A photovoltaic solar panel produces electricity in direct proportion to the amount of sunlight falling on it. Because the sun’s angle in the sky influences the intensity of the light received by the Earth, the location of the sun affects how much energy a solar panel generates. Several factors determine the sun’s location relative to the panel, including time of day, season and latitude.
Intensity and Angle
When the sun is overhead, its rays are the most direct and intense. As it becomes lower in the sky, the same area of light from the sun covers a larger area of the Earth. As the area increases, intensity decreases; a solar panel receiving this light produces less electricity. To partially compensate for the reduced intensity, a solar panel can be tilted to match the sun’s angle, although the complexity and upkeep of mechanical tracking systems add considerable cost to a solar energy installation.
Time of Day and Seasons
During the day, the sun’s rays are most intense at noon, weakest at dawn and dusk, and in between at other daytime hours. Other factors such as cloud cover being equal, a solar panel’s output is greatest at noon because the sun’s rays are more direct than at other times. Seasons also affect the sun’s location in the sky. Because the Earth’s axis is tilted at 23.5 degrees with respect to the sun, the seasons change as the planet moves through its yearlong orbit. In the summer, the Northern Hemisphere is tilted toward the sun and receives the most direct rays; during the northern winter, the Southern Hemisphere gets more sunlight. Because the sun is more directly overhead in summer months, a solar panel puts out more power then than during the winter, when the sun’s rays are less intense.
Latitude is a Factor
At the equator, the sun’s rays are the most direct on Earth. As you move toward the poles, the sun’s angle in the sky decreases, as does solar intensity. The weakness of sunlight accounts for the extreme cold conditions near the poles. According to NASA, the sun’s rays are 40 percent as intense there as they are at the equator. The closer a solar panel’s location is to the equator, the greater will be its electrical output.
The Role of Distance
The distance of the sun to an earthbound solar panel changes very little during the course of a year, as the Earth’s orbit is nearly a perfect circle. However, distance plays a major role for the solar panels that power satellites and missions to space. Although some spacecraft can use solar panels, past the orbits of Neptune and Uranus, sunlight is too weak to be a practical power source. Missions very far from the sun use atomic batteries that produce electricity for decades without the need for sunlight.
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