter. If the grid is disconnected and the batteries are full the Victron system will slow down production to match loads, but the SE inverter sees a grid so carries on at full power, but there's nowhere for the power to go. So what the Victron does once setup, is change the frequency, and this stop the SE inverter generating, as it see's an out of spec frequency. New ones will actually de-rate as the frequency increases. If you're staying grid tied without backup there's no need to worry about this as both system will shut down on grid loss.

There's a lot to learn, and a lot to get you're head around.

 

[Bob Smith]

DC coupled batteries are more efficient, therefore less loses. In a DC system such as the Victron system, current flows from the panels through the MPPT to the batteries, apart from the MPPT dropping the voltage down there is no conversion, so it is more efficient.

The batteries are normally connected to a busbars, the MPPT controlers connect to the same busbars, and the inverter connects to the same busbars as well.

My system has a SolarEdge inverter as well, because I have whole house backup the Victron inverter has to be able to control the SE inverter. If the grid is disconnected and the batteries are full the Victron system will slow down production to match loads, but the SE inverter sees a grid so carries on at full power, but there's nowhere for the power to go. So what the Victron does once setup, is change the frequency, and this stop the SE inverter generating, as it see's an out of spec frequency. New ones will actually de-rate as the frequency increases. If you're staying grid tied without backup there's no need to worry about this as both system will shut down on grid loss.

There's a lot to learn, and a lot to get you're head around.

yes and when you think you nailed it. you discover something new even better. Not new as it just came out, new as you just learned about it and it was available all that time but never heard of it.