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davidfg avatar image
davidfg asked

Detect surplus Modbus

I have the Multiplus as ESS with a Fronius inverter. I have limited the grid feed to 100W. When the batteries are full, the power of the Fronius is reduced. It is therefore not recognizable whether there is a surplus. Is there a possibility via Modbus to read out whether a reduction is currently active to use the possible surplus by switching on certain devices?

Multiplus-II
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mikhail-petukhov avatar image mikhail-petukhov commented ·

You can try to read the Fronius registers WMaxLimPct and WMaxLimPct_SF

It is highly probable that Venus controls Fronius' power through these registers.

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thomasw-1 answered ·

Hi @DavidFG ,
In a grid attached configuration a surplus can be easily detected by checking the feed-in.
However I suppose that you ask for a island config. In that case I would check the frequency. In case battery is fully charged, Fronius is throttled with in increased frequency (>50Hz).

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davidfg avatar image davidfg commented ·

Hi,

no I have currently no island only as written the feed limited.

But thank you I will pay attention to the frequency what happens

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thomasw-1 avatar image
thomasw-1 answered ·

@DavidFG ,

In case you have a feedin based config, frequency won't change.
I have actually the same condition. I have a feedin limit of 7700W, whereas pannels can generate 11000W in optimal cases. I start my P2H solution with 1400W consumption after feedin gets larger than 7400W. Since power consumption of P2H is smoothly increased Fronius inverter is less or not throttled anymore. Reality has shown as closer the expected feedin level gets to actual limit as less efficient it worked. Therefore the solution got designed that feedin levels out at 6000W.

With that approach feed 6000W into grid and can use up to 5000W for P2H.

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djdemond avatar image djdemond commented ·
How do you start the P2H solution? I would like to start a device when feed-in value reaches a set amount?
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thomasw-1 avatar image thomasw-1 djdemond commented ·

Hi @DJDemonD ,

good question!

  • First of all I ran some trials, when my heater produced reasonable heat, so that it is worth to heat instead to feed-in energy.
    For me it was ~1.700 watts.
  • In addition I run the solution that overall a feed-in of min. 400 watts remains left. This margin avoids unnecessary battery load, when my internal power usage varies and leaves my solution some more flexibility to adjust P2H power.
  • Overall the P2H solution starts, when ~2.100 watts are available. In my implementation the maximum P2H usage is ~8.800 watts.
  • In order to avoid frequent activations and deactivations, the deactivation is performed, when heating power gets below 1.400 watts
  • Overall my solution checks every 2 seconds the Grid-meter and decides to increase or to lower currently used P2H power. The adjustment takes aorund1 to 2 seconds between measurement and power-adaptation.

This was today's usage
1682095926290.png

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djdemond avatar image djdemond thomasw-1 commented ·

Thank you for taking the time to reply. What I was trying to find out is by what method are you reading the data? And by what method are you using that to operate the switch?

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thomasw-1 avatar image thomasw-1 djdemond commented ·

Meter data is directly requested from ABB meter via a Modbus/TCP-gateway and P2H is controlled by mypv AC•THOR 9s in manual http-mode.

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