A comparison of data from SOLMET/ERSATZ and the National Solar Radiation Data Base

Abstract

This report compares data from the new National Solar Radiation Data Base (NSRDB) with data from the earlier SOLMET/ERSATZ data base. It compares the two data bases, station-by-station, with respect to their long-term average daily values of global horizontal and direct normal solar radiation. We conclude that on an annual basis, NSRDB values for global horizontal radiation are within {plus_minus}5% of SOLMET/ERSATZ values for 60% of the stations, more than 5% greater than the SOLMET/ERSATZ values for 30% of the stations, and more than 5% less than the SOLMET/ERSATZ values for 10% of the stations. On an annual basis for direct nominal radiation, the NSRDB values are with {plus_minus}5% of the SOLMET/ERSATZ data for only 40% of the stations, more than 5% greater than the SOLMET/ERSATZ values for 45% of the stations, and more than 5% less than the SOLMET/ERSATZ values for 15% of the stations. In general, the NSRDB shows higher values of solar radiation for the eastern United States, particularly the Northeast, and lower values for some of the western states (Arizona, Colorado, Idaho, Nevada, New Mexico, Utah, and Wyoming). However, because some of the stations within a state show higher values of solar radiation while others show lower values, this generalization may be misleading when concerned with a particular station. Consequently, the appendices provide tables showing a station-by-station comparison of the NSRDB and SOLMET/ERSATZ data. In addition to comparing annual values, the tables compare the two data bases for the months of August and December. This comparison shows larger differences between the two data bases for December.