Use a solar pool cover to heat pool water. Solar covers capture heat from the sun and transfer it to the water, increasing water temperature by as much as 15 degrees. Solar covers also reduce water evaporation and stop debris from falling into the water. For the most solar heating, use a cover that is silver or black, as these colors absorb the most sunlight.
Install a solar heating system that uses a flat-plate collector. This system can be installed after the pool filter and integrated into the water circulation system. The pool water is redirected to flow across the solar heat collector through small tubes, where it's heated. The water is then transferred back to the pool. The collector system can also cool pool water at night.
A less common option is using solar power to run your pool heater. Instead of plugging the pool heater into your home's electrical system, attach it to a solar panel system. The solar panel converts sunlight into electricity that is used to run the pool heater.