Water circulation without an electric pump.

[spinner]

I just needed to know... in the attached image, if I was to keep the chamber (or plastic drain pipe) heated by the Sun or by some other means, and kept the bottom chamber(the one that's immersed in the consumer water tank)... Would it make the working fluid circulate, without the use of an electric pump ?.

Your design would work, but very poorly.... As it is a direct conflict with the common convection principle (the basics of the fluid/thermal move mech. in the central heating), the only mechanism working in favour would be a (small quantity) expansions of the hot side with a combination of a semi- valve...
A kind of thermal engine....

So, either you'll use a principle mentioned by Yucca (thermal siphon by an elevated heat exchanger), or you'll use a circulating pump to force the thermal flow to the temp. exchanger unit below your sun collectors....

Cheers!