Solar Power » Radiation

Defining standard spectra for solar panels

Solar SpectraThe atmosphere does not just change the overall intensity, but the whole spectral distribution. For instance, most of the high-energy wavelengths that are present in the sun light are filtered out by the ozone layer. Generally, with longer paths through the atmosphere (at higher latitudes or around sunset), the larger the part of infrared light, the low energy spectrum. This filter effect can be expressed by a turbidity factor.

In order to be able to compare solar modules, standard test conditions have been designed. These conditions include spectrum, intensity and temperature. The standard spectra refer to generic locations. They are prefixed “AM”, which stands for “Air Mass” and followed by a number, which refers to the length of the path through the atmosphere in relation to the shortest length if the sun was in the apex. It is roughly


The Committee Internationale d'Eclaraige (CIE) and the American Society for Testing and Materials (ASTM) publish a number of spectra. Their origins are from actual measurements, which are subsequently declared standard. They are also designed such that the spectrum can be reproduced artificially.

Air Mass

Name

Standard

Conditions

Intensity W/m2

Comment

AM-0

ASTME E490

Just outside the earth’s atmosphere

1,353

 

AM-1

CIE Publication 85

Sun overhead, sea level, horizontal surface

1,000

 

ΑΜ-1.5G

ASTM G173-03

(replacing ASTM E891 & E892)

Tilted surface at 37°, zenith 48°, facing due south, albedo 0.3, turbidity 0.29, 20°C ambient temperature

963.8

Global Radiation – these conditions reflect the average of the 48 contiguous states of the US.

AM-1.5D

768.3

Direct Radiation

AM-1.5G

CIE

1,000

Same as AM-1.5G ATM E-892, however it is normalized to 1kW/m2 by simple multiplication.

AM-2

 

Zenith 60°.

 

 

 

 

Downloads: Spectra can be downloaded from the NREDC website at http://rredc.nrel.gov/solar/spectra/am1.5/ASTMG173/ASTMG173.html

References- Definitions of the AM0, AM1.5 and many others from the National Department of Energy: http://rredc.nrel.gov/solar/spectra/
- U.S. Department of Energy: Description of Air-Mass

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