Beer, BMW, and one of the world's best soccer teams, Bayern Munich: Germany's third largest city has a lot going for it. Not content with sporting, culinary and automotive excellence, Munich is also leading the way when it comes to sustainability.

By 2020, the EU hopes that 20 percent of energy will come from renewable sources such as wind, solar and biomass. In Munich, authorities have gone one step further, targeting a 100 percent clean electricity supply by 2025, which would make the city a world leader in sustainability.

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"We forced our utilities company… to invest in renewable energy," Hep Monatzeder, the former mayor of Munich, told CNBC's Innovation Cities. "All the other big cities have to go this way, otherwise we will not protect the earth," Monatzeder added.

Stadtwerke München, or SWM, the city-owned utility company, will need to produce 7.5 billion kilowatt hours of green electricity to meet the target.

An admirable ambition, but achievable?

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With a budget of roughly 9 billion euros, SWM has launched several new clean energy projects, including a hydro power plant on the river Isar, which produces enough electricity to supply 4,000 Munich homes a year. At Munich zoo, even elephant dung has been converted into sustainable fuel.

Despite investing in clean energy projects in and around the Munich area, these are not enough to meet the needs of the city, which is home to more than one million people.