Solar Hot water/pool heating

[Bigboxer]

Does anyone have any domestic hot water systems in use? Pool heating maybe?

Like these....http://img2.mlstatic.com/s_MLA_v_O_f_89679792_7039.jpg

 

[Fabe]

I have looked into these heaters.
Just on theory alone they work .
I would not , however use them as a main hot water source.
Search the net a bit , its chock full of the principles on wich it operates and there are many many sites dedicated to homebrew versions.
The ones i have seen here come from china. A neighbor of mine sells them