If someone asks you to describe a solar power plant you'd likely look to convey an image of row upon row of sun-soaking panels pointing skyward. It's doubtful that the first thought to pop into your head would be of someone's home, unless of course you've already witnessed the likes of the Heliotrope. Sited at the foot of the Black Forest in Germany, this magnificent cylindrical power house is the creation of solar architect Rolf Disch and is the world's first home to produce more energy than it consumes. As the architect announces plans to take his PlusEnergy vision to a global audience, we take a closer look at his first creation.
Towering above the homes and vineyards that surround it stands the Heliotrope home of solar architect Rolf Disch. Whilst a few of the other buildings in the southern German city of Freiburg sport the odd rooftop solar panel to offset some of the spiraling energy costs, using freely available energy from the sun is central to the very design of the Heliotrope. And just like the flora that inspired its name, this solar tower actually follows the path of the sun as it makes its way across the sky.
The main structure of the house is built onto a central load-bearing wooden column that's 47.5 feet (14.5m) high and has a diameter of 9.5 feet (2.9m). The house is designed to rotate around the column at a rate of about 15 degrees per hour, following the path of the sun. It regulates heat entering the home by facing its triple-glazed windows in the sun's direction in winter and pointing its insulated rear sunward during the warmer summer months. Inspection balconies outside also incorporate sunshades to help prevent seasonal overheating.
Snaking around the balconies are special railings that double up as solar thermal tube collectors and provide hot water for the building's domestic needs and supply storage tanks for space heating. As heat from the sun pours through the Heliotrope's windows, it is stored and used by the floor heating system and a geo-thermal heat exchange system makes the most of controlled ventilated air. There's also a low-temperature ceiling radiation system that helps keep rooms nice and toasty when needed.
On the building's roof sits the impressive solar sail. It's made up of highly-efficient monocrystalline silicon solar cells and is able to independently rotate on a two-axis system, allowing for both horizontal and vertical adjustment for optimum tracking. This design is said to achieve an energy gain of between 30 and 40 percent over conventional fixed-panel units.
Access to the 590+ square feet (180m²) of living space in the upper structure is via a spiral staircase that winds its way up the central column. And there's even more space on offer to the occupants in the base structure. Other pro-environment features of the design include a dry compost toilet and a grey-water well, where the home's waste water is combined with rain water for re-use.
Unless you're already aware of the Heliotrope, it may surprise you to learn that Disch's home was completed in 1994, at a time when green architecture was still in its infancy. It was the world's first home to produce more energy than it consumes and in spite of its age, continues to lead the field in energy efficiency and solar architecture technology. In fact it is said to produce up to five times more energy than it consumes, with the surplus fed into the public power grid.
Of course, there's a bit of give and take in operation here – the Heliotrope supplies surplus power to the grid but draws from the grid when solar power is not sufficient to operate the power plant. This is considered a more efficient and green method than using batteries to store and draw, which may contain varying degrees of nasty heavy metals.
The Heliotrope template has been used to build an energy-producing showroom at Hansgrohe's plant in Offenburg, the solar architect has also produced plans for a large hotel and even a special exhibition hall for the Shanghai EXPO 2010.
About five minutes away from Disch's home is a solar settlement that uses many of the technologies found in the Heliotrope but incorporated into a less futuristic-looking and more familiar form. Hidden from view behind a 410 ft (125m) long, five story high commercial building are 59 two and three story townhouses. All of the buildings in the settlement have large photovoltaic roofs and produce more energy than they consume. And now the solar architect is looking to expand his PlusEnergy vision beyond Germany.
Disch believes that U.S. states like Hawaii, Florida and California – which already have systems in place to financially encourage the use of renewable energy – would benefit from the roll-out of homes based on his proven vision. Announcing an international push outwards, Disch's company said: "PlusEnergy is a dual solution which exceeds the highest ecological standards and puts money back in the pockets of owners. Rolf Disch has proved that ecology and economy, function and form can be happily combined to bring double profits: for investors and the environment."
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