30Would you prefer a one-minute snippet to introduce you to the AM1.5 spectrum? Check out our “A Brief Intro of AM 1.5G Spectrum” chapter on YouTube. If you are looking for greater knowledge on the AM1.5 spectrum, continue reading on.
What is the Air Mass (AM1.5) Spectrum?
As we read in the prior chapter on AM0, AM1.5 is the most commonly used spectrum and is more generally used to reference almost all terrestrial applications. While AM0 signified the lack of atmospheric interference, the AM1.5 spectrum represents the thickness of the atmosphere at the zenith angle of z=48.2°. It shouldn’t be surprising that the zenith angle chosen of 48.2° wasn’t arbitrary. While it isn’t a perfect number, it is highly representative, as we will soon find out.
Why is AM1.5G Solar Spectrum the Standard?
When you consider the size of the Earth and all the various locations people live in, it becomes easy to see the need for a standard spectrum. With most major population centers of the world (Europe, China, Japan, the United States, northern India, southern Africa, and Australia) lying in mid-latitudes, an AM number representing mid-latitudes is the most commonly used to characterize the performance of solar cells.
During the summer months, the AM number for mid-latitudes is less than 1.5, and higher figures apply during the morning and evening. Therefore, AM1.5 is a useful representation of the atmosphere thickness as a yearly average for mid-latitudes. This air mass of 1.5 was selected as the standard spectra in the 1970s for standardization purposes based on a solar radiance analysis in the United States.
What is the Air Mass (AM1.5, AM1.5G, AM1.5D) Solar Spectrums?
A few suffixes are added to the AM-specified spectra, and they take into account different effects to maximize the specificity of a spectrum. This extra detail makes it easier for researchers worldwide to compare their results by ensuring that all aspects of sunlight behaviour are considered and called out.
What is the Air Mass (AM1.5G) Spectrum?
The “G” in AM1.5G stands for “global,” the first of the suffixes that add more information and specificity to the spectra.
AM1.5G (100 mW/cm2) corresponds to a global spectrum that includes diffuse and scattered light. It also specifies that it’s considering light that will be received by a 37-degree tilted surface (which, when atmospheric curvature and vertical density profile are taken into account, corresponds to the solar zenith angle of 48.2 degrees mentioned above). It also tends to be the spectrum Photovoltaic researchers use as the reference spectrum.
What is the AM1.5D Spectrum?
The “D” in AM1.5D stands for directed and corresponds to sunlight that directly shines on a point on Earth (i.e. with no reflections or scattering).
The AM1.5D (90 mW/cm2) corresponds to the amount of light removed through scattering effects. As you can see, when AM1.5D is compared to the AM1.5G spectrum, it has a 10 mW/cm2 lower energy than the AM1.5G spectrum.
The following graph illustrates the power loss between the three spectrums, making the difference between AM0, AM1.5G, and AM1.5D easy to visualize.
The AM1.5G Spectrum and Solar Cell Testing
With the knowledge of the AM spectrums and the suffixes that follow them, it becomes apparent why the AM1.5G spectrum was chosen as the Earth’s reference spectrum. As mentioned, it is one of the most commonly used spectrums, if not the most, when it comes to testing. The AM1.5G spectrum is the go-to standard for solar cell testing and research.
If you want a solar simulator to test the various Air Masses covered in the prior chapters, head to our Class AAA solar simulators page.
For those looking to continue the solar simulation journey, the next chapter will explore how we measure light.
