OP
hawgraham
I had an ImmerSun unit installed 2 days ago. I have now had a chance to analyse how it works. Unfortunately there is a problem in that the unit outputs bursts of 3kw sine waves. In otherwords part of the power being put to the immersion heater is coming from the mains not your PV panels. Over a period of time the unit does output the average power quoted, but because of the way it works it would not be able to run off grid. If you think about i,t if your immersion heater is 3kw then that is the power it will take unless the voltage applied to it is reduced (like when you run it from an 110v transformer). This unit does not reduce the voltage it just outputs 3kw pulses, if you have 500w to spare from your panels the unit will still output 3kw pulses with a gap inbetween so that over a period of time the average power output is 500w. Most of the time you are still putting 500w into the grid. Your household meter does not run backwards so when the 3kw pulses are used 2.5kw of it is coming from the grid (in this case) so over a period your meter will clock up power used.
If you want to see what I mean just stick a current clamp on the cable and stick an oscilloscope on the end.
If you want to see what I mean just stick a current clamp on the cable and stick an oscilloscope on the end.