Solar pool heaters can be very cost-effective and easy to install in both existing and new pools. Solar collectors can easily increase the temperature of thousands of gallons of water by several degrees, to about 70º-80º F (20-25º C).
Before installing a solar pool heater
Be aware anyway. Solar pool heaters are very effective at extending the swimming pool season and at increasing comfort, but it doesn't replace conservation methods and design improvements for energy savings.
These last type of methods and improvements include reducing the pool pump’s run-time, using pool covers, rethinking the design of the pipe and filter system, installing windbreaks around the pool, keeping the thermostat setting as low as possible or using multi-speed pumps instead of single-speed units (see: Swimming pool Energy Conservation Measures).
They are very important, and solar pool heating doesn't replace them.
Solar panels for swimming pools
Solar panels used in swimming pools are the unglazed (or in some cases the glazed) collectors used in other solar applications, especially to heat water for domestic uses.
Most solar pool collectors are unglazed: they use special rubber or plastic polymers, treated with ultraviolet light inhibitors for a longer lifespan. Unglazed panels are less expensive and can easily raise the water temperature up to the desired levels (70ºF-80ºF/ 20ºC-25ºC). If you don’t intend to use your outdoor pool during cold weather, they are are the best choice.
For colder climates, or to extend the swimming season into the colder months, it is possible to use glazed solar panels. They involve copper tubing on an aluminum plate, and have a special glass covering to boost efficiency.
They are the best option for hybrid-solar solutions, that is, for applications where the panels are also used to supply domestic hot water year-round. As expected they are a bit more expensive.
In sunny and warm climates, the panel’s surface area should be at least 1/2 of the pool’s surface. That may be enough to extend the swimming pool season into spring and fall.
In cooler or cloudier climates, you will need to increase the surface area to the double, that is, to an area approximately equivalent to pool’s surface area. Keep in mind these figures.
Collectors mounting, orientation and tilt
Collectors should be mounted on roofs or racks like with other solar thermal applications. The rules about orientation to sun and the optimal tilt for the solar panels are the same. See, on these issues: Solar Efficiency: Shade, Sunlight and Tilt and Racks and Trackers for Solar Collectors. Image credit: Fafco
Just like common pools, solar swimming pools require a pump able to supply the water to the solar panels. You will need a larger pump than the one required by common pools, or a dedicated small pump (see Multi-Speed Pool Pumps).
For details on solar pool installation, you can take a look at Installing a Pool Heating System, FSEC.
In the USA, for collectors and solar pool systems certified by the FSEC (Florida Solar Energy Center), see: FSEC: Approved solar systems for pool heating and their manufacturers; FSEC: Certified solar pool heating collectors and their manufacturers or the Solar Pool Panels Manufacturers listing of RSPEC.