Photovoltaic (PV) energy yield estimation at various geographical locations depends on a number of factors the most important of which, is the solar resource. Therefore, the main source of uncertainty needs to be investigated. Energy yield estimates are commonly based on satellite or ground-based derived irradiation data. This work focused on the analysis and comparison of different sources of solar radiation in the UK and the quantification of modelling uncertainties based on 10 years of hourly irradiation data (2005-2014) from ground based meteorological stations and two satellite products.