Effect of selective filtration on silicon solar cells performance
Ahmad Abu-hajar Ahmad Hadidi Omar Hiasat
Winter 2016
Senior Year Project
Faculty Supervisor: Prof. Mohammad Hamdan
Department of Mechanical Engineering, Amman-Jordan
Abstract
Furthermore copper sulfate solution (CuSo4.5H2O) has the ability to transmit the visible
part of the solar spectrum except the red color, if white light (ordinary sunlight, for
example) passes through copper sulfate solution, some wavelengths in the light are
absorbed by the solution. Copper (II) ions in solution absorb light in the red region of the
spectrum. The light which passes through the solution and out the other side will have all
the colors in it except for the red. This mixture of wavelengths is seen as pale blue (cyan).
Rather than that copper sulfate solution also has the ability to block a large portion of the
long wave part of the solar spectrum due to the presence of five water molecules in its
composition.
Results
The hourly average output power and the hourly average surface temperature for the three
panels were plotted vs time. The average temperature of the liquid absorption filter as it
exits the glass filter was also plotted versus time.
Figure (2) :The average output power versus time .
Background: Overheating in PV panels
Average surface temperature of
the panel vs Time
Overheating has a negative impact on the performance of the PV cells, as the PV
panel is exposed to excessive solar radiation its temperature increases significantly,
which leads to a drop in its performance as the efficiency of the PV cell might
decrease by 0.5%/°c due to overheating.
Source: chemwiki.ucdavis.edu/Inorganic_Chemistry/Coordination_Chemistry…...........
Experimental setup
Average surface temperature of the
panel (oc)
The aim of the project was to study the effect of using selective liquids as absorption filters on
the performance of the PV cells. This was carried out by using copper sulfate solution
(CuSo4.5H2O) and distilled water as absorption filters to decrease the overheating of the
panel by blocking the unwanted part of the solar radiation (long wave part) and transmitting
the right part (ultraviolet and visible light) into the PV panel. The liquids were tested on two
separate panels and their performance was compared with the performance of a reference
panel.
The performance of the PV cells improved when using both liquids as absorption filters,
however the performance of the PV panel was better when distilled water was used as an
absorption filter. The performance of the panel was enhanced when distilled water was used
as an absorption filter at an average of 31.33 % compared to the performance of the
reference panel while using the copper sulfate solution has enhanced the performance of the
panel by an average of 11.3% compared to the performance of the reference panel.
Overheating is mainly caused by the long wave part of the solar radiation (Infrared waves), the PV
material does not usually respond to the photons of the long wave rays, it will not absorb them as
their energy band gap is lower than the energy band gap of semi-conductor material of the PV cells,
therefore they are mainly converted into heat thus the solar to electrical conversion efficiency of the
PV cell is reduced. Better performance of the PV panel can be achieved by blocking this unwanted
part of the solar spectrum from reaching the PV panel. The infrared waves are not too harmful as
they might be used for other thermal applications.
50
45
40
35
30
25
8
10
12
14
16
Time
reference panel
water filtered panel
CUSO4 filtered panel
Figure (3) :The average temperature of the panel versus time .
Source: , “Active Optimal Control Strategic for Increasing the Efficiency of Photovoltaic cells”,
University Of Kentucky, Kentucky state
The system was manufactured locally, which contains three PV panels two of them
were meant to be used for testing the liquid absorption filters while the third one was
used as a reference panel. A chiller unit was designed and glass filters were
manufactured taking into consideration the cavities inside which the filtration liquid will
flow. Furthermore sensors were installed and a computer code was written for data
acquisition purpose.
Copper sulfate
filtered panel.
Reference
panel
Introduction to liquid absorption filters
Figure (4) :The average outlet temperature of the liquid absorption filter versus time .
Discussion
Overheating effect can be minimized by blocking the unwanted part of the solar radiation (long
wave part) and transmitting the useful part to the PV panel (short wave part), selective liquid
absorption filters were recommended for this purpose. Liquid absorption filters were selected
upon their spectral properties, stability within a range of temperature and environmental safety.
Source:pveducation.org/pvcdrom/solar-cell-operation/effect-of-temperature.
Distilled water
filtered panel.
Chiller units
Figure (1) : The experimental setup.
Overheating decreases the energy band gap of the semiconductor material of the PV cells.
As the system is switched on, the filtration liquid starts to flow from the tank (the
chiller unit) towards the glass filter by means of a pump and forms a layer inside it,
which allows the liquid to transmit the wanted part of the solar radiation into the PV
panel. The readings of the parameters such as the open circuit voltage, the short
circuit current, the temperature of the filtration liquid as it leaves the glass filter and
the surface temperature of the panel is then obtained and stored in the data
acquisition system. The filtration liquid then flows back to the chiller unit to be cooled
down. The filtration liquid continues flowing in this loop until the system is shut down,
as it collects at the tank in the chiller unit.
When the energy band gap of the semi-conductor material is reduced, lower energy is needed to
break the bonds between the electrons of the semi-conductor material which results in a slight
increase in the output current flow of the PV panel and a drop in its output voltage. The increase
of the current flow and the drop in the output voltage affects the PV panel by decreasing its
output power.
Procedures
Source: ijritcc.org/download/ICAET15TR021562.pdf
Distilled water and nonorganic salts solutions were recommended to be used as absorption filters. In
this project the liquids were selected due to their distinctive spectral properties, distilled water was
found to be able to partially block the infrared waves and transmit the whole visible part as well as a
small portion of the short wave part of the solar spectrum due to its high absorbance in the long wave
range and low absorbance in the visible and short wave part.
Step 1: The full system was initially tested to detect any malfunction or leakage in
the pipes.
Step 2: Distilled water and copper sulfate solution (CuSO4.5H2O) were used as
absorption filters in two separate panels in order to compare the performance of
the filtered panels with the performance of the reference panel simultaneously. The
chiller unit tanks of both panels were filled with both liquids in order to flow in the
system’s loop.
Step 3: The system was tested daily from 8:00 am to 5:00pm. The parameters of
each panel such as the open circuit voltage, the short circuit current and the
surface temperature of the panel were recorded every ten minutes and stored on a
Microsoft excel file found on a laptop connected to the system’s main circuit board
via USB. The temperature of the liquid absorption filter as it enters and leaves the
glass filter of the panel was also recorded on the same Microsoft excel file besides
the parameters of the PV panel.
Step 4: The readings were then processed by calculating the average values of the
open circuit voltage, the short circuit current and the surface temperature of the
three panels at each hour using Microsoft excel program. The average outlet
temperature of the liquid absorption filters was also calculated at each hour. The
average output power was calculated for each panel using the following relation:
Source: , “Active Optimal Control Strategic for Increasing the Efficiency of Photovoltaic cells”,
University Of Kentucky, Kentucky state
Source: hyperphysics.phy-astr.gsu.edu/hbase/chemical/watabs.html
Using distilled water as an absorption filter has improved the performance of the filtered panel
with respect to the reference Panel by 30 % for the first day, 35% for the second day and by
29 % for the third day. Using copper sulfate solution as an absorption filter has improved the
performance of the filtered panel with respect to the reference panel by 12 % for the first day,
13 % for the second day and 9% for the third day.
Using water as an absorption filter enhanced the performance of the PV panel more than
using the copper sulfate solution as an absorption filter. That might be related to the
theoretical studies which indicate that the distilled water does not absorb any wave length in
the visible part of the solar spectrum unlike the copper sulfate solution which absorbs a
portion of the visible part of the solar spectrum in the red region. Therefore lower energy is
transmitted to the PV panel when using copper sulfate solution as an absorption filter which
affects the performance of the panel in a negative manner. The copper sulfate solution is also
expected to transmit a small portion of the long wave part of the solar radiation which might
be considered as another reason for the copper sulfate filtered panel to have lower
performance than the water filtered panel.
the distilled water filtered panel which showed the best performance had the lowest average
surface temperatures compared with the copper sulfate filtered panel and the reference
panel. The copper sulfate filtered panel also was cooler than the reference panel although its
performance was better. The inverse proportion between the surface temperature of the PV
panel and its output power can be explained theoretically as the PV panel is overheated the
energy band gap of the semiconductor material of the PV panel decreases thus lower energy
is needed to break the bonds between the electrons in the semiconductor material. The easy
liberation of electrons affects the PV panel by decreasing its output power.
The average surface temperature of the distilled water filtered panel was lower than the
average surface temperature of the copper sulfate filtered panel which can be related to the
fact that the distilled water has a higher absorbance in the long wave part of the solar
spectrum unlike the copper sulfate solution which has a lower absorbance in the long wave
part of the solar radiation due to its composition which has only five water molecules
compared to distilled water. Thus a small portion of the infrared waves is transmitted to the
panel, which results in rising the temperature of the copper sulfate filtered panel more than
the distilled water filtered panel.
It is noticed that the distilled water had left the glass filter of the PV panel with a higher
temperature than the copper sulfate solution and that might be due to the fact that the distilled
water has a higher absorbance in the long wavelength range of the solar spectrum unlike the
copper sulfate solution that has a lower absorbance in the long wave part of the solar
spectrum due to its composition which contains only five molecules of water compared to
distilled water. Thus its temperature does not increase as in the case of using distilled water
as an absorption filter.
References