Diverting power to immersion heater on full battery charge

I can’t find a specific entry about this - maybe my searches are wrong - , so hence this post.
We have an off-grid house, with a PV system and a solar thermal system.
We would like to divert power to an immersion heater when our batteries are fully charged as our solar thermal doesn’t cut it unless the sun is full-on.
Can anyone point me at a post for this please?

the simplest method would be through your solar charge controller if you have those option. (the option are found on most programmable Chinese solar/wind charge controller)

via the solar/wind charge light/dump control once battery is fully charged it diverts the power to the hot water tank.

just a thought

When there is surplus power and your batteries are fully charged, does the system’s frequency increase until the PV inverter starts to reduce its output?

If so, you could monitor the frequency and start diverting surplus power once a pre-set value has been reached. I may be able to help via mk2pvrouter.co.uk. There is an email address on my Shop page.

Robin Emley