Outdoor swimming pools absorb up to 85% of direct solar energy from the water's surface.
However, when not in direct sunlight, pools lose energy and warmth in cooler air.
A solar pool cover optimizes solar energy absorption and conserves heat by sealing it in the water. It can raise the temperature of a pool as much as 20° Farenheit within a week.
According to the Energy Star organization, covering a pool when it is not being used is the most effective way to save on heating costs.