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Deutch avatar image
Deutch asked

Rule for Combining AC and DC coupling in off grid system

Hello @Guy Stewart (Victron Community Manager) and @Alexandra,

I would like to know how much DC coupling to apply in an AC off grid system for a well balanced system.

Does the amount of power to be installed on the DC side in an off-grid AC system depend on the capacity of the batteries? If so, what should be the power on the DC side, to avoid the batteries being flat? If there is a generator, is it necessary to add a DC coupling, or would it be interesting to start the generator automatically in case of low batteries?

Thank you

AC PV Coupling
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2 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Deutch,

Have you watched my training on AC PV yet? See here - https://www.victronenergy.com/blog/2021/06/08/victron-training-videos/

Introduction to AC PV Basic Training with Guy Stewart (33 mins)

I go into some of these details there - if you have watched it and still need further expansion let me know.

The specific timestamped chapters are:

Chapters
Introduction
Basic grid connected topography
Where to place PV with a MultiPlus
Off-grid AC PV design
Optimal design when only using AC PV Off-grid
Deciding whether to use AC or DC PV
The 1:1 Rule
Frequency Shift Power Control
AC vs DC PV - Pros and Cons
AC PV on the Input or the Output?
AC PV Brand Compatibility
When to use an Energy Meter
Setup and Programming Steps
Adding the necessary Assistants
Grid-connected ESS assistant
Off-grid PV inverter Assistant
Fronius AC PV Setup
Fronius Zero feed-in
GX device setup
Adding a PV inverter to a GX
Manual IP Addressing
GX device settings for AC PV
Configuring the Energy Meter
Setting Fronius Zero Feed in on GX
Advanced System Diagrams
Support
Training Review
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Deutch avatar image Deutch commented ·

Thank you for your interesting feedback @Guy Stewart (Victron Community Manager) ,


Your support has been very helpful to me

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Alexandra avatar image
Alexandra answered ·

Hi @Deutch

The training mentioned by Guy is most useful.

For the DC coupling question. In the training a black start is mentioned as the reason for the DC coupling on the AC off grid system. It is good practice.


Each system design is usually user based so a few considerations. So how big the battery bank ratio is to the DC solar will determine how fast the system will self recover from the black start especially if there is no one on the site to deal with things.

Yes program the generator and that is interesting. Just remember things don't always go according to plan. With a geneator somone may forget to fuel it, or the start battery is flat, or somone left it in manual start (on the generator) and the system cannot start it when it needs to.

Sizing the array to prevent a fully depleted bank is a tall order, usually the users of the system need to manage to some degree their loads and expectations of the AC PV side. So make sure you get them involved and aware of the system limitations, such as night time loads verses battery bank size and bad solar day use age as well.

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Deutch avatar image Deutch commented ·

Hello @Alexandra ,

Thank you very much for quick and intersting feedback.

What you just mentioned is very important, I often tend not to involve the users and sometimes there are small problems that arise. I have for example a customer who called because his generator was starting up two to four times a day, and he wanted to save fuel because it was starting to put a strain on his budget.The thing I didn't explain to the users was that they had a 5000VA Multiplus, that they couldn't go over the 4000W bare, and that if that happened, the generator would automatically start.

Then the users took advantage and even plugged in the stove, the air conditioners, left the light on, and the generator started automatically because sometimes they went up to 6500W of consumption, so I understood the importance of training the users on how the system works

Thank again .



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