Thermal syphon yes.
Typically a tank is mounted above aseries of straight pipes.
Have to be straight though any bend and th syphon fails.
Normally to heavy for roof mounting
Link to a simple controller to get the op started.
http://www.reuk.co.uk/Solar-Water-Heating-Pump-Controller.htm
Using arduino would be better as it could datalog to show how well system is working.
My system uses glass tubes and water is not circulated through them.
Heat pipe conduct to hot end placed in low mass water manifold.
Outside in free air the hot end can reach 100s of deg c.
At 3 bar system pressure pump off in the sun , steam is vented.
Whatever the arrangement, delta t controller is the nor mal method of contr
ol.
Parabolic is a poor choice for this application , more suited to high temp applications such as cooking which i origionaly thought th op was attempting.