Eddi or Alternative??

I'll have the question with my knowledge on this.

1- Yes it is doable through HomeAssistant but not convinced it'll work as well and efficient as a proper diverter. I may be wrong on that statement though.

2- IMO, i'd pay the extra money for a brand which I am familiar with and have excellent customer service support. I've contacted them few times and they are brilliant. Well worth paying extra for.

3- You dont need a second harvi. The solis monitors your PV generation. Do you mean you'd like to see it in the MyEnnergi App? If so, you can clamp a CT in the live cable coming from the inverter.

Thats all or nothing though. You can't control how much the immersion heater gets. Eddi provides the granularity to put 1kw in if that's your excess.

If you've a 3kw heater you're on the upper limit of the Shelly's amp rating too.

I would question the benefit of an Eddi, my logic is that with a smart meter, you could use one of the night plans to heat the Hot water at night with a simple time switch, e.g. Electric Ireland 2am-4am @ €0.1228/kWh ex Vat, Energia 2am-6am €0.1288/kWh ex VAT or SSE 2am-5am €0.1139kWh ex VAT and take the export value of the solar kWh that are generated and credited at €0.21, €0.18 and €0.24 respectively instead of heating water with them.

Fair point however if you needed to reheat the hot water tank during the day you could switch on the immersion via the time switch for a 1-2 hour window depending on your needs around the peak of the solar production curve during the day thus creating the best chance of catching solar kWhs if they are there.

I am installing a PV system too and struggling to see the advantage of an Eddi at 600 euro. A well insulating new tank should lose very little water heat through the day. Would it not be better to heat at night and leave the solar do its thing during the day. I presume the electric power from the PV will feed the immersion without an Eddi? It would be in the summer that this is most important as the CH will heat the water in the winter.

Price depends of course on how much you pay. New they are €632 incl. VAT from midsummer.ie

But if you get trade discount and don't pay VAT, it's only a bit over half that price 😂 With of course the second hand value higher than that even after using it a year or two. So basically it doesn't cost anything.

'Sets the maximum current that the eddi will draw (including when boosting). This is useful if the supply current is limited, like a 13A fused spur rather than a 16A MCB.' - Zappi is the same, can limit itself. But it limits it all the time. Could be useful if there is a short cheap-rate time window and have a lot of other devices pulling a heavy load.