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  1. THE SOLAR CHIMNEY Solar Energy I Physics 471 2002-03-1 By Elif YURDANUR Sırma ŞEN Instructor: Prof.Dr.Ahmet ECEVİT Dept. of Physics, M.E.T.U., Ankara.

  2. Table of Contents Page

  3. 1. Introduction It is well-known that the energy sources we have are either limited, hazardous or dangerous. The solar energy, however, is continuous and ecologically friendly (nonpolluting) [1]. It has started to play an important role in our lives. There are many ways of using the solar energy. One of them is the solar chimney, which canconvert the solar energy into electrical energy directly. A solar chimney is as shown in Figure 1. -1-

  4. Fig.1 The Solar Chimney in Manzanares [2]. -2-

  5. The solar chimney is composed of three main parts: The Collector The cover which helps the air to be heated. The Turbines The device through which the warmed air passes in order to generate electrical energy. The Chimney The pipe where the hot air from the turbines rises up. -3-

  6. 2.1. The Collector The collector is a cover in which the air is heated. The coveris approximately5 meters high and has no sides, it has only horizontaltop covering as shown in Figure 2. Fig.2 The Collector [2]. -4-

  7. Fig.3 A View from the Inside of a Collector [2]. As seen in Figure 3, the inside of a collector is about 5 meters high. -5-

  8. The air below this cover is heated by means of greenhouse effect. For this process, the collector should be made up of a transparent material such as glass or plastic film so that the solar radiation can enter inside. The covering admits the short-wave radiation component. However it retains long-wave radiation from the heated ground, and transfers its heat to the air flowing above it to the chimney [2]. -6-

  9. 2.1.1. Construction of the Collector Size: The height of the collector is ideally between 2 and 6 meters [2]. There is no limitation for the area of the collector. If we have larger area, we can generate more energy. For example, for a 10MW energy output, 2.5x105 m2 area is required [3]. The height of a collector should slightly increase towards the conjunction with the chimney so that the air is diverted to vertical movement with minimum friction loss. -7-

  10. Life Span: It is determined by its resistance to dust and sand. With proper maintenance, its life span can easily be 60 years or more [2]. In addition, the collector can be more efficient by double-glazing the parts near the tower. In this way the collector can retain heat more successfully as the air temperature increases from the perimeter towards the tower. -8-

  11. 2.2. The Turbines Turbine is a device in which the electrical energy is derived. The air warmed in the collector rises up towards the chimney and runs the turbine. This results in rotational energy in the turbine. This can be seen in the Figure 4. Fig.4 Heated Air Rises Up [4]. -9-

  12. This rotational energy is converted into electrical energy. For this process one turbine whose blades cover the whole cross-section of the chimney or many smaller turbines distributed around the circumference of the chimney wall can be used [2]. -10-

  13. For both choices, turbines should always be placed at the base of the chimney as seen in the Figures 5 and 6. Fig.5 A Single Turbine [2]. Fig.6 Small Turbines [2]. -11-

  14. 2.2.1. Construction of the Turbines Size: Either a large number of small turbines with horizontal axes may be arranged around the base of the chimney, or one large, say a 100 MW turbine with a vertical axis is placed in the chimney’s cross-section [5]. If small turbines are to be chosen, for instance 6 small turbines, they must be selected in such a way that the blade lenght of each turbine will be a sixth of the chimney diameter. -12-

  15. Life Span: The turbine’s life span is based on its resistance to rapid pressure and speed changes of the air [2]. Moreover, if smaller turbines are used instead of a single large turbine, the overall cost will be lower [5]. -13-

  16. 2.3. The Chimney The main body of the plant which the warmed air flows through can be seen in the Figure 7. Fig.7The Chimney [2]. -14-

  17. In collector, the air temperature rises up and therefore air gains a velocity to go upward in the chimney. However this amount of temperature rise is partically independent of the efficiency of the chimney. This efficiency (n) is determined by the outside temperature (T0) and the height of the chimney (Hc); which can be seen by the relation: n ~ Hc / T0 (eqn. 1) [2]. -15-

  18. n~ Hc /T0 (eqn.1) The chimney should be as tall as possible. The wind speed in the open air around the collector is significantly less than the air velocity through the air channel [6]. The chimney can make particularly good use at nights when the outside temperature T0is very low. At nights? Why? How? The ground heats up during the day time and emits its heat at night [7]. -16-

  19. 2.3.1. Construction of the Chimney Size: The chimney must be as tall as possible. Life Span : The life span of the chimney depends on its material and its standing style. The chimneys can be classified into two groups in terms of their standings: • Free-standing (reinforced concrete), • Guyed tubes as shown in the Figures 8 and 9. -17-

  20. Fİg.8 Free-standing (reinforced concrete) [2]. Fig.9 Guyed Tubes [2]. -18-

  21. The life span of a reinforced concrete tower in a dry climate is at least 100 years. On the other hand, guyed tubes has a shorter life span. Besides these, altough the efficiency of the chimney increases by the increase in height, there is a practical limitation for building such a long chimney. The ideal height is 1000 m. -19-

  22. 3. Cost With the support of construction companies, the glass industry and turbinemanufacturers, a rather exact cost estimate for a 200 MW solar chimney could becalculated. The energy production costs of the solar chimney, coal and combined cycle power plants are charted by "Energie in Baden-Württemberg“ as shown in the Table 1 [4]. -20-

  23. energy production costs Comparison between the energy production costs of two 200 MW solar chimneys and400 MW coal and combined cycle power plants according to the present business managerialcalculations. Comparison between the energy production costs of two 200 MW solar chimneysand 400 MW coal and combined cycle power plants according to the present business managerialcalculations. Table 1Energy Production Costs[4]. -21-

  24. In short term, it may seem more expensive than the other resources. In long term, since solar chimney has no ecological harm and noconsumption of resources, not even for the construction, it has more advantages. The Chart 1 shows the solar chimney’s costs in 40 years. -22-

  25. Chart 1 Energy Production Costs from Solar Chimneys, Coal and Combined Cycle Power Plants Depending on the Interest Rate [4]. -23-

  26. 4.Conclusion To sum up, the principle of the chimney consists of three basic steps: Hot air is produced by the sun under a large roof. This flows to a chimney in the middle of the roof and is drawn upwards. This updraft drives turbines installed at the base of the chimney, and the electricity is produced [2]. -24-

  27. Generating electricity from the solar energy is important, especially for future, since it is unlimited. The solar chimney is a cheap and useful example of this energy. The other sources of energy will become exhausted but sunlight will still be falling on earth with undiminished strength for many many years [8]. -25-

  28. References 1. Williams,J.R.(1977).Technology and applications;Ann Arbor Science Publishers Inc,p.138,139. 2. Schlaich,J.(1995).The Solar Chimney;Edition Axel Menges,p.7,16-21,27,51,53. 3. Taylor,R.H.(1983).Alternative energy Sources;Adam Hilger Ltd,p.292. 4. Solar Chimney-Technology.Retrieved 28 November 2002 from; -26-

  29. 5. Solar Chimney-Technology.Retrieved 11 November 2002 from; 6. Solar Chimney Power Plant versus Wind from the Sun Power Plant.Retrieved 11 November 2002 from; 7. Solar Chimney-Principle.Retrieved 11 November 2002 from; -27-

  30. 8. Messl,H. and Butler,S.T.(1974).Solar Energy;Pergamon Press,p.276. -28-