Having solar heat would be the best and cheapest option would it not? In an ideal world, it probably would be, however we live in Winnipeg and our climate varies a lot from season to season. Solar systems are prone to leaks from frost, roof damage from leaking water, cooling your pool down at night if the diverter valve is not shut off, and shortened swimming season dependant on the sun. Solar pools take a long time to heat up and with a relatively short swimming pool season, making the most of your swimming season is important when you have invested in your swimming pool.
Solar systems are prone to leaks because of the many connections and glued joints they have. Removing all of the trapped water out of your solar system for the winter can also be a challenge. There are alternatives such as gas or electric heat pumps that do cost more to operate however extend your swimming season and make your pool usable all summer instead of only after a week of scorching heat. Ya we are a bit bias towards them.