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daren-connor avatar image
daren-connor asked

Can the PV inverter support assistant be configured to start ramping down at 57.6v instead of 54v?

At the moment the absdorption saying is 57.6v for absorption but the PV inverter support assistant ramps down Fronius when the batteries are at 54v so it takes far too long to charge the batteries under solar. When the generator is on, it will charge at 180amps until 57.6v then go into absorption then float as it's supposed to but when it's under solar it will charge at 180amps to 54v then ramp down considerably so even though the charger wants the power the PV inverter assistant won't allow it. Can the setings be changed in the PV inverter support assistant to chasnge it from 54v to 57.6 as per the charger setting?

offgridFroniusAssistants
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daren-connor avatar image daren-connor commented ·

What would happen if the pv inverter support assistant was not used?

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ daren-connor commented ·

Without the PV assistant, the multi would not raise the frequency, the PV wouldn’t get the message to ramp down and AC would go into overvoltage and the battery would overvoltage/overcharge.

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daren-connor avatar image daren-connor Guy Stewart (Victron Community Manager) ♦♦ commented ·

Then Why does the stupid assistant ramp down at 54v & not at 57.6v as per the charger? The generator does it as per the charger settings so why can't it do the same thing under solar? Why does the assistant require 19hours to charge the batteries from 60% & the generator under charger settings can do it in 4 without any issue?

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ daren-connor commented ·

A battery at 57.6V doesn't have the buffer available thats often necessary to absorp moments of too much PV. A PV overshoot will lead to peak in DC Voltage which immediately translates into peak in AC Voltage.


Generators and PV operate very differently.

A generator is a very stable power supply compared to a PV array. The Multi is able to demand a specific load and the generator will provide it, and no more.

The output from AC PV will fluctuate a lot, as there is passing clouds, etc. The AC PV will PUSH whatever production there is at the time according to it's power point, and the Multi has to deal with it. It can adjust it to a certain degree with the frequency, but this isn't always quick enough as the batteries get full. When loads turn on or off, or when there is clouds, it doesn't get to choose how much power is coming from the PV and the system has to absorb.

Also, in the situation of a generator, it is connected to the AC input of the Multi. This is able to be disconnected if necessary (for example a big load turns off very suddenly on a full battery while generator is running).

The AC PV is connected to a different part of the Multi, the AC output. This is not designed to be switched off during normal operation, and when it is, all other loads go with it. A blackout effectively.

With the current tools, you can adjust the frequency points that will increase the amount of PV your AC PV inverter will provide at various points. But be aware that this may effect the system stability, for example if the battery is full, the sun comes out from behind a cloud when a large load turns off.

We will also get in touch and see if we can find another solution for your situation.

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daren-connor avatar image daren-connor Guy Stewart (Victron Community Manager) ♦♦ commented ·

Well that just makes the entire system highly inefficient on solar. If the solar can't charge the batteries In the same timeframe or within acceptable time frame then it is highly inneficiuent. It takes 5 hours at most on generator to charge batteries. At the rate if charge of the PV inverter, I need 19 hours of sunlight to charge my batteries. That is unsustainable, inefficient & now it's becoming costly.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ daren-connor commented ·

I agree.

Your example there is quite an extreme case.

I think there is some scope to increase your systems efficiency.

There is a good article here that goes into a little bit of detail about the advantages and disadvantages of AC vs DC coupled solar in off grid:

https://www.cleanenergyreviews.info/blog/ac-coupling-vs-dc-coupling-solar-battery-storage

The basic conclusion is that for efficient battery charging DC PV with an MPPT is more efficient.

When running large daytime AC loads, AC solar is more efficient.

There are the fundamental extra steps of transformation, conversion and rectification. BUT there are also secondary additional effects of heat, response, stability and capacity.


Your question and comments have inspired me to write a further elements into the Victron documentation for AC PV systems. With more detailed explanation of the behaviour, limitations and the electrical theory behind it to help improve system design outcomes.

Though this might take a while.

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daren-connor avatar image daren-connor Guy Stewart (Victron Community Manager) ♦♦ commented ·

Do you know how embarrassing it is to have 18kw of solar panels & a 15kw inverter & still have to start the generator after a full day of sun?

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bart avatar image bart Guy Stewart (Victron Community Manager) ♦♦ commented ·

I solved this with an over-voltage relay combined with a timer delay (10 minutes) on the AC of the PV. This avoid over-voltage shutdown of the multplus, while PV charging is only lowered (stopped) when relay is triggered.

Works fine in my situation, but I do have some solar on low voltage DC too.

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daren-connor avatar image daren-connor commented ·

Is this Victron customer service? What an utter & complete waste of time. VICTRON IS BLOODY USELESS. Bloody equipment doesn't work right & your customer service stinks. F O

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ daren-connor commented ·

Hi Daren, this is not Victron customer service, please read the community guidelines - https://community.victronenergy.com/questions/5889/new-victron-community-guidelines.html

Customer Support for Victron products is described here - https://www.victronenergy.com/support

Your Victron dealer can help with system design to make sure you have the right components for what you are trying to do.

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

The PV inverter assistant doesn’t support adjustable voltage threshold points at the moment, only frequency adjustments.

I agree it would be a good improvement and will pass along the feedback to the developers.

I believe this voltage point was chosen as the most reliable in testing to prevent overshoot.

Perhaps in your specific situation you could adjust the frequency points to allow more PV power later into the charge cycle. Be aware of the possible consequences though where the system overvoltage and shuts down if the PV inverter doesn’t respond quickly enough to changing conditions.

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daren-connor avatar image daren-connor commented ·

It just annoys me that I have as much solar power as I have generator power yet both charge completely different but use the same charger settings, the only difference being the PV assistant. It slows everything down to a trickle. My PV inverter is constantly in state 560 ramped down.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ daren-connor commented ·

I understand the frustration. We will get in touch with you to see if we can find a solution.

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porcini avatar image porcini commented ·

I have one question. If a 15S instead of a 16S LiFePO4 battery is used the voltage is even below 54V when the battery is fully charged. But PV inverter assistant can be used anyway. So what happens? Isn't that ill thought through? Lead acid has disadvantages here even though it is less sensitive against overvoltage. But with LiFePO4 the charging current isn't reduced?

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Paul B avatar image Paul B porcini commented ·

you get voltage overshoot on the DC charging and the inverters shut down

a solution that I used was to Install the relay in the Grid tie output and then connect this to the W1 relay of my mutlipus (I also use a hi low relay control so that the contactor was not connected to the multiplus relay. I then setup a assistant to open and close the relay based on battery voltage IF it was exceeded a set voltage. this then effectively turned the grid tie off. how ever this is basically a hard off for the grid tie. but it work for me.


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wayne-1 avatar image wayne-1 commented ·

Good day Guy,


Have you had feedback from the Developers on having voltage threshold points, to assists with fully utilizing the PV inverter?

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Andrew Ayles avatar image Andrew Ayles commented ·
Hello all. I also have a multiplus ac coupled to sma (10 kw pv, 5kw sma, 5kva 48v multiplus, 1700 Ah agm battery bank). At the time with larger daytime loads ac coupling seemed to make sense. Another big factor for me was also plenty of autonomy for the long spells of overcast weather we get in winter. With the multiplus ramping the sma down so soon on battery voltage with large battery capacity it results in the bulk/absorbtion phase often not getting completed while I sit watching vrm with the frequancy only .1 or .2 hertz off of the cutoff frequency for the majority of the day. I have played around with the frequency set points to try to increase the the charge current for a longer period of time but with no real success (it results in the sma shuting down due to instability or too many disconnect/reconnects). I have tried the sma with the changed frequency set points which seemed to work better but then on days with sun then cloud then sun i would get back to the unstable situation again with the sma shutting down. I then tried putting the sma on ac2 out with an assistant to shut off on high dc voltage just for these sun/cloud/sun situations but found it still was not a suitable work around . The conclusion i have come to is for people with ac coupling with large arrays and battery capacity victron need to look at making the voltage that they ramp the charging back at a set point that can be adjusted maybe through the pv inverter assistant (just as the frequency end points can be set in the assistant). I think this would make the ac coupling more versatile and able to cope better with both small and large battery banks and avoid us having to charge by generator.
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Chris avatar image
Chris answered ·

There is LITERALLY no logic to how it works from my experience.
I have two almost identical systems. Inverters / Batteries / MPPTs (all off grid)
Same settings in the Multis on both
Frequency shift works (very nicely) on one (this also has an AC PV inverter installed on the AC out.
It does not work at all on the other.

This is not an isolated case.

Drives me nuts

The documentation is also pants..... :/

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