The diagram illustrates the structure of a simple solar panel and shows how it can be used to heat either air or water.
Overall, the panel consists of a shallow box covered with transparent glass, and it works by allowing sunlight to heat the contents inside. Depending on whether air or water flows through the system, warm air or warm water is produced at the outlet.
At the top of the panel, a layer of transparent glass covers a dark, flat base. This glass allows sun rays to pass through while trapping heat inside the box. On one side of the panel there is an inlet, through which air or water enters, and on the opposite side there is an outlet for the heated substance.
In the air-based system, cool air enters the panel through the inlet. As sunlight heats the interior surface, the air inside becomes warmer and then exits the panel as warm air. In the water-based system, water flows through a coiled pipe inside the panel. The sun rays heat the panel and the pipe, raising the water temperature before it leaves the outlet as warm water.