Solar radiation resource assessment is one of the most important exercises towards implementation of large-scale solar power projects. The quality of resource makes significant impact on the selection of  technology to be used at a specific location for solar electricity generation. In this study, inter-comparability of several solar radiation databases (i.e. ground, satellite and statistical) is assessed in Indian context. The  long-term measured Global Horizontal Irradiance (GHI) over 23 representative locations is compared wih the  GHI obtained from satellite and weather databases. Direct Normal Irradiance (DNI) is estimated through long-term measured global horizontal and diffuse irradiance using basic sun-earth geometry and compard  with the DNI obtained from different solar radiation and weather databases. It is observed that with respect to  long-term measured data of GHI the average range of deviation varied from 0.20% to 22.53% whereas DNI varied from 0.64% to 35.12% across select locations. Impact of the variation due to solar radiation resource  assessment on the annual electricity generation and levelized cost of electricity of grid-connected solar power projects is also underlined.