This line shapefile contains horizontal photovoltaic solar power resource levels of watt hours per meter squared (Wh/m2) for direct solar irradiance in the contiguous United States using 500-meter interval contour lines. Horizontal photovoltaic panels are those that are positioned on a flat surface. This layer is a part of a collection of GIS data containing renewable and electric energy information for the U.S., including data on transmission lines, power plants and electricity substations.This layer can be used for estimates of solar resource potential.