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Laurens D avatar image
Laurens D asked

Dynamically adjusting ac grid point in ess.

Hallo Ladies and Gents,

I will keep this short because I lost the form while submitting, unfortunately.

When turning on ESS you will also be turning of powerassist, though this is a function I still would like to use on certain times.

I noticed when changing the AC Gridpoint to a negative you will send back power however when it is in the positive it will charge the battery; if there is a need for that. When keeping it at 0 it will stay as idle.

I would like to use node-red to change the AC Gridpoint depending on the current load of the house; with an external sensor so this can happen each second, or even more often or less often.

But is there any concerns when changing this often? Like wear of the flash storage memory, can cause issues with the inverter (because a lot of changes in a short time)?

Are there better ways to handle such situations, in short I want to:

1. Be able to charge the battery when it's cheap.

2. Being able to assist my current load when the power prices are high (so using 100 watt I want the gridpoint to be -100w).

3. Being able to discharge the battery back to the grid company when I want.

Is this the way to go? Any suggestions I would love to hear them even if it differs from my current way of doing things, would love to hear feedback! Thanks!


ESSpowerassist
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3 Answers
andy156 avatar image
andy156 answered ·

Point 2. I think you haven't totally understood the set point control here.

The load is a fixed amount. You can vary the grid point which then lets the system work out what happens at the inverter.

load - inverter= grid point.

ie if load is 100 and inverter is putting out 100 then grid point = 0

However we vary grid point and the system uses this to calculate what the inverter is doing.

so

load - grid point = inverter

so if you want the grid to have no export/import you set it to zero and not -100 as you said

so

100-0 = inverter now puts out 100w to support the load.

if you wanted to export 100w at the same time you set grid to -100.

100--100=200. so the inverter puts out 200w.

It really is as simple as saying I want to export at a time so set the grid point to a value of '-export amount' and the system will try and achieve it within the system spec allowances.

If you had pv on the ac side and a battery you wanted to export you would need to poll the pv production and add it to the maximum inverter capability to set the set point. In node red this can happen every 5 seconds using the built in nodes. You might get a faster loop using the MPPT side of things.

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Laurens D avatar image Laurens D commented ·

Might be me getting you wrong, or you are getting me wrong here.

I am aware it's a fixed amount but it's configurable so I can set it based on my needs.

With 0 it could be essentially off or well, it tries to keep at that value, though it can spike a bit higher and lower between the two so it's basically suggested to always leave it on a low value (I think the manual says 50 but 10 or 30 in my case would also be okay)

With a negative value so -100 you will start to export that fixed amount; the idea is to change this depending on load; so I'm using the TV and computer that equals to 400 watt, it will be set externally depending on that power usage to -400 so 400 - 400 = 0 usage of grid.

when using this in the positive it will allow more power to be taken from the grid, so +2000 will allow you to charge with 2000 watts (likely minus the critical load, which most of the time 0 - 30 watt, with some peaks around 80 watt; so 1920?).

It's a rather easy setup, when I get a home on my own I will try to add solar and it'll be more fun :-)

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andy156 avatar image andy156 Laurens D commented ·

Yes you set it. But if you set it to -400 it will power the 400 watts load AND export 400 leading to a total of 800 watts leaving your battery.


You are correct with the import. A set point of 2000W will end up with 2000W-load going to the battery.


If you don't want to discharge to the grid or take power from the grid set the Setpoint to zero. Then the loads on AC Out will be fed from the battery and PV.

It will ignore the zero value if your battery is fully charged and you have excess PV and you have feed in enabled.

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Laurens D avatar image Laurens D andy156 commented ·

Ah, so you mean the load that's used in AC out? Yeah, I understand that's counted as different.

Ehm, as far I'm aware the -2000 for example is only for the inverter saying what to throw back to the grid, so basically that happens; but the load on the battery is indeed the AC-OUT1/2 load and the efficiency losses of the inverter.

so -2000 might take 2300 from the battery (due efficiency); let's say there is 200w load on ac-out it will come to 2500w taken from the battery.

Thanks, things like this is making me understand the system more and more, at the moment it's more for playing; it's fun :-)

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andy156 avatar image andy156 Laurens D commented ·
I've just thought, I had assumed you had the loads on the AC Out. But you could well be talking about the loads connecting in parallel on AC IN. If that was so then you are right about having a minus value to match the loads. There are so many ways of setting these up.
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Laurens D avatar image Laurens D andy156 commented ·
Yeah, sorry about that on critical load I have only my freezer because I thought that was handy, but it's not really required.

The rest of the house uses the normal grid, which is why I would like to send power back to the grid depending on the load (using that same grid), so that it evens out (0% grid so to say, 100% battery).


Which makes me think, I probably can do short burst with more power instead of evenly (depending how much is used in that hour/15 minutes); the meter will probably even it out *thinking face*.


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Alexandra avatar image
Alexandra answered ·

@Laurens D

Spend a bit more time with the ESS manual.

Power assist is not off with ESS, it is just no longer user configurable/ adjusted. The system now decides what to do to balance grid, input current limit, battery and solar depeding on user setttings in the GX. So it also varies grid set point as needed.

1. Scheduled charging for times when grid is cheap.

2. Input current limit, battery reserve SOC all play into this

3. Not played with scheduled feedback. Definitely would need a node red flow.

Since feedback to grid is not an issue for you a grid set point of 0W is perfect for you. Feeding in excess solar in grid feed in overrides the 0w set point.

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Laurens D avatar image Laurens D commented ·

You are right! with power assist I had another idea in mind where it would use the AC-IN to stabilize the grid and send back when you are using power (for example 150w tv, it will send 150w from the battery so it can balance out as 0)

1. Yeah, this is a way of doing things; but I do not think home homeassistant plugin will allow for this; it would change depending on day because it's using stock prices (so it's not always charge at night for example).

2. That is certainly true but it just delivers and take what it can right? Let's say when you set it at -1000 it will attempt to deliver +/- 1000 watt back to the grid, if other devices takes a part of that power it will just decreased from the actual amount that is delivered to the supplier grid. In my case there is no solar unfortunately.

3. Yup

Might be worth mentioning, the system is made like this:

There is a separate grid group connected to ac-in, and on the AC-out in the multiple for critical loads is only used for the freezer (not important but was easier that way for me).

So the only way to give support to my other home devices is sending power back to the grid.

The BMS itself gives warnings when the capacity/voltage is too low so stops (also victron is set, it also received data from the bms itself) and when it's full the BMS will also stop the charging.


I'm a bit worried setting the ac gridpoint a lot of times might cause issues in the long term.

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tom w avatar image
tom w answered ·

@Laurens D

Do you have an external grid meter that measures the consumption and feed in from and to the grid for the Multiplus?

All yours questions and answers indicate to me that your ESS is set to use the internal grid meter of the Multiplus.

With an external grid meter and a set point of "0W" the Multiplus will automatically adjust the feed in power to compensate for consumption or charge your battery if you feed in excess PV energy to the grid. There is no need to adjust anything to keep your grid balance around "0W"

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Laurens D avatar image Laurens D commented ·

@tom w

Yes, I am using the internal meter of the multiplus; I did have a separate group that was not doing anything, so I used that however it's unfortunate because I cannot modify this to add an external meter, I do have a p1 meter though but the Victron cannot do anything with that itself.

> There is no need to adjust anything to keep your grid balance around "0W"

I see, so with that it can compensate the devices usage and put in power to keep the grid balance to 0, are there other ways to do this?


For my reference, the 'feedin' means putting it in something, So multiplus to Grid power or Multiplus To battery? To avoid confusion from my side.


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tom w avatar image tom w Laurens D commented ·

My bad, you don't have a PV, you just want to charge the battery when the energy is cheap. Please forget about the feed in of excess PV power.


What kind of grid meter do have?

Maybe it's supported by the community.

I'm using a Shelly 3EM grid meter which is supported by scripts from Fabian Lauer: https://github.com/fabian-lauer/dbus-shelly-3em-smartmeter


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Laurens D avatar image Laurens D tom w commented ·
Using two meters at the moment, one is the Tibber Pulse with P1 connection, and the other is home wizard with a p1 meter also; with uses the dsmr5 protocol.
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tom w avatar image tom w Laurens D commented ·

As a Tibber customer you should be able to get your momentary consumption from the cloud. See https://www.home-assistant.io/integrations/tibber/ for details. It should be possible to modify Fabian's script to use Tibber's API similar to the Shelly integration in Venus OS.

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