Executive SummaryTypical Meteorological Year (TMY) data sets provide industry standard resource information for building designers and are commonly used by the solar industry to estimate photovoltaic and concentrating solar power system performance. They are the basis for system performance and economic models such as PVWatts, 1 System Advisor Model (SAM), 2 and Solar Prospector. 3 Historically, TMY data sets were only available for certain station locations, but current TMY data sets are available on the same grid as the National Solar Radiation Database (NSRDB) data and are referred to as the gridded TMY. This gridded TMY data is derived from the 10-km by 10-km gridded NSRDB data (including the years from 1998 to 2009). A gridded TMY file is created by concatenating 12 typical meteorological months from statistically analyzed and selected individual months from the entire set of available years. The selected months (which may be from different years) are then joined to make one serially complete year. A typical meteorological month is generated through cumulative distribution frequency (CDF) analysis in which a typical month is selected closer to the long-term monthly average CDF (Wilcox and Marion 2008). For example, in this case the month of January was selected from the 12 Januarys during the 1998 to 2009 period. The remaining months were selected in similar fashion. Ten indices were used to select a TMY month. These are described in Table 1. The indices are essential for selecting the typical month using a weighting factor for each parameter, which ultimately includes considering the monthly mean and median and the persistence of weather. The series of steps that were carried out to acquire the typical month is described in the Users Manual for TMY3 Data Sets (Wilcox and Marion 2008).A system performance analysis for photovoltaics and concentrating solar power projects should generally consider high weighting factors for the solar components; as such, some of the meteorological parameters in Table 1 might not be relevant for these applications. For this reason, typical direct (normal irradiance) year (TDY) and typical global (horizontal irradiance) year (TGY) data sets were also produced, whereby the weighting focused on the irradiance components of the data rather than the meteorological data. The weighting factor for each solar component is described in Table 1. The process of generating TDY and TGY data sets is tailored to generating solar component values that are as close as possible to the long-term means for those parameters (as opposed to the "typical" conditions defined by the usual TMY statistical analysis) and are not influenced by other parameters. In this report, a comparison of TMY, TDY, and TGY data sets were performed to better understand the impact of ancillary weather variables upon them.We analyzed the temporal and spatial variability of the typical year data sets. The spatial variability was calculated using the coefficient of variations of adjacent pixels on a monthly basis for the TD...