Preliminary Investigations of Outdoor Meteorological Broadband and Spectral Conditions for Evaluating Photovoltaic Modules and Systems

Historically, flat-plate photovoltaic (PV) modules have been rated at "peak-output" for power generated under Standard; Reporting Conditions (SRC) of 1000 Watts per square meter W/m2 global irradiance at a standard temperature (25degC) and reference spectral distribution. We examine the direct-normal irradiance, spectral distribution, ambient temperature, and wind speed to be used for evaluating flatplate and concentrator module performance. Our study is based upon the 30-year U.S. National Solar Radiation Data Base for conditions observed when the global irradiance on a 2-axis-tracked surface is 1000 W/m2. Results show commonly-used values for concentrator testing of 850 W/m2 for direct-normal irradiance and 20degC for ambient temperature are appropriate. Wind speed should be increased from 1 m/s to a more frequently observed 4 m/s. Differences between the reference direct-normal spectrum and spectra measured at three sites when broadband direct-normal irradiance and global-normal irradiance are near SRC irradiances suggest revisions to the reference spectra may be needed.