So long as you have solid PVC plumbing on your above ground pool there is no reason why you cant use a solar heating system.

Solar heating is the most inexpensive but has its limitations. The most you can get is about 35 degrees Celsius no matter how big the system is. This is because thats the maximum temperature that the water can get to in the absorber on the roof. It is also dependant on roof location and direction. An angled North facing roof is best.

These days you can even buy D.I.Y. solar kits that only require some plumbing and common sense. The best absorbers use oval aspect tubing for maximum heat absorption and one piece manifolds for minimum leakage.