Description

The free-form hydroelectric power station was built in Kempten on the River Iller, a town with a long tradition of water-powered mills and textile factories that dates back to early industrialisation. The first water-to-electricity plant went into operation as early as 1903. After production ceased in the mid-1990s, the Allgäuer Überlandwerk (AÜW), the primary utility company in the Upper Allgäu – where hydroelectric power accounts for approx. 25 percent of energy demand – also took over this power station. The listed factory buildings were converted into waterfront flats and a competition for the renewal of the power plant was announced in 2005 – due in part to stricter noise pollution regulations and the town’s desire to revitalise the riverside.
The design, which takes its cue from the way in which stone is eroded by water, has injected new architectural vitality into the area. The staff identify with their building, there are daily guided tours, and visitors number in the thousands. The power plant’s output has also more than doubled to 10.5 million kW thanks to a tripling of the intake capacity, as have CO2 savings. The construction was completed in just under three years at a cost of 15 million euros.
The architectural ensemble, which extends over a length of almost 100 metres and accommodates hydraulic engineering and operating technology, must respond to various various demands – from urban planning to the organically shaped hydraulic engineering requirements and the orthogonal operating engineering. The result is a large sculpture that is attuned to the dynamics of water and picks up its forms.
The shell is a concrete shell cast in six sections that rest on the technical structure beneath. The shell – which has an average thickness of 25 cm – is stretched over ribs about four metres apart that are cast together with the shell. This comparatively generous thickness – compared to historical precedents – is the product of bad experiences with minimised material constructions, the fact that its specifications hardly correspond to a geometrically ideal figure, and that crack size tolerances and new standards provided little leeway for more slender dimensions.
The curved surface of the shell between the concrete ribs were cast on carpenter’s board formwork with hand-linked reinforcement bar work. This formwork is capable of use up to inclines of 40 degrees. The ribs, upright walls and slabs are cast in sections but without joints. A C 30/37 mixture, which is common in outdoor uses, was used without chemical additives or special aggregates.
The structure has two faces, made possible by the building material concrete. The inside is rough, textured, shaded and grey, the material, boardmarks and joints are visible, the construction is exposed, the ribs rhythmical, making the flow of forces legible and emphasising the supports. By contrast, the outside is smooth, sanded, light. Openings and joints disappear under a stretchable, waterproof three-layer PU coating, as is common in bridge construction. This was mixed with grit made of gravel from the river.
The shape of the project is not the product of parametric design, but was developed through hand sketches, plans and above all numerous models. Its sculptural form draws inspiration from images of stream pebbles, rounded stones, pools, edges and overhangs.

Originally published in Bauwelt  13.2011, pp. 18-23, abridged and edited for Building Types online, translated by Julian Reisenberger

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