From 2006 to 2013, I lived and worked near Vienna, Austria. For most of that time, starting in 2008, I taught a class each spring semester at the University of Bayreuth, in northern Bavaria. I would typically travel there and back on a German high-speed train, sinking myself into lecture preparation on the way up and relaxing in the dining car on the way back. I wouldn't pay much attention to the landscape flying by outside because I had seen it so often. But every now and then, I would take a look. The interesting thing is that I always could immediately tell whether or not the train had passed the border between the two countries. It wasn't because of any particular change in the landscape or vegetation, in the architecture of the buildings, in the cars on the road, or the way the villages were laid out. All these things were essentially the same, whether I was in Austria or in Germany. The difference was on the rooftops. On the German side of the border, it seemed like every second house, barn, or commercial building had a set of solar photovoltaic (PV) panels on top. In some places, every building in sight had a PV installation. Not infrequently, the train would whip past a farmer's field that was now covered with PV panels as well, mounted on metal frames about a meter above the ground. In Austria, they were absent.

That was southern Germany. In northern Germany, the situation was the same, except that what you see isn't so much PV panels on the roofs, but windmills in the fields. Just about everywhere, gently turning in the wind that blows moderately across the flatlands. Crossing the border from the Netherlands in the west, or Poland in the east, the contrast of windmills in the sky is just as strong as it is with PV panels in the south. Denmark, to the north, has policies for wind that are not too different from Germany's. And the Danes, too, have lots of windmills. Policies make a difference.