Folks I have researched this topic in great detail, those that know me are aware that I developed a solar cart with the help of a close friend who is a solar engineer.
I have been talking with him for the past few weeks about solar heating our to be built pool and spa in very near future.
Bottom line is this is very simple to calculate, it is the surface area of the pool as the first part of the puzzle to the sq ft of the panels, not rocket science.
THere is also a flow rate thru the panels to consider, too fast will not allow time to heat, to slow will get it hot but not circulate enough water to have it work.
The basic panels cost about less than $2,000 plus the labor to install. My pool is going to be about 18-20', I'm planning on 4 4X12 panels.
Generally a solar pool install should cost $2500-$3,000, if you can't find anyone at about that price I'll start a new biz.
But folks you need to know where in relation to your roof TRUE south is not a guess but the angle.
The majority of if not all the panels MUST be on the south side, if there's not enough room then you can add east/west facing panels.
If someone told you they go on the west side........well the question is do they know what they are doing.
another issue to be aware of is what is IMO the unprofessional way some have been installed with pipes all over the place like monkey bars, that can be done in much cleaner aesthetically looking way.
One other point, they must be mounted where the entire system is on a slight angle to allow it to drain for freezing.
I just took a system down off a roof in The Villages two weeks ago (I rather not say who installed it) [U can PM me] but it was absolutely level and could not drain.
The sealant was not put in place adequately, and lastly all PVC pipes on a solar system MUST be painted they plastic and most importantly the glue joints break down with the suns UV. This installer did none of that and that is solar install 101.
So down load an app for a compass and see what you have.
Rant over
