vicuser77 avatar image
vicuser77 asked

ESS export to grid mainly at defined hour intervals

Hello community!

I have the following task: find a way to use the Multiplus II to export energy to the grid at programmable hour intervals (day, night, independent of PV production times).

Why: At the moment I receive 0.05 € per exported kWh so I am studying the possibility to change my energy subscription to a hourly tariff based on the market price of energy. Each day the prices vary wildly from less than 0.01 € at noon to 0.90 € in the evening and 0.80 € at night with some peaks even more than that. My goal is to store PV production during the day and export it during the best paying hourly time slots to shorten my amortization period.

My system: Multiplus II 8000 as ESS with 60kWh LiFePO4 battery and a Fronius 8kW on the output, grid metering is done by the Multiplus II, all consumption occurs on output

Current usage: I am already exporting mainly at off peak times (mornings and afternoons) because the grid is swamped with PV energy at noon, raising the system voltage close to PV inverter shutdown values (> 256 Vac). Also my grid connection is not the best as I get about 0.8V raise for each kW exported.
I solved this by automatically lowering the battery max charge power value in Cerbo GX when the grid voltage is low (preventing battery charge) and raising the battery max charge power when the grid voltage is closer to 250 V to direct more energy to the battery.
2 x 3kW water heaters are on standby and ready to activate if grid voltage raises over 252 V when the battery is full.
This whole setup works perfectly and the Multiplus II stays connected to the grid while the Fronius PV inverter never trips anymore.
Before implementing this adjustment, at around 11AM the batteries were full, the PV inverter would shut down due to over voltage protection and the Multiplus II would disconnect from the grid.
This whole automation is done using MQTT and Node Red thanks to the Victron system being so open and friendly.

Back to my new task and problem:
I have found no way to directly program the Cerbo GX to export at any desired hour. Is there a way to force Multiplus II to export during the night from battery storage? That would be the best option since I only have to program the system to export energy during the best time slots.

Second solution that I can see would be to implement a smart meter connected at the grid point. Read data from this smart meter and send it to Cerbo. When export is desired I can change consumption data in order to make the Multiplus II invert more than is consumed on the output.
Can the Multiplus II cover consumption on the input if fitted with a smart meter at the grid point?

Third solution (that I try to avoid) would be to use an extra battery inverter only for export purposes. This would again increase system costs and change the amortization period for worse. If this remains the only choice, does Victron have a product that fits this use case?

Not afraid of programming it all, just wanted to run these options by the community, maybe there is some info that I am missing - been using this Victron system for only 3 months now.

Multiplus-IIESSEnergy MeterFronius
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2 Answers
vicuser77 avatar image
vicuser77 answered ·

Looks like I found my answer: ESS mode 2 and mode 3.

In particular ESS mode 2 seems to be exactly what I am looking for.
Grid power setpoint will allow me to use a low value to prevent the system from using grid power and a negative value when I want to inject during best paying time slots.

Played a little with the topic Settings/CGwacs/AcPowerSetPoint and it seems like it works without any changes directly with my current ESS setup. Applying a negative value will force the Multiplus II to export that precise amount of power and applying a positive value will allow it to consume.
Problem solved, thanks a lot Victron for the great system!

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nickdb avatar image
nickdb answered ·

Go look at the modifications section, plenty of folk doing this already with nodered and the various other methods available.

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