question

maartenvt avatar image
maartenvt asked

Powerassist in ESS system development

In an ESS system, the powerassist function is disabled by the ESS assistant.

In Belgium the government is going to charge a tax based on the peak power, besides the existing taxes on the amount of imported energy.

This will make the powerassist function of the Multiplus II or easysolar important.

Now we are dependent on integrators to add the powerassist software on a raspberry pi-based module that adds this function to the ESS.

I find it disappointing that Victron is not willing to integrate this function in the ESS assistant.

Is there really nobody in this community that is able to make this work? I am willing to pay a fee for that...

I have a 9kwh battery pack that is set on min SOC of 25%, to be able to deliver backup power when necessary, like an outage of the grid, or the grid voltage raising above the max allowed grid parameter, making the inverters disconnect from the grid.

But there are 2 situations I can think of, in which I want a deeper discharge of the battery.

  1. Powerassist: When the AC input grid power of the house exceeds 4KW, the battery should assist the grid with extra power, so that the input gridpower stays below 4kW. After the power demand in the house gets lower again, the battery may charge back to 25% SOC with low charging gridpower. By the way, Charging the battery with grid power must always keep the total import ac power below 4kW, which is not the case now when setting a higher SOC for instance... A button in the ESS control with a boost charge power would be handy though, when you want to charge the battery asap.
  2. Weather forecast-based deeper discharge: Nothing to do with powerassist. But the battery may discharge deeper in the evening, when the next day a lot of sun is predicted.


ESSSOCfeature requestpowerassist
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3 Answers
Alexandra avatar image
Alexandra answered ·

@maartenvt

Power assist is sort of still there in ESS.

With a combination of grid set point and incoming current limit, as well as allowing the battery to discharge the useage from grid can be minimised under the peaks. Minimum state of charge can be set, where it will only recharge to that percentage if there was a grid outage and it was drawn lower than that.

Couple this with lower charging from grid etc it is well within reach.

We have poor grid connection where we are and use these features to start huge loads using solar and battery.

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And about the wether pattern prediction, not sure about where you are but the wetherman cant wven get it right not sure how that would be automated.

Most of our clients do this for thselves based on needs or wants, easy to de even for least tech savvy ones.

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Hello Alexandra,

thanks for commenting... I tried to analyze your advise, and to implement this in my ESS Home System as built as you can see in the diagram below.

Schema extern-1.jpg

But I find it hard to interpret your settings as being manual settings whether automatic settings. Are these settings in the VRM or VE Configure?

I neither want to change settings that are in some situations optimal, but in other situations less interesting.

Could you please clarify your answer a bit more? Thank you.


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schema-extern-1.jpg (169.2 KiB)
@maartenvt

The basic idea is in the ess manual.

Settings are explained in the commissioning section.

Power assist at lower battery levels is not something I have tried.

And allowing a deeper discharge on a cloudier day can be set by you as min soc in the ess menu. Although going much below 25% makes no sense from a backup point of view? But see chapter 6 of ess manual it explains more.

Grid set point is what you tell the Victron to keep its useage to if there is enough solar. And the main incoming amperage is set on the multi so it does not exceed that. Ess to some degree does shift the grid point around depending on the combination of settings you put together. So it needs some familiarity with the system.

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In the manual in section 4.2 it says in a note that the power assist settings will be ignored so it is not possible to use ESS and that the inverter injects energy when the consumption exceeds the power contracted with the external network.
I hope you review this point and try to implement it because I'm in the same situation, I have to pay for a peak power when I could supply those peaks from the battery....it's a shame
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@maartenvt

We use the input current limit down. To under 30A depending on the power assist ability of the inverter. Ess will dynamically shift the grid point but never goes over the current limit even if the load is higher (unless the battery soc reserve is met or the sustain feature becomes active). If solar is large enough to cover then neither grid nor battery is used. I have so e systens even set to 20A input.

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multivictor avatar image
multivictor answered ·

@maartenvt : Why 4 kW? The capacity rate starts from 2.5 kW.

@Alexandra : It is a Flemish tax and not a Belgian one, so he lives in Flanders, the northern part of Belgium.

Btw, for the weather forecast to set the SOC I use the Solcast Api toolkit, much better than the local weather forecaster. :-)

@shaneyake : Can you post your solution here? Many Flemings will thank you.

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@MultiVictor. Why not limit the input power to 2,5kW? Good question. I see that the peak power is max 6500W in the house.

In the monitoring of the grid company I can see that the average monthly capacity peak power of house is around 4kW.

In january, when the solar and battery was sleeping, we had a higher peak and that's what I want to prevent with the power assist. And slowly charge the battery with low grid power during the day, at times the consumption of the house is low.

The max power of the inverter in the ESS settings is limited to 2600W. That was recommended. But I don't know why this 5KW Multiplus II can't be set to 4000W instead? What's healthy for the battery and the inverter in the long run? And a high discharge power makes the system also inefficient. But that's maybe better than having a higher AC input peak.

In that perspective I could maybe set the max input power to 2,5kW or 3kW when I limit the inverter to 4000W?


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What is your battery size/specs? That might be your limiting factor.


The multiplus will take care of itself no need to limit its power. We have units that run at 100% power from 10am till 6pm everyday in the summer without any problems for years now. Once the multiplus gets hot it will throttle it's output down.
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shaneyake avatar image
shaneyake answered ·

This can be achieved using the large firmware. Using NodeRed you can control the inverter setpoint to hold your grid connection below a threshold. You run ESS in external mode which gives NodeRed full control and then have a PI controller set the inverter setpoint so that it holds the grid at 0W or some setpoint. Once you hit your Low SOC, instead of putting the inverter in standby, you get it running but change the inverter Pi controller input to battery power and try hold that at 0W. You can then set limits on the Pi controller so that the setpoint commanded can not exceed the 4kw or whatever you would like to program.

I use solacast API for the PV forecast and that determine the min SOC you would like to use for the next 24 hours. This is also done in NodeRed.

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