Solar chimney

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This article is about various uses for the convective motion of heated air in a chimney, especially power generation. For various other meanings of the term "Solar Tower", including the astronomical instrument and other uses of the term, see solar tower (disambiguation).

A solar chimney is an apparatus for harnessing solar energy by convection of heated air.

In its simplest form, it consists of a black-painted chimney. During the daytime, solar energy heats the chimney, thereby heating the air within it, resulting in an updraft of air within the chimney. The suction this creates at the chimney base can be used to ventilate, and thereby cool the building below. In most parts of the world, it is easier to harness wind power for such ventilation, but on hot windless days such a chimney can provide ventilation where there would otherwise be none.

This principle has been proposed for electric power generation, using a large greenhouse at the base rather than relying on heating of the chimney itself.

The main problem with this approach is the relatively small difference in temperature between the highest and lowest temperatures in the system. Carnot's theorem greatly restricts the efficiency of conversion in these circumstances.

1 Power station designs
2 See also
3 External links
- 3.1 Articles

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Power station designs

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History

In 1903, Spanish Colonel Isidoro Cabanyes described the first solar chimney in the magazine "La energía eléctrica" (Lorenzo, in Spanish)^[1]. One of the earliest descriptions of a solar chimney power station was written in 1931 by a German author, Hanns Günther. Beginning in 1975, Robert E. Lucier applied for patents on a solar chimney device; between 1978 and 1981 these patents, since expired, were granted in the USA^[2], Canada^[3], Australia^[4] and Israel^[5].

More recently Schlaich, Bergerman and Partner, under the direction of German engineer Prof. Dr. Ing. Jörg Schlaich, built a small scale working model of a solar chimney in 1982 in Manzanares, (Spain), 150 km south of Madrid, which was funded by the German Government. This power plant operated successfully for approximately 8 years and was decommissioned in 1989. The chimney had a diameter of 10 metres and a height of 195 metres, with a collection area (greenhouse) of 46,000 m² (about 11 acres) obtaining a maximum power output of about 50 kW.

During operation, optimization data was collected on a second-by-second basis. This data has been licensed to EnviroMission and SolarMission Technologies Inc. (USA based licence holder), who plan to develop the concept under the brand name Solar Tower. At the beginning of 2005 they started collecting meteorological data at a proposed site in New South Wales, Australia, with the intent to have a fully operational Solar Tower power station in 2008.

The maximum power output from the concept can be up to 200 MW. The proposed solar chimney was originally to be 1 km high, and the base 3.5 km in diameter (for a total of about 10 km²). The solar chimney would thus extract about 2% of the solar power (1 kW/m²) that falls on the area it covers.

However, reports now indicate that due to improved heat absorption materials being used for the greenhouse, the chimney height and base diameter will be substantially reduced to increase efficiency.

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Byproducts

The most significant byproducts from proposed designs are distilled water (made from ocean water or ground water) and in certain instances agribusiness produce may be suitable under the outer perimeter of the greenhouse area of the power station is grown under the solar collector.

Agribusiness including Fruits and vegetables, as well as medicinal and aromatic essential oils made from herbs and flowers, seaweeds and planktons, blue-green algae, have all been suggested as suitable crops for these scenarios. Residual biomass might also create additional heat during composting, as could the various distillation, food processing and manufacturing operations. Other byproducts may include ethanol and methane, biodiesel and all manner of vegetable and plant derivatives.

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Comparisons

Solar chimneys will have a superior level of greenhouse abatement by producing only clean green sustainable electricity, no coal or gas fired electricity generator is able to compete with the clean emission free credentials of a solar chimney.

To replace a typical 2000 MW black coal-fired power station, about 10 solar chimneys of the capacity of the proposed test plant would need to be built (depending on scale and capacity). This would also abate more than 14 million tonnes of greenhouse gases from entering the atmosphere annually.

Several other technologies exist that can convert solar energy into electrical energy.

The solar chimney is part of the solar thermal group of solar conversion technologies. There are two other designs that work in the same way. The first is the solar trough design and the other is the solar dish/stirling design. Of these technologies the solar solar dish/stirling has the highest energy efficiency (the current record is a conversion efficiency of 30% of solar energy). Solar trough plants have been built with efficiencies of about 20%. The solar chimney has an efficiency of less than 2%. However, due to its greater scale and simplicity, the solar chimney may have an economic efficiency approaching or exceeding that of the other methods.

Australia's only existing solar power station, White Cliffs Solar Power Station, was originally built using solar dish steam boiler technology, but has now been upgraded to photovoltaic to obtain almost twice the electric output from the same dishes.

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