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Improvement in solar panel efficiency using solar concentration by simple mirrors and by cooling

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Abstract

Concentrated photovoltaic technology (CPV) uses optics such as mirrors and lens to focus sunlight on solar cells for the sake of generating electricity. CPV has advantage over non-concentrated photovoltaic as less number of solar cells are required for the same power output. Along with duration and intensity of sunlight, temperature also has great effect on the performance of PV module as high temperature significantly reduces output power. This research paper explains a practical approach to enhance the efficiency of solar panel by the use of mirrors and cooling mechanism. These reflectors are cheap, easy to handle, simple enough to use and need no extra equipment or devices to use. But CPV operate efficiently in concentrated light as long as the solar cells are kept cool by means of some heat sinks. Experimental results indicate appreciable enhancement in overall output of solar panel. Experimental readings obtained from a) without reflectors and without cooling b) with reflectors and without cooling c) with reflectors and with cooling are compared. Corresponding results obtained from different conditions showing improvement in efficiency up to 32% in case (b) and 52% in case (c) are tabled and plotted.
Improvement in Solar Panel Efficiency Using Solar
Concentration by Simple Mirrors and by Cooling
Rizwan Arshad*, Salman Tariq, Muhammad Umair Niaz, Mohsin Jamil††
* School of Mechanical and Manufacturing Engineering
National University of Science and Technology Islamabad
rizwan.arshad@smme.edu.pk
†Department of Electrical Engineering
University of Engineering and Technology Taxila
†† School of Mechanical and Manufacturing Engineering
National University of Science and Technology Islamabad
AbstractConcentrated photovoltaic technology (CPV) uses
optics such as mirrors and lens to focus sunlight on solar cells for
the sake of generating electricity. CPV has advantage over non-
concentrated photovoltaic as less number of solar cells are
required for the same power output. Along with duration and
intensity of sunlight, temperature also has great effect on the
performance of PV module as high temperature significantly
reduces output power.
This research paper explains a practical approach to enhance the
efficiency of solar panel by the use of mirrors and cooling
mechanism. These reflectors are cheap, easy to handle, simple
enough to use and need no extra equipment or devices to use. But
CPV operate efficiently in concentrated light as long as the solar
cells are kept cool by means of some heat sinks. Experimental
results indicate appreciable enhancement in overall output of
solar panel. Experimental readings obtained from a) without
reflectors and without cooling b) with reflectors and without
cooling c) with reflectors and with cooling are compared.
Corresponding results obtained from different conditions
showing improvement in efficiency up to 32%in case (b) and 52%
in case (c) are tabled and plotted.
Keywords Efficiency improvement, passive cooling, simple
mirrors, concentrated photovoltaic, four sun technology
I. INTRODUCTION
nergy is the fundamental need for mankind today. It
ensures better quality of life. For daily use uninterrupted
energy has become a necessity for humanity now a days.
As blood is to body electricity is to economy of any country so
without it economy will tremble and it will be very hard to
sustain it. All over the world energy is one of the leading issues
and every country is looking for energy resources as its
demand is increasing sharply. Non-renewable energy resources
are either too expensive or damaging the environment and also
they are eventually going to end in near future. That’s why the
world is moving towards renewable energy resources which are
naturally replenished in a relatively small period of time.
Though hydroelectric is very cheap renewable energy source
but it is not available to all places in the world while on the
other hand solar has the potential to take over the whole power
generation [1],[13-14]. From over the centuries, sun is
providing energy in both forms: light and heat. Today, solar
energy is used to produce electricity by using photovoltaic
cells.
II. PRINCIPAL OF SOLAR CELL
Solar cells are made up of semiconducting materials, such as
silicon, which are doped with different impurities [7]. This
produces unequal distribution of free electrons (n-type) on one
side of junction and excess of holes (p-type) on other side of
junction. Solar light has photons which hit the solar panel and
excite the loosely bound electrons which are designed to move
only in one direction in solar cells and thus electron-hole pairs
are created in respective junctions and electricity is obtained in
external circuit.
Whatever the size is, a typical solar cell produces 0.5-0.6 volt
DC under no load and open circuit condition. The current and
voltage (power) ratting of a PV cell mainly depends on its
efficiency, size (surface area) and is proportional to the
intensity of light striking the surface of cell. For example,
under peak sunlight conditions, a typical commercial PV panel
of surface area 160 cm-2 (25 inch-2) will produce 2 watts peak
power. If the intensity is 60 percent of peak it will produce
about 1.2 watts. So intensity adds a lot to efficiency [8].
Extensive research shows that output of a PV cell can be
increased by two methods: fabrications and passive devices [2-
6]. Passive devices are used widely to enhance the efficiency
as fabrication is expensive one.
III. EFFECT OF IRRADIANCE
Efficiency of solar cell is greatly affected by the amount of
solar irradiance. It is one of the most dynamic factors which
change the solar array performance [9]. It is measure of
amount of solar radiation from the sun striking on specific
surface.
It is commonly expressed in watts per square meter (W/m2).
Under ideal conditions a solar panel should receive an
E
292
2014 International Conference on Robotics and
Emerging Allied Technologies in Engineering (iCREATE)
Islamabad, Pakistan, April 22-24, 2014
978-1-4799-5132-1/14/$31.00 ©2014 IEEE
irradiance of 1000 W/m2 but unfortunately this is not true in
most environments. Irradiance depends on geographical
position, angle of sun to solar panel and amount of energy
wasted by reflection from dust particles or from fog or clouds.
Therefore change of irradiance means change of output
performance of solar panel.
IV. TEMPERATURE EFFECT
Conducting materials consist of free electrons and some
electrons are held tightly by the nucleus of atoms. When
irradiance increases, more packets of photons strike the panel
and this energy is absorbed by the atoms and electrons and they
collide with each other emitting more electrons from the atoms
and thus raising the temperature. Increase in temperature leads
to increase in resistance to the flow of current. Efficiency is
also dependent on temperature. At high temperature output
performance of solar panel reduces as compared to a lower
temperature [10]. According to estimation for every degree
rise in temperature, efficiency of PV module decreases 0.5
percent. PV modules are usually manufactured at 25oC (77oF)
and can be operated above 20oC.
V. COOLING
Based on the study of Akbarzadeh and Wadowaski [15],
under concentrated solar radiation the performance of solar cell
reduces 50% when its temperature rises from 460C to 84oC.
Therefore, an efficient cooling system is quite essential to
maximize solar cell’s efficiency and to prevent the cell from
degradation and damage. Photovoltaic panels can be cooled
actively or passively. The difference between active and
passive is that active system requires some external power
source to run while passive system needs no additional power
source [11-12].
VI. EXPERIMENTAL SETUP
The proposed following approach of improving solar panel
efficiency is based on experimental data (readings and graph)
obtained from three different methods. All these readings were
recorded during three bright sunny days of month April. A
mono crystalline solar panel made of silicon semiconductor
was used for this experiment. An iron made frame was
designed with space for solar panel and for three mirrors.
In this experimental technique active cooling system was used
for improving efficiency of PV module.
A PVC plastic pipe with holes at the bottom was fixed over
the solar panel frame which was further fed from a rubber pipe
from a water tank which was filled by an electric motor. One
mirror from above and two from sides were reflecting solar
radiation on the solar panel which was placed in the middle.
This technique can be named as four sun technology also. This
analysis is based on following three methods i.e. a) without
mirrors and without cooling b) with mirrors and without
cooling c) with mirrors and with cooling.
VII. RESULTS
TABLE I.
CHANGE IN CURRNET, VOLTAGE AND POWER W.R.T
CONCENTRATION AND COOLING
Voltage
Current
Power
Concentration
12.98
1.91
24.84
Without
15.02
1.92
28.838
1 mirror
15.43
1.93
29.625
Plus cooling
16.11
1.94
31.253
2 mirrors
16.50
1.94
32.011
16.71
1.95
36.929
16.91
2.23
37.709
This table is giving information about how the performance
measures of solar cell are changing with respect to change in
environmental conditions which in this case are changing
concentration and cooling step by step. It can be clearly seen
from the experimental readings that without concentration
solar panel is not even producing its rated power i.e. 30 watts.
Just by adding a mirror increases its output power
approximately 4 watts. Similarly output power goes on
increasing by increasing concentration and cooling.
Fig.I Hourly changing Irradiance
293
TABLE II.
HOURLY COMPARISON OF THREE METHODS
Time
Without
mirrors and
cooling
With
Mirrors
and
without
cooling
Three
mirrors
plus
cooling
8:30 AM
19.17
25.12
22.7848
9:00 AM
20.01
26.58
24.7756
9:30 AM
20.60
28.00
26.5125
10:00 AM
21.21
28.40
30.4433
10:30 AM
22.05
27.50
32.1758
11:00 AM
23.63
28.05
34.6399
12:00 PM
24.44
30.81
36.4188
12:30 PM
24.91
30.91
37.6444
01:00 PM
24.80
32.26
37.709
01:30 PM
24.20
31.80
36.66
02:00 PM
23.44
29.94
35.5450
02:30 PM
22.26
29.45
32.2936
03:00 PM
20.22
29.34
30.0969
03:30 PM
19.81
27.87
27.6212
04:00 PM
19.02
27.56
26.0064
04:30 PM
18.09
27.10
25.3455
Fig II. Hourly changing power output of solar panel under three different
conditions a) without mirrors and without cooling b) with mirrors and without
cooling c) with mirrors and with cooling
Fig III. Percentage improvement in solar panel efficiency using a)
three mirrors without cooling b) three mirrors plus cooling
VIII. DATA ANALYSIS
A. Without mirrors and without cooling
Though this method was practiced by most of the people from
all over the world a few years ago but now a days this method
is almost losing its value due to its low efficiency. The curve
from fig.2 clearly shows that output power by using solar
panel without mirrors and without cooling is not only far less
than other two methods but also less than its rated power.
Solar irradiance, most of the time in this case is also round
about 750w/m2.
B. With mirrors and without cooling
Efficiency of solar panel can be increased by increasing solar
irradiation on solar panel. As we have seen from the graph that
irradiance is continuously changing with respect to time so
output power largely depends on irradiation. As earth has only
one sun so reflecting mirrors can also be named as sun. So
here in this case solar radiations from four suns are striking on
solar panel and the results are also encouraging. Second Curve
of fig.2 and first curve of fig.3 is showing the corresponding
output characteristics of this method. In fig.2 from 8:30 AM-
11 AM curve follows an increasing trend but then up to 1:30
PM follows a decreasing trend. This is because in these peak
hours as irradiance received is at its maximum so temperature
effect dominates in these hours of the day and power output
decreases. Collisions between atoms and electrons are
hindering the flow of current and thereby increasing resistance
which eventually leads to increase in temperature and cause
reduction of output power. It can also be verified from Fig.3
that efficiency of solar panel during these hours is less than the
other hours of the day but at the same time its efficiency is
better than using solar panel without mirrors and without
cooling.
Approximately, on average 32% efficiency was improved by
this method.
294
C. With mirrors and with cooling
Results obtained from this method were encouraging as for
about 6 hours of the day its output power is far greater than the
method explained in section B. It can be observed form the
fig.2 that only for a single hour of morning from 8:30 AM-
9:30 AM and one hour in the evening from 3:30 PM-4:30 PM
its output is less than the second method. The reason of this
low power and low efficiency is that because for performing
this method cooling was started at sharp 8:30 AM and ended
at 4:30 PM as already discussed in previous sections that when
electrons absorbs sufficient heat energy they collide with each
other and with other atoms thus producing free electrons.
During these hours although solar panel is receiving same
amount of solar energy from the sun as the method in section
B but at the same time in this method cooling is removing
away some of heat energy from the solar panel so making it
less efficient than using mirror and without cooling method
only for two hours. This method was approximately 20% more
efficient than second one and 52% more efficient from the first
one.
CONCLUSION
The results of the experiment for improving efficiency of solar
panel using mirrors and cooling were come out to be highly
encouraging. Using mirrors plus cooling is better than the
other two as efficiency is approximately 52% in this case.
Output power from simple solar panel without using mirrors
was 24 watts and from solar panel with mirrors and cooling
was 37.709 watts which means instead of purchasing new
solar panel one can obtain 52 percent more power from the
same solar panel using this technique.
FUTURE RECOMMENDATIONS
Of all the other two methods, last one was efficient but it still
needs to be improved. One can enhance its efficiency beyond
52 percent by following these recommendations.
Stop cooling solar panel in the early and last hours of the day.
This will definitely increase further output power.
As this whole experiment was without following maximum
power point tracking technique (MPPT). So one can combine
these two techniques to improve efficiency.
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