Modelling and simulation of solar radiation data processing with ...

Simulation Modelling Practice and Theory 16 (2008) 721–735

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Simulation Modelling Practice and Theory

journal homepage: www.elsevier .com/ locate/s impat

Modelling and simulation of solar radiation data processing with Simulink

Chao Shen, Ya-Ling He *, Ying-Wen Liu, Wen-Quan TaoState Key Laboratory of Multiphase Flow in Power Engineering, School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an Shanxi 710049, PR China

a r t i c l e i n f o

Article history:Received 27 June 2007Received in revised form 2 April 2008Accepted 3 April 2008Available online 28 April 2008

Keywords:Solar radiation data processingSolar energyModellingSimulationSimulink

1569-190X/$ - see front matter � 2008 Published bdoi:10.1016/j.simpat.2008.04.013

* Corresponding author. Tel.: +86 29 82665930; fE-mail address: [email protected] (Y.-L.

a b s t r a c t

This work presents one program developed to process solar radiation data. The programprovides several options of horizontal radiation mode and tilted surface radiation modeto estimate the radiation at any time intervals as well as to find the position of the sun,using the graphical programming language Simulink. The model can conveniently connectwith pre-existing models built with Simulink and its results are of importance for improv-ing the simulation accuracy of solar energy system and/or air-conditioning system. Theprogram is an open source and available at the web site http://nht.xjtu.edu.cn/qtxx/cxdm.htm. Any user can utilize, expand and develop the contents of the program.

� 2008 Published by Elsevier B.V.

1. Introduction

The research interests in renewable energy, especially the solar energy, are continuously increasing because of the risingprice of the traditional energy resources and the serious environmental pollution. The solar energy can be studied in twoways, the experimental study and the numerical simulation study. Simulations are numerical experiments and can givesome kinds of thermal performance information as can physical experiments.

Typical simulation programs have been described by Soteris A. Kalogirou [1]. TRNSYS [2] is a widely used program inmodular thermal process of solar energy. It consists of the subroutines that represent the components in typical solar energysystems and users can readily write their own component subroutines if they are not satisfied with those provided. HoweverTRNSYS is not a user-friendly program, so more and more attentions have been given to user-friendly program to simulatethe solar energy system and/or air-conditioning system. Several studies have been published on the modelling and simula-tion of solar energy system and air-conditioned system with Simulink [3–9]. Simulink is a graphical program that allows sys-tems to be modeled by drawing a block diagram on the screen. So users can create, model, simulate and analyze dynamicsystems interactively. Yu et al. [3] built the reusable models of an air-conditioned room in office building with Simulinkand bond graph respectively. They used the two different approaches and calculated the 11-day temperature history of aroom respectively. Buzas et al. [4] developed the model of a solar hot water system and analyzed its thermal behavior. Theirsimulation results will give the appropriate components and the optimal size of a solar domestic hot water system to bebuilt. Any technique that aims the use of solar energy should start with the research of the radiation data available in theregion being studied. Detailed solar radiation data become more and more important with the increasing number of studieson solar energy devices and/or air-conditioning systems dynamic behaviour. However, the solar radiation is over-simplifiedin both of the above models. Buzas et al. assumed the solar radiation as a sine function of time, while Yu used the insolationdata of the studied region that is generally taken at 1-h intervals and on a horizontal surface as the solar radiation model.

y Elsevier B.V.

ax: +86 29 82669106.He).

http://nht.xjtu.edu.cn/qtxx/cxdm.htm

http://nht.xjtu.edu.cn/qtxx/cxdm.htm

mailto:[email protected]

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722 C. Shen et al. / Simulation Modelling Practice and Theory 16 (2008) 721–735

However, estimates of radiation on a tilted surface or at time intervals other than 1 h are required in almost every simulationof solar energy and/or air-conditioning system. Furthermore, to the author’s knowledge, no solar radiation data process pro-gram has been built with Simulink to simulate the solar energy system and/or air-conditioning system.

The purpose of this paper is to introduce the program that is built with Simulink to interpolate radiation data, calculateseveral quantities related to the position of the sun, and estimate insolation on surface of either variable or fixed orientation,such as the surface of a solar energy collector or walls of a room. Global radiation on a tilted surface or the walls of a room isusually required for solar energy system or air-conditioning system. The model of solar radiation data processor built withSimulink provides several options for calculating the horizontal radiation components as well as estimating the global radi-ation on a tilted surface.

2. Modelling and mathematical description

The solar radiation data processor includes initializing subsystem, data reading subsystem, declination calculation sub-system and central processing subsystem. Fig. 1 shows the flow of information between the subsystems of the processor.The scheme of the solar radiation processor with Simulink is shown in Fig. 2. Simulink uses a graphical environment, basedon block diagrams that support different operations, such as arithmetic functions, input/output, data handling, transfer func-tions, state space models, etc. Comparing Fig. 2 with Fig. 1, it can be seen that the program built with Simulink is useful whenshowing complex interactions between different subsystems of the program. The results of the simulation include the radi-ation on a horizontal surface and tilted surface, sun position, incidence angle for the tilted surface and slope of the tilted sur-face. The modelling and mathematical descriptions of these subsystems are described below.

2.1. Initializing subsystem

The initializing subsystem is used to initialize the parameters of the solar radiation data processing program. IE denoteswhether the solar time is taken as simulation time. When IE is less than 0, the simulation time equals solar time, otherwise,the simulation time will be corrected according to the value of IE. The second parameter n represents starting date of thesimulation, so it ranges from 1 to 365. ALAT represents the latitude of the area considered, and its unit is degree. SHIFT isthe difference between the longitude of the standard meridian for the local time zone and the longitude of the studied area,and it is used to convert standard time to solar time by applying corrections. The difference in minutes between solar timeand standard time is

Solar time� standard time ¼ 4SHIFTþ E ð1Þ

E is the equation of time, it is the correction accounting for the perturbations in the earth’s rate of rotation which affect thetime of the sun crosses the observer’s meridian [10]:

E ¼ 229:2ð0:000075þ 0:001868 cos B� 0:032077 sin B� 0:014615 cos 2B� 0:04089 sin 2BÞ ð2Þ

where

B ¼ ðn� 1Þ 2p365

ð3Þ

Initializesubsystem

Controlsubsystem

Declinationsubsystem

Centralprocessingsubsystem

No Sunsubsystem

File of TMYweather data

File ofresult

Time

Globeradiation

Directradiation

The differencebetween startand stop littlethan 1% ofsimulationinterval

Start time afterSunset or Stoptime BeforeSunrise

Fig. 1. Flow diagram illustrating the solar radiation processor.

Fig. 2. Scheme of solar radiation processor.

C. Shen et al. / Simulation Modelling Practice and Theory 16 (2008) 721–735 723

and n = day of the year. Thus 1 6 n 6 365.The fifth parameter Sc is the solar constant 1367 W/m2.

2.2. Data reading subsystem

This subsystem reads solar radiation data at regular time intervals from a weather data file and makes it available to othersubsystems as time varying forcing functions.

2.3. Declination calculation subsystem

Declination angle d indicates the angular position of the sun at solar noon (i.e. when the sun is on the local meridian)relative to the plane of the equator, north is positive and south is negative (�23.45� 6 d 6 23.45�). The declination anglecan be calculated by the equation

d ¼ 23:45 sin ð284þ nÞ360365

� �ð4Þ

The sunrise and sunset hour angle, time shift due to the eccentricity of the earth’s orbit and the variation of extraterrestrialradiation due to variation in sun to earth distance should also be calculated in the subsystem. The modelling of the declina-tion calculation subsystem with the Simulink is shown in Fig. 3.

2.4. Central processing subsystem

The central processing subsystem, as is shown in Fig. 4, is the heart of the solar radiation processor. It includes sun posi-tion finding block, extraterrestrial radiation calculation block, global radiation, beam radiation and incidence angle for slopesurface calculating block, horizontal radiation model block, tracking model block and tilted surface radiation model block.These blocks will be introduced in detail in the following sections.

2.4.1. Sun position finding blockThe position of the sun is specified by giving the solar zenith and solar azimuth angles. The solar zenith angle hZ is the

angle between the vertical and the line of sight of the sun. Its value is 90� minus the angle between the sun and the

6DECL

5ECC

4CC1

3SS1

2WS1

1ET

cos

Trigonometric5

tan

Trigonometric4

sin

Trigonometric3

cos

Trigonometric2

tan

Trigonometric1

acos

TrigonometricFunction6

sin

Trigonometric

-C-

TIMESTART2

round

RoundingFunction1

fix

RoundingFunction

Product4

Product2

Product1

Product

f(u)

Fcn1

f(u)

Fcn

f(u)

E0T(XX)

Divide1

Divide

-C-

Constant4

1

Constant3

-1

Constant1

24

Constant

Add1

Add

3ALAT

2DAY1

1TIME

Fig. 3. Declination calculation subsystem.

12AZM

11SLOPE

10THETA

9HDIFF

8HBEAM

7HT

6HD

5HB

4HHOR

3solar azimuth

2ZENITH

1HEXTRA

HB

HHOR

SAZM

AXAZM

AXSLP

ALF

TANASL

COSTTP

ZENITH

SLOPE

RB

COSSLP

HGRF

HBEAM

THETA

AZM

Hhor

TRACKING MODE

SAZM

ZENITH

AXAZMAXSLP

ALFTANASLCOSTTP

ZenithSazm

TILTED SURFACE Radiation

HEXTRA

HD

HB

SLOPE

RB

COSSLP

Hextra

Hb

Hd

HDIFF

TILTED SURFACE CORRELATION

DDELTHRATIOCCSSCOSHRSINHRWALATDECL

HRATIO1

COSZEN

SAZM

ZENITH

Sun posintion finding block

XIN(1)XIN(2)TIMEDTIMEI1DDELT

DTIME1

XIN1

XIN2

SET DATA VARIABLES

Product1

Product

W1

W2

ALAT

DECL

w1w2

COSHRSINHR

WAlatDecl

NO POINT IN CONTINUING IF THERE IS NO SUN

WS

ET

SHFT

DTIME1

DTIME2

WD1

WD2

HOUR ANGLES

XIN1

HEXTRA

HRATIO1

Coszen

Hextra

HD

HB

HHOR

HORIZONTAL RADIATION

f(u)Fcn

-C-Constant

Time

dtime2time

dtime1DDELT

CHECK NEW DATA

ECCSCSSCCWD1WD2XIN1W1W2

Xin

HEXTRA

HRATIO

Cc

Ss

EXTRATERRESTRIAL RADIATION

14XIN2

13XIN1

12Time

11SC

10SHFT

9ALAT

8DECL

7ECC

6CC

5SS

4WS3

ET

2W2

1W1

Fig. 4. Central processing subsystem.



horizontal and it ranges from �90� to 90�. The solar azimuth angle cS is the angle between the local meridian and the pro-jection of the line of sight of the sun onto the horizontal plane. Its value is positive for the west, negative for the east andranges from �180� to 180�, zero solar azimuth is facing the equator. The solar zenith angle hZ is given by the trigonometricEq. (5), and solar azimuth angle is determined by Eqs. (7) and (8).

hZ ¼ cos�1ðsin d sin /þ cos / cos d cos xÞ ð5Þ

c0 ¼ sin�1 cos d sin xsin hZ

� �ð6Þ

If : cos x Ptan dtan /

� �then cS ¼ 180� � c0 ð7Þ

else : cos x <tan dtan /

� �then cS ¼ 360� þ c0 ð8Þ

Fig. 5 shows the Simulink component model for sun position finding.

2.4.2. Extraterrestrial radiation calculation blockExtraterrestrial solar radiation is the solar radiation outside the earth atmosphere. The intensity of the extraterrestrial

radiation is inversely proportional to the square of the distance between the earth and the sun. The study of the extrater-restrial radiation is of great importance because it indicates the maximum possible radiation that could be expected onthe earth surface. The model adopts the global radiation between times td1 and td2 read from the weather data files. Then,by summing integrals if necessary, the global radiation between hour angles xd1 and xd2 is found. The hour angles xd1 andxd2 are chosen so that xd1 6 x1and xd2 P x2, where x1 is the angle at the start of the time step and x2 is the angle at the endof the time step. If sunrise or sunset occurs during the time step, then the portion of the time step will be ignored when thesun is below the horizon.

The global extraterrestrial radiation between hour angles x0 and x00 is calculated from [2]

H0jx00

x0 ¼Z x00

x0E0Scðcos / cos d cos xþ sin / sin dÞdx ð9Þ

where E0 is the eccentricity correction factor of the earth’s orbit. Duffie and Beckman [12] presented the following expressionfor E0,

E0 ¼ 1þ 0:033 cos2np365

� �ð10Þ

After integrating between time steps of angles x0 and x00, Eq. (9) may be rewritten in the following form:

H0jx00

x0 ¼ ScE0ðcos / cos dðsinðx00Þ � sinðx0ÞÞ þ sin / sin dðx00 � x0ÞÞ ð11Þ

The global extraterrestrial radiation per hour is

H0 ¼ ScE0ðcos / cos dðsinðx00Þ � sinðx0ÞÞ þ sin / sin dðx00 � x0ÞÞ=ðx00 � x0Þ ð12Þ

The ratio of the extraterrestrial radiation for the time step to that one over the entire period of data collecting will be

HRATIO ¼ ScE0ðcos / cos dðsinðx2Þ � sinðx1ÞÞ þ sin / sin dðx2 � x1ÞÞScE0ðcos / cos dðsinðxd2Þ � sinðxd1ÞÞ þ sin / sin dðxd2 � xd1ÞÞ

ð13Þ

4ZENITH

3SAZM

2COSZEN

1HRATIO1

Switch

W

ALAT

SINHR

DECL

SINZEN

SAZM

Subsystem

In1 Out1

SUBsinSIN

Product

acosFCN1

f(u)FCN

Divide-C-

DELT

-C-Constant

> 1e-00Compare

To Constant

|u|Abs

9DECL

8ALAT

7W

6SINHR

5COSHR

4SS

3CC

2HRATIO

1DDELT

Fig. 5. Sun position finding block.


The radiation on the horizontal is interpolated from data using the curve of extraterrestrial radiation. The extraterrestrialradiation calculation model is shown in Fig. 6.

2.4.3. Horizontal radiation mode blockAs can be seen in Fig. 7, the block has two methods to obtain the data of beam and diffuse radiation on a horizontal sur-

face from the data of global radiation on the horizontal surface. In addition, any user/developer can expand and develop thecontents of the block if they are not satisfied by the two methods.

In mode 1, the breakout of horizontal diffuse and direct insolation is taken from the correlation of Liu and Jordan [11]. Thecorrelation of Liu and Jordan is actually a relationship between daily diffuse and daily global radiation [12]. However, it isregarded as hourly relation here. The equation of hourly correlation of Liu and Jordan is

Hd

H¼ 1:0045þ 0:04349kT � 3:5227k2

T þ 2:6313k3T ð14Þ

where H is the global radiation on a horizontal surface, Hd is the diffuse radiation on horizontal surface, and kT is an hourlyclearness index can be defined as:

kT ¼HH0

ð15Þ

Beam radiation will be calculated by the algebraic equation

Hb ¼ H � Hd ð16Þ

The second mode uses the relation for estimating the beam and diffuses components of global radiation established by Boeset al. [13]. In Boes’s model, the following relations are used.

Hdn ¼ ð1:3304kT � 0:3843ÞSc ð17Þ

where Hdn is direct normal beam radiation

Hdn ¼maxð0;minðHdn;0:739ScÞÞ ð18Þ

The beam radiation is given by

Hb ¼ Hdn � cosðhzÞ ð19Þ

Diffuse radiation will be calculated by the algebraic equation

Hd ¼ H � Hb ð20Þ

Fig. 6. Extraterrestrial radiation calculation.

Fig. 7. Horizontal radiation model.


2.4.4. Tracking model blockThe tracking model block with Simulink is shown in Fig. 8. Four types of tracking models are incorporated into the track-

ing block to handle various surfaces for which the determination of incident radiation is often needed due to their impor-tance and wide utilization. These four types of tracking models include fixed surface model, single-vertical axis trackingwith fixed slope and variable azimuth model, single-sloped axis tracking model and two-axis tracking model.

8Hhor

7AZM

6THETA

5HBEAM

4HGRF

3COSSLP

2RB

1SLOPE

AXSLP

SAZM

SLOPE

AZMVERTICAL AXIS

ZENITH

SAZM

SLOPE

AZM

TWO-AXIS TRACKER

Slope & Azm

HHOR

HB

ZRNITH

SAZM

Hhor

SLOPE

RB

COSSLP

HGRF

HBEAM

THETA

AZM

Subsystem

AXSLP

AXAZM

SAZM

ALF

COSTTP

TANASL

ZENITH

SLOPE

AZM

SINGLE-AXIS TRACKER

MultiportSwitch

-C-ITRK

AXAZM

AXSLP

SLOPE

AZM

FIXED SURFACE

9ZENITH

8COSTTP

7TANASL

6ALF

5AXSLP

4AXAZM

3SAZM

2HHOR

1HB

Fig. 8. Tracking model.


2.4.4.1. Fixed surface model. Fixed surface model is used for fixed surface that does not track to maximize incoming radiation.The position of the surface is denoted by the slope and azimuth of the surface. These parameters may be constant or may befixed for a period of time. The slope of the surface is given by

b ¼ C ð21Þ

The surface azimuth also may be constant or may be fixed for a period of time, i.e.

c ¼ C ð22Þ

2.4.4.2. Vertical axis tracking model. The vertical axis tracking model is used for handling a tracking surface with a fixed slopeand variable azimuth that rotates around a vertical axis. Fig. 9 shows the scheme of a vertical axis tracking system. The track-ing surface will receive the most beam radiation if the azimuth of the surface keeps up with the azimuth of the sun. The slopeof the surface at any instant is

b ¼ C ð23Þ

The surface azimuth should keep up with the azimuth of the sun so that the tracking surface can receive the most beam radi-ation, i.e.

c ¼ cS ð24Þ

2.4.4.3. Sloped axis tracking model. Sloped axis tracking model handles the general case of a surface rotating about a single-axis that is always parallel to the surface. Fig. 10 illustrates the scheme of the sloped axis tracking system. For a plane rotat-ing about a horizontal axis [2], the slope of the surface at any instant is given by

b ¼ tan�1ðtan hZ cosðcS � cÞÞ ð25Þ

where the surface azimuth c is given in terms of the axis azimuth as

c ¼ c0 þ 90� if cS � c0 > 0 ð26Þc ¼ c0 � 90� if cS � c0 < 0 ð27Þ

If a plane tracks about a single-axis that always parallel to the plane, but the axis is tilted from the horizontal with a fixedangle, both azimuth and slope of the surface vary with time. In this case [2], the slope and the azimuth of the surface aregiven by

b ¼ tan�1 tan b0

cosðc� c0Þ

� �ð28Þ

c ¼ c0 þ tan�1 sin hZ sinðcS � c0Þsin b0 cos h0

� �ð29Þ

where h0 is the incidence angle for a surface with slope and azimuth equal to those of the axis. The block of the single-axistracking model built with Simulink is shown in Fig. 11, it is consisted of sloped axis tracking model, vertical axis trackingmodel and horizontal axis tracking model.

2.4.4.4. Two-axis tracking model. Two-axis tracking surfaces are considered in the two-axis tracking model. In this case, thesurface is adjusted continually so that the rays of the sun are always perpendicular to the surface. The beam radiation on thesurface is maximized when c = cS and b = hZ.

Fig. 9. Single-vertical axis tracking.

Fig. 10. Single-sloped axis tracking.

Fig. 11. Single-axis tracking model.


2.4.5. Tilted surface radiation and correlation blockFor the purpose of solar energy system design and performance calculations, an estimate of the total radiation incidence

on the tilted surface is of importance. Three radiation correlation models for estimating the total radiation on a tilted surfaceare provided in the block, users/developer can readily built their own models if they are not satisfied with those provided inthe block. Fig. 12 shows the scheme of the model built with Simulink. Each model needs the knowledge of global and diffuse(or beam) radiation on a horizontal surface as well as the position of the sun. The global radiation of a tilted surface is cal-culated by adding beam, reflected and diffuse radiation. The beam and reflected radiation is projected onto a tilted surface.The geometric factor that is the ratio of beam radiation on the tilted surface to that on a horizontal surface at any time is usedfor calculating the contribution of beam radiation on a tilted surface. The factor is given by

Rb ¼Gb;T

Gb¼ Gb;n cos h

Gb;n cos hZ¼ cos h

cos hZð30Þ

where h and hZ are the incidence angle of beam radiation on tilted surface and horizontal surface, respectively. The incidenceangle h on a tilted surface with sloped angle b and azimuth angle c can be calculated by the equation

cos h ¼ cos hZ cos bþ sin hZ cosðcS � cÞ ð31Þ

The beam radiation on a tilted surface can be calculated by

HbT ¼ Hb � Rb ð32Þ

Fig. 12. Tilted surface radiation correlation subsystem.

Fig. 13. Scheme of two-axis sun tracking system.

Fig. 14. Solar zenith angle.


Fig. 15. Solar azimuth angle.

Fig. 16. Global radiation on horizontal surface.


The reflected radiation on a tilted surface is not possible to be calculated in detail, because it is affected by many factors. Inthis case, it can be calculated by assuming that the ground acts as an isotropic reflector. The ratio of reflected radiation on atilted surface to the global radiation on a horizontal surface Rr is given by

Rr ¼ 0:5ð1� cos bÞqg ð33Þ

where qg is the reflectance of the ground.The contribution of reflected radiation on a tilted surface can be calculated by

IgT ¼ I � Rr ð34Þ

The contribution of diffuse radiation to a tilted surface is determined by using one of the tilted surface radiation models pro-vided in the subsystem. The first model is the isotropic diffuse model that was derived by Liu and Jordan [14]. The modelsupposed that the diffuse radiation is uniformly distributed over the whole sky dome. The ratio of diffuse radiation on a tiltedsurface to that on a horizontal Rd is given by,

Rd ¼1þ cos b

2ð35Þ

Fig. 17. Diffuse radiation on horizontal surface.

Fig. 18. Global radiation on the two-axis tracking surface.


Thus the contribution of diffuse radiation on a tilted surface supposing isotropic sky is:

IdT ¼ Id � Rd ð36Þ

The second tilted surface radiation model is the Hay and Davies model [15] which is based on the assumption that all of thediffusion can be represented by two parts, the isotropic and the circumsolar. Thus the diffuse radiation on a tilted collector is,

Id;T ¼ Id ð1� AiÞ1þ cos b

2

� �þ AiRb

� �ð37Þ

where Ai is an anisotropy index which is a function of the transmittance of the atmosphere. For beam radiation, it can bewritten as

Ai ¼Ibn

Ion¼ Ib

Ioð38Þ

The third tilted surface radiation model uses the model that was modified by Reindl et al. [16] from the Hay and Daviesmodel. In Reindl’s model, the contribution of diffuse radiation on the tilted surface is

Fig. 19. Beam radiation on the two-axis tracking surface.

Fig. 20. Diffuse radiation on the two-axis tracking surface (isotropic diffuse model).


Id;T ¼ Id ð1� AiÞ1þ cos b

2

� �1þ f sin3 b

2

� �� þ AiRb

� �ð39Þ

where Ai is defined by Eq. (38), and modulating factor f is defined by

f ¼ffiffiffiffiffiffiffiffiIb=I

pð40Þ

3. Example of application

To test the capacity and validity of the solar radiation data processing model, the simulation of the solar radiation on anazimuth/elevation two-axis tracking plane for 3 days has been carried out. Fig. 13 shows the scheme of the two-axis sun track-ing system. The azimuth/ elevation tracking includes one axis rotating about the zenith axis that perpendicular to the surfaceof the earth with a tracking angle c equivalent to the azimuth angle of the sun cS. While the other axis is parallel to the surfaceof the earth and is rotating with a tracking angle b equal to the solar zenith angle hZ. In the two-axis tracking system, the twomotors operate all day long so that the rays of the sun are always perpendicular to the surface. The direct normal solar radi-

Fig. 21. Incidence angle for the two-axis tracking surface.

Fig. 22. Slope angle of the two-axis tracking surface.


ation and global solar radiation on horizontal of each hour of Xian from 0 o’clock of 1 January to 24 o’clock of 3 January wereread in by the data reading block, and were given as input to the central processing subsystem. The duration of the simulationwas set to be 72 h and the time step of the simulation was 1 h. The duration and the time step of the simulation are adjustedconveniently just by change the simulation start time, stop time and the time step in the Simulink environment. However, it isnot so convenient to adjust these parameters in TRNSYS program as in Simulink. The outputs of the simulation include theradiation on a horizontal surface and tilted surface, sun position, incidence angle for the tilted surface and slope of the tiltedsurface. With Matlab in background, powerful tools for data processing and graphical presentation of results are available.Figs. 14–22 show the comparison of these results of the processor built with Simulink and those of the TRNSYS. It can be seenthat the results of the processor with Simulink are highly consistent with those of the TRNSYS.

4. Conclusion

In this paper, a novel approach to simulate the solar radiation data processing with Simulink is presented. The modularapproach in Simulink enables grouping of models into hierarchies, which simplify development, utilization and overview of


the components and subsystems involved. The block communication is organized by a set of data arrays. The interface struc-tured in this way provides a flexible and user-friendly programming environment, and at the same time, making it possiblethat the models can be exchanged and connected with the pre-existing models conveniently. It is convenient to calculate theposition of the sun, the radiation on a horizontal surface and the radiation on a tilted surface with either kind of trackingmodels by using the program presented in this paper. These parameters are of importance for the design of solar energy sys-tem and the optimization of air-conditioning buildings. An example of the solar radiation on a two-axis tracking plane pro-cessed by the program was illustrated in the paper. The results of the program show a fairly good coincidence with those ofTRNSYS.

Acknowledgements

This study was supported by the National Science Fund for Distinguished Young Scholars from the National Natural Sci-ence Foundation of China (No. 50425620) and the Key Project of National Natural Science Foundation of China (No.50736005).

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