In Switzerland, the government has made ambitious plans for a major energy transition. There is a planned phase out of nuclear facilities by mid-century, their capacity replaced by an expansion of hydroelectric infrastructure, new geothermal installations, and a considerable number of new solar and wind plants. The principle challenge of this transition is the variational nature of renewable energy. For example, Switzerland generates significantly more hydroelectric power during the snowmelt season than in mid-winter, and solar power has lower yields in the winter. Thus a 100% renewable Switzerland is a desirable goal but brings great challenges, which require specific methods of management. In this work, we carry out a first order assessment of a future Swiss energy system powered exclusively by renewable energy, and highlight the principle operational risks. We approximate yields from the various renewable sources as a function of time using meteorological data for the five year period: 2010-2014. We then highlight power surpluses and deficits with respect to domestic demand. In these situations, energy trade or energy storage must be elicited. We also perform simple power flow simulations of this fully renewable Swiss energy system, allowing us to calculate a lower estimate of the storage facilities required to smooth out seasonal variations. The conclusions raise several fundamental questions concerning the optimal infrastructure investments to be made as Switzerland undergoes its energy transition.