Say you have a Multiplus II (or EasySolar II), with ESS and Grid connected (where, as said a lot of times, you cannot zero the feed-in, there are always “traces” of back feed, to the utility meter). Several times, you go off-grid (interruption of power, or intentionally).
Now, suppose you have other sources of AC power, which you want to use (for cost or redudancy reasons), via a transfer switch to the ACin of MPII (Grid - none - Other). The other could be:
a Genset, either “simple”, or inverter.
a EV with its V2L socket
a power station (those 1-2kWh+ big power banks, with AC inverter)
Since the ESS is bi-directional, i.e. “follows” the incoming AC, but occassionally feed it (current towards the “other” source), what do you expect to be the behaviour of the above devices? Is it safe to inject current to their AC output?
Alternatively, what other mode of MPII, instead of ESS, could be (temporarily?) selected, when planned to connect to such “other” input device?
(I do not know how Quattro deals with its second ACin - meant for generator - I am talking about MPII’s single ACin)
I am still hesitating to put another inverter in front of MP2, in ESS mode (such as from a power station - huge power bank with AC out). I do not know what the “feed-in” of ESS mode will cause to an external inverter.
Maybe I could use “keep battery charged” and disconnect the ACin before SOC reaches e.g. 80%. Or maybe I need to switch from ESS to simple “UPS mode” (which does not back feed) - but how this can be switched with an easy and reversible way? I still have mains grid as an input option, where I wish to have ESS.
Take for example an EV, with V2L option. When it is cloudy and battery runs low, but you have car’s battery charged, you may wish to inject some of its juice to the home battery. But if you need the car, you revert unhappily to mains grid (with ESS), to charge the home battery.
If you want absolutely no feed in, you shouldn’t be using ESS.
Your system would be classified as off-grid, at least sometimes. Victron recommends not to use ESS in such cases. (You may need bigger batteries in such cases).
You can still connect to AC-in when not using ESS. You can then control when to use or ignore AC-in through the Virtual Switch or assistants. I don’t know if this works with ESS.
Another idea I have not tested is to set the multi to charge and stop charging at appropriate voltages.
I have set up two identical systems on MP2 GX, one runs ESS, the other simple “UPS”. For the UPS I am using ignore-AC assistant, to charge from grid when SOC is below critical (40% in that case - leave some juice for outage), or when consumption exceeds MP2 limits (2kW in that case).
But ESS is nice, for parallel operation with the grid: “Give me all the inverter can do and almost all battery has, then fill in from grid” (a novice explanation of power assist, ESS etc). Of course, grid kWh costs and I’d like to complement house battery from other sources (power station, EV V2L, GenSet), directly from AC (and not DC to DC charger), that way I could “power assist” as well - when in need of more kW (e.g. welding machine).
Now, my hesitation to connect anything else but the grid to ACin: The grid is a huge battery. When you are feeding-in (even small amounts, like “set point”), there are 000’s of consumers around to absorb this power. But if you have an inverter, in front of ACin, or a GenSet, where this power goes? I am attaching an electronic schema of a hybrid inverter (that I sourced from another, nice guy). I worry whether in a case that a big load switches off (e.g. a 3kW kettle), the MP2 and station/EV/GenSet will go big bang!
I agree ESS is nice, but unfortunately, not appropriate in all cases. I wouldn’t use ESS in your situation.
I think there is a self-consumption assistant that gives the functionality of ESS. Unfortunately, it is depreciated in favour of ESS. I guess it still works. Have you tried it? I don’t know how it behaves regarding grid.
I don’t see how you can use ESS with no feed-in. I wish ESS had the option to lean on the battery instead of the grid.
ESS has the rather misleading feature of no grid feed-in. Some people take that literally. Minimal feed-in would be more accurate.
