You're wise to consider solar pool heaters.
They definitely save you money in the long run being relatively free energy but their up front cost is rather staggering in some cases.
In can be enough that the unit doesn't pay for itself for 5-10 years.
This option is great for the environment and there are hundreds of thousands of these units being used in the United States today, growing more each year.
Your first step is check with local dealers to see what the most common unit types are installed in your area.
Because the solar panels can be quite large you first need to consider available space and how it will look in your pool area.
You can choose between glazed and unglazed collector panels.
The unglazed panels are often 75% cheaper but the glazed collectors are much more efficient energy converters.
Instead of collection only 150,000 BTUs, the glazed panel will collection 450,000 BTUs or more.
If you live in warmer climates and just need a little heat boost the cheaper option is fine.
Unglazed panels are recommended only for areas that need to heat the water only 5 degrees above the surround air temperature.
Obviously in many parts of the country this is just not enough.
For colder climates you must get the glazed panels.
Overall, you have to decide if your climate requires that you even bother heating the pool.
But as a general rule, if you want to extend it's outdoor use to cover an earlier spring and later fall then you'll need a way to heat it.
And solar is definitely a great option to consider.