puitl avatar image
puitl asked

Multiplus 2 ESS, Fronius Symo on AC-Out 1 and grid-lost: Symo turns off for 2 minutes


In my ESS with 3x MP2 and an Fronius Symo on AC-Out 1 the Symo turns of for about 2 minutes if the grid is lost.

After the 2 minutes it restart´s and run´s on the micro-grid of the Multi´s.

Why is that?
I assumed that the Symo is running without a brake in this case...

ac coupling
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

3 Answers
michaelvh avatar image
michaelvh answered ·

Is your symo country code configured as MG50 or 60? They sometimes need a few seconds to adapt to a change in the grid or could throw an error for a short time. Clears up quickly usually, should not turn off completely.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

pedaaa avatar image pedaaa commented ·


i have seen similar behaviour on my ESS with Fronius Symo at AC-Out1.

The Symo is configured to MG50.

If Grid fails, the Symo shuts off right away and then boots again after some delay time.

i have only tested it a few times so far, so I´m not sure, if it ALWAYS kicks out and then comes back, or if it sometimes would stay alive?

Could someone answer this with confidence?

Its a very interessting question, as it would affect the 1:1 rule in my opinion.

IF.... the Fronius Symo would always be kicked out immediately at grid failure, then

we could oversize it a bit over 1:1 rule.

Because we can use the Multiplus AUX relay to switch at grid failure.

And we could use this signal to power limit the Fronius.

(by setting Fronius I/O configuration to an power limit suited to 1:1 rule)

Why would you do that?

because this would give you a big advantage:

You can oversize above 1:1 rule at regular ONGRID operation.

- and once grid fails:

- the "oversized" Symo will be kicked out anyhow, so it can´t do any damage

- once it reboots, it will only operate with power limited because of hardwire input

- so it can run OFFGRID with limited power to perfectly respect 1:1 rule.

So the big question is:

will the Symo ALWAYS be kicked out immediately!! at grid failure?? And then come back with some delay?

if so... that design idea can be done without much worries

0 Likes 0 ·
pedaaa avatar image pedaaa pedaaa commented ·

is anybody here, that has done some more testing, on Fronius Symo behaviour (if on AC-Out with MG50 grid code), during grid failure?

1. does it shutdown in any case and then reboot? or does it only shutdown randomly?

2. if it shuts down, is it immediately at grid failure, or with some delay?

0 Likes 0 ·
michaelvh avatar image michaelvh pedaaa commented ·
You should never go over the 1:1 factor. Better to oversize the PV array but not the inverter, or use additional DC-coupling, or use AC-in for extra inverters.

The Symo will not always shut down. I have 2 cases where they happily keep inverting without shutting down. Sometimes at reduced power for a few seconds before ramping up again, sometimes they keep full output trough the grid failure. I guess it depends on the grid is was connected to before and the change it detects.
0 Likes 0 ·
baxter avatar image
baxter answered ·

I can only share what I observed during operation, the Symo shuts down after grid loss, reboot and re-connect to offgrid provided by the Multis. This happens with national grid code AND MG50.

1 comment
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

pedaaa avatar image pedaaa commented ·

yes, i saw the same at my tests so far.

But as Michael said above, he saw some cases where they kept providing full power... if this really would be true it could cause problems in such a rare case.

I think i will test it some more times. As now i am still safe within 1:1 rule, so no risks...

If the Symo kicks out 9 of 10 tests, i think i will still go with the strategy of little oversizing ONGrid + limiting, once OFFgrid.

As potential risks of damage is super low then

0 Likes 0 ·
puitl avatar image
puitl answered ·

This could be the reason for the Symo-shutdown:

Table with general suggested settings for 50Hz and 60Hz frequency

State 50Hz 60Hz .
Start 50.2 60.2 Hz
Minimum 52.7 62.7 Hz
Disconnect 53.0 63.0 Hz

Note that although the MG50 for instance has a higher start frequency of 51Hz, there is no real drawback using the proposed value of 50.2Hz. The system will just increase the frequency until the PV inverter regulation kicks in. The value of 50.2Hz will work with a broader range of PV inverters/grid codes.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Related Resources

Additional resources still need to be added for this topic