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Design of circular collector solar chimney electric power generation

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International peer-reviewed academic journals call for papers, http://www.iiste.org/Journals

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  • 1. Journal of Energy Technologies and Policy www.iiste.org ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online) Vol.3, No.6, 2013 9 Design of Circular Collector Solar Chimney Electric Power Generation Amir Abass Omran , Farhan Lafta Rashid* , Ashwaq Hilal Mohamad and Fadhil Saeed Hasan Ministry of Science and Technology, Iraq-Baghdad *E-Mail: engfarhan71@gmail.com Abstract Solar chimney electric power generation is one of the concepts in renewable energy technology (RET) application. The power station is based simply on the principle that warm air rises. This paper presents the design of a circular collector (instead of square collector) solar chimney to be used in rural areas of developing countries. The design involves heating air using solar energy and the chimney effect to raise the hot air up the chimneystack. The velocity of the hot air is increased by the use of a convergent nozzle to a velocity suitable to run a wind turbine. The kinetic energy of the hot air is then converted to electricity by a wind turbine. The calculations carried out show that the power that can be generated by a circular collector solar chimney of specific dimension exhibit a minimum threshold value of = 2.65. Our calculations show that for = 2.65, an appreciable electric power (P=103 Watts) can be generated by a sturdy and physically viable solar chimney whose dimension has been determined to be L = 150 m, H = R = 1.5 m. This the minimum dimension of a practical solar chimney electric power station that would serve approximately fifty (50) households in a typical rural setting. Keywords: Renewable energy; Solar chimney; Electric power, glass chimney, solar radiation. Nomenclature W heat exchanged [J] T temperature [K] H heat exchange coefficient or heat transfer coefficient [W/m2 K] H height above the collector [m] A collector area [m2] K thermal conductivity [W/m K] Re Reynolds number[dimensionless figure] Pr Prandtl number[dimensionless figure] Pi instantaneous power [W] L length [m] m mass [kg] ρ density [kg/m3] R radius [m] u velocity [m/s] Cp specific heat at constant pressure [J/kg K] α diffusivity [m2/s] the temperature ratio of the difference between the collector surface temperature and the temperature at the turbine (Ts–TH) to the difference between the air mass temperature under the roof and the collector surface temperature (Tm–Ts) kinematic viscosity [m/s] Introduction As a consequence of the rising worlds demand for electric energy it is necessary to use alternative possibilities to the conventional generation of electricity. The focal point is on the renewable energies. The sun plays a major role if its potential is used properly. It produces huge amounts of energy. In one hour it radiates enough energy to earth to cover the yearly energy demand of the whole world. If just 0.1 % of the solar energy would be used, the problems of energy supply could be solved[1]. Solar chimney electric power generation is one of the concepts in renewable energy technology (RET) application. The power station is based simply on the principle that warm air rises. Air underneath a glass ceiling is heated by solar radiation and rises through a chimney. The warm air which has just risen is replaced by air from the edge of the glass ceiling which flows inward, and will then itself begin to heat up. In this way the Sun’s heat radiation is converted into kinetic energy of constantly rising air to drive turbine built into the chimney. The turbine then converts the wind power by means of a generator into electrical energy[2]. Solar updraft power plants are the most sustainable natural resources for electric power generation. During
  • 2. Journal of Energy Technologies and Policy www.iiste.org ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online) Vol.3, No.6, 2013 10 service, they are completely free of carbon-dioxide emissions, since they use solar irradiation as fuel. If one incorporates all materials required for the plant construction in an energy balance, measured by CO2-emissions, one ends up with around =10 g of CO2 per kWh of produced electric work, depending on the service life- duration of the plant. Since design service-lives are 80 to 120 years, CO2-emissions and production costs of the electric current are by far the smallest ones of all renewable energies even if renewals of the turbo-generators and parts of the glass-roof are included[3]. The Solar Chimney, operates like a hydroelectric power plant, but instead of water, it uses hot air. This is particularly useful in arid areas, which are plentiful in Africa, even south of the Sahara[4]. Apart from working on a very simple principle, solar towers have a number of special features[5]: 1. The collector can use all solar radiation, both direct and diffuse. This is crucial for tropical countries where the sky is frequently overcast. 2. Due to the soil under the collector working as a natural heat storage system, updraft solar towers can operate 24 h on pure solar energy, at reduced output at night time. If desired, additional water tubes or bags placed under the collector roof absorb part of the radiated energy during the day and releases it into the collector at night. Thus solar towers can operate as base load power plants. As the plant's prime mover is the air temperature difference (causing an air density difference) between the air in the tower and ambient air, lower ambient temperatures at night help to keep the output at an almost constant level even when the temperature of natural and additional thermal storage also decreases without sunshine, as the temperature difference remains practically the same. 3. Solar towers are particularly reliable and not liable to break down, in comparison with other power plants. Turbines and generators - subject to a steady flow of air - are the plant's only moving parts. This simple and robust structure guarantees operation that needs little maintenance and of course no combustible fuel. 4. Unlike conventional power stations (and also some other solar-thermal power station types), solar towers do not need cooling water. This is a key advantage in the many sunny countries that already have major problems with water supply. 5. The building materials needed for solar towers, mainly concrete and glass, are available everywhere in sufficient quantities. In fact, with the energy taken from the solar tower itself and the stone and sand available in the desert, they can be reproduced on site. Energy payback time is two to three years. 6. Solar towers can be built now, even in less industrially developed countries. The industry already available in most countries is entirely adequate for solar tower requirements. No investment in high-tech manufacturing plants is needed. 7. Even in poor countries it is possible to build a large plant without high foreign currency expenditure by using local resources and work-force; this creates large numbers of jobs while significantly reducing the required capital investment and thus the cost of generating electricity. One big advantage of solar updraft power plants is the possibility of a 24/7 operation. This is possible because of the constant heat emission of the heat stores. These are realized by water tanks under the glass roof as well as heated ground. Therefore the heat, saved during the day, can be released in the night. This opportunity makes the operation possible during darkness and without fossil burning[6]. There are a number of reasons as to why a large area of land must be used as a solar collector. These reasons include the fact that the overall conversion efficiency from solar energy to electricity is 2–3%. There is a temperature drop with altitude of about 10 C0 for a 1000 m chimney. Large quantities of warm air have to be lifted from the ground to chimney top which results in gravitational energy loss. The air that leaves the chimney is above ambient temperature at that altitude also resulting in thermal energy loss. As ambient air is drawn into the collector and warmed, expands with little increase in pressure and the majority of solar input is lost in the simple expansion of air before it reaches the turbine [7–11]. In this paper a design of circular collector solar chimney electric power generation will be established and compared with previous work[2].
  • 3. Journal of Energy Technologies and Policy www.iiste.org ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online) Vol.3, No.6, 2013 11 Chimney Transparent material Turbine air flow air flow H R solar collector Figure(1) Circular Collector Solar Chimney Theoretical Analysis The heat energy transferred from the patch is given by : = ℎ − …………………….(1) When and are the temperatures at surface converted by the selective material and any position H in the covered area A and h is the converted transfer coefficient is given by: h=h (Re, Pr, K, L) in a case of a turbine[12]: ℎ = 0.036 / . ……………………(2) Known for circle collector surround the square of side L . The area of the surface is given by : = + = ! i.e. = "/√2 So converted area is: = % = & " Substitute in Eq.(1) = & " ℎ ' − ………………….(3) On the other hand heat transferred from the patched area to air under the canopy is given by: = () *+ , − ' ………………….(4) Where: , is the temperature of mass of air inside the chimney. () is mass flow rate (Kg/s) ,which given as: () = ρ- U + ………………………….(5) Where /0 is the ambient density of the air . 1 is the velocity with which the mass flows The cross section area of the opening around the circular patch of radius (L/√2) as: + = 2%L/√23 + = √2%"3 So the Eqs.(4) can be written as:
  • 4. Journal of Energy Technologies and Policy www.iiste.org ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online) Vol.3, No.6, 2013 12 4 = √2%"3/01*+ , − …………………….(6) For the circular chimney of radius R and velocity V which air impinges on the rotor blades of air turbine is given by : % 5 = √2%"31 ………………….(7a) 1 = 6!7 √ …………………..(7b) Hence the heat transfer to the air under the chimney is (after Substituting Eq.(7b) in Eq.(6)): 4 = √2%"3/0*+ 5 √2"3 , − 4 = %/0*+ 5 , − …………..(8) Combination Eqs.(3) and (8) we get: & " ℎ ' − = %/0*+ 5 , − ℎ = 89:;6!7 ! <=><? <@><A ……………..…..(9) 5 = !B 89:;6! <@><A <=><? ……………..(10) 5 = . C & D & E & F G G 89 G6! HI G J:; G K L J M <@><A <=><? D ∴ = <@><A <=><? …………………….(11) 5 = &^ . C & D F G G 89 G6! HI G J:; G K L J M D ..……………..(12) By using Eq. (7a) the instantaneous electric power Pi produced by a single turbine is readily derived as : P = C Q /, % 5 …….……………….(13) Where : /0 is the density of the air at temperature , and factor C Q is the ideal limit for extraction of power . From Eqs.(11) and (13) , the instantaneous electric power is : P = 3.0 × 10> T U " D 3 E V % 2 P = 1.1 × 10> T WG W!6H …………………..(14) Where T at 300K and 1 atmospheric pressure at dry air: T = 8= G 89 WG0G:; WG KL = 1.148 ∗× 10> ………….(15) Eq.(14) shows that the instantaneous electric power depends mainly on the dimensions of the solar chimney for given temperature ratio τ . Substituting Eq.(15) into Eq.(14) yield: P = 1.2628 × 10>E U " D 3 E V D
  • 5. Journal of Energy Technologies and Policy www.iiste.org ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online) Vol.3, No.6, 2013 13 Table(1) Solar Chimney Electric Power Generation of Square Collector [2] τL=150mL=200mL=300mL=400mL=500m 0.5003E-132E-136E-10 1.51.3E-101.3E-084.2E-060.000320.009 2.52.7E-070.0000270.0090.6819.38 3.50.0000430.00431.4106.13015.7 4.50.00180.18761.554601.6130784.3 5.50.0383.81248.893360.942653433 6.50.4646.715302.5114399832513832 7.54399.5130912.597868712.78E+08 8.526.22611.8855748.1639747801.82E+09 9.5138.913852.445385403.39E+089.64E+09 10.5623.6762159.9203658041.82E+094.33E+10 11.52441.1243298.1797130975.96E+091.69E+11 Table(2) Solar Chimney Electric Power Generation of Circular Collector [present work] τL=150mL=200mL=300mL=400mL=500m 0.5008E-136.3E-110.00058 1.53.5E-100.0000000270.0000110.00090.02 2.50.000000740.0000580.0241.954.685 3.50.000110.0093.79299.098500.5 4.50.0050.39164.712970.8368648.16 5.50.18.033341.7263161.17479364.7 6.51.298.3940998.73224645115234734.6 7.510.6841.8350315.127586744784049213.6 8.569.85502.72289938.41.8E+085125169802 9.5370.629184.2121449029.56E+0827181819989 10.51663.1130958.6544978604.29E+091.21973E+11 11.56509.67689522133081881.68E+104.77411E+12
  • 6. Journal of Energy Technologies and Policy ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online) Vol.3, No.6, 2013 Results and Discussions Figure(2) shows the relationship between output power of circular collector as a can see that the output power increases exponentially with ( value of τ beyond which appreciable power (10 generating plant with a circular collector threshold value of τ for each specified dimension of the chimney. chimney power plant that would generate energy of t R = 1.5 m. This specific dimension requires that compared with that in table(2), we can see that the circular collector solar chimney gives more output power than square shape because it gives more heat transfer surface than the square. There are a number of reasons as to why a large area of include the fact that the overall conversion efficiency from temperature drop with altitude of about 10 lifted from the ground to chimney top which results in gravitational is above ambient temperature at that altitude also resulting in thermal the collector and warmed, expands with little increase in pressure and simple expansion of air before it reaches the turbine Conclusions From the present work we can deduce the 1-In Fig.(2) the curves show that there exist threshold values power (P=103 W) can be produced by a solar chimney of specific instantaneous electric power increases exponentially. 2-The circular collector gives more output power by 1.5% than the square collector solar chimney. 3-The circular collector installation solar chimney. 0 500 1,000 1,500 2,000 2,500 3,000 3,500 0 0.5 1 1.5 2 Power(Watts) Fig.(2) Curves showing simulated power output for circular collector solar chimneyes of different lengths when H=R= Journal of Energy Technologies and Policy 0573 (Online) 14 ) shows the relationship between output power of circular collector as a function of ( can see that the output power increases exponentially with (τ). The curves show that the minimum threshold beyond which appreciable power (103 W) can be generated by a viable solar chimney power collector is approximately 2.65. Thereafter the power increases rapidly after each for each specified dimension of the chimney. The dimensions of a reasonably stu power plant that would generate energy of the order of 103 W, for example, is L = 150 m, H = 1.5 m and 1.5 m. This specific dimension requires that τ = 10.15. from our calculations in table(1) which were compared with that in table(2), we can see that the circular collector solar chimney gives more output power than square shape because it gives more heat transfer surface than the square. ber of reasons as to why a large area of land must be used as a solar collector. These reasons include the fact that the overall conversion efficiency from solar energy to electricity is 2 drop with altitude of about 10 C0 for a 1000 m chimney. Large quantities of warm air have to be ground to chimney top which results in gravitational energy loss. The air that leaves the chimney temperature at that altitude also resulting in thermal energy loss. As ambient air is drawn into and warmed, expands with little increase in pressure and the majority of solar input is lost in the of air before it reaches the turbine [13–17]. From the present work we can deduce the following conclusions: he curves show that there exist threshold values of the temperature ratios, W) can be produced by a solar chimney of specific dimensions. Above the threshold values, electric power increases exponentially. The circular collector gives more output power by 1.5% than the square collector solar chimney. ation has higher stability and more heat transfer area than the square 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 τ ) Curves showing simulated power output for circular collector solar chimneyes of different lengths when H=R=1.5m www.iiste.org function of (τ), in which we The curves show that the minimum threshold by a viable solar chimney power the power increases rapidly after each The dimensions of a reasonably sturdy solar W, for example, is L = 150 m, H = 1.5 m and from our calculations in table(1) which were compared with that in table(2), we can see that the circular collector solar chimney gives more output power than land must be used as a solar collector. These reasons electricity is 2–3%. There is a Large quantities of warm air have to be energy loss. The air that leaves the chimney s ambient air is drawn into the majority of solar input is lost in the of the temperature ratios, τ at which significant dimensions. Above the threshold values, τ, the The circular collector gives more output power by 1.5% than the square collector solar chimney. and more heat transfer area than the square collector 9.5 1010.51111.5 ) Curves showing simulated power output for circular collector
  • 7. Journal of Energy Technologies and Policy www.iiste.org ISSN 2224-3232 (Paper) ISSN 2225-0573 (Online) Vol.3, No.6, 2013 15 References [1] Stefanie Fiedermann, Jadranka Halilovic and Torsten Bogacz,2009," Solar potential of the Sahara Desert with an introduction to solar updraft power plants". [2] Frederick N. Onyango, Reccab M. Ochieng,2006," The potential of solar chimney for application in rural areas of developing countries", ELSEVIER, Fuel 85 , 2561–2566. [3] H.-J.Niemann, F.Lupi, R.Hoeffer, W.Hubert , C. Borri,2009, "The Solar Updraft Power Plant: Design and Optimization of the Tower for Wind Effects". [4] Reinhard Harte , Gideon P.A.G. Van Zijl,2007," Structural stability of concrete wind turbines and solar chimney towers exposed to dynamic wind action",ELSEVIER, Journal of Wind Engineering and Industrial Aerodynamics 95,1079–1096. [5] Jörg Schlaich, Rudolf Bergermann, Wolfgang Schiel, Gerhard Weinrebe,2004," Design of Commercial Solar Updraft Tower Systems – Utilization of Solar Induced Convective Flows for Power Generation", Schlaich Bergermann und Partner (sbp gmbh), Hohenzollernstr. 1, 70178 Stuttgart, Germany. [6] Egger, Daniel (2002): Moderne Solartechnologien und ihre zukünftigen Perspektiven. ETH Zürich. [7] Weinrebe G, Schiel W. Up-draught solar tower and down-draught energy tower – A comparison. In: Proceedings of the ISES solar world congress 2001, Adelaide. [8] Schlaich J. The solar chimney: electricity from the sun. Geislingen, Germany: C. Maurer; 1995. [9] Von Backstro¨m TW, Gannon AJ. Compressible flow through solar power plant chimneys. ASME J Sol Energy Eng 2000;122(3):138–145. [10] Padki MM, Serif SA. On a simple analytical model for solar chimneys. Intl J Energy Res 1999;23(4):345–9. March 25. [11] United Nations environmental programme (UNEP). Chemical pollution: a global overview. Geneva: UNEP; 1992. [12] Tiwari GN, Sangeeta S. Solar thermal engineering systems. NewDelhi: Narosa Publishing House; 1997. [13] Weinrebe G, Schiel W. Up-draught solar tower and down-draught energy tower – A comparison. In: Proceedings of the ISES solar world congress 2001, Adelaide. [14] Schlaich J. The solar chimney: electricity from the sun. Geislingen,Germany: C. Maurer; 1995. [15] Von Backstro¨m TW, Gannon AJ. Compressible flow through solar power plant chimneys. ASME J Sol Energy Eng 2000;122(3):138–145. [16] Padki MM, Serif SA. On a simple analytical model for solar chimneys. Intl J Energy Res 1999;23(4):345–9. March 25. [17] United Nations environmental programme (UNEP). Chemical pollution: a global overview. Geneva: UNEP; 1992.
  • 8. This academic article was published by The International Institute for Science, Technology and Education (IISTE). The IISTE is a pioneer in the Open Access Publishing service based in the U.S. and Europe. The aim of the institute is Accelerating Global Knowledge Sharing. More information about the publisher can be found in the IISTE’s homepage: http://www.iiste.org CALL FOR PAPERS The IISTE is currently hosting more than 30 peer-reviewed academic journals and collaborating with academic institutions around the world. There’s no deadline for submission. Prospective authors of IISTE journals can find the submission instruction on the following page: http://www.iiste.org/Journals/ The IISTE editorial team promises to the review and publish all the qualified submissions in a fast manner. All the journals articles are available online to the readers all over the world without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself. Printed version of the journals is also available upon request of readers and authors. IISTE Knowledge Sharing Partners EBSCO, Index Copernicus, Ulrich's Periodicals Directory, JournalTOCS, PKP Open Archives Harvester, Bielefeld Academic Search Engine, Elektronische Zeitschriftenbibliothek EZB, Open J-Gate, OCLC WorldCat, Universe Digtial Library , NewJour, Google Scholar

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