Vorlesen Stuttgart engineers are planning the first commercial solar power station in the world in the Australian desert. The thousand-meter-high chimney in the center of the complex will be the tallest building in the world. The electricity generated in it should not be much more expensive than energy from coal or gas. Does this look like the entry into the solar energy age? Thousand meters high, the tower of hundreds of thousands of tonnes of concrete and steel towers over the Australian desert. It is the tallest structure in the world. Like little things, the Eiffel Tower or the television tower at Berlin's Alexanderplatz would be next to it. Inside the tube, a strong wind blows: air, heated by the sun under a kilometer-wide glass roof around the tower, flows upwards at a speed of up to sixty kilometers an hour like a chimney. It drives wind turbines at the foot of the tower, which generate around 1, 500 gigawatt hours of electricity per year - enough energy for around 200, 000 people.

This scenario could already become reality in 2005. EnviroMission plans to build the world's first commercial wind turbine on a plain near the small town of Mildura in southeastern Australia. It should provide a maximum of 200 megawatts - about one sixth of the power of a nuclear power plant. At least according to the optimistic plan of the energy company is to be started in the coming year with the construction.

For the Stuttgart engineer Jörg Schlaich, this would be a lifelong dream come true: The generation of electricity from solar energy on a grand scale. For decades, the self-employed planning engineer and professor at the University of Stuttgart has never left the idea of ​​the updraft power plant. The Stuttgart engineering office Schlaich, Bergermann and Partner, whose co-founder he is, is now to implement it. The principle is simple: a glass roof lets in sunlight, but the air heated by the light does not go underneath. If you put a circular roof in the middle with a chimney, the heated air flows upwards at high speed (animation). The roof and the chimney, which are now to be built in the Australian desert, certainly have gigantic proportions. The roof measures around five kilometers in diameter, rising from a height of 2.50 meters at the outer edge to around 35 meters at the center. There towering tower with a diameter of about 170 meters. The colossus of concrete and steel is held in shape by huge spoked wheels inside.

Not gigantomania drives the engineers to plan the updraft power plant with such huge proportions, but it is the laws of physics: The higher the tower and the larger the roof, the more effective it works, because the higher the temperature difference between the hot air the roof and the cold at the top of the tower. display

"You get that today, " says Wolfgang Schiel confidently. The engineer responsible for the project at Schlaich, Bergermann and Partner sees no insurmountable technical problems in the construction of the giant. Despite its size, planning is in principle nothing out of the ordinary. Compared with a slim television tower with heavy antennas and platforms, the tower with a diameter of 170 meters is "an inelegant, thick tube" with comparatively uncomplicated statics, according to Schiel. "We are building bridges in typhoon areas, and then we can do that." Nevertheless, engineers must be careful when choosing the location. The tower can indeed be constructed so that it survives even century storms. But the glass roof would not withstand a heavy hail with egg-sized hailstones. With the now planned location in the Australian desert, however, the planners are on the safe side in this regard.

The technical problems are therefore solvable. Only the money could make the project fail. The construction of the tower and especially the glass for the roof consume a lot of money. Initial estimates assume a total cost of between € 300 million and € 450 million - money that EnviroMission will be able to raise, at least in part, only through expensive loans, even after the IPO last year.

An expert opinion of the energy provider Baden-Württemberg (EnBW) on behalf of the Stuttgart-based engineers has shown that an upwind power plant can keep up with coal or gas in terms of cost-effectiveness: at an interest rate of less than eight percent or less, the kilowatt-hour of electricity from the Aufwindkraftwerk even cheaper. With the interest rate and the willingness of the banks to invest in such an unprecedented project, the profitability stands and falls. Because almost the entire costs are incurred when building the system. Unlike coal-fired power plants, where new fuel needs to be replenished constantly, the running costs of operating the wind turbine are minimal.

Five years ago, the construction of the first commercial wind turbine failed once before due to the futile search for investors. At that time, a similar power plant was to be built in the northern Indian state of Rajasthan as now in Australia. But this time the conditions are much cheaper, explains Schiel. The planners, for example, are opposed by the fact that in Australia the demand for electricity corresponds very well to the performance curve of the updraft power plant over the course of a day. As most homes and businesses have air conditioning systems running, the demand for electricity is highest on hot afternoons - and that is precisely when the storm in the largest tube blows the strongest.

If necessary, however, the power curve of the power plant could also be adapted to a rather constant power requirement: water tanks under the glass roof could store the heat of the afternoon. The power plant then produces electricity even at night.

ddp / bdw - Ulrich Dewald

science.de

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