The International Energy Agency (IEA) claims in a report that up to 45% of power generated annually could come from renewable energy sources in some advanced economies without significantly increasing long-term power-system costs (The Power of Transformation; IEA, 2014). This raises the possibility that certain regions could be using 100% renewables during our lifetime (see also J. A. Mathews and H. Tan Nature 513, 166–168; 2014).

This possibility is backed, for instance, by analyses in India by the conservation group WWF and the Energy and Resources Institute (see go.nature.com/7shcug), and in Australia by the Australian Energy Market Operator (see go.nature.com/wtt1ps).

As noted in the IEA report, progress in integrating renewables depends on cost constraints, local weather and daylight patterns, and the flexibility of existing power systems.