question

Hmm that's a good point.

I suppose the check for that would be does the acin rcd hold if you manually switch it back on once grid is connected? If it does then I think you've worked it out that it's the transferring from offgrid to grid that's the cause.

I dont think the earth relay switches earths as you mention (and anyway the house board is connected directly to earth rod i imagine so it's not like the earth is switching), However the earth relay i think activates/disables a neutral earth link. That's what i think earth relay does which may be the cause. Not sure what the solution is though sorry.

Bear in mind that when running on grid power, the L-N relays are engaged inside the Inverter which essentially connects AC-In to AC-Out1 (and AC-Out2 via a further relay). So any cumulative earth leakage from your house loads will be sensed by the RCD on AC-In. It's not uncommon for house appliances to have significant earth leakage and even 3 or 4 circuits might be enough to cumulatively trip a 30mA RCD. If you did want to retain an RCD in the AC-In circuit then you'd probably need to get a 100mA one and when I looked into this I found them to be quite pricey. I also don't think I could find one that was type tested for my Fusebox branded consumer unit. That would mean I would have to install a different brand which is okay but not ideal. That's when I started to question whether I even needed RCD protection on AC-In and ultimately decided I didn't.

It could just be a spike in load and ESS not quite keeping up, ET112 or similar meter does tend to have a slightly delay. It might just be something like fridge compressor kicking in/off?

Yeah, I used to use a CT clamp and it was pretty responsive and minimised grid import and export. But I now use an ET112 and it does have ramp up and ramp down delays. This was improved IIRC in the Cerbo GX v3.0 release so upgrade to that if you haven't already. There are also other supported energy meters which are much faster now.

That's pretty much what I get as well, although I have a "PV Charger" instead of "PV Inverter" because mine is DC coupled via Victron MPPTs and I presume yours is AC coupled to AC-Out1. That's good because your PV will continue to work even in island mode.

As for grid set point, I've got mine set to 0w but it really just depends on whether you want to minimise grid import or minimise grid export as to where you choose to set this. If you set this negative then it'll be a constant drain on your batteries which might be more of an issue in the winter when you're less likely to filling your batteries from PV. What you don't want to be doing is charging the batteries during cheap rate at say 9.5p and then just slowly draining them back to the grid at 4.1p or even 0p depending on your tariffs.

So I would say set it to 0w initially and run for a full billing month. Then analyse your consumption either by downloading data from VRM or from Octopus if you're with them. You'll be able to see how much grid import you have outside of scheduled charging times and if that is too much for your taste then set grid setpoint at -20w or even -50w. I don't think I'd go much further than that especially as we get into the autumn/winter.

That said, I have on occasion set my grid setpoint massively negative (eg. -3500w) at times when I have more solar than I can possibly absorb and my batteries are already at 100% early in the day. Why I do this is because recently on very sunny days, I was seeing PV power of anything up to 6.4kW (it's a 6.8kWp array facing due south at 14 degree slope) but it varies quite a lot due to clouds etc. So my average PV might be 3.5kW but with peaks of 6.4kW. But since my inverter can only export a maximum of 4.4kW, once the batteries are 100% full, the maximum my MPPTs will capture from the PV array is 4.4kW and I therefore can't absorb the peaks of 6.4kW. So if I can set a large negative setpoint then the batteries go down to maybe 95% and therefore I can capture the full 6.4kW from PV when the sun is strongest. This only works if the average PV output is less than 4.4kW, otherwise I simply can't export fast enough to keep the batteries below 100%.

HTH

Edit: Just to add - if our EV is at home and needing charged, then I prioritise EV charging over export because it's pretty much always better to consume energy in the home than to export it and then import it later. The Octopus Flux tariff might change that dynamic though in certain cases.

@mjs500 type A, type B is an arm and a leg through Hager for stronger DC leakage but that’s not what’s tripping it