Guardian: It is 6C outside, and a dusting of snow can be seen on the Schauinsland - the low hill overlooking Freiburg, where the good burghers of the southwest German city take their children hiking. In Meinhard Hansen's apartment, however, it is perpetual summer; the sun streams in through tall, south-facing windows and a gauge on the wall reads '24C'. Next to it, the words 'Heizung 0' appear in a small glass window. 'Heating, zero,' Meinhard translates. 'In fact, we haven't switched the heating on for weeks.'...