The Swedish electricity supply system benefits strongly from the natural conditions which allow a high share of hydroelectricity. A complete supply is, however, not possible. Up to now nuclear power is the other workshop horse to serve the country with electricity. Thus, electricity production in Sweden is basically CO2-free and Sweden has reached an environmental status which others in Europe plan to reach in 2050. Furthermore, there is an efficient exchange within the Nordic countries, Nordpol, which can ease possible capacity problems during dry cold years. In this study we investigate to what extent and with what consequences the base load supply of nuclear power can be replaced by intermittent wind power. Such a scenario leads unavoidably to high wind power installations. It is shown that hydroelectricity can not completely smooth out the fluctuations of wind power and an additional back-up system using fossil fuel is necessary. From the  operational dynamics, this system has to be based on gas. The back-up system cannot be replaced by a storage using surplus electricity from wind power. The surplus is too little. To overcome this, further strong extension of wind power is necessary which leads, however, to a reduction of the use of hydroelectricity if the annual consumption is kept constant. In this case a fossil-free energy form is replaced by another, however, more complex one. A mix of wind power at 22.3 GW plus a gas based back-up system with 8.6 GW producing together 64.8 TWh would replace the present infrastructure with 9 GW nuclear power producing 63.8 TWh electricty. The specific CO2-emission increases to the double in this case. Pumped storage for the exclusive supply of Sweden does not seen to be a meaningful investment.