Modern distribution network architectures have greatly changed due to the increasing proliferation of the network with power converters of renewable distributed generators (RDGs) and switching electronic loads. While these RDGs may offer benefits to the distribution network operator in terms of network loss reduction, the quantification of such benefits is usually investigated on the basis that harmonics from the power converters are negligible. In this paper, the electrical power losses in a network with significant penetration of photovoltaics (PVs) is assessed. The harmonics from the power conditioners of the PVs and network background distortions have been taken into account in the analysis. Technical insights from study of practical distribution networks are presented.