Introduction to Air Mass

Sunlight is electromagnetic radiation composed of photons. In space, photons travel without any obstruction. However, when sunlight enters Earth’s atmosphere, it is affected by air molecules, water vapor, dust, and other particles. As it reaches the Earth’s surface, its energy gradually decreases. To quantify this attenuation, scientists introduced the concept of “Air Mass” (Solar).

Air Mass represents the atmosphere’s influence on solar radiation reaching the Earth’s surface. It quantifies the thickness of atmosphere that sunlight must traverse. The greater the air mass, the thicker the atmospheric layer the sunlight must pass through, resulting in more severe energy attenuation.

Factors Affecting Solar Radiation Attenuation

• Air Mass: Air Mass indicates the thickness of atmosphere that sunlight must traverse. Greater air mass means longer travel distance through the atmosphere, resulting in more severe attenuation.
• Solar Incidence Angle: The solar incidence angle is the angle between the direction of incoming sunlight and the horizontal plane. A larger incidence angle results in sunlight traveling through more atmosphere, leading to greater attenuation.
• Atmospheric Composition: Different atmospheric components absorb different wavelengths of light. For example, the ozone layer absorbs most ultraviolet radiation, while water vapor absorbs infrared radiation.

Definition of Air Mass

Air Mass can be defined using the following formula:

AM = 1 / cosθ

Where:

• AM is Air Mass
• θ is the solar incidence angle

Common Air Mass Values

Common Air Mass values include:

• AM0: AM0 refers to solar radiation in outer space before entering Earth’s atmosphere. At this point, the Air Mass is 0 as sunlight hasn’t passed through any atmosphere. AM0 solar irradiance is 1367 W/m², also known as the solar constant.
• AM1.5: AM1.5 corresponds to a solar incidence angle of 48.2 degrees. At this point, sunlight travels through approximately 1.5 times the thickness of Earth’s atmosphere. AM1.5 solar irradiance is 1000 W/m². AM1.5 is commonly used as the standard incident energy for evaluating the performance of terrestrial solar energy conversion devices and components.
• AM1.5G: AM1.5G represents the standard spectrum at the Earth’s surface. The AM1.5G spectrum’s energy distribution closely matches that of the solar spectrum and is commonly used as the reference spectrum for standard testing of solar energy conversion systems.

Solar Spectrum Variations

By Robert A. Rohde – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2623187

Changes in Solar Spectrum

As sunlight passes through the atmosphere, its energy is attenuated by absorption and scattering from various atmospheric components. Shorter wavelengths are more susceptible to absorption. Consequently, the solar spectrum at the Earth’s surface differs from its space spectrum.

• Light with wavelengths below 300 nm: Absorbed by atmospheric oxygen, ozone, and nitrogen.
• Light at 900 nm, 1100 nm, 1400 nm, and 1900 nm: Absorbed by water vapor.
• Light at 1800 nm and 2600 nm: Absorbed by carbon dioxide.

In addition to absorption-based attenuation, sunlight undergoes scattering as it passes through the atmosphere. Scattering occurs when light changes direction upon encountering objects. Atmospheric components such as air molecules, dust particles, and cloud droplets all scatter sunlight. This scattering causes sunlight to reach the Earth’s surface from various directions, resulting in the blue appearance of the sky.

Xenon Light Source

In photochemical experiments, xenon light sources combined with AM 1.5G filters are commonly used as solar simulators. Xenon light sources have an energy distribution remarkably similar to the solar spectrum, making them excellent solar light substitutes.

Enlitech’s SS-X is an AM1.5G standard spectrum solar simulator that utilizes a xenon short-arc lamp as its broadband light source. The xenon lamp’s color temperature of 6000K closely matches natural sunlight (5500K).

Product Features

• Xenon Short-Arc Lamp
• High-Precision Spectral Matching
• Temporal Stability of Irradiance
• Automatic Light Intensity Control
• Dust Cover

Applications

• Perovskite Solar Cells: Efficiency measurements of perovskite solar cells
• Organic Solar Cells: Efficiency measurements of organic solar cells
• Tandem Solar Cells: Efficiency measurements of perovskite/silicon tandem solar cells

The SS-X Solar Simulator is a powerful and reliable solar simulation instrument, serving as an ideal tool for solar cell research and development.