question

The first thing I would say is that you can't create a situation where AC IN and AC OUT (of the Multiplus) are ever connected together.... Excuse me if I misunderstand, but you say "What I want to do is run AC out 1 from the multiplus to power just our main house fuse board" and then "I will connect the AC in via a 32A breaker from the main switch"..? So, the main house fuse board is connected to the grid and you are connecting AC out 1 back into the same system?

I would suggest that an ESS system that does what you are trying to do is just connected to AC IN. This is effectively a parallel system that supplements the grid? (analagous to a grid tied system) with all the loads on the input side. As you only have a 3000VA inverter you would only need a G98 which is generally very easy to obtain. Not sure what your DNO region is but with UK Power Networks for example you can do it all online, for no cost?

In answer to your original question regarding "where" to put the ET112. Assuming you are configuring as a "Grid" meter, wherever you put that in the system is the point where ESS will try to achieve the "Grid Setpoint" that you enter in the ESS menu.. So, for example if you install it after a 32A MCB from your main consumer unit then that is the point that will be controlled (rather than the "real" grid entry point which would normally be the point that you are controlling)

Hi @Vagabondrobb
install your ET112 just after the main house breaker, closest to your DNO meter. so that you can monitor your total grid draw, or export

firstly a 48/3000 is only 2400Watts, so just over 10amps.
so a 16A breaker (would be fine) from the main switchboard as long as the breaker is after the ET112

so it goes.. DNO meter, main breaker, ET112, and them wire in the MP 48/3000

then use node red to set the 'grid point', if you are drawing power from the grid, set the MP grid point to a negative and match the wattage. this will power the house load from your battery, or solar
if the load is over 2400w the grid will have to make up the difference
but by doing it this way there is no passthrough, so your house will just work as normal.

And you could run a pair of 48/3000 or a 48/5000, you just have to cap your output to 3.6kWh
most DNO's will allow that

I have a pair of 48/5000 (as a passthrough) and a second 48/3000 (as a cascading system, like this), it's just all capped to 6.9kWh export, (set by my DNO).

and if you google, there is no legal requirement for a MCS... but you will get paid more for your export if you have it.

@Vagabondrobb
yes if you just want to run certain circuits, that's fine
and it's up to a max of 32amps. sometimes you read it and its 32A of grid plus 10amps of invertor
but I think that is the max total, with or without the invertor

but the question you should ask yourself, is what is the 'base' load for your house. ?
my base load is about 200w/h so about 4.8kWh per day.
and covering that, and anything up to 2400w would be more efficient., more beneficial as you will use more of "Your solar"

have you seen the cheap Chinese "Sun 2000 GTIL2 Inverter" ?
watch this video https://youtu.be/RcOt8sMgzsQ
but as you watch it, reallize that you can set your 48/3000, ET112, solar and battery to work the same, using node red and a Cerbo GX

my 48/3000 just plugs into a 13amp socket, (remember if you do that the plug can be "hot", live if the 48/3000 is on) and my 48/3000 just makes power, as and when it's needed
no passthrough limit, no complicated wiring it in (other than the ET112). all works off the AC IN cable

And you do realize that if you make excess solar, it will get used by your own loads, before it exports. whether the loads are before or after the invertor.

In my mind, unless you are wanting to run 'off grid' (at 2400watts you are not) there is no real benefit to setting it up as a passthrough unit.

EDIT: you could still wire some lights and a power point for the TV and phone charges to the AC out. so that you could run off the battery for the days that the power goes out.

EDIT: and at 10kW of solar, would you export much from Scotland ?
if the system just plugs in, it's a battery backup. and your DNO would not need to know about it, as long as it did not export anything (just my thoughts)

Well, I’m kind of limited at the moment to what I can do - I can’t export without MCS, I can’t generate higher than 3.6kw (because I don’t have MCS and SP wont let me connect via G100 without it - which is what SPEN offered originally when I wanted a larger system). So I’m trying to make use of what I have for the moment.

With 10kw panels I fill my 2 x pylontec 4.8s up pretty fast - 2 hours on a good day - so I will usually have an abundance of solar energy. If I can at least use as much of the 2.4 kw as possible through circuits that are low powered (and can be used at night) and ones I can specifically make use of during the day - washing machine for example, that’s all electricity I’m not paying for.

Im not exporting anything.

It’s far from ideal I know, but it’s a temporary first step.

I plan to make another application to SPEN for a bigger system (add a 48/5000) and switch to octopus. Eventually I will get there!

In the mean time I will check that SUN 2000 video out!

Many thanks