The National Solar Radiation Database (NSRDB) was produced by the National Renewable Energy Laboratory under the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy. The 1991-2010 NSRDB is an update of the 1991-2005 NSRDB released in 2006 and archived at NCDC. The serially complete hourly data provided in the NSRDB update are provided in two output formats: 1) ground-based solar and meteorological dataset, and 2) 10 km gridded output produced by the SUNY model. The 10 km gridded output is from the State University of New York/Albany (SUNY) satellite radiation model developed by Richard Perez and Clean Power Research. Data in the NSRDB are a slightly modified version of the SolarAnywhere dataset distributed by Clear Power Research. The modifications are detailed in the NSRDB User's Manual. The model uses hourly radiance images estimated from Geostationary Operational Environmental Satellite (GOES) imagery, daily snow cover data, and monthly averages of atmospheric water vapor, trace gases, and the amount of aerosols in the atmosphere to calculate the hourly total irradiance (sun and sky) falling on a horizontal surface. Atmospheric water vapor, trace gases, and aerosols are derived from a variety of sources. In simple terms, this satellite model uses the inverse relationship between reflected irradiance (that reflected by clouds and atmosphere back to space and the satellite sensor) and ground irradiance (that transmitted through the atmosphere to the Earth's surface). The high-resolution 10-km gridded data set from the SUNY model provides a consistency in modeled output data for its period of record for the years 1998 to 2009, the period for which necessary GOES imagery was available for the project. The SUNY model produces estimates of global and direct irradiance at hourly intervals on the 10-km grid for 49 states, excluding Alaska, where the geostationary satellites cannot resolve cloud cover with necessary detail. Although GOES images provide up to 1-km resolution, in the SUNY model, these data are down-sampled to 10-km resolution (0.1 degree x 0.1 degree). This resolution is adequate for most solar radiation resource applications and represents a practical trade-off between resolution and processing and data storage considerations. The model uses both GOES-East and GOES-West satellites for complete spatial coverage of the United States.