Most people associate Munich with BMW, Siemens or millions of beer-drinking revellers in Lederhosen at the Oktoberfest. Less well known is that the capital of Bavaria is also a European champion of renewable energy, thanks to its municipal utility Stadtwerke München (SWM).

While other German cities have sold their public utilities to pay off debt, Munich has bolstered SWM and in 2008 embarked on an ambitious €9bn ($10.2bn)