Solar radiation data have been acquired over approximately a five year period (1996 to present) at 15 sites in Texas (Texas Solar Radiation DataBase – TSRDB). These data are compared with comparable sites in the National Solar Radiation DataBase (NSRDB). Comparison of the TSRDB and NSRDB data for eleven (11) coincident or nearby locations show reasonably good agreement between the global horizontal values. Relative to the NSRDB, individual monthly average differences between the two sets range from −20 to +13%, and the annual averages varied from −9 to +8.5%, with positive values meaning the TSRDB values are higher. Overall, the TSRDB global horizontal data are about 2% lower than the NSRDB. However, there are considerable differences in the direct normal values, with the TSRDB values generally being higher. The monthly average differences ranged from −18 to +36%, and the average annual difference for the compared locations is about +5%. The greatest deviations for direct normal data are for coastal locations in the winter, with the three compared coastal locations exhibiting an average difference of about +30% for the combined months of December and January. Also, the TSRDB data for the Trans-Pecos region in west Texas exhibits significantly higher direct normal solar radiation throughout the year than does the NSRDB.

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