As world leaders prepared to discuss a major climate change treaty in Paris last week, Germany had a couple of especially windy days, which drove the share of wind energy in the German grid above 50 percent and the spot price of electricity to zero, or so close to it as to make no difference.

All that's missing to make 100 percent renewable energy feasible is cheap and ample storage that would help to smooth supply. That requirement no longer looks impossible.

Few countries have the political will and resources for something like Germany's ambitious, painful and expensive energy transition program, known as Energiewende. Yet by going through with it, Germany has helped to spur the development of technology that may work for others without massive subsidies soon.