Hybrid Thermal-photovoltaic Tracking Solar Collector

8/11/2019 Hybrid Thermal-photovoltaic Tracking Solar Collector

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HARIRI CANADIAN UNIVERSITY

HYBRID THERMAL-PHOTOVOLTAIC TRACKING SOLAR

COLLECTOR

Done by

MAHER A. TAI BOU DARGHAM

ADHAM M. AL HASSANIEH

Submitted to

DR. RIDA NUWAYHIDDR. MOHAMMED TAHA

This senior project submitted in partial fulfillment of the requirements of the BS degree of the

Mechanical & Electrical majors of the College of Engineering at the Hariri Canadian University

MECHREF, LEBANON

May, 2010


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Copyright 2010 All Rights Reserved

Adham M. Al Hassanieh

Maher A. Tai Bou Dargham


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ACKNOWLEDGEMENT

We would like to thank Dr. R. Nuwayhid and Dr. M. Taha for their time and valuable

guidance during this project and Mr. Minem Al Hassanieh for his technical support and

consultancies. We would also like to thank our friends and family for their assistance and

motivation.

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ABSTRACT

After the recent expand of energy demand accompanied by a non promising future of

current energy resources due to their drought or uncleanness, the need for substitutes that will

replace those diminishing and unclean ones became a must. For that reason, our project came up.

This project is a hybrid thermal-photovoltaic tracking solar collector that is designed to heat up

water through sun radiation using a parabolic trough to concentrate the radiation on a water pipe

and a single axes solar tracking system to track the sun and keep the hybrid system functioning

optimally. In addition, our system includes a photovoltaic array mounted over the water pipe to

charge a battery and insure energy for control and tracking. Since, the efficiency of the

photovoltaic cells (PVs) drop upon the rise of its temperature a cooling system is established

through natural air convection. It is extremely safe, clean, natural and renewable.

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TABLE OF CONTENTS

ACKNOWLEDGEMENT....... ii

ABSTRACT.... iii

TABLE OF CONTENTS..... iv

LIST OF FIGURES. vi

LIST OF TABLES....... vii

Chapter page

1.MECHANICAL SYSTEM......... 1

1.1 Device geometry.. 1

1.1.1 The parabolic trough...... 1

1.1.2 Dimensions..... 1

1.1.3 Insolating process..... 3

1.1.4 The pipe and photovoltaic cells.... 6

1.1.5 The actual design...... 8

1.1.6 The built device.... 8

1.2 Solar radiation...... 10

1.2.1 Thermal radiation...... 10

1.2.2 The earths motion about the sun.. 10

1.2.3 Calculating angles. 11

1.3 The tracker....... 14

1.3.1 First degree of freedom..... 14

1.3.2 Second degree of freedom.... 15

2. ELECTRICAL SYSTEM....... 16

2.1 System description........ 16

2.1.1 Charge controller.......... 16

2.1.2 Regulator. 17

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2.1.3 Sensor signal manipulation... 18

2.1.4 Astable 555 timer.. 21

2.1.5 Monostable 555 timer............... 23

2.1.6 Combinational logic.............. 25

2.1.7 H-bridge and DC motor............ 26

2.2 Summary of electrical system... 28

3. TESTING AND NUMERICAL ANALYSIS.. 29

3.1 Data logging...... 29

3.1.1 Test 1.... 29

3.1.2 Test 2.... 30

3.1.3 Numerical analysis....... 32

3.1.4 Results discussion.... 36

APPENDIX............. 38

REFERENCE............. 39

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LIST OF FIGURES

Figure Page

1. Parabola. 1

2. Device planned design... 3

3. Solar rays on the trough. 5

4. Sectional view of the pipe & PVs.. 6

5. The actual design (front)... 8

6. The actual design (back)... 9

7. Declination angle.. 12

8. Solar latitude variation.. 149. Angle of tilting.. 15

10. Multisim simulation of the charge control. 17

11. Multisim simulation of the regulator circuit... 18

12. Multisim simulation of the comparator circuit... 20

13. Multisim simulation of the comparator circuit... 21

14. Multisim simulation of the astable circuit.. 22

15. Astable waveform as it appeared on the scope... 23

16. Multisim simulation of the monostable circuit... 24

17. Monostable waveform as it appeared on the scope.... 24

18. Combinational logic circuit.... 26

19. Multisim simulation of the h-bridge circuit.... 27

20. Block diagram of electrical system.... 28

21- Temperature at the inlet & outlet of the pipe..... 29

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LIST OF TABLES

Table Page

1. Sensor behavior . 19

2. Truth table.. 25

3. Temperature in the tank..... 30

4. Results 35

5. Results.... 36

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CHAPTER 1

MECHANICAL SYSTEM

1.1 Device geometry

1.1.1 The parabolic trough

The main part of the device is a parabolic trough. This trough is designed to face and

track the sun, solar beams fall perpendicularly on the trough. The insolated face of the

trough is covered with mirrors.

1.1.2 Dimensions

The equation of the parabola is , where x is between 0 and 25 cmThe following MATLAB code generates the curve that shows the dimensions in cm

MATLAB code

******************************************************************************x=0.00001:0.001:20;y=10*(sqrt(x));z=-10*(sqrt(x));

plot(x,y,x,z)axis equal

axis([-5 30 -50 50])grid on******************************************************************************

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Figure 1: Parabola

The trough is 1 meter in height; the area of the trough is as follows

MATLAB code

************************************************************************syms x;y=sqrt((x+25)/x); %length of the parabolic trough

L=2*int(y,0,20); %total Area of the parabolic troughA=(100*L)*(10^-4);Apv=(15*100)*(10^-4); %area of PVs and the glass chamber

Ainso=A-Apv; %insolated Area%total Area minus the shadow of the solar PVs

-------------------------------------------------------------------------------------------------------A= 1.0024Apv =0.1500Ainso=0.8524

************************************************************************

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A set of photo voltaic cells are installed above the trough and their area is Apv=0.15 m

The area of the whole trough A=1.0024 m, the insolated area of the trough is Ainso=0.8524 m

Figure 2 represent the device plan

Figure 2: Device Planned Design

1.1.3 Insolating process

The rays falling on the trough are reflected to one point- the focus- at a distance 25 cm

from point (0,0) on the trough

MATLAB code

************************************************************************

x=0.00000001:0.001:25;

%----------------------------------------------------------------------------------------%equation of parabola

y=10*(sqrt(x));z=-10*(sqrt(x));%----------------------------------------------------------------------------------------

%equations of tangents to the curve

dy=5./(sqrt(x));

dz=-5./(sqrt(x));a=20;ax=15;ay=10;az=5;aw=1;

b=10*(sqrt(a));

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bx=10*(sqrt(ax));by=10*(sqrt(ay));

bz=10*(sqrt(az));bw=10*(sqrt(aw));

b1=-10*(sqrt(a));b1x=-10*(sqrt(ax));b1y=-10*(sqrt(ay));

c1=a+(b1*5/(-sqrt(a)));

c1x=ax+(b1x*5/(-sqrt(ax)));c1y=ay+(b1y*5/(-sqrt(ay)));c1z=az+(b1z*5/(-sqrt(az)));c1w=aw+(b1w*5/(-sqrt(aw)));

%----------------------------------------------------------------------------------------

%equations of rays and reflected rayss=tan(2*(atan(-b/(c-a))));

sx=tan(2*(atan(-bx/(cx-ax))));sy=tan(2*(atan(-by/(cy-ay))));

sz=tan(2*(atan(-bz/(cz-az))));sw=tan(2*(atan(-bw/(cw-aw))));

s1=tan(2*(atan(-b1/(c1-a))));s1x=tan(2*(atan(-b1x/(c1x-ax))));s1y=tan(2*(atan(-b1y/(c1y-ay))));

s1z=tan(2*(atan(-b1z/(c1z-az))));s1w=tan(2*(atan(-b1w/(c1w-aw))));

y3=s*(x-a)+b;

y3x=sx*(x-ax)+bx;y3y=sy*(x-ay)+by;y3z=sz*(x-az)+bz;y3w=sw*(x-aw)+bw;

z3=s1*(x-a)+b1;z3x=s1x*(x-ax)+b1x;z3y=s1y*(x-ay)+b1y;

z3z=s1z*(x-az)+b1z;z3w=s1w*(x-aw)+b1w;

y4=b;

y4x=bx;y4y=by;y4z=bz;y4w=bw;z4=b1;

z4x=b1x;z4y=b1y;z4z=b1z;z4w=b1w;

k=(-b/s)+akx=(-bx/sx)+ax,ky=(-by/sy)+ay,kz=(-bz/sz)+az,kw=(-bw/sw)+aw,

k1=(b/s1)+a

k1x=(bx/s1x)+ax,k1y=(by/s1y)+ay,k1z=(bz/s1z)+az,k1w=(bw/s1w)+aw,%----------------------------------------------------------------------------------------

%plotting the equations

plot(x,y,x,y3,x,y4,x,z,x,z3,x,z4,x,0,x,y3x,x,y4x,x,z3x,x,z4x,x,y3y,x,y4y,x,z3y,x,z4y,x,y3

z,x,y4z,x,z3z,x,z4z,x,y3w,x,y4w,x,z3w,x,z4w)axis equal

axis([-5 30 -50 50])

%----------------------------------------------------------------------------------------%the point of intersection of the reflected rays and the x-axis

%k =25

%kx =25%ky =25

%kz =25

%kw =25%k1 =25

%k1x =25

%k1y =25

%k1z =25

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%k1w =25

************************************************************************

Figure 3: Solar Rays on the Trough

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1.1.4 The pipe and photovoltaic cells

A pipe, photovoltaic cells, a glass and aluminum chambers are placed along the focal axis of

the parabola in a configuration explained later in this section. The main parts are:

1- The Pipe

2- Glass chamber

3- Insulation

4-

Insulation

5-

Aluminum fins

6- Photovoltaic cells

7- Air gaps between insulation and the fins and the glass chamber are empty

Figure 4: Sectional view of the pipe and PVs

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The pipe

Since copper has conductivity 401 w/m.C, the pipe used is made of copper to increase the heat

transfer rate to the fluid flowing inside the pipe from the radiation reflected by the trough. The

pipe is painted black since the emissivity of black painted bodies is relativity high (=0.98),

increasing the emissivity of the surface will also increase the heat absorption by the pipe.

Glass Chamber

The glass chamber of thin glass walls will decrease heat loss from the pipe and consequently

heating the air inside the chamber. Heating the air inside the chamber will decrease its density

and since this chamber is oriented vertically the light air will levitate increasing the pressure at

the bottom of the chamber where some air is supplied to balance the pressure difference. The air

supplied at the bottom of the chamber will be controlled by decreasing the air inlets. At two

designated positions in the beam, the glass chamber is joined with the air chamber beneath the

finned aluminum via two vents to benefit from the natural convection and increase the air

convection in the air chamber by the jet effect generated. This convection will increase heat loss

from the fins and reduce the temperature of the PV cells that are in contact with the aluminum

fins and increasing their efficiency.

Insulation

The insulating material used is foam of low thermal conductivity 0.026 w/m.C. Using insulation

will increase the temperature inside the air chamber and block heat from the chamber to the air

gap under the fins.

Aluminum fins

The aluminum fins are used to increase heat loss from the PV cells

Photovoltaic Cells

Photovoltaic cells are used to supply electric power to the electric components in the device. 4

cells (15 cm x 15 cm) are used, each delivers 6.7 volts

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1.1.5 The actual design

The actual device did not differ a lot from the planned design, but some adjustments were

done for reasonable causes.

Additional fins were added along the length of the pipe to maximize the insolated area of

the pipe consequently maximizing the heat transferred to the fluid flowing inside the

pipe.

Counter masses were added on the opposite side of the trough to minimize the load on the

axis of the motor consequently enhancing the rotation of the trough and optimizing power

consumption.

Instead of 4 PV cells 2 cells were used since 2 cells are quite enough to charge the 12-

volts battery and PV cells are relatively expensive. This change didnt affect the

dimensions of the glass chamber. The two PV cells were placed at the bottom of the

chamber (lowest temperature).

1.1.6 The built device

Figures 5 & 6 illustrate all the parts of the device:

Figure 5: The actual design (front)

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The parts as shown in figure 5:

1- The storage tank

2- The inlet of the tank

3- The outlet of the tank

4- The outlet of the pipe and the corresponding thermostat

5- Day-night and solar tracking sensors

6- The aluminum chamber

7-

Photo voltaic cells (PVs)

8-

The inlet of the pipes thermostat

9- The inlet of the pipe

10-The parabolic trough

Figure 6: The actual design (back)

The parts as shown in figure 6:

1- Flexible piping

2-

Tank stand

3- Counter masses

4- Motor

5- Tilt arm

6- Bearings

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1.2 Solar Radiation

Solar radiation has major effects on heat gain of a surface. Different factors contribute to

maximize or minimize these effects; the most effective factors are the location of the sun in the

sky, clearness of the atmosphere, nature of the surface and its orientation. Determining the

position of the sun with respect to the earth during the day and throughout the year is very useful

in predicting the amount of solar radiation on a specific location on the earth.

In designing a solar collector and in making energy studies it is very important to determine the

total solar energy striking a surface and the amount of thermal radiation absorbed.

1.2.1 Thermal Radiation

The thermal radiation energy striking a surface undergoes three actions: absorption,

reflection and transmission.

1- Absorption is the fraction of the total incident radiant energy absorbed by the surface

and transformed into thermal energy. Each surface is characterized by its

absorptance ().

2- Reflection is the fraction of the total incident radiant energy reflected or returned by

the surface. The reflectance () of a given surface affects the amount of reflection.

3- Transmission is the fraction of radiant energy passing through transparent surfaces

without undergoing any change. The amount of transmitted radiation is affected by

transmittance () of medium

+ + = 1

Maintaining this equation will lead to more precision in calculating the energies generated upon

insolating a surface.

Another additional term is used which is emittance (). In fact, some surfaces generates radiant

energy, the amount of this energy is affected by the temperature of the body and the

characteristics of the material. Sometimes this emitted energy is neglected if it is very much less

than the reflected energy for example in mirrors and shiny (reflective) surfaces. [2]

1.2.2 The Earths Motion about the Sun

The suns position in the sky is a major factor in the effect of solar energy on a surface.

The earth moves in a slightly elliptical orbit about the sun. The plane in which the earth

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rotates around the sun (approximately once every 365.25 days) is called the elliptic plane

or orbital plane. The mean distance from the center of the earth to the center of the sun is

approximately 92.9 x 10miles (1.5 x 10km). The perihelion distance, when the earth is

closest to the sun, is 98.3% of the mean distance and occurs on January 4. The aphelion

distance, when the earth is farthest from the sun is 101.7% of the mean distance and

occurs on July 5. Because of this, the earth receives about 7% more total radiation in

January than in July.

As the earth moves it also spins about its own axis at the rate of one revolution every 24

hours. There is an additional motion because of a slow wobble or gyroscopic precession

of the earth. The earths axis of rotation is tilted 23.5 with respect to the orbital plane.

As a result of this dual motion and tilt, the position of the sun in the sky, seen by an

observer on earth, varies with the observers location on the earths surface and with the

time of day and the time of year. For practical purposes the sun is so small seen by an

observer on earth that it may be treated as a point source of radiation.

1.2.3 Calculating Solar Angles

The direction of sun rays is a function of three main quantities:

a- Location on the earth

b-

Time of the dayc- Day of the year

These three quantities are described by the latitude, hour angle and the suns declination

respectively.

The latitude (l) is the angle between the line connecting the center of the earth to a given

point on the earth surface and the lines projection on the equatorial plane. This latitude is

used on globes and maps to describe the location of a point with respect to the equator.

The hour angle (h) is the angle between the line connecting the center of the earth to a given

point on the earth surface and this lines projection on the line that connects the earths center

to the suns center. The hour angle will be zero at local solar noon, have its maximum value

at at sunset, and have its minimum value at sunrise.

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The suns declination () is the angle between the center of the earth and the center of the sun

and the projection of this line on the equatorial plane. The following equation can be used to

determine the declination in degrees: [2]

Where , and n is the day of the year, .

The following MATLAB code generates a graph to show the declination angle throughout

the year.

MATLAB code

************************************************************************

%calculating the declanation angle throughout the year%n is the number of the day 1


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The solar altitude angle () is the angle between the suns ray and the projection of this ray on

the horizontal surface. This angle is obtained by the following equation: [2]

The suns zenith angle (z) is the angle between the suns rays and the normal to the surface at a

given point:

The maximum altitude (max) is at the solar noon where h=0

The following MATLAB code generates the graph of the variation of the maximum solar altitude

angle throughout a typical year in Mechref village in Lebanon where l=33.64.

MATLAB code

************************************************************************%calculating the declanation angle throughout the year%n is the number of the day 1


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Figure 8: Solar latitude variation (beta)

1.3 The Tracker

The whole device is mounted on a vertical axis (z-axis) of 60 cm height fixed to a base in the

horizontal plane (xy-plane). The vertical axis is connected at its top end to a horizontal axis via a

hinge that allows the horizontal axis to rotate in the (xz-plane). The solar trough is mounted at

the end of the horizontal arm via a hinge that allows it to rotate in the plane normal to the

horizontal axis.

1.3.1 First degree of freedom

The horizontal axis is rotated manually. The angle between the vertical axis and the

rotating axis (T1) is a function of maximum solar altitude max

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Figure 9: Angle of Tilting

Throughout a year, max varies between 34 and 80. The daily and monthly variation of

beta angle is 0.1 and 3.8 respectively, since these two values are very small its enough

to adjust angle (T1) once every one month. The following equation determines the error

in case of monthly adjustment

The A=0.5 corresponds to the length of the arm holding the trough in meters and L=1

corresponds to the length of the trough in meters. D is the distance variation in the

direction perpendicular to the arm.

1.3.2 Second degree of freedom

The trough is actively rotated via a rotor. The rotor rotates in the forward direction for an

adjustable duration at day time and stops whenever the trough is exactly perpendicular to

the rays of the sun. The trough resets back to its zero position by night fall. The sensor

function is explained in detail in the sensors section.

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CHAPTER 2

ELECTRICAL SYSTEM

2.1 System Description

The basic role of the electrical system installed in the project is to receive electrical energy from

PV array, control the charging of a lead acid battery, and finally use the stored energy to control

the single axis tracking of the sun through a relatively simple but smart mechanism that is

feasible and less energy consuming than programmed trackers that are instantaneous. It is a

periodic control rather than a perpetual (continuous) one.

To simplify our explanation we can divide our electrical system into seven main categories

which are the following:

1) Charge controller.

2) Regulator.

3) Sensor signal manipulating.

4)

Astable 555 timer.

5) Monostable555 timer.

6) Combinational Logic.

7) H-bridge and DC motor.

2.1.1 Charge controller

The system includes a photovoltaic array composed of 2 (15x15cm) PV cells connected

in series such that the open circuit voltage rounds about 14 volts during sunny days.

Since there is no enough instantaneous power, the need of battery storage is urgent to

collect the small power and store it for later use.

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The energy produced is used to charge the 12 volts, 1.2 Ah, lead-acid battery through the

circuit shown in Figure 8.

Figure 10: MULTISIM simulation of the charge controller circuit.

A Darlington transistor is used to reduce the bias current. A Zener diode is used to maintain a

constant voltage drop between base of Darlington and line potential. In addition, a Blocking

diode is used to prevent the discharge of the battery back into the PV cells in case of power

leakage in the latter due to night or low sun intensity condition.

2.1.2 Regulator

The main role of the regulator (L7805) is to output 5v dc having a 12v dc input from the battery.

Its output voltage being maintained constant is used as Vcc for the control circuitry.

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Figure 11: MULTISIM simulation of the regulator circuit.

2.1.3 Sensor Signal Manipulation

Only two photocells were used as sensors to detect:

Day or night:

The photocell (S1) is used to detect that. Its location could be any open area on the

system.It is mounted on the upper part of the system as shown in figure +++

In or out of desired sun position:

The photocell (S1) is used to detect that. This situation is established by putting the

sensor in a dark thin enclosure which is oriented to a position of the sun as shown in

figure +++; once the sun is in the required position the photocell resistance will drop

causing a signal to be processed to take the right action.

The photocells are simply variable resistances. Their resistance decrease as absorbed light

increases.

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To make use of this characteristic, we use a comparator (LM339) the inputs of which are

connected to two voltage dividers, the first input through a 1K resistor to ground and

through the photocell to Vcc. However, the second through a potentiometer whose

resistance is adjusted to the critical value that is very close to that which remains low

output in a relatively dark position.

The comparator outputs zero if photocell is in dark position (high resistance which mean

low voltage to comparator), once the photocell is in light position (low resistance which

mean high voltage to comparator) the comparator outputs a logic signal 1 to be used

later.

Table 1 shows when the sensor is on state and when it is off state

Sensor On state Off state

S1 Day Night

S2 ~89 Anything else

Table 1: sensor behavior

The angle is taken between incident sun ray and the horizontal with reference axis

horizontal to the east.

Dark positions: - For S1 night.

- For S2 out of desired position.

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Figure 12: MULTISIM simulation of the comparator circuit (dark sensation).

Light positions: - For S1 day.

- For S2 in the desired position.

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Figure 13: MULTISIM simulation of the comparator circuit (light sensation).

It is noticed that the logic 0 is established by figure 10 as 0.7v and logic 1 is

established by figure 11 as 2.9v. This shift from 0 and 5v respectively can be solved by a

driver that is used to turn 0.7v to zero and 2.9v to5v.

2.1.4 Astable 555 timer

This timer is used as a repetitive pulse generator with relatively high duty cycle that will

play the role of triggering the monostable timer once every 6.26 minutes to correct the

position of the system to the desired position.

This timer is designed to function only during day time since its Vcc pin is driven by the

output of the sensor S1 signal manipulating which is only high during daytime.

The timers reset pin is usually kept high.

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Choosing R1, R2, and C2:

R1 = R11 + R12 = 270k + 270k = 540k

R2 = 1k; C2 = 1000F

Ton= 0.693(R1+R2) C2 = 374.913 s 6.25 min.

Toff= 0.693(R2) C2 = 0.693 s 0.01 min. (triggering time)

Ts=Ton+ Toff 6.26min.

Circuit diagram

Figure 14: MULTISIM simulation of the astable circuit.

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Figure 15: Astable waveform as it appeared on the scope (not in real dimensions).

2.1.5 Monostable 555 timer

This timer is used to control the switching of two transistors in the H-bridge in response

to the repetitive triggering done by the astable timer. (More time than needed since reset

exists).

Once the timer is triggered, It produces an output being the input of the H-bridge for

forward motion.

The timers reset pin is usually kept high through a 10K pull up resistor but forced low

when desired position attained by the sensor S2 high output passed through a NOT gate

to be low, and thus terminating forward motion.

Note that this timer is also designed to function only during day time since its Vcc pin is

driven by the output of the sensor S1 signal manipulating which is only high during

daytime.

ChoosingR1 and C2:

R1 = 270k

C2 = 22F

Ton= 1.1(R1. C2) = 6.534 s

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Note that this time is a threshold not reached since in normal operation the timer will be

stopped very early.

Circuit diagram

Figure 16: MULTISIM simulation of the monostable circuit.

Figure 17: Monostable waveform as it appeared on the scope (not in real dimensions).

Key A in the simulated circuit of figure 16 represents a trigger due to Astable low state.

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2.1.6 Combinational logic

Inputs: X1 fromS1 signal manipulating (day = 1 ; night = 0)

X2 from S2signal manipulating (Ok = 1; Ok = 0)

*Ok means system in desired position as S2 reads.

*! Ok means system not in desired position as S2 reads.

Outputs: Y1 used for forward motor drive.

Y2 used for backward motor drive.

During daytime: we need to correct the position of the system through forward motor

drive every 6.26 minutes and stop (reset) the forward motion when it reaches the desired

position.

During nighttime: we need to drive the motor back to the morning position just when the

night is there and stop the system till the day is there again.

Truth table

X1 X2 Y1 Y2

0 0 0 1

0 1 0 1

1 0 0 0

1 1 1 0

Table 2: truth table

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Logic circuit

Figure 18: combinational logic circuit.

2.1.7 H-bridge and DC motor

Since the motor is to be controlled in the forward and reverse directions the use of the H-

bridge (L298) is essential.

The circuit clarifies the main idea of operation despite the unnecessary details of pin

connections according to datasheets.

During the day the bridge drives the motor every 6.26 minutes to correct the position of

the trough to the right one as recorded by S2.

Once the night arrives, the bridge drives the motor backward to the morning position and

stops when reaching a switch that disconnects the bias of the backward motion.

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Figure 19: MULTISIM simulation of the H-bridge circuit.

A mechanical switch is installed at the line used to control backward motor drive at the

morning system position in order to prevent uncontrollable motion; the switch is on

unless the system reaches the first morning position where its backward movement is

prohibited to prevent system instability or damage.

Another mechanical switch is on the final position allowable for safety considerations.

The motor is accompanied with a braking system to avoid freewheeling.

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2.2 Summary of electrical system

In conclusion the electrical system can be summarized as follows:

Figure 20: block diagram of electrical system.

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CHAPTER 3

TESTING AND NUMERICAL ANALYSIS

3.1 Data Logging

Temperature was read from 4 points in the device: at the pipes inlet (Ti) and outlet (Te), in the

tank (Ttank) and temperature of the aluminum fins under the PVs.

3.1.1 Test 1

Testing Date: April 26, 2010

During this test the device was allowed to rotate and track the sun while about 12 liters of

water were stored in the tank. The vent combining the air chamber with the glasschamber was completely closed. Figure 21 shows the temperature at the inlet of the pipe

(Ti) and the outlet (Te) as they vary with time.

Figure 21: Temperature at the inlet and outlet of the pipe (C) v/s time

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The temperature in the tank was as follows

Time Temperature (C)

11:00 am 15

11:30 am 17

12:00 pm 20

12:30 pm 30

1:00 pm 51

1:30 pm 60

2:00 pm 79

2:30 pm 94

3:00 pm 90

3:30 pm 84

4:00 pm 80

4:30 pm 76

5:00 pm 72

Table 3: Temperature in the tank

The temperature of air under the fins varied between 29 and 40 degrees uniformly.

3.1.2 Test 2

Testing Date: April 27, 2010

During this test the device was allowed to rotate and track the sun while about 12 liters of

water were stored in the tank. The vent combining the air chamber with the glass

chamber was completely opened.

Temperatures in the pipe and the tank was very much similar (almost identical) to

temperatures obtained in Test 1 but the temperature of air under the fins varied between

25 and 30 degrees uniformly.

During the two tests the plume of water was very visible at the inlet of the tank (outlet of

the pipe). Figure 20 (b) shows a thermo-graph of the water plume.

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(a)

(b)

Figure 22: The Water Plume (a) normal (b) thermo-graphically-enhanced.

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3.1.3 Numerical analysis

In order to evaluate the device efficiency and the amount of heat absorbed by water the

following computations and analysis were done.

The Following MATLAB code have two inputs temperature at the pipes inlet (Ti) and

temperature at the pipes outlet (Te) and computes the following outputs [1]

- Mass flow rate of water

-

Volume flow rate of water

-

Face velocity of water

- Heat absorbed by water

- Area concentration ratio

-

Heat concentration ratio

- Amount of radiation supplied

************************************************************************

D=0.02; %inner diametere of the pipe(m)

L=1; %length of the pipe(m)Ti=20; %temperature at inlet(C)

Te=40; %temperature at exit(C)

Tb=(Ti+Te)/2; %bulk mean temperatue(C)

r1=D/2; %inner radius pipe(m)r2=r1+(2*10^-3); %outer radius of the pipe(m)

k1=401; %conductivity of copper(w/m.C)

Aso=2*pi*r2*L; %surface outer area of the pipe(m^2)Af=2*0.03*1; %Area of fins(m^2)

%---------------------------------------------------------------------------------------------------------

%water properties%reference

%http://www.thermexcel.com/english/tables/eau_atm.htm

%Heat Transfer - A Practical Approach - Yunus A. Cengelif Tb>0 & Tb10 & Tb


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u=0.00114; %dynamic viscosity(kg/m.s)

elseif Tb>20 & Tb30 & Tb40 & Tb50 & Tb60 & Tb70 & Tb80 & Tb90 & Tb


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%---------------------------------------------------------------------------------------------------------

Ac=(1/4)*pi*(D^2); %cross sectional area (m^2)

As=pi*D*L; %surface area (m^2)%---------------------------------------------------------------------------------------------------------

Lc=As/(2*pi*r2); %characteristics lenght

solarbeta=80; %beta angle(review solar radiation section)gx=9.8; %gravity in the X-axis

g=gx*(cosd(solarbeta)); %gravity in the direction of the flow in the pipe

beta=2/(Ti+Te);Gr=(g*beta*(Te-Ti)*(Lc^3))/(v^2); %garshof number

Ra=Gr*Pr; %Rayleigh number

m=(gx*beta*D^3*(Te-Ti))/(12*u); %mass flow rate (kg/s)

Q=m*(Cp*(Te-Ti)); %heat gain by waterV=m/d; %volume flow rate of water (m^3/s)

Vm=V/Ac; %mean velocity (m/s)

qs=Q/As; %surface heat flux(w/m^2)

%---------------------------------------------------------------------------------------------------------Ainso=0.8524; %insolated Area of the trough(m^2)

alfae=0.2; %Emissivity of the mirroralfapipe=0.8; %emmissivity of the black painted pipe

%---------------------------------------------------------------------------------------------------------

qreflected=Q/alfapipe; %

Qreflected=qreflected/((Aso/2)+Af); %heat Delivered to the outer surface of the pipe andfins(w/m^2)

qincident=qreflected/(1-alfae);

Qincident=qincident/Ainso;CR=qs/Qincident; %heat Concentration ratio

%---------------------------------------------------------------------------------------------------------

cr=Ainso/(As+Af); %Area concentration ratio************************************************************************

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Tables 4 and 5 show the temperatures read from the thermostats and the corresponding

computed results [1]

() ()

(/)

(/)

(/)

1100 110 20 0.00 .0 0.01

110 1200 12 2 0.00 .10 0.011

1200 120 2 0.00 .0 0.0111

120 100 0.001 .120 0.00

100 10 0 0.002 .20 0.01

10 200 0.00 .0 0.01

200 20 10 120 0.002 2.0 0.00

20 00 110 12 0.0022 2.20 0.00

00 0 11 0.00 .10 0.011

0 00 0 110 0.00 .0 0.01

00 0 100 0.00 .00 0.01

0 00 0 0 0.00 .10 0.01

Table 4: Results

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() ()

()

()

1100 110 20 200.21 . 1.2 12.

110 1200 12 2 1.1 . 1.2 2.20

1200 120 2 202.11 . 1.2 1.

120 100 1.00 . 1.2 22.1

100 10 0 2. . 1.2 .102

10 200 .01 . 1.2 0.0

200 20 10 120 1.2 . 1.201 2.10

20 00 110 12 120.1 . 1.201 1.1

00 0 11 2.00 . 1.2 .0

0 00 0 110 . . 1.2 2.22

00 0 100 0.12 . 1.2 0.

0 00 0 0 0.0 . 1.2 .20

Table 5: Results

3.1.4 Results discussion

The duration of the test was about 6 hours, during this duration data was collected

discretely as shown in tables 4 and 5. Heat absorbed by water varied between 120 W and

409 W, with an average value Qavg :

The average amount of radiation Qrad(avg)

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The face velocity of water was about 0.011 m/s (1.1 cm/s) which is very reasonable since

the plume of water was clear as seen by the naked eye to have the same speed.

The maximum temperature reached in the storage tank was 94 C this temperature is

supposed to be higher since its proportional to the amount of radiation, and the radiation

did not reach its yearly maximum value during the test. The maximum reported amount

of radiation by NASA during year 2010 is 800 W. [3]

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APPENDIX

Dr. M. Taha, Dr. R. Nuwayhid, Mr. Maher Bou Dargham and Mr. Adham Al Hassanieh

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REFERENCES

[1]Yunus A. Cengel, Heat Transfer: A Practical Approach,2nd ed. Publisher McGraw Hill

Professional, 2003. Print.

[2]Faye C. McQuiston, Jerald D. Parker, and Jeffrey D. Spitler, Heating, Ventilating and Air

Conditioning Analysis and Design, 2004. Print.

[3] NASA, www.nasa.gov. 2010.

[4]Adel S. Sedra and Kenneth C. Smith, Microelectronic a.gov Circuits, 5th edition, 2007. Print.

[5] All datasheets, www.alldatasheets.com. 2010.

Documents

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