Where can I find solar radiation data for specific land areas?
The Measurement and Instrumentation Data Center (MIDC, http://www.nrel.gov/midc/) provides Irradiance and other Meteorological Data from several stations. Have you also check in: https://mapsbeta.nrel.gov/nsrdb-data-viewer/? Some of the data maybe until the end of 2012 used to be in http://rredc.nrel.gov/solar/old_data/nsrdb/. Good luck!