Both the Elon and Geyserwise will heat your water using PV panels. The problem is that many companies over promise and under deliver. I found the Geyserwise system is definitely more efficient. If you use ohms law, you will quickly see that only the Geyserwise system make good on the promises. I have also done some test on resistive element with no mppt, resistive element with mppt and the Geyserwise element with mppt. The Geyserwise system outperformed the other systems every time.