SilverMane

My basic test showed not much less power used by a AC PTC element vs a normal AC element. The normal 2kW element is only a fraction of the cost of a PTC element. 
If you know the temp of the geyser you can use the value of 175Wh per degree increase for a 150L geyser or 233Wh per degree for a 200L geyser. Check what is the temp early in the morning and then decide how long should the element be switched on to get the geyser to 42 degrees for the morning shower. 
@GreenFields Sunsynk do indicate cycling every day but not more than 700 cycled per year.