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Is it OK to have a solar i-boost immersion heater as well as an ac coupled battery inverter?
Thinking that they both have ct coils to detect when fit solar is being exported.
I know that people seem to have issues with ev chargers draining batteries unless they are wired in a particular way, not sure if there could be a similar issue, either deciding which has priority to use the excess solar, or if any battery discharge could be seen by the I boost as excess?

The reason for my question is that I've been at my parents, who have just had the battery +inverter fitted to supplement their existing fit solaredge set up.
They're having a few issues and I'm in discussion with the supplying company, so any helpful hints appreciated

Many years ago when these solar diverters were a thing this was much discussed. The solution was to have your battery inverter target zero export and your diverter (i-boost) target 50W export. This would result in the battery being charged first and any excess over the charge rate of the battery or when the battery was full would go into the immersion.

However that is all in the past. Nowadays off-peak electric is 7p/kWh and you get paid 15p/kWh for your export. So it is better to use off-peak electric to heat your water and allow your solar to go to the grid. People who have a diverter have turned it off or had it removed.

Thanks Stinsy,
That makes sense.
They don't have a smart meter yet, so no cheap rate, but I did consider they would be better filling the battery first, replacing full price electricity, rather than using the 'spare' electricity to heat water, as gas is cheaper

Stinsy wrote: ↑Thu Feb 06, 2025 9:53 pm Many years ago when these solar diverters were a thing this was much discussed. The solution was to have your battery inverter target zero export and your diverter (i-boost) target 50W export. This would result in the battery being charged first and any excess over the charge rate of the battery or when the battery was full would go into the immersion.

However that is all in the past. Nowadays off-peak electric is 7p/kWh and you get paid 15p/kWh for your export. So it is better to use off-peak electric to heat your water and allow your solar to go to the grid. People who have a diverter have turned it off or had it removed.

My Eddie has only just paid itself back and I don't intend to really use it this year for that reason.

During the summer i still use my Iboost, as i dont export (im still on deemed FIT export) , and I generate far far more solar than i need so my batteries are always full. The rest gets dumped into the HWC. We use the unvented shower then with free HW.

In the winter when my batteries are not full and we do not generate enough to keep them full in poorer weather, i turn the Iboost off to prioritise all solar into the batteries to run the house. In such a time i use the immersion on E7 cheap rate in the evening, or alternatively the electric shower if we've forgotten. On sunny winters days (like today,100% SOC since 9.45am) i will manually switch the Iboost on again to divert to the HWC.

Dont seem to get any issues with things working this way, but it is a pita to have to switch things on/off

Photo attached shows the CT clamps positions. Top CT (closest to suppliers meter) is the Iboosts. Bottom CT is my sunsynks.

HTH's