Today, the primary source of solar radiation data for the United States comes from measurements made by the National Weather Service at 26 SOLMET (SOLar METeorlogical) stations from 1952 to 1975. In addition, mathematical models estimated data for 222 ERSATZ (synthetic) stations where no solar radiation measurements were made. Because the equipment did not always accurately measure the solar radiation and the models used were limited in their application, the data do not always correlate well with more recent field measurements. To provide better data, we developed a National Solar Radiation Data Base. This data base covers 30 years (1961-1990) and comes from information recorded by more accurate instruments and from better models. In 1992, this new database was available for 250 sites.
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