I had a completely off grid 2.2kw system at my home. But this system is not cost effective and very high maintenance. This gave me the idea of putting up solar panels and hook it directly to the water heater to reduce the cost of the entire system.

4x SunPower 320watts panel give a total of 1280watts rated.
1x Disconnect box
1x DC Shut off switch
1x High Voltage DC power meter

The panels are powering the stock 240v/4500 heating element. Because of this element resistance, it does not fully utilized the power coming from the solar panels (does not run at MPPT). However, still able to achieve 5-6kw on a good day and 1-2kw on cloudy days during winter time... summer? don't know yet.