I have just added a page about how to build a Tristar Follower (as I call it) that uses an AC heater connected to your inverter to dump surplus power (usually into heating water) when the battery does not need it. It uses phase control to do this smoothly.
It’s a pretty simple electronics project with only a handful of passive components to wire up. I have built quite a few of them now and they work nicely. The Tristar is good at deciding when to dump power but DC loads are not so useful, whereas an AC heater in your water tank can produce a lot of hot water without having to burn any fuel.