For my house, I put in a heat pump with a decently sized storage tank and all it takes is a simple timer - it comes on at 10am and heats until the tank is at le

For my house, I put in a heat pump with a decently sized storage tank and all it takes is a simple timer - it comes on at 10am and heats until the tank is at least 60 degrees C (for Legionella prevention). This works to power it entirely from my solar almost all the time (I've only had it for a year, but I think in that time over 98% of my water heating would have been directly from my solar). Where I am, there tends to be surplus solar energy in the grid at that time anyway, so where I am at least, you don't even need anything super smart that tracks real-time energy pricing or anything. As long as you avoid the morning and evening peak, which this always does (it's finished heating usually well before 1pm, and the peak doesn't usually start until 4pm at the earliest in Winter).