I thought I would throw out this link to a white paper written by a local solar company here in Tucson called Engineered Solar (formerly Sun Power of Arizona). Let me say up-front that I have absolutely no affiliation with this company other than I was researching solar pool heating options and this was one company that was recommended to me. My thought originally was to do the standard thing that most folks around here with flat rooftops do - HelioCol black plastic solar collectors. I have sufficient rooftop area on my casita near the pool (~700 sq ft) for my pool (~468 sq. ft) to put up solar heating. However, the owner of the company (an instructor at the University of Arizona), wrote a white paper on the various solar heating options making certain assumptions about heating efficiency, pumping efficiency, utility costs, etc. It is here -
The one intriguing option I saw, which is certainly not the cheapest or fastest in terms of ROI, is installing solar electric to run a heat pump and to use that setup to collect solar energy and heat a pool slowly. I like the elegance of the idea because it eliminates the need to pump water up to a roof top and simply collects electrical power for the sun to run a heat pump. Seems interesting (and a bit pricey!!).
I would welcome anyone's additional thoughts or spit-ball throwing at the analysis.