The content originally appeared on: CNN Paul Hockenos is a Berlin-based writer focusing on renewable energy in Europe. He is the author of four books on European issues, most recently 'Berlin Calling: A Story of Anarchy, Music, the Wall and the Birth of the New Berlin.' The opinions in this article are those of the author. View more opinion on CNN. (CNN)American friends visiting my downtown Berlin apartment at the height of summer always guffaw at my rinky-dink plastic fan, […]