The Heliotrope, designed by Ralph Disch [Image Source: Andy Wright, Flickr]

The Heliotrope is a rotating solar home which gave rise to the Sonnenschiff Solar Development and also the German solar sector as it is today. It was designed and developed by architect Ralph Disch in 1994 and is able to generate five times the energy it consumes. It is precisely its ability to rotate to face the sun, whatever its position in the sky is, which enables the Heliotrope to achieve this, along with the help of triple-pane thermal glass windows, some solar thermal pipes and a large solar array mounted on its roof. The Heliotrope is therefore one of the world’s first truly zero-energy homes.

The building is named after a biological process called a heliotropism, which is used by plants in the Arctic to capture the maximum amount of light from a growing season that is distinctly shorter than anywhere else. However, the Heliotrope also embraces another biological process, paraheliotropism, in which plants turn in order to avoid direct sunlight. The Heliotrope achieves this through one side of the building having a thermally insulated wooden side, rather than glass, which means it can turn in order to provide shade when it is needed.

The 6.6 kilowatt hour solar array mounted on the Heliotrope’s roof generates enough energy to make the structure net energy positive. A hand rail system, also located on the roof, doubles as solar thermal tubing in order to provide heat and hot water. Greywater and rainwater is collected and reused and there is also a composting toilet system.

Ralph Disch’s interest in solar began some twenty-five years ago when he fought to prevent a nuclear power plant from being built near his hometown of Freiburg, Germany. He now runs his own architecture firm, Rolf Disch Solar Architecture and is widely considered to be a solar pioneer with regard to residential, retail and commercial building and design. The concept of buildings being able to generate more power than they use, known as Plus Energy, was developed by Disch during the construction of the Heliotrope and is now widely used in German residential, commercial and retail premises. Disch describes it as an integrated ecological and architectural concept that is superior to other low-energy or zero-energy designs such as the Passivhaus. Plus Energy utilizes a number of interesting techniques, such as capturing enough energy during the day to heat a building during the night and using large windows facing North and South in order to capture as much light as possible, thereby reducing the need for light bulbs. These techniques also allow the buildings occupant to sell excess energy back to the national grid, thereby generating an income.

The Heliotrope also has a wood chip boiler for use on cloudy days when the amount of solar energy is reduced. Disch lives in the prototype himself, but two others have been constructed, each costing around $2 million to build. These are located in Offenburg (constructed by Hansgrohe) and Hilpolstein. The first of these is used as a visitors center and showroom for Hansgrohe, which is itself an eco-orientated company, while the second is a dental laboratory

The whole structure revolves around a central pole which is 14 meters high and contains a central staircase and electric installation. It was constructed in a modular fashion and is roughly based on a ‘revolving treehouse’ idea. This gives the design enormous flexibility, enabling each building to be used for a wide variety of purposes.

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