I was thinking about a similar idea. I couldn't find a suitable DC immersion heater to connect directly. An off the shelf on-grid or off-grid inverter wouldn't

I was thinking about a similar idea. I couldn't find a suitable DC immersion heater to connect directly. An off the shelf on-grid or off-grid inverter wouldn't have made sense either. A massive variac wouldn't be cheap. A purpose built inverter/mppt would be good but I'm not an electrical engineer so I don't know how to make one.