nickdb avatar image
nickdb suggested

Feature request: ESS inverter limits

We have a use case to limit the inverter power during the ESS battery discharge cycle, this is easily done by setting the default ESS limit.

This provides for better use of the batteries and a more predictable SOC at the end of the discharge period.

Unfortunately this default also limits PV use for AC loads during the day when we want higher limits for surplus PV.

Is it possible to either split these limits or to add an "override" in the actual charge schedule?

MPPT ControllersMultiplus-IIESS
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Keith Arnold avatar image
Keith Arnold commented

Could be similar logic as the limit soc except when grid loss.

inverter limit except when excess solar available, will work. Add it to my wish list.

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markus-001 avatar image
markus-001 commented

I automatically adjust the max inverter power using node red, available on the Venus large image.

Tie the max inverter power to the MPPT power plus say 700 watt. So at night your max inverter power will be set to 700 watt and in the day when there is PV power coming in the max inverter power rises to match what’s coming off the PV. I have this running on a few systems some with two MPPT’s no problems at all.

Besides that there is so much more you can do with node red, you can switch the relays use the digital inputs I even feed in by changing the grid set point to negative based on an energy feed coming out of a utility meter 150 meters away over the LAN on a micro grid. Just be sure to add a watchdog timer / trigger to the flow so if the Venus fails to receive the energy readings with in a set time the watchdog timer fires a 0 for the grid set point. Once the energy data is received again the grid set point is adjusted once again.

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nickdb avatar image nickdb ♦ commented ·

Is the a dummies guide to getting node red working and doing the above?

For those of use less developer orientated :)

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markus-001 avatar image markus-001 nickdb ♦ commented ·

@nickdb There's quite a bit of node red information as well as java script available on the web, unfortunately it took me quite a few months to figure it out, now that I know how it's a few minutes work, I have no problem to help you through it so you can get going quickly, let me know and maybe we communicate via email instead.

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nickdb avatar image nickdb ♦ markus-001 commented ·

@Guy Stewart (Victron Community Manager) is there a secure way to send contact info or would you be so kind as to pass my email to markus via email? Thanks

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tfj avatar image
tfj commented

Another (probably simpler but more expensive) way of solving this problem, is by integrating a IMT Si-RS485TC-T-MB irradiance sensor from Ingenieurbüro Mencke & Tegtmeyer GmbH with your system. The IMT sensor is already compatible with the Venus GX - see Venus manual section 1.10.

Reading the irradiance value and cell temperature from the sensor, you can calculate the maximum available PV power from your PV array.

Using the available PV power as reference, you can set the Maximum Inverter Power to limit the discharge current from the battery when the grid is available. You can then bias this value (positive or negative) by looking at other parameters like the battery State of Charge and Time of Day.

I have implemented this via a Cron Job calling a Bash Script every 5 minutes throughout the day.

The system performance is acceptable, although it still needs some fine tuning - especially in the determination of irradiance values (measurement intervals and averaging algorithm) as well as the frequency of setting the Maximum Inverter Power. The offset according to Battery SOC also still has to be optimised.

Question: Are there any potential problems or negatives associated with automatically adjusting the Maximum Inverter Power in the ESS every 5 minutes or even more frequently perhaps? Any comments will be appreciated.

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Hendrik Coetzee avatar image
Hendrik Coetzee commented

@tfj - I have been manually adjusting the inverter limit setting for a while now.

I have also wondered if there are any potential negatives to doing this. So far nothing blew up for me.

And yes, I'm also looking at automating the adjustment. I have also come to the conclusion that the "right" way to make this is work is to integrate some form of irradiance sensor, seperate from the power system. For many reasons I probably won't be going that route any time soon however.

So what you are doing, is more or less the gist of what I'm implementing (I'm just using MQTT instead of on-device bash script, for my own reasons).

And again, so far I have not seen anything or anybody shouting "noooo what are you doing you idjit" on wards march I guess.

I am curious, when looking at battery power, does your script look only at the current power, or do you look at, for example, the average over the last 5min?

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