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cobraphil avatar image
cobraphil asked

Zero feed-in with ESS, SMA and no AC-IN usage

I just install a Multiplus-II in Papua New Guinea where blackouts and brownouts happen on a daily basis. It is installed on my house which is located on a college campus with other houses. We have enough sun here that I can run disconnected from the grid which I have been doing since the install was completed. Batteries are still 70% in the morning and fully charged by 11:30am. I want to use my excess solar to assist the campus. So my goal is to:

  1. Each morning, charge my batteries to 100% solely from solar before sending power to the campus.
  2. Once the batteries are 100% charged, send the extra solar to the campus which is connected to AC-IN.
  3. Never use the AC-IN to power my house or charge my batteries unless my batteries are depleted.
  4. Never use my batteries to supply power to the campus.
  5. Achieve zero feed-in to the grid.

I have the added complexity of another solar system on someone else's house as noted in the diagram. I understand that the GX can monitor the SMA by using the WebConnect module to help with the frequency shift power control.

It sounds like a fairly simple scenario, but with all of the options available in the ESS assistant, and the possibility of damaging equipment that is not mine, I want to make sure it is setup correctly. As far as having a qualified installer....well we are located way out in the bush, about 450km from the nearest authorized installer. It would take someone a plane ride to get here.

I have downloaded and installed the ESS Assistant. But when it started asking about the frequencies of the other inverter, I uninstalled it and ended up here asking this question. I do have permission from the owner of the inverter to move forward, but I am looking for some advice on what settings to use, both in the ESS assistant and the ESS settings in the GX (raspberry pi) and how to properly interface to the SMA.

It will be possible to feed-in to the grid once both systems are online which we are not allowed to do in Papua New Guinea. So, I also have a Mutliplus-II current transformer for my house and an ET112 energy meter with Zigbee transmitters for the campus meter.

Missing from the picture is a GX (raspberry pi), Lynx power in module, and Smart Shunt.

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2 Answers
Andy avatar image
Andy answered ·

You're saying, you're not allowed to feed any power back to the grid. How does the campus AC coupled solar avoid that if it produces more power than is being used on the campus? Or is it that underrated that this just not occurs?

The ESS assistant is asking for the frequency of the inverter in case you have one installed on your side of the meter like in this example below. If the grid fails the Multi can control the output of the AC inverter through frequency shifting, depending on your load and battery SOC.

ac-coupled-pv-on-output.jpg

Back to your graphic. You will not have any control from your system to the SMA inverter to control its output. It will just pump out as much power as it can from the solar connected.

You have installed your Victron meter after the campus meter, so your GX should know how much power is needed on the whole campus and then adjust the Multi accordingly. You have to basically turn off your Multi once the batteries are full and let it export your solar to the campus grid with a zero feed in setting. Not sure if this can be programmed with ESS and the Multi. Seems like a complex task. Once you have a meter installed, the Multi always tries to keep it at zero, so will use your battery to power the load (campus).

But I'm not a 100% expert with the Multi and ESS, just from what I read and understood...


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cobraphil avatar image
cobraphil answered ·

Thank you Andy for your thoughts.

The SMA system alone would never be able to produce enough power to feed-in to the grid. But with both systems together, it is possible.

So, in the ESS assistant, do I select the option that an inverter is not connected? In that case, do I need to worry about the two inverters syncing up when both are exporting to the campus power gird? That is one of my main concerns, that the two inverters are not fighting one another or causing damage if one is trying to "outrun" the other.

I do have experience in programming. So if I need to move to mode 2 or 3 of the ESS system and write some node-red code, I am comfortable and willing to do that. But if that is not necessary, and I can set parameters to accomplish my goals, that would be best.

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shaneyake avatar image shaneyake commented ·

The other inverter won't have any issues as it directly connected to the grid.

You will need some way to monitor the campus grid usage so you can throttle your system up and down. You will need to run Mode 3 to prevent the system from discharging the battery to cover campus usage.

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cobraphil avatar image cobraphil shaneyake commented ·

Just to confirm, when I start exporting to the campus grid, I do not have to be concerned about syncing-up with the SMA in any fashion? The two inverters will work together without issue? And when the grid is down, my Victron inverter will detect this and shutdown all export on AC-IN as the SMA already does?

I have a Mutliplus-II current transformer for my house and an ET112 energy meter with Zigbee transmitters for the campus meter monitoring.

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shaneyake avatar image shaneyake cobraphil commented ·
Correct as the SMA inverter is connected to the grid, you will not be syncing up with the SMA you will be syncing to the grid. Yes, the LOMs will detect the grid failure and disconnect.


Okay cool, then mode 3 will be able to work in this condition.

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cobraphil avatar image cobraphil shaneyake commented ·

Next hurdle. I am working on getting ESS mode 3 to work through Node-Red. But now I am stuck on getting AC-IN to connect. I have checked all of the settings that I could find that may be causing the issue.

  • Grid country code is entered.
  • Charger is enabled.
  • Virtual switch is set to Do not use.
  • Inverter Switch is set to ON, not Inverter
  • Accept Wide Input Frequency range is enabled.
  • UPS function is OFF
  • Conditional AC Input Connection is disabled.
  • AC input 1 ignored shows No on display.

I believe I have tracked it down to the input frequency. It bounces between 50.1, 50.4, 50.6. But with the Wide Input Frequency range enabled, I figured it would still connect. I've been monitoring it for about 9 hours now and it still has not connected. This is power directly from the grid, no generator. My other thought was that it was a setting from the ESS mode 3 that I have not been able to test or get working yet because of the lack of AC-In connection. Thoughts? Any way to widen the acceptable frequency range? Is this definitely the cause? I have had AC-IN connect several times over the last week, but did not monitor input frequency because it worked. Now can't get it to connect.

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shaneyake avatar image shaneyake cobraphil commented ·

What grid code are you using?

I would keep the UPS function ON

Conditional AC Input Connection is disabled. What are you referring to here?
Maybe screen shot to help.
AC input 1 ignored shows No on display. Can you also post a screen shot?
What assistants are you running? Screen shot would be great.

That kind of frequency shift is still acceptable if it is a slow change.
My systems ride through much worse.


It is most likely an assistant that isn't configured correctly or grid code.

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cobraphil avatar image cobraphil shaneyake commented ·

Without making any changes, it finally connected overnight. Once connected, it stayed connected through the frequency swings. Seems like only the initial connection is affected. I have a Node-Red flow running that appears to be controlling the ESS parameters as intended. ESS is disabled (Inverter only mode) until the batteries are charged, then it switches to ON mode, connects to the campus grid and feeds-in the extra solar to the campus while not feeding-in to the power grid, and keeps the batteries at 100%. Once the solar drops off and battery SOC drops to a pre-determined level, it switches back to Inverter mode and pulls from the batteries until the next morning. I was able to do this using only ESS mode 1. I initially was testing with mode 3, but it was not working as I thought it should. I appreciate everyone's help.

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shaneyake avatar image shaneyake cobraphil commented ·

What do you mean by "Inverter only mode" ?
You can't disable ESS.
So is your system disconnecting from Grid using the AC-IN contactors? or are you staying Grid-tied just only covering the load on the inverter output.

Mode 3 only works if in the ESS menu is set to external control.
You also then need to change the inverter setpoint vs the ESS system setpoint for mode 1 and 2.

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cobraphil avatar image cobraphil shaneyake commented ·

If the batteries are not fully charged, I change the inverter from ON to Inverter Only mode via Node-Red, which as you said, does not disable ESS, but it does disconnect it from AC-IN essentially not allowing the ESS function to operate. Once the batteries are charged, I switch the inverter back to ON also via Node-Red, which connects AC-IN and ESS is functional again. The ESS setpoint is also changed by Node-Red depending on how much power the campus is importing from the grid, and how much the inverter is exporting to the campus. This allows me to use only battery/solar for my house (0$ electric bill) while exporting all extra solar to the campus (helping their electric bill) and still maintain zero feed-in to the power grid which is prohibited in Papua New Guinea.

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shaneyake avatar image shaneyake cobraphil commented ·
Okay cool, that makes sense.
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