"Excess energy is dumped into the hot water storage tank.".. Nice way to save.
I'm assuming you are using a resistive heating element for that.
I have been thinking along those same lines, since I have to burn oil to heat my hot water.
However, I'm starting to think that a heat-pump hotwater heater would be a better way to go.
(Since my array is going to be pretty smallish).
Airgenerate.com | Adaptive Energy Solutions
video:
AirTap Water Heater Heating Element - Fine Homebuilding Video
I guess it uses about the same power as a small window AC..
Not suitable for storing very many KWHs, unless I get a really big water tank!