Energy and utilities company Hamburg Energie has joined forces with IBA Hamburg to transform a former Nazi anti-aircraft flak bunker into a green energy power plant. The Hamburg-based "Energy Bunker" has already begun producing energy for the local community, but once running at full capacity will provide up to 3,000 homes with heating, and another 1,000 homes with electricity.

Originally constructed in 1943 to serve as an anti-aircraft bunker, complete with gun turrets, the 42 m (137 ft) -high building also sheltered local people from Allied bombing raids during WWII. Though the British Army made an attempt to demolish the building on the war's close, blowing up its massively thick walls was deemed too dangerous to nearby buildings. The British ultimately settled on destroying much of the interior, and the bunker remained in this neglected state for over 60 years.

Plans to transform the building into a green energy hub first arose in 2006, with the renovation proper commencing in 2011, following extensive safety tests. The total cost of the project came to €26.7 million (roughly US$36.5 million) and was funded by both the the European Regional Development Fund (ERDF) and the Hamburg Climate Protection Concept.

The Energy Bunker is outfitted with several sustainable technologies. The main feature is a 2 million liter (528,000 US gallon) water reservoir that acts as a large heat store and plugs into the existing Reiherstieg district heating network. The reservoir itself is heated by several methods: a biomass power plant and wood chip burning unit which feed into a large boiler, a solar thermal array installed on the roof of the bunker, and waste heat produced by a nearby industrial plant.

A large photovoltaic system is installed on the south-facing facade of the building to produce electricity, and the wood chip burning unit is also used to produce electricity. A peak-load boiler and large battery array ensure that the energy output is kept steady at all times.

In addition to the production of green energy, Energy Bunker also contains a war memorial, cafe, and visitors center, where people can learn more about the building's history.

Source: IBA Hamburg