Photovoltaic Efficiency Measurements

Abstract

A variety of performance indicators have been employed by the photovoltaic (PV) community to rate the performance of PV cells, modules, and arrays. The PV power conversion efficiency under a set of standard reporting conditions serves as a basis for meaningful comparisons of PV performance, within and among PV technologies. PV efficiency is defined as 100 times the maximum PV electrical power density produced divided by the incident light power at a reference PV temperature, total irradiance, and spectral irradiance. Standard reporting conditions commonly used by the PV community are summarized in Table I.The direct and global reference spectra were generated by a comprehensive Monte-Carlo computer model and actually integrate to 768 W m−2 and 964 W m−2. The terrestrial PV community has arbitrarily assigned a 1-sun total irradiance of 1,000 W m−2 for the global and direct reference spectra. The term “direct” in Table I refers to the direct-normal (5° field of view about the sun) component of the global spectral irradiance distribution. The term “global” in Table I refers to the spectral irradiance distribution on a 37-tilted south-facing surface with a solar zenith angle of 48.2° (AM1.5). The terms AM1 or AM1.5 are often used to refer to standard spectra, but the relative optical air mass (AM) is a geometrical quantity and can be obtained by taking the secant of the angle between the sun and the zenith.