Although it looks like a stranded UFO, the Heliotrope is firmly anchored in the suburbs of Freiburg, Germany. The futuristic home harnesses solar energy in two ways: solar panels generate electricity while glass tubes exposed to the sun heat water.  

Not that innovative? Think again: the cylindrical house sits on a giant pole, rotating to track the sun’s path for maximum access to solar energy. The Heliotrope is Germany’s first energy positive house, producing more energy than its inhabitants consume. 

The project started 25 years ago, when Heliotrope inventor and architect Rolf Disch was protesting against plans for a nuclear power plant near Freiburg while also thinking about concepts for renewable energy use in private homes. 

A couple of projects already existed—conically shaped houses with high energy collection potential—but Disch wanted to develop a house that would generate more energy that it actually needed, supplied by renewable energy only. "This idea needed an experimental, futuristic and iconic design. The Heliotrope was born," explains Tobias Bube, Disch’s spokesman.  

Almost exclusively made of wood, the Heliotrope resembles a giant tree house, rotating slowly around a central axis. A timer turns the house 180 degrees during 12 hours, one or two degrees every ten minutes, to capture the maximum sunlight.  

But the Heliotrope is far from being a bumpy ride. "You only feel the movement when you concentrate on it," Bube says. "Because of the pole, the house might sway a little when it’s windy but there’s no need to be afraid of vertigo."

The photovoltaic panels on the roof have a capacity of 6.6 kilowatts. The supportive railings double as passive water heating pipes for the house below. Computer controls make sure that the panel is always optimally adjusted towards the sun.

The main building is divided into two parts. One half is equipped with triple glazed windows for passive solar energy capture.  

The other half is a fortress of insulation to guarantee a cool interior on hot summer days. And during a sunless cold spell, wood chips and solar thermal heating systems help keep things warm.  

To limit water usage, a gray water circuit for washing dishes and clothes collects rainwater. Waste water is purified in a cascade pool. And a waterless, dry-compost toilet system rounds out the picture of the eco-home. 

Ultimately, the heliotrope produces about five times more energy than it consumes. However, the Heliotrope is a luxury solution: fully equipped, it would cost some two million dollars. 

Nevertheless, in 2000 the Schlierberg Solar Settlement in Freiburg installed Heliotrope technology in 50 homes and a commercial building called the “Sun Ship” creating an energy positive community.  The settlement delivers a surplus of about 36 kilowatt hours per square meter.

"For the solar installments, no German bank would give us a loan," Bube recalls. "Too expensive, too risky, too crazy, they said. Luckily, we found a private investor for Schlierberg, so we didn't have this problem."

Even though solar energy is widely supported and reasonable financing is possible, an energy positive family home will cost around 10 percent more than its standard counterpart.  

Supporters say, however, that the investment in renewable energy will pay for itself over time in saved heating costs and income from feeding surplus solar energy into the national grid.   

This concept received a setback in 2010 when the German government reduced feed-in tariffs for rooftop photovoltaic panels. But according to the German Energy Agency (DENA), a private investment in solar panels still pays off, even with subsidies reduced by 16 percent.

For Rolf Disch solar energy is still cheap, especially if producers are able to use electricity directly, without detouring via the main grid. Disch plans on reaching an energy surplus of 200 kilowatt hours per square meter and hopes to use this extra energy directly for electric transportation. 

"Once solar electricity is as cheap as conventional electricity, we won’t even need state-subsidized feed-in compensation any more", muses Bube. "People could start using the electricity directly for electric cars, for example. They would have their own filling station on the roof."

Perhaps Rolf Disch might have to offer future Heliotropes with extra space for a garage.