" Here is the hybrid system that I have installed for your interest.  It is working well despite the lack of sunshine this winter.  Interesting it never froze once, in this cold winter of 2009, as the controller took care of keeping the water moving on demand.  This did mean more circulating losses (70 W), as you mentioned when I bought it.  There is a heat tracing cable available as a back up should it freeze, but this was not necessary.  I will further modify it before next winter to have both the timer and the controller working in tandem for times when it is very cold and there is enough sun to keep the heater warm but not sufficient to start the pump. "