question

I am reading this: https://www.victronenergy.com/media/pg/Energy_Storage_System/en/configuration.html

However, it's trying to cover too many scenarios at once. I'd need to mind map that in a diagram to digest it.

Items I don't like the look of. "Grid code password required". Grrr. The DNO have thus far replied with absolute silence. I figure they aren't interested in what I'm doing. It might prove difficult to get that, through official channels anyway.

ESS seems to be focusing on Victron gear integrations. Understandable. However it looks as though it bases battery levels on it's SoC. SoC is the most useless figure on any battery management system, always has been. You need expensive gear like VE smart shunts to get it even ball park right.

The other concern I have is surrounding the topology of the inverter and if it can do as I wish at all. As I understand it the Multiplus inverter uses a generated sine wave into a transformer. If AC-In is present this sinewave will be phase locked with the AC-In and it's amplitude increased to match it. Resulting in net 0 current.

Should an AC load come on inverter AC-Out side it will pull the transformer voltage down, but as it's now locked on the low impedence grid connection current will immediately flow from grid to the AC load. In addition, if enabled, the charger will allow current to flow backwards through the DC/AC converter and thus charge the batteries at the same time as supplying the AC loads.

Now. In my scenario I want it to produce power from the batteries to the AC loads. The only way it can achieve that, if I understand the topology correctly, is by increasing the amplitude of the inverted AC ABOVE that of the grid, so that net current flows 'from' the batteries. However, that also puts back pressure on the grid, which can lead to "export".

How does the multiplus handle this scenario? Does it uncouple the AC-In / AC-Out if the inverter is favoured over AC-In? How else can it push current in only one direction?

The blunt option is to put a smart switch on the inverter AC input and take control away from it. However, if I understand correctly I am far, far safer with the grid connected and the inverter in phase-sync with it and also coupled to the grid PNE.

Hi @Paul Campbell

If you don't want to export, and even hope to be 'offgrid' much of the time, then don't use ESS. You have other Assistants onboard your Multi that can control ACIN on your terms. Take a look at the Generator Start/stop Assistant (in the Multi), but use the IgnoreAC function to switch ACIN rather than start a genset.

No grid code, 'smart switch', or fiddling needed. Ask if you need help with it, but it's far simpler than ESS.

Thank you. Gives me a lead. I'll go down that path.

Got good news. The "tamed spark" says he will install the ground rod and help me install and make safe the AC side with RCD etc. Gonna cost me a days labour at hourly rate and parts/expenses, but at least he got the gist of what I needed and is happy he can make it safe. Including putting the panels up on the garage roof (instead of ground mounted in the garden) and earth them up.

Tested the above with "contrived" values, like 100W load and 26.6V for battery which where easy to achieve conditions. Works under both conditions fine.

The only thing is the charger gets enabled with the AC input, which I haven't decided if that's always what I want. The other more complicated Ignore AC Input Virtual switch I think might cover that scenario as it includes charger enable/disable thresholds I believe.

Happy enough. Thanks for pointing me in that direction :)