The solar system is also used to heat the swimming pool water. A larger bank of panels is located on the hillside below the pool. On sunny days, the sun heats a sensor near the pool. This sensor compares the temperature of the water in the pool with that of the temperature of the panels. When there’s enough temperature difference between the two, a valve opens and water is sent to the solar panels to heat the pool. When the sun goes away, the sensor cools and it automatically shuts the valve.