Xinping Zhou Jiakuan Yang and Bo Xiao

School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), 1037 Luoyu Road Wuhan, Hubei 430074, P.R. China

Solar chimney power generating technology is a solar thermal technology on a large scale which combines three parts: a collector, a high chimney (reinforced concrete chimney or floating chimney that can stretch up to several thousand meters), and turbines installed at the chimney base. The best locations of these systems are vast desert regions with high solar insolation and large daily range of temperature. As reported by Zhou et al. in 2008, special microclimate conditions will result around the solar power generation belts consisting of many commercial solar chimney power plants. Resulting rainfalls will support the growth of different types and quantitities of plants, including herbs, shrubs, and even trees. This will promote restoration of desert land and even create fertile soil and modify the local ecology. Produced plants can be used for biofuel. Furthermore, vegetables can be planted in the periphery of the collector acting as a green house and as a result benefit agricultural production. Other plants can then be used as a source of power as fuelwood or biomass to produce biogas. Many ecological and agricultural benefits are eminent in this respect.

Keywords: solar energy, power generation, grassland, ecology management

Deserts and desertified lands are vast accounting for one third of land area on the surface of the earth. The area of deserts and desertified lands increase year by year [1]. Desert and desertified lands [3] in China cover 171 million hectares, accounting for 18 % of the Chinese land area. They comprise a vast desert belt, 4500 km from east to west, 600 km from south to north and stretching west to the Tarim Basin and east to the Song Nen Plain, which enlarges by 2460 km2 per year. The deserts and desertified lands are gradually degraded from grasslands or forest lands due to bad natural climate condition and unreasonable human aBSTRACT

activity such as overgrazing [2]. These deserts or desertified lands are not available for agricultural and residential use. The ecology in these lands where precipitations are less than the sum of evaporations and percolation to the underground through sands and the plants including herbs, shrubs, and trees are extinct is increasingly destroyed. The destruction poses a great threat to human life by producing sandstorm downstream.

There exist high solar insolation and large daily ranges of temperatures in these vast lands. Increasing needs to satisfy the improvement of better standard of life in the recent years has put a big constraint on fossil fuels, the main energy source, which is being exhausted at a fast rate, hence greenhouse effect being is being aggravated [4], It is therefore, urgent to develop technologies utilizing renewable and clean energy source to solve the above problems for energy needs in future. Solar chimney power generating technology (Figure 1) is a promising large-scale power generating technology [5-9]. The best locations for these systems are vast desert and desertified regions where the land may be free [10] with high solar insolation and large daily ranges of temperatures. The technology was first described in a publication by G√ľnter in 1931 and tested with the 50 kW Manzanares prototype plant in the 1980s [4,11]. The solar chimney power system combines three familiar components: an air collector, a chimney situated in the center of the collector, and turbine generators installed at the chimney base. It works on the principle that the turbines are driven by airflow produced by buoyancy derived from hot air heated inside the collector. Additional tight water-filled heat storage placed under the inner collector roof [12] or solar-pond thermal storage system [6] supports continuous 24 hour operation of turbines. For commercial power plants producing energy economically, not only a large collector area is necessary for collecting a large amount of solar energy, but also a very high gigantic chimney. The height is needed only for the larger driving force that is proportional to the height and also to make the best use of the heat available. The height combined with a large collector surface area will reduce the cost of energy production.

Wind

Wind

Solar Chimney
Figure 1. Schematic diagram of solar chimney power system.

The gigantic chimney may be reinforced concrete chimney that can stretch more than 1000 meters within the technological restrictions [5] or floating chimney that can stretch up to several thousand meters [8]. Recently, the Australian government decided to support the construction of a prototype solar chimney power plant with a 1 km high solar chimney. The proposed solar plant in Mildura, Australia, can produce 200 MW of electricity [13]. The Chinese local government is supporting the construction of a 600 m high experimental floating solar chimney prototype in a desertified land in Gansu Province.

As reported by Zhou et al. [10,14], special microclimate conditions will result around the solar power generation belts consisting of many commercial solar chimney power plants resulting from the volume of warm air that carries many tiny granules as effective condensation nuclei of moisture transferred from the ground level to a high altitude.

The special microclimate conditions accompanied by the operation of solar chimney will occur 24 h. In the free atmosphere, the velocity and direction of wind at a high height usually vary little [15]. This can produce continuous rainfalls above a long and narrow region which in turn can produce abundant water, which is the crucial factor of restoration of desert lands [1]. This is also the reason why oases are usually formed at the foot of high mountains where precipitations in the high-mountain environment are more than that of deserts, with one part staying in solid phase on the mountain top and the other flowing down to irrigate the oases at the foot of the mountain. In the restoration of deserts and desertified lands to grassland, the types of pioneer plants grown are selected according to the conditions of the local lands, the wind, and water supports including rainfalls and underground water [1] and phytocoenosis is evolved from herbs to shrubs to trees. Rainfalls resulting from the special microclimate conditions will support the restoration of deserts and desertified lands by supporting the growth of different types and quantitities of plants.

The desertified lands can be finally reformed to fertile soils, which have strong waterholding capacity and reduce the evaporation of water, thus increasing surface runoff. The surface runoff can be used in the restoration of the desertified lands away from the rainfall regions and the lands under the outer collector roof. This will help in modifying the local ecology.

Vegetables or fruits can be planted in the periphery of the collector acting as a green house [16,17] and as a result benefit agricultural production. On the other hand, a wet cultivated ground is often darker than a dry flat one, so that this albedo effect generates a synergy among agricultural and power productions.

Other plants can then be used as a source of power as fuelwood or biomass to produce biogas. Many ecological and agricultural benefits are eminent in this respect by using grassland around huge solar chimney belt.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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