The electricity self-consumption level of a family household is determined both experimentally and by modelling. The effect of rapid fluctuation in PV production and electricity demand, and especially the effect of the temporal resolution of their measurements, are studied. For accurate determination of the self-consumption level, temporal resolution of at least 30 s for the load profile and at least 10 min for the PV production measurements are suggested. The effect of temporal resolution becomes negligible when a local electricity storage system is added. Keywords: Small Grid-connected PV Systems, storage, gird integration