TOPIC: SOLAR CELLS
WHAT IS THE BEST ANGLE FOR A SOLAR PANEL?
SYNOPSIS
This is a guided student-designed investigation that builds on the experience the students gained in Practical Activities 2, 6 and 7.
This practical activity provides further valuable training for students in experimental design, which should help prepare them for their open student-designed investigation (Practical Activity 9).
APPROXIMATE TIME REQUIRED
60 minutes
BACKGROUND INFORMATION FOR THE TEACHER
Designing experiments
See the background information on designing experiments, on pages 91—93 of this resource.
Tilt angle
Figure 1.The ideal tilt angle for a solar panel.
Ideally the best angle for a solar panel is one in which the panel is perpendicular to the Sun’s rays, so that the intensity of the light is a maximum. The problem with this is that the angle of the Sun’s rays to a fixed point on the Earth’s surface depends on the latitude of the fixed point, the time of day and the season.
The seasons
Figure 2.Earth’s seasonal movement around the Sun.
The changes in the seasons are caused by the tilt of the Earth’s axis to the plane of the Earth’s orbit as it moves around the Sun. The angle of the axis to the vertical remains fixed at 23.5⁰ and affects the times of sunrise and sunset, and the variation in the Sun’s altitude in the sky throughout the day for all positions on the Earth’s surface.
As shown in Figure 2, in December, the South Pole is pointing more towards the Sun. As a result, the southern hemisphere has longer periods of daylight and the light has greater intensity than that reaching the northern hemisphere. It is the opposite way around in June, when the South Pole points away from the Sun. This is why there is more solar energy available in the southern hemisphere in our summer period than in our winter period, and why the seasons are the opposite in the northern and southern hemispheres.
Figure 3 shows the apparent pathway of the Sun over a point in the southern hemisphere over summer and winter.
Figure 3.The apparent path of the Sun over a particular point on the Earth’s surface in the southern hemisphere.
Atmospheric reduction of sunlight
Figure 4. A schematic diagram of what happens to the energy radiated out by the Sun as it enters the Earth’s atmosphere.
The intensity of light is also linked to the distance that the Sun’s rays travel through the atmosphere. The amount of sunlight absorbed and scattered by air particles, including dust and water vapour, depends on the distance the light travels through the atmosphere. For this reason, the maximum intensity of sunlight at the top of mountains is higher than at sea level, and is greater at the Equator than it is near the poles.
Figure 5 shows why sunlight is less intense when the Sun is not directly overhead.
Figure 5.The effect of atmospheric particles on the intensity of sunlight in summer and winter.