lborne said:
Here is central - southern Florida, most people use heat pumps. They are essentially A/C units operating in reverse. They don't work well in cold climates like the norhtern US. They have high initial costs, are large, and will last you about as long as a typical central A/C unit 10-15 years.
A heat pump is a good option to take the chill off the water towards the start and end of the swim season. In most regions they are not good for deep winter months (i.e. late November - early February, however this certainly varies by area).
Solar, if done properly (at least in this area) can work in conjunction with a solar cover.
A solar cover is very important to use no matter what type of heater you are using. A solar cover saves money as it stops heat loss. Without the solar cover the top of the pool simply has zero insulation. Some people don't want to mess around with a big solar cover and use a "liquid" solar blanket which is a bit less efficient but much easier and doesn't look bad on top of the pool. There is an option of adding an automatic feeder for the liquid blanket to be added to the pool.