Energy Conversion and Management 52 (2011) 2360–2366

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Energy Conversion and Management

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Simulation of a sloped solar chimney power plant in Lanzhou

Fei Cao, Liang Zhao ⇑, Liejin GuoState Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, PR China

a r t i c l e i n f o a b s t r a c t

Article history:Received 29 September 2010Received in revised form 13 December 2010Accepted 20 December 2010Available online 18 February 2011

Keywords:Sloped solar chimney power plantSolar chimney power plantSolar chimneySolar energyNorthwest China

0196-8904/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.enconman.2010.12.035

⇑ Corresponding author. Tel.: +86 029 82668287; faE-mail address: lzhao@mail.xjtu.edu.cn (L. Zhao).

Solar chimney power system is one large-scale utilization style of solar energy, which has drawn highattentions worldwide. Though scholars all over the world have made many researches on the solar chim-ney power system, reports of sloped solar chimney power system are still few. A sloped solar chimneypower plant, which is expected to provide electric power for remote villages in Northwest China, hasbeen designed for Lanzhou City in this paper. The designed plant, in which the height and radius ofthe chimney are 252.2 m and 14 m respectively, the radius and angle of the solar collector are 607.2 mand 31� respectively, is designed to produce 5 MW electric power on a monthly average all year. The per-formances, such as the airflow temperature increase, pressure, the airflow speed, system efficiency andsolar collector efficiency, of the built sloped solar chimney power plant are simulated and presented. Sim-ulation results show that parameters of the sloped solar chimney power plant are symmetrical and sta-ble; the power plant has better performances in spring and autumn days; the overall efficiency of thepower plant is low. Considering the abundant solar radiation, environmental friendliness, easy manage-ment and low population density, the sloped solar chimney power system is of high value to NorthwestChina.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Solar energy is thought to be a kind of renewable, sustainableand endless energy. As human beings is suffering from energyshortage, pollution and green house effect, solar energy has be-come a hot research field from 1900s till nowadays. Large-scaleutilization of solar energy is one of the main purposes of the solarengineering researches. Solar chimney power plant is one large-scale utilization style of solar energy. The solar chimney powerplant concept was originally investigated in 1903 by Cabanyes[1]. In 1931, a description of a solar chimney power plant was pre-sented by Gunther [2]. The basic study on the solar chimney con-cept was performed by Doctor Schlaich in the 1970s. In 1981, hisresearch team began the construction of a pilot solar chimneypower plant in Manzanares, Spain [3,4].The pilot plant consistedof a horizontal solar collector, a group of wind turbines, a hotshortage layer and a vertical solar chimney. The chimney of theprototype had a height of 195 m and a diameter of 10 m; the solarcollection area was 46,000 m2. From then on, scholars all over theword have done lots of theoretical research on its heat, mass trans-fer and energy conversion. In 1983, Haaf etc. carried out basic re-search about energy balance, design and cost of the Manzanaresdemonstration power plant [3]. Mullet made detail analysis aboutthe efficiency of the solar chimney power plant, and concluded the

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feasibility of building solar chimney power plants in developingcountries [5]. Lodhi made researches on the thermal and heatshortage of the solar chimney system [6]. Yan researched the influ-ence of fluid and chimney temperature [7]. Pasumarthi and Sherifbuilt a complete mathematical model and analyzed the experi-mental and theoretical performances of a demonstration solarchimney power system [8,9]. In 2005, Bilgen proposed that a solarchimney power plant with a sloped solar collector along a hillsidehad higher performances at high latitudes [10]. After Bilgen, Zhoudeveloped Bilgen’s study and proposed a solar thermal power plantwith floating chimney stiffened onto a mountainside [11].

Fig. 1 shows the schematic of solar chimney power plants.Fig. 1a is the classical solar chimney power plant studied bySchlaich [3]. This solar chimney power system has a horizontalsolar collector and a high vertical solar chimney. Fig. 1b shows an-other solar chimney power plant style, proposed and studied byBilgen and Zhou. This kind of solar power plant has a sloped solarcollector and a short vertical solar chimney. It is called the slopedsolar chimney power plant (SSCPP). Reports of SSCPP are few com-paring to the study of the classical solar chimney power systems.Moreover, though some scholars had made valuable feasibilityanalysis for classical solar chimney power plants, such as Gannon[12], Lodhi [6] and Dai [13], the report about feasibility analysisof SSCPP is still few. And, Northwest China is one of the most abun-dant areas in the amount of solar radiation. So, it is remarkable tohave a feasibility analysis of building SSCPP in Northwest China. Inthis study, we would like to do some preliminary work for SSCPP

Nomenclature

A area (m2)cp specific heat (W (m2 K)�1)f friction loss coefficientg acceleration of gravity (m/s2)h heat transfer coefficient (W (m2 K)�1)H monthly average solar radiation (J/m2); height (m)L length (m)M mass flow (kg/s)P pressure (Pa); electronic power generation (W)Q energy (J)ref ground reflectanceR radius (m)S annually solar radiation (J/m2)T temperature (K)Time annually average sunshine hour (s)U compound heat coefficient (W (m2 K)�1)v air velocity (m s�1)x turbine pressure drop coefficientz altitude (m)

Greek symbolsq air density (kg m�3)g efficiencyb angle (�)

s transmitive ratioa absorption ratiod solar declination angle (�)x sunset angle (�)u latitude (�)

Subscrips1 the glass2 the heat shortage layera ambientb barecoll collectorchi chimneyd difusedele electricity powerf airflowin innero at the outlet of the collectorout out of the systemp heat shortage layerr reflects sunsettot totaltur wind turbine

F. Cao et al. / Energy Conversion and Management 52 (2011) 2360–2366 2361

feasibility analysis in Northwest China. We mainly focus on theperformance simulation of a 5 MW sloped solar chimney powerplant assumed to be built in Lanzhou and main tasks of this studyare:

1. To build a simplified mathematical model according to basicsolar radiation, heat transfer and heat conduction theories.

2. To design the configuration sizes of a 5 MW sloped solar chim-ney power plant assumed to be built in Lanzhou City.

3. To simulate and analyze the main performances of the powerplant.

2. System description

Main parts of the solar chimney power plant are the solar col-lector (with a heat shortage layer below), the solar chimney andthe air turbine. As is shown in Fig. 1a and b, sunlight transmitsthrough the transparent glass and heats the air and heat shortagelayer below. Ambient cold air enters the collectors from the

Fig. 1. Schematic of solar chimney power p

periphery of the collectors and is heated in the form of heat con-vection when flowing along the collector channel. Due to the pres-sure generated by the density difference between the warm airflowand ambient cold air, the airflow enters into the chimney. With theair turbine, the kinetic energy of the airflow transfers into the elec-tric energy. The airflow with low speed and temperature finallyflows out from the top of the chimney under buoyancy effect. Maindifferences between the classical solar chimney power system andSSCPP are the solar collector angle and the chimney height. Solarcollectors in the classical style are set horizontally, whereasSSCPP’s are laid along a mountain surface. And Bilgen’s studyshows that SSCPP has much shorter chimney height than the clas-sical style has because of the buoyancy effect caused by the solarcollectors of SSCPP [10].

3. Mathematical model

In the model building process, some necessary assumptions arecarried out:

lants: (a) the classical style; (b) SSCPP.

2362 F. Cao et al. / Energy Conversion and Management 52 (2011) 2360–2366

(1) The flow resistance losses are ignored.(2) Boussinesq assumptions are used for air density.(3) The solar collectors are laid to the direct south and the azi-

muth angle effect is not considered.(4) The wind turbine is thought to be ideal, and the turbulence

caused by the wind turbine is neglected.

3.1. Solar collector

The received solar radiation on a b angle surface, Ht could becalculated as:

Ht ¼ Ht;b þ Ht;d þ Ht;r ð1Þ

whereas, solar radiation on the horizontal surface is:

H ¼ Hb þ Hd ð2Þ

where H is the total soar radiation on the horizontal surface, Ht,b isthe bare solar radiation, Ht,d is the diffused solar radiation and Ht,r isthe reflected solar radiation. They could be calculated by the nextthree equations

Ht;b ¼ HbRb ð3Þ

Ht;d ¼ HdRd ð4Þ

Ht;r ¼ refHRr ð5Þ

where Hb is the monthly total bare radiation on the horizontal sur-face, Hd is the monthly total diffused radiation on the horizontalsurface. ref is the ground reflectance. According to Muneer’s litera-ture, ref is 0.25 here [14]. And Rb, Rd and Rr are the coefficients. Theycould be calculated in the following equations

Rb ¼cosðu� bÞ cos d sinxts þ p

180

� �xtsðu� bÞ sin d

cos u cos d sinxs þ p180

� �xs sin u sin d

ð6Þ

Rd ¼Hb

HoRb þ

12� 1� Hb

Ho

� �ð1þ cos bÞ ð7Þ

Rr ¼1� cos b

2ð8Þ

where u is the latitude, xs is the sunset angle, xts is the sunset an-gle toward the sloped surface, d is the solar declination angle and Ho

is the solar radiation out of the atmosphere.The monthly total solar radiation on the sloped surface finally

could be expressed as:

Ht ¼ HbRb þ HdHb

HoRb þ

12

1� Hb

Ho

� �ð1þ cos bÞ

� �þ 1

2refHð1� cos bÞ

ð9Þ

Sunlight transmits through the glass and heats the air and heatshortage layer under the glass. So the incident Ht could be dividedinto three parts: reflected radiation Href, radiation transmitsthrough the glass H1 and radiation absorbed by the glass H2

Ht ¼ Href þ H1 þ H2 ð10Þ

Href could be calculated by Eq. (5). And H1 and H2 could be calcu-lated by the next equations

H1 ¼ HbRbðsaÞb þ HbHb

HoRb þ

12

1� Hb

Ho

� �ð1þ cos bÞ

� �ðsaÞd ð11Þ

H2 ¼ HbRbab þ HdHb

HoRb þ

12

1� Hb

Ho

� �ð1þ cos bÞ

� �ad

þ 12qHð1� cos bÞar ð12Þ

where a is the absorption rate, s is the transmittance ratio of theglass cover and (sa) is the absorption rate during transmission pro-cess, which are related to the material. Detailed theory could befound in [15].

The annually average effective solar radiation on a sloped sur-face S1 and annually average absorbed solar radiation by the glasscover S2 are expressed as:

S1 ¼P12

i¼1H1;i

Timeð13Þ

S2 ¼

P12

i¼1H2;i

Timeð14Þ

where Time is annually average sunshine hour, H1,i means monthlyaverage solar radiation absorbed by the glass cover in the number imonth and H2,i is the monthly average solar radiation absorbed bythe heat shortage layer in the number i month.

The schematic of a solar collector and its thermal balance dia-gram are shown in Fig. 2. In the collector, there are three groupsof thermal energy balance, which are: the thermal balance of theglass, the thermal balance of the ground and the energy balanceof the air. They are presented in Eq. (15)–(17) separately.

Thermal balance equation of the glass covers:

S2 þ UtðTa � TcÞ þ hrðTp � TcÞ þ h1ðTf � TcÞ ¼ 0 ð15Þ

Thermal balance equation of the heat shortage layer:

S1 þ UbðTa � TpÞ þ h2ðTf � TpÞ þ hrðTc � TpÞ ¼ 0 ð16Þ

Thermal balance equation of the air in the collector:

h1AcollðTc � Tf Þ þ h2AcollðTp � Tf Þ ¼ Q ð17Þ

where:

M ¼ qoAchiv f ð18Þ

Q ¼ McpðTo � TaÞ ð19Þ

Tf ¼To þ Ta

2ð20Þ

In the above equations, Ta is the ambient air temperature, Tc isthe collector cover temperature, Tp is the heat shortage layer tem-perature (here ground is the heat shortage layer), Tf is the airflowtemperature, To is the airflow temperature at the outlet of the col-lector, Acoll is the collector area, M is the air mass flow, Q is the en-ergy absorbed by the solar collectors, qo is the airflow density atthe outlet of the collector and vf is the average airflow speed. Ut,

Fig. 2. Schematic and thermal balance of the solar collector.

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75450

500

550

600

650

Fig. 3. Annually average total solar radiation on different slope surfaces in Lanzhou.

Table 1Designed configuration sizes and main common parameters of the SSCPP.

Subjects Parameters/unit Values

F. Cao et al. / Energy Conversion and Management 52 (2011) 2360–2366 2363

hr, h1, Ub and h2 are the heat transfer coefficients. Detail calcula-tions of the heat transfer coefficients are in the studies by Bilgen[10] and Pasumarthi [8].

3.2. Chimney

The chimney is the ‘‘engine’’ of the system. The pressure createdby the chimney is used for three parts: the friction losses in the col-lector and the chimney DPf, the kinetic energy losses at the chim-ney exit DPKE, and the rest is used by the wind turbine DPt

DPtot ¼ DPf þ DPKE þ DPt ð21Þ

where DPf and DPKE could calculate according to hydrodynamicprinciples as:

DPf ¼ fLth

D12qavrv2

avr ð22Þ

DPKE ¼12qchiv2

chi ð23Þ

where Lth is the length of the collectors, f is the friction loss coeffi-cient, qavr is the average airflow density, vavr is the average airflowspeed, vchi is the airflow speed out of the chimney and qchi is the air-flow density at the outlet of the chimney.

As the friction losses in the collector are ignored in the simula-tion study, Eq. (21) could be rewritten as:

DPtot ¼ DPKE þ DPt ð24Þ

Pressure developed because of air density difference betweeninlet and outlet in the chimney is calculated as follows:

DP ¼Z outlet

inletgðqa � qðzÞÞdz ð25Þ

where qa is the ambient air density.For a vertical adiabatic chimney, by integrating Eq. (25), the

next equation is obtained:

DPtot ¼ ðqa � qoÞgHchi ð26Þ

We assume the air density variation is linear between the col-lector inlet and outlet according to Refs. [4,16]. According to math-ematical and physics theories, the pressure generated by thecollector and chimney are:

DPcol ¼qa � qf

2gHcoll ð27Þ

DPchi ¼ ðqa � qf ÞgHchi ð28Þ

where qf is the average air temperature in the collector, Hchi is thechimney height, DPcoll and DPchi are the pressure generated in thecollector and chimney separately.

Finally, the total pressure because of buoyancy could be ex-pressed as:

DPtot ¼ DPKE þ DPt ¼12qf v2

chi þ DPt ¼ DPcoll þ DPchi

¼ ðqa � qf Þg Hchi þ12

Hcoll

� �ð29Þ

Designedparameters

Collector angle, h/� 31

Chimney height, Hchi/m 252.2Chimney radius, Rchi/m 14Collector Radius, Rcoll/m 607.2

Commonparameters

Efficiency of the turbine, gt 0.8

Product of transmittance and absorbance of thecollector (sa)

0.65

Cover heat loss coefficient, a/W m�2 K�1 10.0

3.3. Power generation and thermal efficiency

The power generated by the turbine, Pele is:

Pele ¼ gtDPtvoutAchi ð30Þ

where gt is the turbine efficiency vout is the airflow speed at theoutlet of the solar collector.

The collector efficiency can be expressed as:

gcoll ¼Q

Ht � Acollð31Þ

The system efficiency is:

gsys ¼Pele

Ht � Acollð32Þ

4. Configuration sizes of the SSCPP

Slope angle of the solar collector is an important parameter inthe SSCPP design. In this simulation study it should be fixed first,as the other parameters are highly related to it. Fig. 3 shows theannually solar radiation on a surface with different angles. Fromthe figure, it is obvious that the maximum solar radiation receptionappears at the surface angle near 30�. Considering solar radiationon the collector surface is mainly determined by the slope angle,the angle where maximum radiation reaches the glass collectoris chosen as the solar collector angle. After detailed calculation,the chosen angle is 31�. Other authors such as Wei et al. [17] haveanalyzed the slope’s effect for receiving insolation and investigatedon the optimal slope angle of collector in SSCPP. It is suggested thatthere are other collector angle optimization principles, and here weonly concern the annual total radiation on the collector surfaces.

After fixing the collector angle, the configuration sizes of SSCPPto be built in Lanzhou could then be confirmed through simulta-neous Eqs. (15)–(19), (29) and (30). There are 7 unknown parame-ters and 7 equations are summarized. So, the equations could besolved through iterative calculations. Some common parametersused in the equations are chosen according to [13]. Other meteoro-logical parameters such as the ambient temperature data and thesolar radiation data, etc. are supplied by the National Meteorolog-ical Information Centre. The values of designed configuration sizesand common parameters are shown in Table 1.

2364 F. Cao et al. / Energy Conversion and Management 52 (2011) 2360–2366

5. Results and discussion

5.1. SSCPP performances in different months

Fig. 4 shows the solar radiation falling on the solar collectors.The solar radiation falling on the collectors is of high importanceto the whole system. To have a comparison, the solar radiationon a horizontal surface is also diagrammed in Fig. 4. From the fig-ure, it is found that only between mid-April and August 1st, the so-lar radiation on the horizontal surface is larger than on the slopedsurface. In the winter half year, the solar radiation on the slopedsurface is much larger than on the surface. Reason for the larger so-lar radiation on the horizontal surface between mid-April and Au-gust is the longer solar radiation reception time on the horizontalsurface than on the sloped surface. By integrating the areas underthe two curves, it is found that the total solar radiation absorbed bythe collector surface of the sloped solar chimney power system islarger than on the horizontal surface.

The main performances of the SSCPP are shown in Fig. 5. In thefigure, the temperature increase through the solar collector (tem-perature difference between the ambient air and the airflow), theairflow speed at the collector outlet and the pressure created bybuoyancy effect are diagrammed in curves with different coloursand shapes.

Jan Feb Mar Apr May Jun8

10

12

14

16

Month in

Tem

pera

ture

incr

ease

/ K

Air s

peed

/ m

s-2

Fig. 5. Performances (airspeed, temperature in

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec200

250

300

350

400

450

500

550

600

650

Sloped surface Horizontal surface

Sola

r Rad

iatio

n / M

J m

-2

Month in the year

Fig. 4. Solar radiation falling on the solar collectors from January to December.

Curves in Fig. 5 show that:

(1) The maximum airflow speed (15.38 m/s) appears in March,the minimum airflow speed (14.28 m/s) appears in Novem-ber, the second maximum airflow speed (15.16 m/s) appearsin September and the second minimum airflow speed(14.56 m/s) appears in February.

(2) The variation of airflow speed during the whole year time isnot strong, and the average airspeed through the year is14.80 m/s.

(3) The airflow speed first decreases from January to February,then increases from February to March; after that, the air-flow speed enters into a platform from March to September,where a small decrease appears between July and August;finally, the airflow speed first decreases and then increases,with a turning point in November.

(4) The curve of the airflow speed is approximately symmetri-cal, the symmetry axis is near mid-June.

(5) The maximum temperature increase (9.84 K) appears inMarch, the minimum temperature increase (8.43 K) appearsin November, the second maximum temperature increase(9.80 K) appears in September and the second minimumtemperature increase (8.55 K) appears in December.

(6) Similar to the airflow speed tendency, there is a platform inthe temperature increase, which appears between Marchand September.

(7) The curve of the temperature increase is approximatelysymmetrical, with symmetry axis in July.

(8) The maximum pressure (144.99 Pa) locates in March and theminimum pressure (123.68 Pa) appears in July.

(9) Pressure tendency in a year is almost the same as airflowspeed and temperature increase, whereas no significant flatplatform appears in pressure tendency.

(10) The performances of the SSCPP are stable all through theyear.

Comparing the three curves in Fig. 5, it is found that the tenden-cies of the three curves are analogical: the maximum values appearin March and September (in the pressure curve, September has thesecond maximum value); the minimum values appear between inJune; besides, the three curves are roughly symmetrical, and thesymmetry axis locate between June and July.

Jul Aug Sep Oct Nov Dec

Temperature increase Air speed Pressure

the year

100

110

120

130

140

150

160

170

180

Pressure / Pa

crease and pressure) of SSCPP in one year.

F. Cao et al. / Energy Conversion and Management 52 (2011) 2360–2366 2365

5.2. Efficiency of the SSCPP

Fig. 6 shows the solar chimney efficiency and system efficiencyof the SSCPP during a year. The highest solar collector efficiency(66.04%) appears in January and the minimum solar collector effi-ciency (62.52%) appears in July. The highest system efficiency(0.64%) appears in January and December; the minimum systemefficiency (0.57%) appears in July. From Fig. 6, it is obvious thatthe system efficiency and solar collector efficiency have similarcurve tendencies through a year: efficiencies are both large in win-ter and spring days, whereas low in summer and autumn days,with the turning point in July. And, the two curves are approxi-mately symmetrical to July. Comparing to other power generationplants (fuel, water and nuclear), the system efficiency of SSCPP istoo small. The ultimate reason for this low efficiency is the originaldrawback of the solar energy: low energy density and discontinu-ousness. However, the endlessness of energy resource, environ-mental friendliness and easiness to manage are SSCPP’s especialadvantages comparing to fuel, water and nuclear power generationsystems.

5.3. Discussions

It is found from Fig. 5 that in summer and autumn days, whenthe solar radiation is strong, the temperature lift is not high butseems being kept at same level as that in March. Not only the tem-perature increase, the airflow speed and the system pressure havethe same tendencies. Moreover, system efficiency and solar collec-tor efficiency are both smaller in summer days. Detail expressionsabout the temperature increase, system pressure, airflow speed,system efficiency and solar collector efficiency are summarizednext with the help of Figs. 7 and 8.

Firstly, we would like to highlight that the temperature increaseis the difference between the airflow and the ambient temperature.Fig. 7 shows the ambient air temperature Ta, the airflow tempera-ture Tf, the heat shortage layer (ground) temperature Tp and theglass cover temperature Tc tendencies in a year. The figure showsthat in summer days the airflow temperature is higher, whichagrees with the common knowledge. However, the ambient tem-perature air temperature is also larger. The gap between the air-flow temperature and the ambient air, which is defined as thetemperature increase, is larger in winter days and smaller in sum-mer days. Thus, a platform from March to September is created inFig. 5.

Jan Feb Mar Apr May Jun0.56

0.57

0.58

0.59

0.60

0.61

0.62

0.63

0.64

0.65

Monthe in

Syst

em e

ffici

ency

/ %

Fig. 6. Efficiency of the

Then, Eq. (29) suggests that the system temperature correlatesto the density difference between ambient air and the airflow tem-perature (qa � qf). According to the Boussinesq assumptions, den-sity differences are the results of the temperature differences. Asthere is a small decline in the temperature increase curve in June,a fall in June in the pressure curve is created. Also, from Eq. (29), itis found that the system pressure correlates to the efficient heightdifference ðHchi þ 1

2 HcollÞ; which is a designed constant but largenumber. So, in the system pressure difference curve, the small den-sity difference effect is enlarged, causing a larger difference be-tween the maximum and minimum system pressure (21.31 Pa).

Finally, in Fig. 7, temperature of the heat shortage layer Tp islower in summer days, which suggests that more energy is lostin summer days according to its the energy balance equation (Eq.(16)). Reason for that is the higher airflow speed in summer days,which enhances the heat convection between the heat shortagelayer and the surrounding. The airflow is forced by the pressuredifference. Lower system pressure in summer days causes the plat-form in the airflow speed curve in Fig. 5 from March to September.

Fig. 8 shows the total solar radiation on the sloped surface,effective solar radiation absorbed by SSCPP and the total powergeneration in each month. It is found that in summer days, thethree are all the largest and in winter they are all smaller. In sum-mer days, the energy loosing (gap between the total solar radiationand effective solar radiation) is larger. And, the increase proportionof the effective radiation and power generation is smaller than thatof the total radiation. So, in Fig. 5 the solar collector efficiency andthe system efficiency are smaller in summer days.

Studies by Zhou et al. [18] show that the population in thenorthwest plateau covering 26.8% of the total land of China onlyaccounts for 0.94% of the total population. In Northwest China,the population density is very low, and majority of plateau landis unused. This is one reason and the advantage that can be takento use the plateau lands for SSCPP construction and installation.Another advantage is Northwest China is abundant for solar en-ergy. If all the regions of Qinghai-Tibet Plateau are used as con-struction sites of solar chimney power plant, the yearly totalpower from SCPP which could reach 86.8 million TJ is enough tosatisfy the energy need of the whole country in 2008 [18]. More-over, mountain areas which suitable for SSCPP construction arealso abundant in Northwest China, as is well known that the Tian-shan Mountain, the Tanggula Mountain and the Kunlun Mountainetc. are all locate in Northwest China. Moreover, considering theendlessness, environmental friendliness and management easiness

Jul Aug Sep Oct Nov Dec

system efficiency collector efficiency

the year

62

63

64

65

66

67

Solar collector efficiency / %

SSCPP in one year.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

0

12

24

36

48

60

72

Tem

pera

ture

/ oC

Month in the year

Ta

Tf

Tp

Tc

Temperature increase

Fig. 7. Ambient air temperature Ta, airflow temperature Tf, heat shortage layer (theground) temperature Tp and glass cover temperature Tc tendencies in a year.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0

100

200

300

400

500

600

Sola

r rad

iatio

n/ M

Jm-2

Month in the year

Total radiation Effective radiation Power generation (x10)

Fig. 8. Total solar radiation, effective solar radiation and power generation in eachmonth.

2366 F. Cao et al. / Energy Conversion and Management 52 (2011) 2360–2366

of SSCPP, we could conclude that SSCPP in Northwest China cansupport the development of China. To overcome the disadvantageof low efficiency, SSCPP is suggested to be built together with otherrenewable energy resources such as hydroelectric power, windpower and geothermal energy.

6. Conclusions

In this study, a simplified mathematical model was first estab-lished. Then a 5 MW solar chimney power plant was designed forLanzhou City. Finally, its performances (airflow speed, airflow tem-perature increase, pressure, system efficiency and the collectorefficiency) through a year were simulated and presented. The casestudy suggests that

(1) Temperature increase in the solar collector, airspeed at theinlet of the chimney and pressure have the same curve ten-dency throughout the year.

(2) Performances of SSCPP is better in spring and autumn daysand the system parameters’ tendency during the year isstable.

(3) Though the collector has high thermal efficiency, the overallefficiency of the system is low.

(4) Though the sloped solar chimney power plant has lowpower efficiency, its energy resource endlessness, environ-mental friendliness and management easiness are of highvalue for Northwest China, where pollution and environ-mental problems have drawn high attention by the Chinesegovernment.

For a complete feasibility analysis of building SSCPP in North-west China, the economic analysis is required indeed, which theauthors think could be the next research direction. And the systemoptimization is also an important research direction.

Acknowledgments

The research was funded by the National Natural Science Foun-dation of China (Nos.: 5050602, 50821064) and Program for NewCentury Excellent Talents in University (No.: NCET-08-0440). Theauthors also would like to thank Miss. Tian YANG from Departmentof English, Yan’an University for her helpful language support. Andspecial thanks will be given to the National Meteorological Infor-mation Centre for its data supporting (Chinese Radiation Climatevalue data proceeding – Lanzhou Section (1993–2000)).

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