Lab 5: Solar Energy and Solar Panel Orientation

From dawn to dusk, the sun travels from east to west across the sky. During the course of the day, a fixed solar cell will show an increase in power from sunrise to solar noon and a decrease from solar noon to sunset. There are several factors that cause this change in current output:

Figure 1: The sun and earth.
  1. Over the course of the day, the earth’s rotation brings the solar panel closer to the sun from dawn to noon and further from the sun from noon to dusk. In figure 1, the path of light traveling during solar noon is shorter than the path at dawn.
  2. At dawn and dusk sunlight must travel through more of the earth’s atmosphere than at noon. Traveling through the atmosphere reduces the amount of sun that arrives at the solar cell. In figure 1, the light at solar noon travels through less atmosphere than the light at dawn.
  3. Throughout the course of the day the sun’s angle changes in relation to the solar panel, causing changes in the solar panel’s output. In figure 2, the solar panel is pointed directly up. Sunlight, represented by the yellow rectangle, shines down on the panel. At solar noon, the light shines directly down on the panel and 100% of the rectangle hits the face of the solar panel. When the sun is 45° off from normal to the panel face, 71% of the total rectangle hits the face of the solar panel and 29% misses the solar panel.
Figure 2: Light hitting a solar panel directly (solar noon) and from an angle (45°).

Although all these reasons are responsible for changes in current output, it is the third reason, the angle of the solar panel in relation to the sun, which is improved upon by using a solar tracker. The purpose of this lab is to understand how solar panel power is impacted by the angle of the sun in relation to the face of the solar cell.