There are a number of ways you can heat your pool: gas, electric, air source heat pump, heat exchanger and, of course, solar.
This said, the future of heat pumps is looking very promising!
Reliable, highly efficient and economical to run, heat pumps extract heat from the air (similar to a reverse cycle air conditioner), and use that heat to produce hot water.
Heat pumps use just a fraction of the energy to generate heat from the air source. Although initially heat pumps take longer to warm up your pool, they are much more economical and will then maintain the heating as well as gas heaters.
Benefits of heat pumps include their high energy efficiency and lower running costs. As a guide, you can save up to 80% over LPG and 50% over natural gas fuelled heaters. And the best thing about heat pump pool heaters is that they operate regardless of the weather.