ESS throttling MPPT without valid reason (AC + DC system, battery not full, reproducible

DIY
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1

I’ve been using Victron ESS for quite a long time now (since around version 3.60), and I need to be honest — this issue with MPPT throttling has been present for a long time and still isn’t properly resolved.

My setup is not unusual: AC-coupled inverter (Fronius) + Victron MPPT + battery.

The problem is very clear and reproducible:

  • Plenty of solar power available
  • Battery is NOT full
  • System should allow full production

Yet the system randomly reduces MPPT power significantly (for example from ~4.8 kW down to ~2.5 kW) without any valid reason.
At the same time, the AC inverter (Fronius) continues producing normally.

This clearly shows that ESS is actively and unnecessarily limiting DC production.

This behavior has been reported for a long time (3.6x, 3.7x), and while 3.80 seems somewhat improved, the core issue still appears in certain conditions.

From a user perspective, this is a serious problem:

  • Loss of production
  • Unpredictable system behavior
  • Lack of trust in ESS logic

To be very direct: systems from competitors (Sigenergy, SolaX, etc.) handle this scenario much more smoothly, without unnecessary throttling or unstable behavior. They simply work without constant tuning.

Victron has excellent hardware and flexibility, but ESS behavior in mixed AC + DC systems still feels inconsistent and not fully mature.

My expectation is simple:
If there is available solar power and the battery is not full, the system should not arbitrarily limit MPPT.

I’m currently testing 3.80.9 and giving it some time, but if this behavior is not fully resolved, it becomes difficult to justify staying with Victron for residential systems where stability and predictability are critical.

I would really appreciate a clear technical explanation:

  • Why is MPPT being limited in these situations?
  • What exact condition triggers this behavior?
  • Is this fully addressed in upcoming versions?

Thank you.I’ve been using Victron ESS for quite a long time now (since around version 3.60), and I need to be honest — this issue with MPPT throttling has been present for a long time and still isn’t properly resolved.

My setup is not unusual: AC-coupled inverter (Fronius) + Victron MPPT + battery.

The problem is very clear and reproducible:

Plenty of solar power available

Battery is NOT full

System should allow full production

Yet the system randomly reduces MPPT power significantly (for example from ~4.8 kW down to ~2.5 kW) without any valid reason.At the same time, the AC inverter (Fronius) continues producing normally.

This clearly shows that ESS is actively and unnecessarily limiting DC production.

This behavior has been reported for a long time (3.6x, 3.7x), and while 3.80 seems somewhat improved, the core issue still appears in certain conditions.

From a user perspective, this is a serious problem:

Loss of production

Unpredictable system behavior

Lack of trust in ESS logic

To be very direct: systems from competitors (Sigenergy, SolaX, etc.) handle this scenario much more smoothly, without unnecessary throttling or unstable behavior. They simply work without constant tuning.

Victron has excellent hardware and flexibility, but ESS behavior in mixed AC + DC systems still feels inconsistent and not fully mature.

My expectation is simple:If there is available solar power and the battery is not full, the system should not arbitrarily limit MPPT.

I’m currently testing 3.80.9 and giving it some time, but if this behavior is not fully resolved, it becomes difficult to justify staying with Victron for residential systems where stability and predictability are critical.

I would really appreciate a clear technical explanation:

Why is MPPT being limited in these situations?

What exact condition triggers this behavior?

Is this fully addressed in upcoming versions?

Thank you.

2

Is your AC PV on AC IN or OUT?
There are circumstances where this behaviour can occur on AC IN coupled PV.

3

The Fronius is connected on AC OUT.

This is a typical AC + DC coupled system (Fronius + Victron MPPT).

Also, I am observing this behavior even when:

  • Battery is around 50–55%
  • Plenty of solar power available
  • No settings are being changed

MPPT briefly drops to very low power (even 0W), then recovers again.

This does not look like a normal operational condition, but rather unstable ESS behavior.

Can you clarify what exact condition in ESS would justify limiting MPPT in this situation?

4

Screenshot_20260401_133216_VRM
Screenshot_20260401_133216_VRM1080×2340 174 KB

Screenshot_20260401_132922_VRM
Screenshot_20260401_132922_VRM1080×2340 166 KB

5

I’m also having something like this with my RS6000 on 3.70. Now starting to notice it as there is more sun during the day.

During the sunny periods, Phase 1 is throttled while a few kW is imported from the grid. This doesn’t make any sense? For now, i’m shutting off DESS during the day. This will cut off the grid import and use all available solar.

Maybe i’m just to stupid to understand the system. :slight_smile:

6

I am seeing exactly the same behaviour.

MPPT is being limited while there is still available solar power, and sometimes even when the battery is not full.

This definitely does not look like correct ESS behaviour.

7

I have exactly the same issue as you.

During sunny conditions, MPPT is being limited or even drops to 0W while the battery is not full and solar power is available.

This does not make sense and looks like incorrect ESS behaviour.

8

The dash indicates PV inverter on AC input though.

9

The Fronius is intentionally connected on AC IN due to feed-in tariff (green bonus), so it must run continuously.

However, this should not cause MPPT to drop to 0W while:

  • Battery is only around 50–60%
  • Solar power is clearly available
  • No settings are being changed

Also, I observe that the system sometimes limits MPPT while still importing power from the grid, which does not make sense.

This looks like incorrect ESS behaviour rather than a configuration issue.

10

Indeed but it is why I asked about AC PV on the Input and you replied it was on AC OUT.

You might want to refer to this topic as it might be related.

11

I had a quick look at your data – I assume you observed this today – and with the exception of two times when it looks like you rebooted the GX (around 11:30 and 14:00), the MPPT seems to be tracking a maximum power point the whole time. If I plot the PV-inverter and the MPPT on together on a graph, they seem to trace a similar pattern too.

I don’t think the issue is related to ESS. The system is configured to feed excess DC-coupled PV into the grid, so the GX will not apply a current limit to the MPPT. The MPPT also never reaches the charge voltage.

Could it be that what you are seeing is just the natural periodic rescan of the MPPT? The MPPT will at times try to find a new maximum power point, and it may temporarily reduce power while it does this.

1 Like
12

As a side node, yes, this happenes for the RS along with DESS in a few situations.

Fix is completed, scheduled to go into a 3.80 for a while, then also ported to a 3.7x release.

(All VEBus Systems and Standalone MPPTs are unaffected by this)

13

Thank you for checking my data.

However, what I am observing is not just a small MPPT rescan.

The power drop is very significant – sometimes MPPT goes from around 4–5 kW down to near 0W, and then recovers again.

This happens while:

  • Battery is only around 50–60%
  • Plenty of solar power is available
  • Fronius continues producing normally

This seems too large and too frequent to be just normal MPPT tracking behaviour.

Also, I sometimes observe MPPT being reduced while power is still being imported from the grid, which should not happen.

Could you please clarify what is the expected behaviour here, and what level of power drop is considered normal during MPPT rescan?

14

Thank you for your explanation.

I understand that MPPT periodically rescans for a new maximum power point.

However, in my case the drop is very large (from ~4–5 kW down to near 0W), which seems too extreme for a normal rescan.

Also, this behaviour repeats multiple times during the day, not just occasionally.

Additionally, I sometimes observe MPPT being reduced while power is still being imported from the grid, which does not seem correct.

Could you please confirm:

  • What is the typical expected power drop during a normal MPPT rescan?
  • Should MPPT ever drop close to 0W under these conditions?

I would just like to understand what is considered normal behaviour.

15

Can you maybe add zoomed-in screenshots from vrm advanced showing the times and issue while active?
Makes it easier to be more focused on responses.
Thanks.

1 Like
16

A rescan usually happens in three sweeps, so you will see it dip down three times, and it can dip down pretty severely. Of course we don’t see that as clearly on VRM, since the data is somewhat averaged out and only logged once a minute at most, but what I see this side looks like rescanning:

image
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In any case, I am not trying to say this is normal, I don’t think we know for sure yet, I’m trying to steer the attention to look in the right place, so we can get the right person on it.

17

Thank you for the detailed explanation, I appreciate it.

I understand now how the MPPT rescan works (multiple sweeps), and that some temporary drops are expected.

However, in my case the drops still seem quite extreme, especially when the power goes from several kW down to nearly 0W.

Also, this behaviour repeats multiple times during the day under stable conditions (battery not full, good solar input, stable AC PV production).

So while I understand the rescan concept, the magnitude and frequency still seem unusual to me.

Thank you for taking a closer look and for forwarding this to the appropriate person — I appreciate your help.

18

After updating to 3.80.13, I observed slightly improved behaviour under low solar conditions. However, I still experienced one drop to near 0W.
Due to limited solar production, the system was not operating at full power, so I could not fully test the behaviour under high PV conditions.
I will continue testing once solar production is higher.

19

After further testing with firmware 3.80.13, I can confirm that the issue is still present.

I have just observed another short but clear drop of MPPT power to 0W in real-time monitoring (see attached video). This happened even though solar production was available and conditions were stable.

While the behaviour seems improved compared to before (less frequent and shorter drops), the problem is clearly not fully resolved yet.

I will continue testing, but this confirms that the issue still exists in the current version.

20

I would be very surprised if it was fixed. Nothing changed. The drop in production is not commanded by the GX device, it appears to be the MPPT itself reacting to something.

A rescan usually happens only if there is a sudden change in battery voltage, and the MPPT has to switch from V/I limited mode back to finding a maximum power point, or periodically (about every 30 minutes if I recall), but the rescan will only take seconds before it is back to full power.