el-gallo-azul avatar image
el-gallo-azul asked

Enabling nighttime export from DC-coupled battery inverter to grid (in addition to daytime export from AC-coupled PV inverter)

I have had a simple grid-tied 5kW PV system for some years.

I have recently added 3 x RedFlow ZBM2 batteries, which means a total of 30kWh, but an available usable 20kWh at any instant (allowing for maintenance strip cycle of these batteries).

I want to reserve 4kWh for my own grid-failure backup use, and export the additional 16kWh to the grid each night. I have rooftop capacity for charging the batteries.

Once the system is configured to export this additional 16kWh to the grid each night, I will know how many more batteries to install, with the ultimate goal of exporting 5kW (1Ø household limit) to the grid constantly, day and night.

As far as I can tell, I have had all the necessary hardware installed, including:

  • MultiPlus-II GX 48|5000|70 battery inverter;
  • SmartSolar MPPT 250|100 MC4 VE.Can charge controller (for the DC-coupled PV array I added); and
  • The associated accessory hardware.

So far, the system is working correctly, charging the batteries, and providing backup power for the house, but the additional grid export is not happening yet, and I'll make the system available to the utility for FCAS once I've sorted the export out. I have not yet seen any additional grid export at all - my usual daily averages of 35kWh production / 21kWh consumption have continued unchanged.

Any suggestions for getting the additional export from the batteries happening?

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2 Answers
Nico Bayer avatar image
Nico Bayer answered ·


you can set the grid setpoint to a negative value. The system will then try to export the set power until your min SOC is reached.

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el-gallo-azul avatar image el-gallo-azul commented ·

That is not intuitive, and hasn't been mentioned in the training materials that I have seen.


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Nico Bayer avatar image Nico Bayer el-gallo-azul commented ·

In an normal installation you try to export all the excess pc during the day and only use the battery for your own consumption. This is more efficient and your battery can be smaler.

But in your case, if i understand it correctly, your max grid feed in is 5kw and your goal is to maximise the export by using the batterys to keep up the export during the night.

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el-gallo-azul avatar image el-gallo-azul Nico Bayer commented ·

Yes. I want to export the maximum permissible feed-in of 5kW to the grid all day and all night.

There is no shortage of energy for my own use (I haven't paid a power bill since 2012), and it is a waste clipping all the potential PV power and flushing everything over 5kW down the toilet.


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David Gould avatar image David Gould el-gallo-azul commented ·
I do this with node red, when the batteries go over the required charge state I change my quattro mode from "inverter "to "on" and have the grid set point at -8000 (-5000 in your case). I can also set the time it does this as I get paid for export by Octopus at different rates at different times of the day.
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nuxland avatar image
nuxland answered ·

Can someone know how can I track how much I have been exporting from battery?
When I export using "Grid Setpoint" to negative value then in Sytem Overview "To Grid" is getting bigger. But I want to know how much have I exported from battery.

I can manually substract from "System Overview" "To Grid" the value that is in "Sola" "To Grid" but is there somewhere a better report?

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