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Chapter 1

What are solar radiation data?

Solar radiation data provide information on how much of the sun's energy strikes a surface at a location on earth during a particular time period. The data give values of energy per unit of area. By showing naturally occurring changes in the amount of solar radiation over the course of days, months, and years, these data determine the amount of solar radiation for a location. The units of measurement are expressed as kilowatt-hours per square meter (kWh/sq m), megajoules per square meter (MJ/sq m), langleys (L), or British thermal units per square foot (Btu/sq ft).

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.

Chapter 2: Why do we need solar radiation data?

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