question

mm-azimut360 avatar image

Upgrading with a second PV system - What are the possible and valid variants? (Parallel, cascading...)

Hello there!

I would like to propose a game for Victron experts and enthusiasts who are reading this post. Let's imagine we have a typical PV system with panels, batteries, an inverter charger, loads and the presence of the utility grid. If, at some stage, we want to keep the present system (which is not too old, and its size is not small, not too large) and add a second system of similar size or even larger than the first one, what variants or possibilities would be the most optimal/advisable or more advantageous? Which ones would be valid, but not advisable? Which ones are not technically possible? I know it is a bit of an open question, but it would be interesting to read all opinions. Please take it as a game.

As a general guideline the aim is to increase the size of the system, while keeping the original one. Loads should still be supplied in the case of grid failure. Excess energy can be fed or not to the grid (up to you).

If you like you can give opinions based on the following diagrams (I believe they are all self explanatory, but if not please ask). Number 1 is the original system. For the others, in red the system I believe is not possible technically. In purple a system I believe has little benefit, but still possible. In green all other viable possibilities. For these, subindexes 1 and 2 do not mean 'original' and 'new' inverter - please feel free to place every inverter/charger in the position you like.

I know its obvious, but here you have the meaning of each letter (panels, charge regulators and grid-tie inverters are not depicted in the diagrams, in order not to add complexity, but both AC and DC coupling can be considered for any or both of the inverter/chargers).

U stands for Utility grid.

I stands for Inverter/charger (Multi, Quattro)

L stands for Loads

B stands for Battery

And of course please let me know if I am wrong in any of my assumptions!! :)

Cheers!

MultiPlus Quattro Inverter Chargerparallelcascading inverters
2systemsvariants.jpg (163.4 KiB)
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2 Answers
mm-azimut360 avatar image
mm-azimut360 answered ·

Hi there!

I've given some thought myself to my own question, and came up with the following thoughts:

1 - BASE

2 - NO: For many reasons: loss of total power AC output. Too much cycling of system 2 and too low cycling of system 1.

3 - NO: 2 AC OUTPUT IN PARALLEL NOT POSSIBLE UNLESS FROM SAME BATTERY BANK

4 - POSSIBLE: System 1 would have higher battery cycling. System would never cycle unless connected to AC IN 1 from the Quattro (which has higher priority)

5 - POSSIBLE: Although cycling of batteries of System 2 probably higher than cycling of system 1.

6 - POSSIBLE: System 1 would have higher battery cycling. System would never cycle unless connected to AC IN 1 from the Quattro (which has higher priority). Connection to grid only makes sense if internal cycling is prioritaire.

7 - POSSIBLE: Two independent systems though.

8 - NO: IF UTILITY OUT, WE LOOSE I2

9 - YES: if load división is done correctly, allows for more or less equal cycling of both systems. If batteries of system 2 are low, they can still be charged from system 1.

If configured as grid-tie, I2 can share excess energy with I1.

If configured as off-grid, I2 should disconnect if I1 goes down, therefore cannot share


So, what I see is that configuration 9 is generally speaking the one with more advantages, as long as the PV and the electrical design (loads) is well done.


Any other thoughts?


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machined avatar image
machined answered ·

I have three different systems tied together but I dont have a grid tie. For me, you just hook it up the same way as your current solar. So if you are running your current solar to a battery and then you just add the second MPPT going to battery. Then you just network them together via bluetooth so they can sync their charging patterns. Its super easy. Or you can add a Cerbo which I highly recommend and then the Cerbo can control the charging via VE Direct. Super easy to do and having multiple MPPTs is usually better.

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