The global consumption of fossil fuels is increasing exponentially since forty years, doubling approximately every 27 years. Close to 50% of the emitted CO2 remains in the atmosphere, i.e. nature is able to absorbs 50% of the CO2 emissions. However, until 2047 the world will emit the same amount of CO2 as was emitted since 1850. The fossil resources are limited and will be consumed between 2047 and 2073. Therefore, a fast transition to renewable energy is required. Beside the production of electricity from renewables the storage is essential for a future energy economy based on renewables in order to provide energy on demand from an intermittent source of energy and to shift energy from summer to winter. The global renewable energy production is growing exponentially and if it continues like that will reach the world energy demand in 2035. The energy requirement are analyzed on the example of Switzerland and the opportunities for the replacement of the fossil fuels with renewables are shown as well as the technical and economic consequences are described. In addition the opportunities for Australia to provide renewable energy for the world are discussed. The seasonal storage and the production of the fuel for aviation are the main challenges. Importing renewable energy during the winter time slightly reduces the storage requirement and the size of the photovoltaics needed, but large storage capacities in the hydroelectric storage lakes as well as for hydrogen remain a big technical challenge. Furthermore, the cost of the energy depends on the storage form and the overall conversion efficiency and has a significant economic impact. Hydrogen plays a crucial role in the renewable energy economy since it is rather easy to produce, abundant and much more efficient than synthetic hydrocarbons. The future energy system will use electricity, hydrogen and synthetic fuels, depending on the requirements of the applications.