The solar spectrum changes throughout the day and with location. Standard reference spectra are defined to allow the performance comparison of photovoltaic devices from different manufacturers and research laboratories. The standard spectra were refined in the early 2000's to increase the resolution and to co-ordinate the standards internationally. The previous solar spectrum, ASTMG159, was withdrawn from use in 2005. In most cases, the difference between the spectrum has little effect on device performance and the newer spectra are easier to use.
Further details on solar spectra are available at: http://www.nrel.gov/solar_radiation/
ASTM G-173-03 (International standard ISO 9845-1, 1992)
Two standards are defined for terrestrial use. The AM1.5 Global spectrum is designed for flat plate modules and has an integrated power of 1000 W/m2 (100 mW/cm2). The AM1.5 Direct (+circumsolar) spectrum is defined for solar concentrator work. It includes the the direct beam from the sun plus the circumsolar component in a disk 2.5 degrees around the sun. The direct plus circumsolar spectrum has an integrated power density of 900 W/m2. The SMARTS (Simple Model of the Atmospheric Radiative Transfer of Sunshine) program is used to generate the standard spectra and can also be used to generate other spectra as required.
Download the solar spectra in an Excel file.
The international measurement laboratories are in the processes of ratifying the new standards. In the meantime, concentrator cells are measured using a low aerosol depth spectrum (Lo-AOD) that is appropriate for typical concentrator locations such as the southwest of USA. It is essentially the same as the ASTM G-173-03 direct data given on this page.