Batch solar water heater?

I live in Florida, and I am thinking of building my own solar water heater using my existing tank. The only way I can a achieve a southern exposure to the panel, without having to move my current tank, is to put the panel on my roof over the tank. My first thought was to build a thermo syphon, but it seems the tank must be above the panel. (not possible for me, no sun on that wall). Is there a way to use a passive batch solar heater, which automatically stores the hot water in my insulated tank below(for use in the mornings)? I am hoping not to have to use a pump, but thought I could run my incoming water to the panel on the roof, then branch the incoming back down(using gravity) back into a my cold water line inside the house. The other branch (with the remaining incoming water)on the roof would go directly into my panel, get heated, then fall down into the tank, to be strored for later hot water use.
The only issue I can see is at the point of the branch , where the incoming water eithers falls south, or goes to the panel. I guess there would be way to compensate for this by making sure the inital pipe before the branch is ABOVE the branch and the panel???
I am very new to this, so I would appreciate anyone's help.