Solar updraft tower: projects
Spanish prototype
In 1982, a small-scale experimental model of a solar chimney power plant was built under the direction of German engineer Jörg Schlaich in Manzanares, Ciudad Real, 150 km south of Madrid, Spain; the project was funded by the German government.
The chimney had a height of 195 meters and a diameter of 10 meters with a collection area (greenhouse) of 46,000 m² (about 11 acres, or 244 m diameter) obtaining a maximum power output of about 50 kW. However, this was an experimental setup that was not intended for power generation. Instead, different materials were used for testing such as single or double glazing or plastic (which turned out not to be durable enough), and one section was used as an actual greenhouse, growing plants under the glass. During its operation, optimization data was collected on a second-by-second basis with 180 sensors measuring inside and outside temperature, humidity and wind speed.
For the choice of materials, it was taken into consideration that such an inefficient but cheap plant would be ideal for third world countries with lots of space - the method is inefficient for land use but very efficient economically because of the low operating cost. So cheap materials were used on purpose to see how they would perform, such as a chimney built with iron plating only 1.25 mm thin and held up with guy ropes. For a commercial plant, a reinforced concrete tower would be a better choice.
This pilot power plant operated for approximately eight years but the chimney guy rods were not protected against corrosion and not expected to last longer than the intended test period of three years. So, not surprisingly, after eight years they had rusted through and broke in a storm, causing the tower to fall over. The plant was decommissioned in 1989.
Based on the test results, it was estimated that a 100 MW plant would require a 1000 m tower and a greenhouse of 20 km2. Because the costs lie mainly in construction and not in operation (free 'fuel', little maintenance and only 7 personnel), the cost per energy is largely determined by interest rates and years of operation, varying from 5 eurocent per kWh for 4% and 20 years to 15 eurocent per kWh for 12% and 40 years.
Future installations
Ciudad Real Torre Solar
There is a proposal to construct a solar updraft tower in Ciudad Real, Spain entitled Ciudad Real Torre Solar. If built, it would be the first of its kind in the European Union and would stand 750 meters tall – nearly twice as tall as the current tallest structure in the EU, the Belmont TV Mast – covering an area of 350 hectares. It is expected to output 40 MW of electricity.
Australian proposal
EnviroMission has, since 2001, proposed to build a solar updraft tower power generating station known as Solar Tower Buronga at a location near Buronga, New South Wales. Technical details of the project are difficult to obtain and the present status of the project is uncertain. In Enviromission's 2009 Financial Statements it is reported that the option fee covering the purchase of the Solar Tower Buronga site has been written off as the company does not intend to purchase the land. This is in keeping with the company's stated intention to concentrate on commercializing its technology in the USA rather than Australia.
On 18 March 2007, the company board announced a merger with the US-based SolarMission Technologies, Inc., but the relationship was terminated on November 1, 2007.
Botswana test facility
Based on the need for plans for long-term energy strategies, Botswana's Ministry of Science and Technology designed and built a small-scale solar chimney system for research. This chimney ran from 7 October until 22 November 2005. It had an inside diameter of 2 m and a height of 22m and was manufactured from glass reinforced polyester material, with a collection base area of approximately 160 m2. The roof was made of a 5 mm thick clear glass that was supported by a steel framework.
Namibian proposal
In mid 2008, the Namibian government approved a proposal for the construction of a 400 MW solar chimney called the 'Greentower'. The tower is planned to be 1.5 km tall and 280 m in diameter, and the base will consist of a 37 km2 greenhouse in which cash crops can be grown.
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