Guaranteeing zero grid feedback with ESS

DIY
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Hi all. Finally got my first string of PV installed into my MPII 48/3000 split phase system with 500 amps of LiFePO4 batteries. For 6 hours this afternoon, my array provided more power than the office consumed. Wonderful feeling and looking forward to my first full day tomorrow.

At this point I have the ESS assistant configured, with Peak Shaving turned on. All is working as I hoped, except for the AC Input which is floating around the ESS Grid setpoint setting. That is expected, although I had to bump it up to 70 watts to prevent it ever going negative.

I am NOT selling power back onto the grid due to a solar unfriendly electric coop. That also means I can never feed power in due to safety concerns. Emphasis on NEVER, as in legally required not too.

I played around with Grid setpoint, from a setting of zero (frequent AC Input on the Remote Console showing a negative wattage, to 50W (once in awhile something like -7Ws), to 100W (nothing so far), but this feels like I’m just reducing the chance, not eliminating it. That, of course, is presuming a -7W implies 7W is being fed to the grid, which may be incorrect.

All that said, I’m looking for a way to guarantee that power is never fed into the grid. Absolute guarantee. Something I can point to when the Coop comes a-knocking due to my dramatically lower power usage. Be nice if I could set Grid setpoint to 0 as well, and cut them off completely.

Does such a thing exist? Is there something I can point to that I would have to enable to cause it to grid-feed?

Using Victron MPPT 450/100s for solar charging, a Cerbo-GX for control, an a Victron Energy Monitor as active devices, all networked together.

Thanks in advance,

Kevin

ps. If I throw my main breaker, the AC Input display goes to “–” and I’ve never caught a voltage on the grid panel after throwing the breaker. So I think all is fine, but have no proof.

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As long as you are connected to the grid there is no way to fully eliminate feed-in.
With bigger loads switching on/off you always have a small peak coming from or going into the grid for a few seconds.

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Best way is to disconnect from grid during the day while there is solar production.
This can be done manually as you are doing, automatically with mechanical means or via software. You will always get some overshoot as M_Lange mentioned. But it is less of an issue with DC coupled PV.

Yes there is a setting in the GX under ESS grid feed in (foud just under grid set point). Just switch it off. And then of course you are already moving the grid set point around. There is a sweet spot in most systems where that works. We also aren’t allowed to feedback with out special licence and meters go into tamper mode if you do. So can say the set point works.

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I do have both ESS “Grid feed-in excess” turned off. I had hoped that would do the trick, but the negative wattage concerned me.

Physically throwing the breaker every morning and night is not really an option.

Thanks for the feedback.

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You can automate the inverter mode with nodered. Switch to inverter only based on time of day, or soc etc. Super easy to do.
Can do the same via vrm as well.

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Once the ESS Assistant is present in the Multi/Quattro, is there a way to programmatically disable and enable it, without having to uninstall ESS Assistant?

Running inverter only definitely addresses the OP’s concerns, but eventually he will run out of battery and want the grid to recharge. Some of us would like the capability to be grid-interactive on a programmatic basis (NodeRED, MQTT, ModbusTCP, etc.)

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Same situation here, EasySolar II GX (MPII 48/3000) in ESS. The inverter is in single phase, in series (all loads are on AC1 and AC2 outputs), so power measurement is done through the internal current transformer.
Grid feed-in is not allowed in my case, so the aim is to have absolute zero feed-in to grid. After a month, there is some 0.4kWh fed back, which might cause me problem with the operator.
When big loads switch off (e.g. heater 2kW, kitchen 1.5kW, washing machine heat/motor, kettle 2kW etc), there is that negative bounce, for just a moment (second or seconds - I do not have oscilloscope for current waveform, I rely on VRM readings and graphs). Most of high loads in a house are like this, i.e. switched ohmic (or motor) for regulation (temperature in cooking etc). There are a few devices that have soft-on, like inverter A/Cs etc, but these also can (be) switch(ed) abruptly off.
In “idle” situations (only lights, TVs etc) I use a Grid set point of 30W, so AC in fluctuates ~ 0 to 50W. When there is plan to operate a big load (heater etc), I temporarily set point to 100W, having less chance to bounce negative (though I’ve seen cases of -400W…!). Even a 30W (average) consumption leads to almost 1kWh taken from grid every day (which would be avoided in off-grid). At hazy winter days, that could be some percentage of the PV production (winter: ~ 5kWh/day).

  • While this is not a nice way (loads might kick-in and out at any time), which would be a solution to easy “prepare” the inverter for high-load switching? Scripts in ESS mode 2? Any other automation, like an input button (“I plan to cook”), or even better, when sensing high load to auto raise the set point to 100-200W, so as to “cope” for the subsequent switch-off of the load? Set point could be relaxed back to 30W, after the load stable returns to low values.
  • Being an electronics power engineer in my early career, I’d appreciate if someone (from Victron?) can explain how the inverter is having difficulty to load regulate when grid-tied (and thus it bounces peaks), while when off-grid manages to regulate well (or there are dips? I cannot probe it)?
  • As proposed also elsewhere here, a (smart) switch could cut the AC in from the inverter, during the day or during “house activity” (heating, cooking). But running on a limited MPII (3kVA - 2.4kW) restricts the loads that can be engaged (e.g. no oven 3.5kW, no concurrent loads), which otherwise get assisted from the grid - not to mention that one must run all loads as “critical” (AC1 out).
  • Maybe there is some other setting, that behaves better for our “absolutely zero feed-in” cases? Maybe not ESS or somehow else tuned? What about peak shaving?
    TIA - newbie here
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The laws of physics will prevent you from guaranteeing absolutely zero grid feedback. No physically implemented control system can respond infinitely fast. You can limit the feedback duration to a second or so, but that’s about as good as it can get.

Knowing a big load is active and about to drop and doing something in advance is an interesting idea. Grid set point could be increased of course, but then you won’t be using your available PV or battery.

Setting “Ignore AC input” would force the inverter to run all of the loads, but depending on your configuration that may not be viable.

The best I’ve been able to do is with an EM530 grid meter, which runs a faster ESS loop (up to 10 Hz). I still see 1 second grid backfeed when the HVAC or water heater turn off.

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If you are trying to avoid any grid feed in, it might be easier to just use AC input control. I had issues with a weak grid that would sag with any load and cause the units to fall out of tolerance. So I just made a hard switch between inverter and grid input.

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So here is where I’m at:

I’m reminded that math and physics don’t really give a damm about my wants or beliefs. So I’m trying to come up with a system that would have huge hysteresis in it - like hours instead of seconds.

I realize this will not be particularly efficient, but should be as close to zero feedback as I can do with my current equipment (MPIIs in split phase, energy monitor, two MPTTs, Cerbo, normally excessive incoming solar power shy those cloudy weeks, 500A-48V battery rack, all networked together):

I’ve no idea is this is doable (feels like it should be but haven’t logged the hours into Node-RED to actually get it to work).

Static rule: AC Current limit is set to 4.5 amps on both inverters. // Allows for some charge current while avoiding any large peak demands

Active Rule 1: If there is PV input from either MPPT then set Ignore AC Input unless SOC < 20%. // presumes all PV input will go towards charging batteries, running load, or just wasted if batteries are fully charged (since I can’t sell back to the grid).

Active Rule 2: If there is no PV input, and SOC < 40%, turn on AC Input // After the sun goes down, run off the batteries until they are drained 60%, then recharge - limited at the current rates specified in Static Rule. Note this revert Ignore AC Input and would not be overridden until Rule 1 kicks in the next morning. The 40% charge should be sufficient to run the facility until load bearing levels of sunshine occur.

Default case rule: If SOC < 10% turn on AC Input. // Provides 10% SOC hysteresis with Rule 1 to avoid cycling the AC Input relays. Prevents most situations of batteries completely discharging, although real-life experience may require percentage adjustments.

Note: the 9 amp total input charge is sufficient to run the facility a few hours into night and PV input is expected a few hours prior to facility usage by people every day.

Ideally, turn ESS Assistants off in the inverters so that only Node-RED is in control. While playing previously I have a vague memory that one of the input fields I need is ESS dependent though.

Could really use a general Node-RED guide written for a procedural programmer (like how to add together the MPPT PV numbers, which I have, along with SOC) with a Victron specific addendum showing which nodes to use to do the Ignore AC Input.

All input variables would be global objects allowing the node logic to run on the latest available data.

Think its time to play some more!

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Thank you for your replies.

Yes, a hard switch (like the fuse/switch on distribution panel, that feeds AC to the inverter, could be kind of control (maybe a smart switch, as I wrote), with some limitations (max power 2.4kW, all loads to “critical”). But not much of progress, wrt my “manual” increase of grid set point, before using higher loads (and that’s me, what about other house users?).

Yes, I understand that following load spikes, while grid-tied, is a different control loop (more harsh) than having load regulation in off-grid situation. Yet, it is awkward to have “traces” of feed-in power (my grid digital meter records those).
What I am after is some automated routine (script?), like “if load on AC outputs is >500W, then increase ‘grid set point’ to 200W” (or noteRed and set off the smart switch of AC in, as Paul suggests - or “ignore AC input”, which btw is greyed out in my case, I cannot change it in console). Put also some hysteresis, so that when load relaxes to e.g <400W, the ‘grid set point’ returns to 30W. Might also be with multiple steps, e.g. Load>500W gsp=200W, Load>1000W gsp=400W, Load>2000W gsp=600W.
I guess this control loop will track e.g. the kitchen oven, switching resistors on/off, with a duty cycle e.g. 10" on, 50" off, for about an hour (or whatever to bake a pie). Or washing machine, with 90’ cycle, resistors on for 5’, motor 5" on 5" off for 60’, spin for 2’, dry for 30’… you get what I mean!
Anyone can guide me how to achieve/program this?
(might be a suggestion to @Victron, a “Dynamic Load Tracking”, dynamically adjusting ‘grid set point’, according to rules, e.g. “set point equal to 10% of load, when load steps up”)

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Hi Kevin. It is not “legal” to use ESS in North America. It can be done, but since Victron does not support any of the relevant grid-interactive certifications in North America, you are forced to use a generic grid code to even get ESS up and running. This is not supported by Victron or your local utility. I don’t recommend using ESS if this is a concern for you. That said, your utility is not going to know if you send a few watts back every once in a while, though I still don’t recommend you use ESS.

Instead, disable ESS and use conditional AC (in VictronConnect) or dedicated ignore AC in the virtual switch settings of VEConfigure. You can configure some very basic rules to not use incoming AC power unless certain conditions are met. It’s not nearly as a feature rich as ESS but Victron has not (will not?) provide this functionality for North America anytime soon.

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Thanks Ed for stating this so clearly. In fact, that is exactly what I did a few days ago (Virtual switch route) and it seems to be meeting my need.

Prior to adding solar, the inverters were very quiet, but my MPPT controllers added some volume so I don’t really care if the inverter fans run now.

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