The Prototype Manzanares Solar Chimney, Spain
A solar flue is an air stream driven by temperature difference in a solar chimney power station. The solar chimney power stations combine three things in one: the greenhouse, the chimney and the turbine. Air underneath a low circular glass roof open at the circumference is heated by radiation from the sun. The roof and the natural ground below it form a hot air collector ("greenhouse"). A vertical tower tube with large air inlets at its base stands in the centre of the glass roof. The joint between the roof and the tower base is airtight. As hot air is lighter than cold air, it rises up the tower. Suction from the tower then draws in more hot air from the collector, and cold air comes in from the outer perimeter. The energy of the air flow is converted into mechanical energy by pressure-staged wind turbines at the base of the tower, and into electrical energy by electric generators coupled to the turbines.
A prototype solar chimney was built and tested in Manzanares (south of Madrid), by Schlaich Bergermann und Partners, the engineering consultancy founded by Professor Jörg Schlaich. The solar chimney delivered power practically uninterrupted from July 1986 to February 1989 with a peak output of 50 kW. Its collector had a diameter of 240 meters, with surface area of 46,000m2. The chimney was 10 meters in diameter and 195 meters tall.
Potential of solar chimney power stationSolar chimney power stations could make important contributions to the energy supplies in Africa, Asia and Australia, because there is plenty of space and sunlight available there.
Solar chimney power stations are particularly suitable for generating electricity in deserts and sun-rich wasteland. Their efficiency increases with the height of the chimney, not linearly, but exponentially. For the power stations to generate electricity economically, not only large glass or plastic roof surfaces are necessary, but also a very high chimney. The height is needed simply from the fact that the updraft is proportional to the height, and also to make best use of the heat available.
Even under very favourable conditions (global solar radiation of 2.5MWh/m2), a 5 MW power station needs a collector roof with 1100m of diameter; a chimney of 445m high and 27m in diameter. To produce 200 MW of power, a 5000m-diameter collector roof as well as a chimney of 1000 m in height and 150 m in diameters are needed. The solar flue reaches a speed of 8m/s if the power plant is under load (the turbine driving the generator to produce electricity). If without load, the solar flue reaches a speed of up to 15m/s.
A single Solar Tower power plant with a collector area of 7000m in diameter built and operated in an area with an annual global solar radiation of 2.3 MWh/m2 will generate between 700 and 800 GWh per year. Thus a small number of Solar Tower power plants can even replace a large nuclear power station.