The aim of this paper is to analyze the influence of some sizing parameters of grid-connected, hybrid wind-photovoltaic systems provided with energy storage and load consumption, on their interaction with the electrical network. These sizing parameters are the sizing factor (defined as the ratio between the yearly energy produced by the renewable generation system and the yearly energy demanded by a consumer), the solar and wind fractions, and the size of the batteries. The analyzed case study is the supply of energy to a typical residential load in Spain. Annual hourly-based series of energy production from wind and photovoltaic installations in operation in Aragon (an eastern region of Spain) are used as data inputs to a Matlab model of the system. Yearly energy balances for hybrid systems with different combinations and sizes of photovoltaic (PV) plant and wind energy conversion system (WECS) plus Battery Storage Systems (BES) are simulated in an hourly basis. These hybrid systems can inject or absorb energy from the grid depending on whether the energy produced is higher or lower than the household consumption and their operational limits are not exceeded. The interaction with the grid is evaluated in terms of energy injected in or absorbed from the grid, electrical (Joule) losses in lines and load duration curves (LDCs). Although the problem is case-dependent and the correct sizing of such systems is only possible with the knowledge of generation and consumption profiles, some general criteria can be extracted from the results of this paper. Conclusions are also valid for pure PV or Wind systems. (C) 2013 Elsevier Ltd. All rights reserved.