Wanted - Pool Heating Ideas

Hi All, I'm looking to heat a pool in good sunny southern Spain thro' the winter months. I have good south facing fenceline and some roof tiling. Are there any ideas or formula for requirements to heat a given pool m3 or surface area m2? Ideal would be solar pump and plastic pipe. Info on pressure or volume pumped thro' 1/2 or 3/4 alkathene would be great. Thanks