Good evening,
Any relay (as the shelly) will not work as it switches “hard” (on/off) but there is a Fronius Ohmpilot and a MY-PV which are proportional, the MY-PV is way more advanced than the Ohmpilot.
Check this link to a topic I made some time ago about an installation we test test things all the time since 2012.
Read it from top to bottom carefully, the advantage is basically that your frequency stays in place (50.05-50.20Hz instead of 51.00-53.00Hz), and to set your clocks every week or so.
That test install has 100KWh batteries, 4200Ah at 24V, yes lead acid, and has basically no “overkill” on panels, only 8KW, so there the gain is very low, as the topic explains.
But, if you “overkill” your solar inverters, yes, it pays off (but it takes many years), but still, a single vacuum CRK12 (about 2KW) panel from Wolf will outdo easily 5000-6000Wp VP panels for hot water, as there on that site 8 are mounted and catch in those round tubes, with reflector below, from sunrise to sun down, instead a VP, these have a 95+% efficiency and a VP not even 30% seen over a full sun day (as these are flat glass), that efficiency is the hot water temperature rise, not the panel efficiency, ok.
When it rains, VP production is zero, CRK12 is then producing easily 40-50 degrees of water, tested since 2012, and frequency controlled hot water since 2016.
In one of my homes we have 1 CRK panel with a 300 liter SS tank, always hot for 4 grown ups to shower, build in 2015, we save 500 liter of gasoil a year due to that panel, and the install was only 2200 euro, calculate, within 3 years back in the pocket before and now within 2 years (as such install is now still the same price) with the Trump actions…
Regards, Jeroen.