As part of its ambitious long term energy strategy, Switzerland plans to phase out nuclear power production and replace most or all of its significant share of national electricity production (40%) by renewables, in particular by photovoltaics (PV) and wind energy. The existing large fraction of hydropower and significant pumped-storage hydro capacity in the mountainous regions of the country will potentially provide valuable balancing and ancillary services for the management of intermittent production from PV and wind. We present a set of calculations based on data from the current Swiss electricity system, which investigate the effect of different PV-wind mixing ratio scenarios on required import and export from foreign neighbors. It is shown that the current hydropower is a good basis to deal with intermittent energy sources and to keep import rates of electricity at current levels in a fully renewable Switzerland as long as the PV-wind ratio is small. For higher PV-shares, forced export and import will increase but appear acceptable if PV-contribution stays below 0.6. Enlargement of reservoir capacity or oversizing of intermittent renewables can further reduce required import effectively. These findings are quantitatively specific for Switzerland but qualitatively transferable to similar mountainous environments with abundant hydropower resources.