SETIT 2005
3rd International Conference: Sciences of Electronic,
Technologies of Information and Telecommunications
MARCH 27-31, 2005 – TUNISIA
CONVERGING LENS SOLAR CONCENTRATOR
AND THEIR POSITION CONTROL USING A
MICROPROCESSOR FOR INCREASING THE
EFFICIENCY OF SOLAR PHOTOVOLTAIC
ENERGY CONVERSION
Srinivasulu Avireni
Department of Electronics and Telecommunications, Faculty of Technology,
Kigali Institute of Science, Technology and Management, Kigali, Rwanda.
Abstract : The paper explains the principle of using a converging lens as solar concentrator. Experiments have been
carried out to reveal the effectiveness of such concentrator for increasing the output of solar cells. A novel arrangement
consisting of a Solar Panel along with Lens Panel, where an array of converging lenses were fitted is proposed for
focusing sunlight on respective solar cells. A microprocessor-based scheme is also proposed for controlling the position
of Lens Panel such that temperature of the focused sunlight on solar cells should not exceed typically around 50°C.
Key words: Solar concentrators, Solar Energy conversion, Photovoltaic cells, Microprocessor based systems.
1 Introduction
Average daily solar insolation in Africa and India is
the highest, i.e. 5.5 KWh/m2 /day in comparison with
3.5 KWh/m2 /day in Europe and the USA [1]. A portion
of this solar energy may be converted into D.C
electricity by Solar Photovoltaic System, which is one
of the simple and clean energy conversions.
Conversion of solar energy to electrical energy is done
by solar cells. Solar cell is basically a p-n junction
device [2,3] and commercially available cells are
usually made with approximately 10 cm diameter.
Solar radiation incident on the surface of the cell
produces voltage between the terminals extended from
p and n type materials. The open circuit voltage of a
single crystal silicon solar cell at full illumination is
approximately 0.5V. When load is connected to the
circuit, the current through the load is directly
proportional to the intensity of solar insolation.
2 Converging Lens Solar Concentrator for
Photovoltaic Energy Conversion
Sunlight contains electromagnetic waves ranging
from 0.001µm to 100 µm.
The energy of one photon is related to the
frequency by
= hf =
Wp
hc
λ
W p = Photon energy (J)
where
h
=
6.63 x 10-34 J – s (known as Plank’s
constant)
f
frequency (s -1 )
=
Velocity of light (ms -1 )
c
=
λ
= Wavelength (m)
Fig. 1
shows the energy carried by a single
photon at various wavelengths. When dealing with
typical sources and detectors of light, it is impractical
to consider the discrete nature of the radiation. Instead
we deal with the so-called macroscopic properties that
result from the collective behavior of a vast number of
photons moving together [4].
-2
1.24 X 10
100
-2
2.48 X 10
50
2.48 X 10
5
-1
1.24 X 10
1.24
1
10
2.48
0.5
1.24 X 10
0.1
Visible
2.48 X 10
Infrared
Ultraviolet
Wave length(micro m.)
0.05
2
1.24 X 10
0.01
2.48 X 10
0.005
2
1.24 X 10
0.001
3
Photon Energy(eV)
-1
SETIT2005
Fig. 1. The energy of photon varies inversely with the wavelength of EM radiation.
Principal axis
P
Fig. 2.
The general energy principles involve a description
of the net energy of the radiation as it propagates
through a region of space.
When the total fraction of incident sunlight
transmits through the lens, the variation of sunlight
intensity with wavelength must be considered. The
solar flux, φ i.e. energy per unit area per unit time is
where TnJ is the transmissivity and ( ∆ Y)n is the
serration width.
By summing over all serrations


 ∑  the total
 n 
fraction SE of incident solar energy transmitted is
[5],
∞
φ = ∫ H (λ ) dλ ≅
∑ H (∆λ )
J
J
=
J
0
∑φ
J
J
SE =
ωJ =
φ J ≡ ω J φ , the weighting factor is
H J (∆λ ) J
φ
H J (∆λ ) J
∑ H J (∆λ ) J
=
J
The fraction of incident solar flux transmitted
through one serration, the nth is obtained by summing
contribution from all wavelength intervals within the
solar spectrum is
T n (Y ) =
∑T
J
nJ
φ J (∆Y ) n
φ (∆Y )n
= ∑ ω J TnJ (Y )
J
n
nJ
φ J (∆Y ) n
J
∑ ∑ φ (∆Y )
J
where, HJ( λ ) is the solar intensity at
wavelength λ .
Defining
∑ ∑T
n
SE =
2
Lω
n
J
∑ ∑T
n
nJ
ω J (∆Y ) n
J
Where Lw is the lens width.
Convex lens converges a set of incident rays
falling on its aperture from a distant object to its focal
point P as shown in Fig. 2. We consider here only thin
lens, hence displacement of the light ray is negligible.
Thus, for thin lenses, the ray through the optical center
of the lens is a straight line [6]. If the distant object is
sun, then sunrays converge to the point P. If you place
Photovoltaic cell at the point P, the numbers of photons
fall on this point raises, which in turn increases the
output voltage of the Photovoltaic cell. The intensity
of the sunrays falling at the point P can be controlled
by moving the lens forward or backward.
SETIT2005
3 Experiments to study the effect of
convergence lens as solar concentrator
Experiment have been performed to
study the effect of the convergence lens as
solar concentrator by using a glass lens
(diameter: 4.4 cm, focal le ngth: 8 cm) and a
Photovoltaic cell (size: 3mm x 1.5 mm). The
experimental arrangement is schematically
shown in Fig. 3.
When sunrays are focused to increase
the intensity of light, temperature also
increases at the focal point as sunlight
contains infrared rays.
Temperature of
sunlight is low in the morning, gradually
increases at midday and will decrease when
evening approaches.
Most of the
commercially available Photovoltaic cells
have maximum temperature rating of 70°C.
If the temperature of the focused sunlight
crosses above 70°C, the Photovoltaic cells
may damage. To avoid such critical situation,
the amount of focusing of sunlight should be
controlled by moving the lens away from or
near to the Photovoltaic cells. Observations
were taken in the aforesaid experiment by
keeping the lens at different positions so that
focusing effect of sunlight falls on the
Photovoltaic cell can be varied.
These
observations are plotted in Fig. 4
It is evident from the curve (Fig. 4(a))
that when the distance between the lens and
the Photovoltaic cell approaches near to the
focal length of the lens, the cell output
increases and it will be maximum at Focal
point. It is also clear from the curve (Fig.
4(b)) that temperature at the focal point
increases when the lens approaches near to
the focal point of the lens.
O/P
PV Cell
Sun
Lens
Output Voltage (Volts)
Fig. 3. Experimental arrangement
0.62
0.6
0.58
0.56
0.54
0.52
0.5
0.48
0
5
6
Distance of Lens from the PV Cell (cm)
(a)
8
Temperature on the PV Cell
(Deg.C)
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60
50
40
30
20
10
0
0
5
6
8
Distance of Lens from the PV Cell (cm)
(b)
Fig. 4 (a). Distance of Lens from PV Cell Vs Output Voltage
(b). Distance of Lens from PV Cell Vs Temperature on PV Cell
amount of focusing of sunlight on respective Solar
cells.
The functional block diagram of a proposed
microprocessor based control system is depicted in Fig.
6. Software for such a system may be written in
assembly language and the proposed flow chart is
given in Fig. 7.
4 A Scheme for Automatic Control of the
Position of Lens Panel over Solar Panel
The schematic diagram of the Solar Panel and
the proposed Lens Panel mo unted over Solar Panel are
shown in Fig. 5(a) and Fig. 5(b) respectively. The
Lens Panel can be motor driven for controlling the
Solar Panel
(a)
Solar Panel
Lens Panel
Lens
(b)
Fig. 5. (a) Schematic of the Solar Panel
(b) Schematic of the Proposed Solar Panel with Lens Panel
SETIT2005
EPROM
MICROPROCESSOR
RAM
ADDRESS BUS
INTERRUPT
DATA BUS
ADC
PA
8255 C0
C1
AMPLIFIER
TEMPERATURE SENSOR
STARD CONVERSION
END OF CONVERSION
PB
DAC
AMPLIFIER
TO THE LENS PANEL
FOR ITS POSITION
CONTROL
DC MOTOR
Fig. 6. Functional Block diagram of the proposed µP based position control system
START
END OF CONVERSION (INTERRUPT)
INITIALIZATION OF
8255
PUSH PSW AND OTHR
REGISTER CONTENTS
START CONVERSION
OF ADC
READ ADC
OUTPUT
WAIT FOR END OF
CONVERSION
OF ADC
CONTROL ALGORITHM FOR
GENERATING MANIPULATED
OUTPUT
FROM Co
SEND MANIPULATED OUTPUT
THROUGH PORT-B TO DAC
END
Fig. 7. Proposed flowchart for controlling the position of Lens Panel
SETIT2005
5 Conclusion
The effectiveness of using converging lenses
as solar concentrators has been experimentally verified.
A solar panel together with a Lens panel, where an
array of converging lenses was fitted for focusing
sunlight on respective solar cells were proposed. Care
should be taken while concentrating sunlight on the
solar cells, because the temperature of the focused sun
light should not exceed the maximum temperature
rating of the solar cells. To avoid such situation and to
safeguard solar cells, a microprocessor based position
control of Lens Panel has been proposed.
References
1.
2.
3.
4.
5.
6.
Mukharjee M.K., ‘Solar Photovoltaic Energy
Conversion’, Journal of the institute of engineers
(India), vol 78, May 1997, p.1-5
Martin.A.Green, ‘Solar Cells’, Prentice-Hall Inc, 1982
Wolf.M.,‘Historical development of Solar cells’, IEEE
Press, Editor C.E.Backus, New York, 1976
Curtis D. Johnson, ‘Process Control Instrumentation
Technology’, Printice Hall, 1977. p. 254-280
Leon.J.Hastings, Steve L.Allums, and Ronald M.Cosby,
‘An analytical and experimental evaluation of the planocylindrical Fresnel lens solar concentrator’, Solar
collectors, Joint Conference American section,
International solar energy society and solar energy
society of Canada, Winnipeg, vol 2, August 1976, p.
275-290
Robert.L.Weber, Kenneth V Manning, Marsh W White,
George A Weygend, College physics, TMH
Publications, New Delhi, 1992
*********
Srinivasulu Avireni
was born in Andhra
Pradesh, India, in
1963. He received the
B.Tech
degree
in
Electronics
and
Communication Engg,
from Sri Venkateswara University, Tirupati,
India in 1986, M.E, degree in Power
Electronics Engineering from Gulbarga
University, Gulbarga, India in 1991, and M.S,
degree in Software Systems from Birla
Institute of Technology and Science, Pilani,
India in 1998. From 1987 to 1989 was in
Electronics and Communication Engineering
Department, Guru Nanak Dev Polytechnic,
Bidar. In October 1991 he joined the
K.S.R.M.College of Engineering, Cuddapah,
as Lecturer in the Department of Electronics
and Communication Engineering, and from
1995 onwards he is an Associate Professor in
the same institute. From 1999 to 2003, he was
an Assistant
Professor in Communication Technology
Department, Defence University Engineering
College, Ethiopia. At present on lien to
Department
of
Electronics
and
Telecommunication Engineering, Kigali
Institute of Science, Technology, and
Management, Kigali, Rwanda.
He is a life member of I.S.T.E. He
published papers both in national and
international journals; his main research areas
are Optoelectronics, Optical communications,
and Electronic Instrumentation.