Derived from SMARTS v. 2.9.2* : ASTM G173-03
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The chart below was created in Excel from numerical data obtained on the National
Renewable Energy Lab (NREL) website.
Although more extensive data is provided there, the values typically sought out
for solar cell (photovoltaic cell, PV cell) are contained herein. The red line is
referred to as AM0 (Air Mass 0) and is the radiation level outside of the Earth's
atmosphere (extraterrestrial). The blue line is AM1.5 and is the radiation level
after passing through the atmosphere 1.5 times, which is about the level at solar
zenith angle 48.19°s, an average level at the Earth's surface (terrestrial). Some
really smart people figured that out, so you just have to believe them.
The region of the electromagnetic spectrum covering visible light is indicated
by the color smear. Note on the right side of the chart that the 3,000 nm point
is labeled as the equivalent of 100 THz, so this spectrum is a long way from the
RF / microwave end of the spectrum. For a chart of the atmospheric absorption in
that region, click here.
The AM0 data is also referred to as ETR, and the AM1.5 is referred
to as Direct+Circumsolar
ETR = Extraterrestrial Radiation (solar spectrum at top of atmosphere) at mean
Earth-Sun distance.
Direct = Direct Normal Irradiance Nearly parallel (0.5 deg divergent cone) radiation
on surface with surface normal tracking (pointing to) the sun, excluding scattered
sky and reflected ground radiation
Circumsolar = Spectral irradiance within +/- 2.5 degree (5 degree diameter) field
of view centered on the 0.5 deg diameter solar disk, but excluding the radiation
from the disk
* SMARTS2 version 2.9.2 is the model used to generate
the American Society for Testing and Materials (ASTM) terrestrial reference spectra
for ASTM Standard G-173-03 "Standard Tables for Reference Solar Spectral Irradiance
at Air Mass 1.5: Direct Normal and Hemispherical for a 37 Tilted Surface".
These spectrum response curves are from a chart in a report published by
NREL:
"Solar Cell Spectral Response Measurement Errors Related to Spectral Band Width
and Chopped Light Waveform"
They represent the most useful region of the electromagnetic spectrum for each
type of semiconductor compound. Many modern cells are multi-layer structures that
combine multiple compounds to harness a much larger portion of the available energy
than would be possible with a single type of solar cell.
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