Autonomous systems on the basis of PV and wind generators in combination with a battery storage are an option for the supply of small electrical loads at remote locations. The systems may be supplied by a wind generator or a PV generator alone, or by a combination of both. To decide on the system configuration that should be applied in a certain case it is necessary to identify all possible configurations that satisfy the desired level of reliability. From these configurations, an optimal one may be extracted by the application of economic measures for example. For European sites we present a new approach to the determination of the combinations of generator and storage sizes that will guarantee a high level of system reliability. A set of equations has been identified that link the sizes of the system components (PV generator, wind generator, battery) directly with parameters that characterize the meteorological conditions at the respective site. The meteorological parameters applied are all gained from data sets given in the European Solar Radiation Atlas and the European Wind Atlas.