Starting from an electricity generation from renewable sources (RESE) of 74 % today (mainly by domestic hydropower), the Austrian climate and energy policy aims not less than 100 % by 2030. The additional generation from wind power and photovoltaics will increase the requirement for reasonable seasonal flexibility. Additional highly cost and energy efficient functional units of flexible hydropower assets will play a key role to meet future system needs in all time frames and to safeguard security of supply. The basic results of this study are a useful orientation for countries with high RESE penetration targets.