Chapter 6 Outdoor Experimental Characterisation of an ...home.eps.hw.ac.uk/~tm74/thesis/chap6.pdf06:30 08:00 09:30 11:00 12:30 14:00 15:30 17:00 18:30 20:00 21:30 Time (hour) Open

PhD Thesis: Tapas Kumar Mallick

184

Chapter 6

Outdoor Experimental Characterisation of an Asymmetric Compound Parabolic Photovoltaic Concentrator


185

6.1 Introduction

An asymmetric parabolic photovoltaic concentrator system was designed and constructed suitable for

indoor and outdoor experimental characterisation. The predicted optical performance is detailed in chapter

3 and a thermofluid analysis undertaken and presented in chapter 4. The optical analysis shows that the air

filled ACPPVC-50 accepts solar radiation incident over a wide angular range with an optical efficiency of

up to 85.15% and collection efficiency of 100%. The isotherms throughout the system; at the aperture,

reflector, solar cell and the aluminium back plate and the air flow were predicted for different solar

radiation intensities. Indoor experimental characterisation was performed using a solar simulator and

measured performance presented in chapter 5. Based on the measured performance in the indoor

experimental characterisation, the reflector support was modified as described in chapter 3 for the outdoor

experimental characterisation. This chapter details the experimental characterisation of two ACPPVC-50

systems. The electrical and thermal measurements for a number of ‘PV’ strings connected in series of the

first ACPPVC-50 system, PV panel with concentrator and without concentrator of the first ACPPVC-50,

and both PV panels with and without concentrators at real time are presented.

6.2 The ACPPVC-50 Systems Developed for Outdoor Experimental

Characterisation

The design and construction procedures for the two systems used for outdoor experimental

characterisation were detailed in chapter 3. Both APPVC-50 systems are shown in figure 6.2.1. Although

the geometrical and physical characteristics of both systems were intended to be the same, during system

construction one of the solar cells short circuited with the rear aluminium plate and was replaced as shown

in figure 6.2.1(a). The replaced solar cell did not affect the electrical output when it was tested under

normal conditions i.e. the short circuit current and open circuit voltage were the same as for the other

strings in the system.

Figure 6.2.1 Fabricated ACPPVC-50 systems for outdoor experimental characterisation: (a) System 1 clearly indicating the location of the replaced solar cell (b) System 2.

(a) System 1 (b) System 2


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6.3 Experimental Set-up for Outdoor Experimental Characterisation

Measurements of current and voltage under forward bias condition for photovoltaic cells were taken

incorporating the loading circuit as detailed in chapter 5. For the outdoor experimental characterisation of

the ACPPVC-50 systems the data acquisition system KI2700 was replaced by a high speed data

acquisition system KI2750 (maximum speed of 2500 rds s-1) and the source meter KI2400 was replaced

by KI2430. All remaining instrumentation was as before. The accuracy and specification of KI2750 and

KI2430 are detailed in Appendix B. The circuit diagram for all measurements is shown in figure 6.3.1.

Figure 6.3.2 details the electrical connections of the source meter and data acquisition system

used for measuring the current and voltage developed by the PV panels when under illumination i.e.

forward bias conditions. A switching relay card is required when two or more PV systems are tested at the

same time, the solar radiation, temperature and wind velocity sensors were connected directly to the data

acquisition card. An internal cold junction compensated data acquisition card (Anon, 2001m) was used for

all temperature measurements in this experiment. The solar radiation sensor was connected to a voltage

channel which was set with the correct calibration factor used for the instrument. The thermocouple

locations at which the solar cell temperature and reflector substrate temperature were measured are shown

in figure 6.3.3. Figure 6.3.4 and figure 6.3.5 illustrates the thermocouple locations used to measure the

temperature of the aluminium back plate for both systems.


187

Figure 6.3.1 Block diagram of equipment for testing of PV systems.

Figure 6.3.2 Electrical circuit connections used for measuring current and voltage generated by the photovoltaic systems through a 40-channel switching card.


188

Figure 6.3.3 Thermocouple connections at the reflector back plate and at either side of solar cell edge to measure reflector and solar cell temperature respectively.

Figure 6.3.4 Thermocouple locations at which the aluminium back plate temperature was measured for System 1.


189

6.4 Experimental Measurements and Data Analysis for the Two Fabricated

ACPPVC-50 Systems

The experiments were performed at the Centre for Sustainable Technologies (CST), at the University of

Ulster, Jordanstown, NI, UK, at 56ºN and 5º6' W. The systems were mounted at 18º, 30º and 0º inclination

angles to the vertical as illustrated in figure 6.4.1 to 6.4.3.

Figure 6.3.5 Thermocouple locations at which the rear aluminium back plate temperature was measured for System 2.

Figure 6.4.2 A non-concentrating and an ACPPVC-50 mounted at an inclination angle of 30º to the vertical.

Figure 6.4.1 System 1 mounted at an angle 18º from the vertical.


190

6.4.1 Electrical and Thermal Performance Analysis of System 1

The electrical output, solar radiation and temperatures from System 1 were monitored for a period of over

24 days. When measuring a single system, the data acquisition terminal was connected directly to the

device output. Programmes were written in “Test Point” (Anon, 2001j) to control the monitoring and

storage of all electrical and thermal measurements. Electrical parameters measured were the output

current from the PV panel, the output voltage, the short circuit current and the open circuit voltage. The

ambient temperature, the cover glass temperature and the aluminium back plate temperature were

measured. A “Linear Sweep” mode was used to obtain each set of I-V curves. Each sweep took 10

seconds to measure current, voltage, solar radiation, temperature and wind speed. A delay of 30 seconds

was implemented between successive sweeps to reset and cool the source meter (Anon, 2001n). The

system was mounted at an angle of 18º to the vertical. The variation of solar radiation, ambient

temperature, aperture cover temperature and average aluminium back plate temperature are shown in

figure 6.4.1.1 for the 21st August 2002. A time delay can be seen between the peak temperature and the

peak solar radiation on that day. This is due to the thermal inertia of the aperture cover and aluminium

back plate.

The I-V curves measured at different times of the day (differing solar incidence angle and

intensity) are shown in figure 6.4.1.2 (a) and figure 6.4.1.2 (b) shows the change of short circuit current

due to change of the solar incidence angle. On this day a period prolonged sunshine prior to and after solar

noon leads to a low value of the short circuit current. This is due to the shading created by the wooden

frame as shown in figures 6.4.1.3 and 6.4.1.4. Figure 6.4.1.5 illustrates the variation in power generated

by the PV panel with the voltage developed by it. The maximum power point shifts towards the left as

shown by the voltage-power curve at 13:00 and 14:00 although for the latter curve the solar radiation was

100 Wm-2 higher compared to the first one.

Figure 6.4.3 A non-concentrating and an ACPPVC-50 mounted vertically.


191

0

10

20

30

40

50

60

06:30 08:30 10:30 12:30 14:30 16:30 18:30 20:30 22:30

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar ra

diat

ion

(Wm

-2)

Ambient temp Aperture cover temp Back plate temp Solar radiation

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 2 4 6 8 10 12 14 16 18 20 22Voltage (V)

Cur

rent

(A

)

8, 45 9, 180 10, 365 11, 552 12, 306 13, 623

14, 722 15, 655 16, 706 17, 430 18, 242

Time (hour), Solar radiation (Wm -2)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

18.6 31.9 44.5 55 62.5 60.7 53.2 42 29.4 15.9

Solar incidence angle (°)Time

Sho

rt ci

rcui

t cur

rent

(A

mp)

(17:00)(16:00)(15:00)(14:00)(13:00)(12:00)(11:00)(10:00)(9:00)(8:00)

Figure 6.4.1.1 Measured solar radiation and temperatures for the ACPPVC-50 on the 21st August 2002.

Figure 6.4.1.2 (a) I-V curves at different times for different incident solar radiation intensities, (b) variation of short circuit current with solar incidence angle and time.

(a)

(b)


192

0

5

10

15

20

25

30

0 2 4 6 8 10 12 14 16 18 20 22

Voltage (V)

Pow

er (

W)

9, 180 10, 365 11, 552 12, 306 13, 623

14, 722 15, 655 16, 706 17, 430 18, 242

Time (hour), Solar radiation (Wm -2)

0

5

10

15

20

25

06:30 08:00 09:30 11:00 12:30 14:00 15:30 17:00 18:30 20:00 21:30

Time (hour)

Ope

n ci

rcui

t vol

tage

(V

)

0

0.5

1

1.5

2

2.5

Sho

rt c

ircui

t cur

rent

(A

)

open circuit voltage short circuit current

Figure 6.4.1.4 Shadow created on the left-end solar cell by the wooden frame at 14:55:39 on 21st August 2002.

Figure 6.4.1.5 Instantaneous power output with voltage developed by System 1 at different times for different incident solar radiation intensities.

Figure 6.4.1.6 Change in open circuit voltage and short circuit current with time for System 1.

Figure 6.4.1.3 Shadow created on the right-end solar cell by the wooden frame at 11:54:32 on 21st August 2002.


193

The variation in short circuit current and open circuit voltage with time is shown in figure 6.4.1.6. The

open circuit voltage increases exponentially with incident solar radiation intensity until it achieves its

maximum value. For a wide range of solar radiation intensities (between 11:00 to 17:00) the open circuit

voltage remained nearly constant. The open circuit voltage decreased around mid day, due to the increase

in PV temperature. The open circuit voltage decreased after 20:00 since solar radiation decreased

significantly. This sudden drop in the open circuit voltage is caused by a shadow cast by the wooden

frame on the left solar cell string as illustrated in figures 6.4.1.4 and 6.4.1.7.

2

3

4

5

6

7

8

5 105 205 305 405 505 605 705 805 905

Solar radiation (Wm -2)

Effi

cien

cy (

%)

0

5

10

15

20

25

30

35M

axim

um p

ower

(W

)Efficiency Maximum power

The efficiency and maximum power generated by the system with incident solar radiation intensity are

shown in figure 6.4.1.8. It can be observed from figure 6.4.1.8. that despite intervals of cloud at low levels

Figure 6.4.1.8 Maximum power output and efficiency of System 1 with incident solar radiation intensity.

Time 10:00 Time 12:00 Time 13:00

Time 15:00 Time 16:00 Time 17:00

Figure 6.4.1.7 Shadow cast by the wooden frame onto the solar cells at different times of the day.


194

of incident solar radiations up to 500 Wm-2, the maximum power output and efficiency were low. This

was because of shadows cast on the PV at either side of the system by the wooden frame. A maximum

efficiency of 7.8% was achieved at 800 Wm-2 solar incident radiation when the maximum power

generated by the system was 26 W.

0

10

20

30

40

50

60

06:30 08:30 10:30 12:30 14:30 16:30 18:30 20:30 22:30

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

ambient glass1 glass2 t5 t6

t7 t8 t9 t10 t11

t12 t13 t14 t15 t16

t17 t18 t19 solar radiation

25

26

26

2728

28

29

29

29

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55 Solar radiation intensity = 470 Wm-2

32

3 3

32

3435

36

36

37

36

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5


42

42

48 47

44

48

48 45

48

46

47

48

47

47

48

48

48

48

48

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

474644434139383635333230282725

Solar radiation intensity = 770 Wm-2 ToC

39

38

43 42

40

43

41 39

43

41

42

43

41

42

43

42

42

43

43

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5


The temperature distribution at the aluminium back plate is shown in figure 6.4.1.9. The highest back

plate temperature of 50ºC was at thermocouple position ‘t12’ near to the centre of the back plate (see

figure 6.3.4). The maximum temperatures recorded by the thermocouples positioned at the top and bottom

of the cover glass were 38ºC and 30ºC respectively. The average ambient temperature was 20ºC. Figure

Figure 6.4.1.9 Diurnal variation of cover glass, aluminium back plate temperature and solar radiation.

Figure 6.4.1.10 Measured temperature contours at the aluminium back plate at time (a) 10:30 (b) 12:30 (c) 14:30 (d) 16:30 on the 21st of August 2002.

(a) (b)

(d) (c)


195

6.4.1.10 shows the measured temperature contours of the aluminium back plate at different times and with

different solar radiation intensities. The peak temperature shifts from left to right as seen from figure

6.4.1.10(a) and figure 6.4.1.10(d). This is due to the following reasons:

• Shading effect as illustrated in figure 6.4.1.7.

• Effective heat loss from the edge reduced due to the second system mounted close to the first

system as shown in figure 6.4.3.

The variation in the rear aluminium back plate temperature at thermocouple positions ‘t5’ and ‘t17’ are

shown in figure 6.4.1.11.

0

5

10

15

20

25

30

35

40

45

50

06:30 08:30 10:30 12:30 14:30 16:30 18:30 20:30 22:30

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

t5

t17

Solar radiation

0

10

20

30

40

50

60

06:30 08:30 10:30 12:30 14:30 16:30 18:30 20:30 22:30

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

t12 t15 solar radiation

Figure 6.4.1.11 Diurnal variation of solar radiation and back plate temperature at thermocouple positions ‘t5’ and ‘t17’.

Figure 6.4.1.12 Diurnal variation of solar radiation and aluminium back plate temperature at thermocouple positions 12 and 15 as shown in figure 6.3.4.


196

The temperature in the central region of the aluminium back plate becomes nearly uniform as shown in

figure 6.4.1.12 at thermocouple positions ‘t12’ and ‘t15’. A temperature difference of 3ºC can be seen in

the central vertical direction of the aluminium back plate at thermocouple positions of ‘t11’, ‘t12’ and

‘t13’ as shown in figure 6.4.1.13. Figure 6.4.1.14 illustrates the variation of back plate temperatures along

the central line in the horizontal direction. At lower intensities of solar radiation i.e. in the morning and

the evening all temperatures are similar. The measured temperature contours at the aluminium back plate

in figure 6.4.1.15 shows that each side of the back plate does not exhibit the same edge heat loss. A peak

temperature difference of 7ºC can be seen between the top and bottom of the aperture cover glass as

shown in figure 6.4.1.16. The average rear aluminium plate temperature was 48ºC, 25ºC above the

ambient temperature as shown in figure 6.4.1.17.

0

10

20

30

40

50

60

06:30 08:30 10:30 12:30 14:30 16:30 18:30 20:30 22:30

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

t11 t13 t12 solar radiation

0

10

20

30

40

50

60

06:30 08:30 10:30 12:30 14:30 16:30 18:30 20:30 22:30Time (hour)

Tem

pera

ture

(o C

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

t6 t9 t12 t15 t18 solar radiation

Figure 6.4.1.13 Diurnal variation of solar radiation and the aluminium back plate temperature at thermocouple locations t11, t12 and t13 as shown in figure 6.3.4.

Figure 6.4.1.14 Diurnal variation of solar radiation and temperature of the aluminium back plate at thermocouple locations t6, t9, t12, t15 and t18 as shown in figure 6.3.4.


197

41.7

41.7

49.8

49.8

44.5

50.4

48.2 44.8

49.8

45.7

46.7

50.1

47.6

47.3

49.2

48.8

47.9

48.2

48.2

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

50.149.548.848.247.647.046.445.745.144.543.943.342.642.041.4

Solar radiation intensity = 770 Wm-2 ToC

0

5

10

15

20

25

30

35

40

45

06:30 08:30 10:30 12:30 14:30 16:30 18:30 20:30 22:30

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)Aperture cover top

Aperture cover bottom

Solar radiation

0

5

10

15

20

25

30

35

40

45

50

Tem

pera

ture

(oC

)

08:00 09:01 10:00 11:00 11:59 13:01 13:59 15:00 16:00 17:00 18:01

Time (hour)

ambient average back plate temperature

Figure 6.4.1.16 Diurnal variation of solar radiation, top and bottom aperture cover glass temperature for System 1.

Figure 6.4.1.17 Variation of average back plate temperature and ambient temperature with time for System 1. All eight PV strings were connected in series.

Figure 6.4.1.15 Measured temperature contours of the aluminium back plate at time 14:50 on the 21st of August 2002.


198

6.4.2 Electrical and Thermal Performance Analysis of System 1 with Seven PV Strings

Connected in Series

The outdoor experimental characterisation was undertaken for nine days with seven PV strings connected

in series. For this period not a single day was continuously clear and sunny. The PV string containing the

replacement PV cell was disconnected for these measurements. The variation of incident solar radiation

with time is shown in figure 6.4.2.1. The methodology of measurement remained unchanged from

previous experiments.

0

100

200

300

400

500

600

700

800

900

1000

1100

07:31 12:42 17:55 08:28 13:16 18:05 10:31 15:32 11:35 16:47 09:04 14:14 19:25Time (hour)

Sol

ar r

adia

tion

(Wm

-2)

11th August9th August 10th August 12th August 13th August

0

100

200

300

400

500

600

700

800

900

1000

1100

07:59 13:07 18:17 08:14 12:42 17:02 09:53 14:17 10:24 13:18 16:10 19:04Time (hour)

Sol

ar r

adia

tion

(Wm

-2)

15th August 16th August 19th August 20th August

Figure 6.4.2.1 The change of solar radiation with time for nine days (a) 9th to 13th August (b) 15th to 20th August. The solar radiation was measured at 55 second intervals.

(b)

(a)


199

Variations in the maximum power generated by the system with incident solar radiation for these

experiments with seven PV strings connected in series are illustrated in figure 6.4.2.2. The maximum

power generated by this system was 20 Watts when the intensity of incident solar radiation was 800

Wm-2. Due to the shading on either side of the system, the maximum power point dropped by up to 1/3rd

of its peak value. At higher intensities of solar radiation, close to either side of solar noon, the maximum

power obtained from the system reached a corresponding maximum value. The solar radiation intensity

was measured on the plane of the experimental apparatus. The corresponding hourly variation of

maximum power generated by System 1 is shown in figure 6.4.2.3.

0

5

10

15

20

25

30

35

0 100 200 300 400 500 600 700 800 900 1000 1100


Max

imum

pow

er (

W)

9th august 10th august 11th august 12th august 13th august 15th august 16th august 19th august 20th august

0

2

4

6

8

10

12

14

16

18

20

22

8 to9.

12to13

16to17

11to12

15to16

19to20

11to12

15to16

19to20

10to11

14to15

18to19

10to11

14to15

18to19

9 to10

13to14

17to18

8 to9.

12to13

16to17

11to12

15to16

8 to9.

12to13

16to17

Hour of the day

Max

imum

pow

er (

W)

9th august 10th august 11th august 12th august 13th august 15th august 16th august 19th august 20th august

Figure 6.4.2.2 Variation of maximum power generated by System 1 with incident solar radiation intensity.

Figure 6.4.2.3 Hourly variation of maximum power of System 1 for nine days in August 2002.


200

6.4.3 Electrical and Thermal Performance Analysis of System 1 with Six PV

Strings Connected in Series

Measurements were conducted for ten days with six PV strings connected in series, both left and right side

PV strings were electrically disconnected from the others. The variation of solar radiation, ambient

temperature, glass cover temperature and average rear aluminium back plate temperature with time are

shown in figure 6.4.3.1. The highest solar radiation observed was 900 Wm-2 apart from a few sharp peaks

that occurred before noon due to cloud. The peak cover glass temperature and average back plate

temperatures did not respond at the same rate and time due to the thermal inertia of the metal plate and

cover glass.

0

10

20

30

40

50

60

09:00 10:12 11:24 12:36 13:48 15:00 16:12 17:24 18:36 19:48 21:00

Time (hour)

Tem

pera

ture

(oC

)

0

200

400

600

800

1000

1200

Sol

ar r

adia

tion

(Wm

-2)

ambient temperature

glass cover temperature

back plate temperaturesolar radiation

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

0 2 4 6 8 10 12 14 16

Voltage (V)

Cur

rent

(A

)

413 500 600 702 750 800 850 900 920

Solar radiation (Wm-2)

Figure 6.4.3.1 Variation of solar radiation, ambient temperature, cover glass temperature and aluminium back plate temperature with time for System 1 with six PV strings connected in series.

Figure 6.4.3.2 The I-V curves for different incident solar radiation intensities for System 1 with six PV strings were connected in series.


201

The I-V curves for different incident solar radiation intensities are shown in figure 6.4.3.2 and the

corresponding voltage vs. power curves are shown in figure 6.4.3.3. At greater solar radiation intensities

the maximum power point shifts towards the lower voltage due to increased PV cell operating

temperature.

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Voltage (V)

Pow

er (

W)

413 500 600 702 750 800 850 900 920Solar radiation (Wm-2)

y = 0.0264x - 0.6176

0

5

10

15

20

25

30

0 100 200 300 400 500 600 700 800 900


Max

imum

pow

er (

W)

0

1

2

3

4

5

6

7

8

Effi

cien

cy (

%)

Maximum power efficiency Maximum power

The variation of efficiency and maximum power generated by System 1 with incident solar radiation is

presented in figure 6.4.3.4. The maximum power varies linearly with incident solar radiation as expected

from consideration of the PV electrical characteristics, however at lower solar radiation intensities the

efficiency increased with incident solar radiation exponentially until it reached its highest value. The fill

factor for the system with six PV strings connected in series for different incident solar radiation

Figure 6.4.3.3 Output voltage vs. power generated for System 1 with six PV strings connected in series.

Figure 6.4.3.4 Variation of efficiency and maximum power generated with incident solar radiation by System 1 when six PV strings were connected in series.


202

intensities is illustrated in figure 6.4.3.5. The highest fill factor of 62% was achieved for a large range of

solar radiation intensities. A low fill factor implies significant electrical power losses from the system.

The variation of temperature with time for the cover glass, ambient and the aluminium back plate at

different thermocouple locations are illustrated in figure 6.4.3.6. The highest temperature was measured

by the thermocouple at location ‘t12’ in the middle of the aluminium back plate. Heat is transferred from

the back plate to the cool air flowing over it, reducing its temperature significantly. Figure 6.4.3.7

indicates that the central region of the back plate achieved the highest temperature measured compared to

the sides of the back plate, due to unequal edge heat loss from the metal back plate.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 100 200 300 400 500 600 700 800 900 1000


Fill

fact

or

10

15

20

25

30

35

40

45

50

55

60

09:00 11:00 13:00 15:00 17:00 19:00 21:00

Time (hour)

Tem

pera

ture

(oC

)

0

150

300

450

600

750

900

1050

Sol

ar r

adia

tion

(Wm

-2)

Ambient Glass cover 1 Cover glass 2 t5t6 t7 t8 t9t10 t11 t12 t13t14 t15 t16 t17t18 t19 Solar radiation

Figure 6.4.3.5 Variation in fill factor with incident solar radiation for System 1 with six PV strings connected in series.

Figure 6.4.3.6 Variation in temperatures and incident solar radiation with time for System 1 with six PV strings connected in series.


203

34.7

36.8

36.8

38.8

38.8

38.8

40.9

40.9

40.9

40.9

40.9

43.0

43.0

43.043.0

43.0

43.0

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5


43.0

46.1

46.1

49.2

49.2

5 1.2

51.2

52.3

52.3

53.3

53.3

53.3

53.3

53.3

53.3

53.3

53.3

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

535149474543413937353331

Solar radiation intensity = 880 Wm-2

ToC

38.8

38.8

38.8

40.9

40.941.9

40 .9

44.0

43.0

43.0 43.0

43.0

43. 0

45.0

45.0 45 .0

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5


33.7

32.7

32.7

33.7

33.7

33.7

33.7

33.7

34.7

34.7

34.7 34.7

34.7

35.7

35.7

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5


6.4.4 Electrical and Thermal Performance Analysis of System 1 With Six PV Strings

Connected in Series Without Concentrator Present

The reflector system was removed from System 1 to provide base data with which to compare the

electrical output of the concentrator system. All the solar cell connections remained the same. The

experimental investigation was conducted on the 2nd of September 2002 for six PV strings connected in

series. The measurements were taken at 30 second intervals for solar radiation, wind speed, output current

and voltage generated by the PV panel, glass cover temperature, ambient temperature, and aluminium

back plate temperature. The variation of incident solar radiation and wind speed with time are shown in

figure 6.4.4.1. The highest solar radiation recorded was 950 Wm-2 on the plane of the experimental test

system. Lower values of solar radiation after solar noon are the result of cloud cover. The average wind

speed was 1.42 ms-1, which increased the convective heat transfer from the aperture cover glass and the

aluminium back plate decreasing PV operating temperatures.

(a) Time 14:00 (b) Time 15:00

(c) Time 16:00 (d) Time 18:00

Figure 6.4.3.7 Measured temperature contours of the aluminium back plate at time (a) 14:00 (b) 15:00 (c) 16:00 (d) 18:00, on the 30th of August 2002.


204

0

0.5

1

1.5

2

2.5

3

3.5

4

06:30 08:30 10:30 12:30 14:30 16:30 18:30

Time (hour)

Win

d sp

eed

(ms

-1)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

Wind speed Solar radiation

Figure 6.4.4.2 shows the I-V curve for the system with no concentrators with six PV strings connected in

series for different solar radiation intensities. Data from the non-fluctuating part of the solar radiation

curve was used to plot I-V curves. One full measurement procedure for current and voltage data took 5

seconds, for which solar radiation fluctuated less than 1% (which did not effect PV output significantly).

The short circuit current increases linearly with incident solar radiation intensity and the open circuit

voltage remains constant as would be expected from basic solar cell characteristics. The maximum short

circuit current generated by the system was 1.6 A at a solar radiation intensity of 900 Wm-2, for the same

PV system with concentrators the short circuit current was 2.5 A for the same incident solar radiation

intensity of 900 Wm-2 (compare figure 6.4.3.2 and figure 6.4.4.2). The short circuit current increased by

1.56 times with the concentrator compared to the flat non-concentrating PV panel.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Voltage (V)

Cur

rent

(A

)

400 597 700 801 900

Solar radiation (Wm-2)

Figure 6.4.4.1 Variation of solar radiation and wind speed with time on the 2nd of September 2002.

Figure 6.4.4.2 I-V curves at different solar radiation intensities for System 1 with six PV strings connected in series and the concentrator system removed.


205

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

06:30 08:30 10:30 12:30 14:30 16:30 18:30

Time (hour)

Sho

rt c

ircui

t cur

rent

(A

)

0

2

4

6

8

10

12

14

16

18

Ope

n ci

rcui

t vol

tage

(V

)

open circuit voltage

short circuit current

The diurnal variation of short circuit current and open circuit voltage is shown in figure 6.4.4.3. From

10:00 to 17:00 the open circuit voltage was nearly constant. This was because the open circuit voltage did

not change at higher incident solar radiation intensity (the concurrent diurnal variation of insolation is

shown in figure 6.4.4.1) but the short circuit current changed in a linear manner with incident solar

radiation intensity. For a photovoltaic module only the solar cell area which is directly exposed to sunlight

produces electricity. The wooden frame of this system created a shadow on some of the solar cells as

shown in figure 6.4.1.7, decreasing the panel’s power output and thus efficiency. Figure 6.4.4.4 shows the

variation of maximum power generated by the panel and its efficiency with incident solar radiation

intensity until 10:00. The “U” pattern of the efficiency curve can be explained by shading from the

wooden frame. The maximum power point and efficiency however in general varies linearly with the

incident solar radiation as shown in figure 6.4.4.5. The increase in efficiency at lower solar radiation

intensities (<=500 Wm-2) is due to the high voltage developed by the PV panel. The maximum efficiency

achieved is 9.2% for incident solar radiation intensities of 700 Wm-2 to 980 Wm-2. The maximum power

generated by the PV system was 16.8 Watts at an incident solar radiation intensity of 970 Wm-2.

Figure 6.4.4.3 Variation of short circuit current and open circuit voltage with time for System 1 with six PV strings connected in series and concentrator system removed.


206

Variation of maximum power and efficiency untill 10:00

0

1

2

3

4

5

6

0 50 100 150 200 250 300 350 400 450


Effi

cien

cy (

%)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Max

imum

pow

er (

W)

Efficiency Maximum power

0

1

2

3

4

5

6

7

8

9

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11

400 450 500 550 600 650 700 750 800 850 900 950 1000


Effi

cien

cy (

%)

2

4

6

8

10

12

14

16

18

Max

imum

pow

er (

W)

Efficiency Maximum power

Figure 6.4.4.6 illustrates the variation of ambient, cover glass and average back plate temperature with

time. The peak cover glass temperature and the peak average back plate temperature do not occur

simultaneously. A 40 minute delay can be seen for the peak average back plate temperature and the

maximum solar radiation, illustrating the “thermal inertia” of the aluminium back plate. A peak

temperature difference of 21ºC can be seen between the rear aluminium plate and the ambient temperature

whereas the temperature difference between the aperture cover glass and the ambient is only 11ºC. The

temperatures at the aluminium back plate are shown in figure 6.4.4.7, the maximum and minimum

temperatures are shown in figure 6.4.4.8. A 4ºC temperature difference can be seen between the highest

and lowest temperatures of the aluminium back plate at thermocouple positions ‘t8’ and ‘t15’ as shown in

figure 6.3.4.

Figure 6.4.4.4 Variation of efficiency and maximum power output from System 1 with incident solar radiation, when six PV strings were connected in series and the concentrator system removed.

Figure 6.4.4.5 Variation of maximum power and efficiency with solar radiation intensity with six PV strings connected in series for System 1 and the concentrator system removed on the 2nd of September 2002.


207

0

5

10

15

20

25

30

35

40

45

50

06:30 08:30 10:30 12:30 14:30 16:30 18:30

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

ambient

glass cover

rear aluminium platesolar radiation

0

5

10

15

20

25

30

35

40

45

50

06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

t5 t6 t7 t8t9 t10 t11 t12t13 t14 t15 t16t17 t18 t19 solar radiation

Temperature sensor at aluminium back plate at the position of

0

5

10

15

20

25

30

35

40

45

50

06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00Time (hour)

Bac

k pl

ate

tem

pera

ture

(o C

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

t8 t15 solar radiation

Figure 6.4.4.6 Variation of solar radiation, ambient temperature, cover glass temperature and average back plate temperature with time when six PV strings were connected in series and the concentrator system removed.

Figure 6.4.4.8 Diurnal variation of solar radiation, maximum and minimum back plate temperatures for System 1 without concentrators when six PV strings were connected in series. Thermocouples were located at the position of ‘t8’ and ‘t15’ as shown in figure 6.3.4.

Figure 6.4.4.7 Diurnal variation of solar radiation and temperatures on the aluminium back plate for System 1 without concentrators when six PV strings were connected in series.


208

6.4.5 Electrical and Thermal Performance Analysis of System 1 Without Concentrator

For a Single PV String

The electrical and thermal performance of System 1 without concentrators was investigated for a single

PV string with five solar cells connected in series. By measuring the open circuit voltage and short circuit

current the electrical output of the 5th solar string (from the left side as shown in figure 6.3.4) was

measured from 8:00 to 20:00 hour on the 6th of September 2002. The I-V curve and its corresponding

voltage vs. power curve for different solar radiation intensities are shown in figures 6.4.5.1 and 6.4.5.2

respectively. The current increases linearly with incident solar radiation as can be seen from figure

6.4.5.1. The short circuit current remains almost constant at higher levels of solar radiation whereas the

open circuit voltage is approximately one sixth of that for six PV strings connected in series (figures

6.4.5.1 and 6.4.4.2) as can be expected from solar cell characteristics. The maximum power point

becomes approximately 15% lower when compared to six PV strings connected in series (figures 6.4.5.2

and 6.4.4.5). The maximum power point shifts towards the right side, i.e. the voltage corresponding to the

maximum power point increases at higher incident solar radiation intensities.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.5 1 1.5 2 2.5 3Voltage (V)

Cur

rent

(A

)

906 852 800 749 702 649 609 560 495

Incident solar radiation (Wm-2)

Figure 6.4.5.1 I-V curve for a single PV string without a concentrator for different solar radiation intensities. The string was the 5th from the left side as shown in figure 6.3.4.


209

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 2 2.5 3

Voltage (V)

Pow

er (

W)

906 852 800 749 702 649 609 560 495


0

10

20

30

40

50

60

70

80

90

100

400 500 600 700 800 900 1000 1100


Fill

fact

or

Figure 6.4.5.3 shows the variation of fill factor with incident solar radiation intensity for a single PV

string of System 1 without a concentrator. The fill factor varies from 68% to 72% for a single string. The

fill factor is relatively high compared to the PV system when two or more PV strings are connected in

series. This is because of the resistive losses ( )ri 2 that occur between consecutive solar cell

interconnections. Figure 6.4.5.4 shows the variation of open circuit voltage and short circuit current with

incident solar radiation for the single PV string. As expected, the short circuit current is linearly

proportional to the incident solar radiation whereas the open circuit voltage tends to a constant above an

incident solar radiation intensity of 500 Wm-2. Variation of efficiency and maximum power generated by

the single PV string with incident solar radiation intensity are shown in figure 6.4.5.5. The highest

efficiency achieved by this single PV string was 11.5% which is higher when compared to multiple PV

Figure 6.4.5.3 Variation of fill factor with incident solar radiation for System 1 without concentrator. A single PV string was considered for this measurement.

Figure 6.4.5.2 Power curve with voltage developed by a single string of five PV cells.


210

strings connected in series. This is due to the higher ( )ri 2 losses for multiple PV strings connected in

series.

0

0.5

1

1.5

2

2.5

3

3.5

0 200 400 600 800 1000 1200


Ope

n ci

rcui

t vol

tage

(V

)

0

0.5

1

1.5

2

2.5

Sho

rt c

ircui

t cur

rent

(A

)

open circuit voltage

short circuit current

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

400 500 600 700 800 900 1000 1100


Max

imum

pow

er (

W)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Effi

cien

cy (

%)

efficiency

maximum power

6.4.6 Electrical and Thermal Performance Analysis of a Flat Non-Concentrating PV

Panel and an ACPPVC-50 Panel Mounted Vertically for Five PV Strings

Connected in Series

An experimental investigation was undertaken for two systems with different numbers of PV strings

connected in series. The first system was a flat non-concentrating system and the second system was the

concentrator (ACPPVC-50) system. The systems characterised experimentally are shown in figure 6.4.6.1,

Figure 6.4.5.4 Variation of open circuit voltage and short circuit current with incident solar radiation for a single PV string of System 1 without concentrator.

Figure 6.4.5.5 Effect of maximum output power and efficiency with incident solar radiation for a single PV string of System 1 without concentrator.


211

the system on the left side is System 1 (fabricated first), characterised experimentally with and without

concentrators described in the earlier sections of this chapter. This experimental investigation was

conducted on the 20th of September 2002 with the measurements taken for twelve hours from 8:00 to

20:00 with 20 second intervals between consecutive sets of data points.

Figure 6.4.6.2 shows total and diffuse solar radiation measured on the plane of the experimental test

systems. The maximum total radiation was 800 Wm-2 and the diffuse radiation was 240 Wm-2. The

variation of short circuit current and open circuit voltage with time for both flat non-concentrating system

and the ACPPVC-50 are presented in figure 6.4.6.3. The open circuit voltage was 0.4 V higher for the

ACPPVC-50 compared to the flat non-concentrating panel whereas the short circuit current for the

ACPPVC-50 was approaching to the value of its theoretical concentration ratio of 2.0. This is due to the

effective solar radiation at the PV surface for the ACPPVC-50 increased by its concentration ratio 2.0.

The major problem with this experimental characterisation is the shadow cast by the top wooden frame

since the PV systems are orientated vertically and therefore cast a shadow on the solar cells, effectively

decreasing the output power of the system. The shadows created by the wooden frame for the flat non-

concentrating PV system and the ACPPVC-50 system are shown in figure 6.4.6.4.

Figure 6.4.6.1 Flat non-concentrating and asymmetric compound parabolic photovoltaic concentrators under outdoor experimental characterisation at the University of Ulster. Both systems are identical with equal numbers of PV cells connected in series in each systems.


212

0

100

200

300

400

500

600

700

800

900

07:00 09:00 11:00 13:00 15:00 17:00 19:00

Time (hour)

Sol

ar r

adia

tion

(Wm

-2)

total

diffuse

0

2

4

6

8

10

12

14

07:00 09:00 11:00 13:00 15:00 17:00 19:00

Time (hour)

Ope

n ci

rcui

t vol

tage

(V

)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

2.2

Sho

rt c

ircui

t cur

rent

(A

)

Voc ACPPVC-50

Voc flat non-concentrator

Isc ACPPVC-50

Isc flat non-concentrator

Figure 6.4.6.2 The variation of total and diffuse radiation with time on the 20th of September 2002.

Figure 6.4.6.3 Short circuit current and open circuit voltage for the flat non-concentrating and the concentrating ACPPVC-50 with time on the 20th of September 2002.

Figure 6.4.6.4 Shadow cast by the wooden frame on the top most solar cells for (a) the flat non-concentrating system and (b) the ACPPVC-50 at noon on the 20th of September 2002.

(a) (b)


213

0

2

4

6

8

10

12

14

16

18

0 100 200 300 400 500 600 700 800 900


Max

imum

pow

er (

W)

flat non-concentrator ACPPVC-50

due to shading

Figure 6.4.6.5 shows that the variation of maximum power generated by the flat non-concentrating PV

panel and the ACPPVC-50 panel with incident solar radiation intensity. Each maximum power curve has

two distinct lines between solar radiation intensities of 200 to 700 Wm-2, this is due to the shadow from

the supporting frame. Apart from an east-west shadow cast by the wooden frame, a third shadow fell on

the PV solar cells as shown in figure 6.4.6.4 when the PV systems were mounted in the vertical plane. A

portion of the top reflector in the ACPPVC-50 reflects incident solar radiation which becomes more

effective compared to the flat non-concentrating PV panel, as a result a significant difference in the

maximum power curve can be seen at lower incident radiation intensities. The upper line of the power

curve at solar radiation intensities from 200 to 700 Wm-2 refers to the power obtained by the PV panels

when there was no shadow cast on the PV cells. The consequences of this shading effect are lower

efficiencies for the systems as shown in figure 6.4.6.6. The highest achieved efficiency for the flat non-

concentrating PV panel was 8% whereas the efficiency for the ACPPVC-50 was 6.6% at incident solar

radiation intensities from 400 to 500 Wm-2. This is because at higher incident solar radiation intensities

the solar cell temperature increases which decreases the open circuit voltage of the PV panel and thus the

PV panel efficiency. Figure 6.4.6.7 shows the power ratio between the flat and concentrating PV panels.

Although the concentrating PV panel has higher power losses ( )ri 2 resulting from a higher current

compared to the flat panel, the maximum power ratio is 1.8 or more because of the partially shaded solar

cells in the non-concentrating panel as shown in figure 6.4.6.4.

Figure 6.4.6.5 Variation of maximum power output for the flat non-concentrating and the concentrating ACPPVC-50 system with solar radiation intensity.


214

0

1

2

3

4

5

6

7

8

9

10

0 100 200 300 400 500 600 700 800 900


Effi

cien

cy (

%)

Flat ACPPVC-50

due to shading

0

0.5

1

1.5

2

0 100 200 300 400 500 600 700 800 900


Pow

er r

atio

The variation of reflector temperature and solar cell temperature are shown in figures 6.4.6.8 and 6.4.6.9

respectively. The solar cell temperature was measured by attaching a thermocouple at the edge of the solar

cell, whereas the thermocouples were attached inside the reflector trough for reflector substrate

temperature as shown in figure 6.3.3. The peak temperature difference between the reflector back plate

and the solar cell was 3ºC. The maximum reflector back plate temperature was 48ºC, the maximum solar

cell temperature was 46ºC for the concentrating PV panel. The peak temperature difference between the

highest and lowest reflector back plate temperatures was 8ºC at thermocouple positions ‘tr43’ and ‘tr38’,

the peak solar cell temperature difference between the highest and lowest solar cell temperatures was 13ºC

at thermocouple positions ‘ts48’ and ‘ts38’. Due to the temperature gradient along the solar cell, a power

drop occurred which decreased the PV panel efficiency.

Figure 6.4.6.6 Effect of efficiency with incident solar radiation for the flat non-concentrating PV panel and the ACPPVC-50 system with six PV strings connected in series.

Figure 6.4.6.7 Maximum power point ratio of the flat non-concentrating PV panel and the ACPPVC-50 system with incident solar radiation for six PV strings connected in series.


215

0

5

10

15

20

25

30

35

40

45

50

07:00 09:00 11:00 13:00 15:00 17:00 19:00Time (hour)

Ref

lect

or te

mpe

ratu

re (

oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

ambient tr25 tr26 tr27 tr28tr29 tr30 tr38 tr39 tr40tr41 tr42 tr43 solar radiation

0

5

10

15

20

25

30

35

40

45

50

07:00 09:00 11:00 13:00 15:00 17:00 19:00

Time (hour)

Sol

ar c

ell t

empe

ratu

re (

oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

ts31 ts32 ts33 ts34ts35 ts44 ts45 ts46ts47 ts48 solar radiation

The temperatures of the aluminium back plate for both the concentrating ACPPVC-50 and the flat non-

concentrating system with time are shown in figures 6.4.6.10 and 6.4.6.11. Back plate temperatures varied

in a similar way with time for both systems. Thermocouple locations are shown in figures 6.3.4 and 6.3.5.

The highest back plate temperature of 44ºC for the ACPPVC-50 occurred at thermocouple position ‘t62’,

for the flat non-concentrating PV system the highest temperature was 41ºC. As expected for both systems

the maximum temperatures occurred close to the central position. The thermal edge loss and the shading

factor close to the edge solar cells resulted in lower temperatures compared to the central region of the

aluminium back plate.

Figure 6.4.6.8 Diurnal variation of solar radiation and reflector substrate temperature for the ACPPVC-50. The thermocouples were connected inside the reflector troughs as shown in figure 6.3.3.

Figure 6.4.6.9 Diurnal variation of solar radiation and solar cell temperature for the ACPPVC-50. The thermocouples were connected at the edges of the solar cells as shown in figure 6.3.3.


216

0

5

10

15

20

25

30

35

40

45

50

07:00 09:00 11:00 13:00 15:00 17:00 19:00Time (hour)

Tem

pera

ture

(o C

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

t51 t52 t53 t54 t55t56 t57 t59 t60 t61t62 t65 t66 t67 solar radiation

0

5

10

15

20

25

30

35

40

45

07:00 09:00 11:00 13:00 15:00 17:00 19:00Time (hour)

Tem

pera

ture

(o C

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)



Panel and an ACPPVC-50 Concentrating Panel Mounted at 18° to the Vertical

for Four PV Strings Connected in Series

Experimental investigations were undertaken for 18° inclined system to reduce shading on the top row of

solar cells. This avoids power losses which otherwise occur due to the shaded top row of solar cells. Four

PV strings were connected in series for this experiment. The test was conducted on the 23rd of September

Figure 6.4.6.10 Diurnal variation of solar radiation and aluminium back plate temperature for the ACPPVC-50 system. The thermocouples were located as shown in figure 6.3.5.

Figure 6.4.6.11 Diurnal variation of solar radiation and aluminium back plate temperature for the flat non-concentrating PV panel. The thermocouples were located as shown in figure 6.3.4.


217

2002 and the measurements were taken over an eleven and a half hour period. The I-V curves for the flat

non-concentrating and the ACPPVC-50 systems for different incident solar radiation intensities are shown

in figures 6.4.7.1 and 6.4.7.2 respectively. Since only four rows of PV strings were connected for both

systems, there were no shaded solar cells from the supporting frame in the east-west direction. The

flattening of the I-V curve near to the maximum power point can be explained by the extra power drop

across the relay card and the resistive losses in each component because the current to voltage ratio.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 1 2 3 4 5 6 7 8 9 10 11

Voltage (volt)

Cur

rent

(am

p)

399 451 501 550 602 651 703 751802 852 901


0

0.4

0.8

1.2

1.6

2

2.4

2.8

0 1 2 3 4 5 6 7 8 9 10 11

Voltage (V)

Cur

rent

(A

)

399 451 501 550 602 651 703 751802 852 901


Figure 6.4.7.1 I-V curves for different intensities of solar radiation for the flat non-concentrating system with four PV strings connected in series.

Figure 6.4.7.2 I-V curves for different intensities of solar radiation for the ACPPVC-50 system with four PV strings connected in series.


218

0

200

400

600

800

1000

1200

07:30 09:30 11:30 13:30 15:30 17:30 19:30

Time (hour)

Sol

ar r

adia

tion

(Wm

-2)

0

5

10

15

20

25

Am

bien

t tem

pera

ture

(oC

)

total radiation

diffuse radiation

ambient temperature

0

2

4

6

8

10

12

07:30 09:30 11:30 13:30 15:30 17:30 19:30

Time (hour)

Ope

n ci

rcui

t vol

tage

(V

)

0

0.5

1

1.5

2

2.5

3

Sho

rt c

ircui

t cur

rent

(A

)

Voc ACPPVC-50

Voc flat non-concentrator


Isc ACPPVC-50

Figure 6.4.7.3 shows that the variation of total solar radiation, diffuse radiation and ambient temperature

with time on the 23rd of September 2002. The maximum total radiation recorded was 960 Wm-2 on the

plane of the test system and the maximum diffuse radiation was 200 Wm-2. The maximum ambient

temperature was 21ºC. The variation of short circuit current and open circuit voltage for both the flat non-

concentrating and the concentrating ACPPVC-50 systems are shown in figure 6.4.7.4. The open circuit

voltage is nearly constant for both PV panels whereas the short circuit current increases linearly with

incident solar radiation intensity.

Figure 6.4.7.3 Variation of total radiation, diffuse radiation and ambient temperature with time on the 23rd of September 2002.

Figure 6.4.7.4 Variation of short circuit current and open circuit voltage for the flat non-concentrating PV panel and the concentrating ACPPVC-50 system with time. Four PV strings were connected in series for both systems.


219

0

2

4

6

8

10

12

14

16

300 400 500 600 700 800 900 1000


Max

imum

pow

er (

W)

ACPPVC-50

flat non-concentrator

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 100 200 300 400 500 600 700 800 900 1000


Max

imum

pow

er r

atio

Figure 6.4.7.5 shows the maximum power point for the flat non-concentrating system and the ACPPVC-

50 system with incident solar radiation intensity. For a concentration ratio of 2.0, the effective solar

radiation intensity at the absorber will increase by a factor of 2 if the optics are perfect i.e. perfect

geometry and no reflection losses. This implies that at a given incident solar radiation intensity the

maximum power point can be doubled for the ACPPVC-50 system compared to the flat non-concentrating

system if the ACPPVC-50 optics are perfect. For both systems the maximum power point varies linearly

with incident solar radiation intensity. The change of power ratio with incident solar radiation intensity is

shown in figure 6.4.7.6. The average maximum power ratio between the flat non-concentrating and the

ACPPVC-50 systems is approximately 1.6. This implies significant additional losses for the ACPPVC-50

system when compared to the flat non-concentrating system. Possible sources of losses and their reduction

Figure 6.4.7.5 Maximum power point for the flat non-concentrating and the concentrating ACPPVC-50 systems with incident solar radiation intensity.

Figure 6.4.7.6 Maximum power point ratio for the flat non-concentrating and the concentrating ACPPVC-50 systems with incident solar radiation intensity.


220

are discussed in chapter 7. The maximum efficiency achieved for the flat non-concentrating system is

almost 8% compared to 6.2% for the ACPPVC-50 system as shown in figure 6.4.7.7

0

1

2

3

4

5

6

7

8

9

10

300 400 500 600 700 800 900 1000


Effi

cien

cy (

%)

flat non-concentrator ACPPVC-50

0

10

20

30

40

50

60

07:30 09:30 11:30 13:30 15:30 17:30 19:30Time (hour)

Tem

pera

ture

(oC

)

0

200

400

600

800

1000

1200

Sol

ar r

adia

tion

(Wm

-2)

ambient temperatureaverage reflector temperature ACPPVC-50average back plate temp flat non-concentratoraverage back plate temp ACPPVC-50average solar cell temperature ACPPVC-50solar radiation

Figure 6.4.7.8 shows the variation of ambient temperature, average back plate temperature of the flat non-

concentrating PV system, average solar cell temperature of the ACPPVC-50, average reflector

temperature of the ACPPVC-50 and average back plate temperature of the ACPPVC-50 with time. A

maximum temperature of 52° can be seen at the reflector surface for the ACPPVC-50. A temperature

difference of 6ºC can be seen between the back plate and the reflector troughs of the ACPPVC-50. All

temperatures were measured at the thermocouple locations detailed in figures 6.3.3 and 6.3.4. The solar

cell temperatures were measured at the edge of either side of the ACPPVC-50 system to prevent shading

Figure 6.4.7.7 Comparison of efficiency for the flat non-concentrating and the ACPPVC-50 with incident solar radiation.

Figure 6.4.7.8 Diurnal variation of solar radiation, ambient temperature, average back plate temperature of the flat non-concentrating system, average reflector temperature of the ACPPVC-50, average solar cell temperature of the ACPPVC-50 and average back plate temperature of the ACPPVC-50.


221

on the actual cells. The temperature at the edge of the solar cell was similar to that of the aluminium back

plate.

0

5

10

15

20

25

30

35

40

45

50

07:30 09:30 11:30 13:30 15:30 17:30 19:30Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

ambient cover glass 1 cover glass 2 t5t6 t7 t8 t9t11 t12 t13 t14t15 t16 t17 t18t19 solar radiation

0

10

20

30

40

50

60

07:30 09:30 11:30 13:30 15:30 17:30 19:30

Time (hour)

Sub

stra

te te

mpe

ratu

re (

oC

)

0

200

400

600

800

1000

1200

Sol

ar r

adia

tion

(Wm

-2)


The measured temperatures at different locations on the aluminium back plate and the cover glass for the

flat non-concentrating PV panel are shown in figure 6.4.7.9. Figure 6.4.7.10 shows the temperature of the

rear aluminium back plate of the ACPPVC-50. The temperature contours of the aluminium back plate for

both the flat non-concentrating system and the ACPPVC at the times of 11:30, 13:30, 15:30 and 17:30 are

shown in figures 6.4.7.11 to 6.4.7.14. Figure 6.4.7.15 illustrates the temperatures at different

thermocouple locations for the reflector trough with time for the ACPPVC-50 system. For both systems,

the central region of the aluminium back plate had the highest temperature when compared to other

thermocouple locations. The thermocouples were located at identical positions on the aluminium back

Figure 6.4.7.9 Diurnal variation of solar radiation and back plate temperatures for the flat non-concentrating system. The thermocouples were located as shown in figure 6.3.4.

Figure 6.4.7.10 Diurnal variation of solar radiation and back plate temperatures for the ACPPVC-50. The thermocouples were located as shown in figure 6.3.5.


222

plate for both systems. Due to shading there is a significant temperature difference between the two sets of

solar cells at either end of the ACPPVC-50 before and after solar-noon as shown in figure 6.4.7.16.

28

29

35

35

31

35 32

36

33

34

35

35

37

3536

37

37 37

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

38373635343231302928

Solar radiation intensity = 710 W-2

ToC

30

32

3235

35

34

35

39

36

36

36

3737

38

37

37

38

38

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

38373635343231302928

Solar radiation intensity = 710 W-2

ToC

37.0

37.0

42.3

38.9

42.7

39.2

42.7

43.4

40.8

40.8

43.8

41.5

43.0

43.0

43.0

43.8

44.2

44.2

44.9

44.5

45.3

44.9

44.9

45.7

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

46454443434241404039383737


ToC

40.243.8

43.8 40.2

43.4

40.7

45.6

48.7

42.9

40.744.7

42.0

44.3

46.9

45.6

49.2

47.8

46.9

46.0

46.5

46.5

48.3

45.6

47.4

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

50494847464544434242414039


ToC

4 040

40

43

41

4244

41

43

43

43

43

43

43

43

43

44

45

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

4948474645444342414039


ToC

43

43

46

46

46

44

47

44

44

46

46

46

49

46

44

47

46

48

45

48

47

49

49

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

4948474645444342414039


ToC

31.0

30.4

31.3

31.3

31.6

31.6

31.3

32.2

31.3

31.9

32.9

32.9

32.6

32.2

32.6

32.9

32.9

33.2

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

35.434.834.133.532.932.231.631.030.429.7


ToC

31.6

31.6

32.6

31.9

32.633.2

34.8

32.9

34.8

35.1

33.8

33.5

35.7

34.4

33.2

34.8

34.1

34.4

Distance (m)

Dis

tanc

e(m

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

35.434.834.133.532.932.231.631.030.429.7


ToC

Figure 6.4.7.11 Measured temperature contours of the aluminium back plate at 11:30 on the 23rd of September 2002 for (a) flat non-concentrator (b) ACPPVC-50.

(a) (b)


(a) (b)


(a) (b)


(a) (b)


223

0

10

20

30

40

50

60

07:30 09:30 11:30 13:30 15:30 17:30 19:30Time (hour)

Ref

lect

or te

mpe

ratu

re (

oC

)

0

200

400

600

800

1000

1200

Sol

ar r

adia

tion

(Wm

-2)

tr25 tr26 tr27 tr28 tr29tr30 tr38 tr39 tr40 tr41tr42 tr43 solar radiation

0

10

20

30

40

50

60

07:30 09:30 11:30 13:30 15:30 17:30 19:30Time (hour)

Sol

ar c

ell t

empe

ratu

re (

oC

)

0

200

400

600

800

1000

1200

Sol

ar r

adia

tion

(Wm

-2)

ts31 ts32 ts33 ts34ts35 ts44 ts45 ts46ts47 ts48 solar radiation


Panel and a Concentrating ACPPVC-50 Panel Mounted 18° to the Vertical for

Five PV Strings Connected in Series

The electrical and thermal performance of both systems was tested with five PV strings connected in

series. Increasing the number of stings connected in series increases the output voltage while the current

remains constant for a given solar incident radiation intensity. The variation of incident total radiation,

diffuse radiation and ambient temperature with time are shown in figure 6.4.8.1. Figure 6.4.8.2 shows the

measured short circuit current and open circuit voltage for the flat non-concentrating and the ACPPVC-50

Figure 6.4.7.15 Diurnal variation of solar radiation and reflector substrate temperatures of the ACPPVC-50. The thermocouples were located as shown in figure 6.3.3.

Figure 6.4.7.16 Diurnal variation of solar radiation and solar cell temperatures for the ACPPVC-50. The thermocouples were located as shown in figure 6.3.3.


224

panel with time. The maximum short circuit current of the ACPPVC-50 was 2.49 A and that of the flat

non-concentrating PV panel was 1.5 A, implying a short circuit current ratio of 1.66, while the open

circuit voltage was similar for both systems at a given solar radiation intensity.

0

5

10

15

20

25

07:00 09:00 11:00 13:00 15:00 17:00 19:00

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

ambient temperature

total radiation

diffuse radiation

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

2.25

2.5

2.75

07:00 09:00 11:00 13:00 15:00 17:00 19:00

Time (hour)

Sho

rt c

ircui

t cur

rent

(A

)

0

2

4

6

8

10

12

14

Ope

n ci

rcui

t vol

tage

(V

)

Voc flatnon-concentrator

Voc ACPPVC-50

Isc ACPPVC-50


The maximum power point for both systems varies linearly with incident solar radiation intensity as

shown in figure 6.4.8.3. The variation of efficiency with incident solar radiation intensity is shown in

figure 6.4.8.4. The maximum power available from the flat non-concentrating panel was 10.8 W

compared to 17.2 W for the ACPPVC-50 which indicates a power ratio of 1.59. The values of efficiency

for both systems are reduced because of the shadow cast by the wooden frame at the lower solar incidence

Figure 6.4.8.1 Total radiation, diffuse radiation and ambient temperature with time on the 21st of September 2002.

Figure 6.4.8.2 Short circuit current and open circuit voltage for the flat non-concentrating and the ACPPVC-50 system with five PV strings connected in series on the 21st of September 2002.


225

angles. The efficiency increased exponentially above a solar radiation intensity of 200 Wm-2 until it

attains a nearly constant maximum value of 8.2% for the non-concentrating system and 6.2% for the

ACPPVC-50 system. Low values of efficiencies can be explained by ohmic losses between the

interconnected solar cells and the cell spacing, this was verified experimentally by using 52-mm and 2-

mm inter cell tab spacing for the individual solar cells and is detailed in chapter 7.

y = 0.0133x - 0.6961

y = 0.0203x - 0.9657

0

2

4

6

8

10

12

14

16

18

20

0 100 200 300 400 500 600 700 800 900 1000


Max

imum

pow

er (

W)

maxp flat maxp ACPPVC-50 maxp flat maxp ACPPVC-50

due to shading

maxp = maximum power pointflat = non-concentrating system

0

1

2

3

4

5

6

7

8

9

10

0 100 200 300 400 500 600 700 800 900

Solar Radiation (Wm -2)

Effi

cien

cy (

%)

Flat non-concentrating system ACPPVC-50

due to shadingbefore solar noon

Figure 6.4.8.5 shows the diurnal variation of maximum power point ratio with incident solar radiation

intensity for the flat non-concentrating and the ACPPVC-50 systems. The maximum power point was

Figure 6.4.8.3 Maximum power point with incident solar radiation intensity for the flat non-concentrating and the ACPPVC-50 systems.

Figure 6.4.8.4 Electrical conversion efficiency with incident solar radiation intensity for the flat non-concentrating and the ACPPVC-50 systems.


226

calculated from each individual I-V curve generated at every set of measurements. A wide range of

incident solar radiation intensities gave a maximum power point ratio of 1.60.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

07:30:00 09:00:00 10:30:00 12:00:00 13:30:00 15:00:00 16:30:00 18:00:00 19:30:00

Time (hour)

Max

imum

pow

er r

atio

due to shading

0

10

20

30

40

50

60

07:00 09:00 11:00 13:00 15:00 17:00 19:00

Time (hour)

Ref

lect

or te

mpe

ratu

re (

oC

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

tr25 tr26 tr27 tr28 tr29tr30 tr38 tr39 tr40 tr41tr42 tr43 solar radiation

Figure 6.4.8.6 shows the measured reflector temperature of the ACPPVC-50 system with time on the 21st

of September 2002. The thermocouples were located inside the individual reflector troughs as shown in

figure 6.3.3. The temperature response is similar to the incident solar radiation intensity. The temperature

of the top reflector trough was higher than that of the lower reflector trough because of convective heat

transfer. Figure 6.4.8.7 shows the measured solar cell temperature with time for the ACPPVC-50 and

figure 6.4.8.8 shows the aluminium back plate temperature and glass temperature with time. A

temperature difference of 10°C occurred between thermocouple locations ‘ts31’ and ‘ts44’. From figure

Figure 6.4.8.5 Diurnal variation of maximum power point ratio with incident solar radiation intensity for the flat non-concentrating and the ACPPVC-50 systems.

Figure 6.4.8.6 Diurnal variation of solar radiation and reflector temperature of the ACPPVC-50 on the 21st of September 2002. The thermocouples were located as shown in figure 6.3.3.


227

6.4.8.8 it can be seen that the average back plate temperature is 28°C higher than the ambient temperature.

This could be 10°C less than in the actual solar cell surface temperature.

0

10

20

30

40

50

60

07:00 09:00 11:00 13:00 15:00 17:00 19:00Time (hour)

Sol

ar c

ell t

empe

ratu

re (

oC

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

ts31 ts32 ts33 ts35 ts44 solar radiation

0

5

10

15

20

25

30

35

40

45

50

07:00 09:00 11:00 13:00 15:00 17:00 19:00

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

Sol

ar r

adia

tion

(Wm

-2)

ambient cover glass 1 cover glass 2 t5 t6 t7

t8 t9 t11 t12 t13 t14

t15 t16 t17 t18 t19 solar radiation


Panel and a Concentrating ACPPVC-50 Panel Mounted 18° to the Vertical With

Six PV Strings Connected in Series

An experimental investigation was undertaken on the 3rd of October 2002 for both systems with six PV

strings connected in series. The highest intensity of incident solar radiation was 950 Wm-2 and the ambient

temperature was 18ºC as shown in figure 6.4.9.1. Measurements were carried out at 30 seconds intervals

Figure 6.4.8.7 Diurnal variation of solar radiation and solar cell temperatures for the ACPPVC-50 on the 21st of September 2002. The thermocouples were located as shown in figure 6.3.3.

Figure 6.4.8.8 Diurnal variation of solar radiation, aluminium back plate and cover glass temperature of the flat non-concentrating system on the 21st of September 2002.


228

throughout the 10 hours of day light. The variation of short circuit current and open circuit voltage with

time for the flat non-concentrating and the ACPPVC-50 systems are shown in figure 6.4.9.2. The sudden

reduction in short circuit current seen in figure 6.4.3.2 occurred due to a reduction in incident solar

radiation resulting from intermittent cloud cover.

0

5

10

15

20

25

08:00 10:00 12:00 14:00 16:00 18:00

Time (hour)

Am

bien

t tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

total radiation

ambient temperature

0

0.5

1

1.5

2

2.5

3

08:00 10:00 12:00 14:00 16:00 18:00

Time (hour)

Sho

rt c

ircui

t cur

rent

(A

)

0

2

4

6

8

10

12

14

16

18

Ope

n ci

rcui

t vol

tage

(V

)

Isc flat non-concentrator Isc ACPPVC-50 Voc flat non-concentrator Voc ACPPVC-50

Figure 6.4.9.3 shows the effect of maximum power with incident solar radiation intensity for both

systems. The change in electrical efficiency with incident solar radiation intensity is shown in figure

6.4.9.4. The maximum efficiency achieved by the flat non-concentrating system was 8.2% whereas the

maximum efficiency for the ACPPVC-50 is 6.5 %. This is due to ri 2 losses in the interconnections

between solar cells. The maximum power from the flat non-concentrating system is 15 Watts and the

maximum power for the ACPPVC-50 system is 23 Watts when the intensity of incident solar radiation

was 950 Wm-2. Figure 6.4.9.5 illustrates the change of the maximum power point ratio of the ACPPVC-50

Figure 6.4.9.1 Total radiation and ambient temperature with time on the 2nd of October 2002.

Figure 6.4.9.2 Short circuit current and open circuit voltage with time for the flat non-concentrating and the ACPPVC-50 system with six PV strings connected in series.


229

to the flat non-concentrating system with incident solar radiation intensity. At lower incident radiation

intensities, the minimum values of the maximum power point ratio are due to shading and the solar

incidence angles. At lower solar incidence angles the optical losses are higher as detailed in chapter 3.

0

2

4

6

8

10

12

14

16

18

20

22

24

0 100 200 300 400 500 600 700 800 900 1000


Max

imum

pow

er (

W)

Flat non-concentrator ACPPVC-50

0

1

2

3

4

5

6

7

8

9

10

11

12

0 100 200 300 400 500 600 700 800 900 1000


Effi

cien

cy (

%)

Flat non-concentrator ACPPVC-50

Variation of the ambient temperature, the average back plate temperature, the average reflector

temperature and the average solar cell temperature with time on the 2nd of October 2002 are shown in

figure 6.4.9.6. A 30ºC maximum temperature rise was measured inside the reflector trough. A 10ºC

temperature difference was measured between the aluminium back plate and the reflector trough. The

wind speed at the back of the aluminium back plate caused a convective flow. For a wind speed of 4 ms-1

or higher the flow becomes turbulent and a higher heat transfer coefficient of 20 Wm-2 can be expected,

thereby lowering the PV cell operating temperature.

Figure 6.4.9.3 Maximum power against incident solar radiation intensity for the flat non-concentrating and the ACPPVC-50 systems.

Figure 6.4.9.4 Electrical conversion efficiency against incident solar radiation intensity for the flat non-concentrating and the ACPPVC-50 system.


230

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 100 200 300 400 500 600 700 800 900 1000


Max

imum

pow

er r

atio

0

5

10

15

20

25

30

35

40

45

50

08:00 10:00 12:00 14:00 16:00 18:00

Time (hour)

Tem

pera

ture

(oC

)

0

100

200

300

400

500

600

700

800

900

1000

Sol

ar r

adia

tion

(Wm

-2)

ambient temperatureaverage back plate temperature flat non-concentratoraverage reflector temperature ACPPVC-50average back plate temperature ACPPVC-50solar radiation

6.5 Conclusions

A detailed experimental investigation into the performance of an asymmetric compound parabolic

photovoltaic concentrator has been detailed in this chapter. System 1, comprised of eight PV strings each

of five cells connected in series, was investigated for electrical performance and system temperatures for

an average of 10 hours for twenty days with and without the concentrators presents. Different numbers of

PV strings were connected in series to investigate the effects of edge shading on electrical and thermal

Figure 6.4.9.5 The variation of the maximum power point ratio for the flat non-concentrating and the ACPPVC-50 system with incident solar radiation intensity.

Figure 6.4.9.6 Diurnal variation of solar radiation, ambient temperature, average back plate temperature, average reflector temperature and the average solar cell temperature for the ACPPVC-50 system.


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performance. The reflector troughs were removed from System 1 to give a flat non-concentrating PV

panel for comparison to the ACPPVC-50. In both cases the active solar cell area was the same i.e. the

electrical output was generated from the same PV cells. With less than a 1% fluctuation in incident solar

radiation intensity for the experimental investigation the power increased by more than 1.62 when using

the concentrator compared to the flat non-concentrating system. The aluminium back plate temperature of

the ACPPVC-50 system was only 12°C higher than that of the flat non-concentrating system. This

indicates significant convective flow at the back of aluminium back plate decreasing the operating solar

cell temperature. The flat non-concentrating system achieved nearly 8.5% electrical efficiency when the

reflector troughs were removed compared to an electrical conversion efficiency of 6.8% for the ACPPVC-

50 with a fill factor of 65%.

A second asymmetric compound parabolic photovoltaic concentrator was constructed to compare

concurrently electrical and thermal performance. Experiments were undertaken for twenty five days with

an average of 10 to 12 hours sunshine. System 1 was a flat non-concentrating system with identical

dimensions to System 2 i.e. the concentrating system. Both systems were investigated for 0° and 18°

inclination angles to the vertical. Different numbers of PV strings were connected in series for both

systems and their electrical and thermal performance monitored. In addition to the east-west shadow cast

by the wooden frame for both systems, a third partial shadow was observed when the systems were

mounted vertically. Short circuit current increased by 1.66 times for the ACPPVC-50 compared to the flat

non-concentrating system whereas the open circuit voltage was similar for both systems. The maximum

power increased by approximately 1.65 for the ACPPVC-50 compared to the flat non-concentrating

system however the maximum back plate temperature increased by only 6.5°C for the ACPPVC-50

compared to the flat non-concentrating system. This indicated significant heat loss from the back

aluminium plate. The highest efficiency achieved by the flat non-concentrating panel was 12% when a

single PV string was considered and that of the ACPPVC-50 was 10.5%. However an average of 8%

electrical conversion efficiency was achieved by the flat system compared to the electrical conversion

efficiency of 6.8% for the concentrator. The tin/lead coated copper tab between individual solar cells has a

resistance of 1.5Ω which implies a power loss of 1.5i2 Watt (where i is the instantaneous current produced

by the PV panel) which is more significant when two or more PV string connected in series. This

indicates that significant power losses occur in the tab between consecutive solar cells in addition to the

optical losses at the reflector as detailed in chapter 3. From the CFD analysis a 6°C temperature gradient

inside the solar cells along the vertical direction was predicted. This will cause electrical mismatch loss

between individual solar cells and may explain the lower electrical conversion efficiency of the ACPPVC-

50 compared to the flat non-concentrating system.

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