A speech given during the International Renewable Energy Storage Conference (IRES) in March 2015 in which Prof. Dr. Ingo Stadler explains how the energy transition process from fossil and nuclear fuels towards renewable energy resources can be realised in a cost-efficient way. It is explained that in many energy sectors energy storage is a well known and well established component. Only in electricity supplies this is not the case. By coupling different energy sectors (electricity, heat, gas, transport) the energy storage tasks can be solved in a cost-efficient way.