After a hot and dry summer, the rain and chill in September brought some relief to parched Germans—but also a reminder of the looming winter. On September 16th Klaus Müller, boss of the Bundesnetzagentur (bna), Germany’s energy regulator, admitted that if it gets very cold “we will have a problem”. He could not rule out the rationing of natural gas, which Germany’s biggest supplier, Russia, has withheld as part of its war in…