Economist: OLD-FASHIONED windmills, no longer used to grind flour, have become tourist destinations in much of the developed world. Most people would agree that wooden windmills fit pleasingly into the landscape, and are charming reminders of a simpler, agrarian past. But opinion is divided about their high-tech descendants, wind turbines, which are springing up across the world as a source of renewable electricity. To some they are a blight on the landscape; to others they are graceful, majestic …