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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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The Effects of Various Topologies on the Performance of PV modules
in solar energy applications.
1
Jyoti H. Ugale, 2M.S.Panse
Ph.D Scholar, Head, Electrical Engineering
V.J.T.I, Mumbai
Email: [email protected]
Abstract- The initial cost of solar energy application is very
high so the optimum utilisation of number of PV cell plays
a very important role. I-V and P-V characteristics of PV
cell depend on various factors so to operate PV cells at
global peak (GP) is a very difficult task. The maximum
power point (MPP) depends on the series and parallel
connection of PV cell and power extraction not only
depends on various topologies but also on the partial
shading condition of PV cells. This paper discusses the
behaviour of I-V and P-V characteristics of shaded as well
as non shaded PV cell under series and parallel connection.
A solar cell is simply a semiconductor diode that has
been carefully designed and constructed to efficiently
absorb and convert light energy from the sun into
electrical energy [5].
Keywords- PV cell, MPP, I-V and P-V characteristics.
I. INTRODUCTION
Solar energy plays vital role in the non-conventional
energy sources. It provides basic and time proven
formula to concur world energy shortage. Energy
generated from renewable from renewable sources has
long promised to satisfy demands for more and cleaner
electricity. Because renewable sources, such as sunlight
and wind, can produce greatly fluctuating amounts of
energy, they are most effectual when excess energy can
be stored until it’s needed.[1,2] The estimated
contribution of photovoltaic’s in solving future problems
with respect to renewable energy in global scale is
presented below
Table: 1.1
Estimated contribution of the renewable energy
Solar PV
Hydro
Wind
Solar thermal
27
22
37
18
It is shown that estimated contribution of the renewable
energy in the production in 2050 photovoltaic
conversion of energy will play in important role in
energy production (27%). Solar energy conversion (PV
& thermal) will reach about 50% of renewable energy
(wind & hydro energy).
PV CELL:
Fig: 1 Simple conventional solar cell
A simple conventional solar cell structure is depicted in
Figure 1.2 Sunlight is incident from the top on the front
of the solar cell. A metallic grid forms one of the
electrical contacts of the diode and allows light to fall on
the semiconductor between the grid lines and thus be
absorbed and converted into electrical energy. An
antireflective layer between the grid lines increases the
amount of light transmitted to the semiconductor. The
semiconductor diode is fashioned when an n-type
semiconductor and a p-type semiconductor are brought
together to form a metallurgical junction. This is
typically achieved through diffusion or implantation of
specific impurities or via a deposition process. The
diode’s other electrical contact is formed by a metallic
layer on the back of the solar cell. All electromagnetic
radiation, including sunlight, is composed of particles
called photons, which carry specific amounts of energy
determined by the spectral properties of their source.
Only photons with sufficient energy to create an
electron–hole pair, that is, those with energy greater than
the semiconductor Photons also exhibit a wavelike
character with the wavelength, λ, being related to the
photon energy, Eλ in Eqn (1)
(1)
Where h = Plank’s constant
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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c= the speed of light.
Only photons with sufficient energy (energy greater than
the semiconductor band gap Eg) create an electron–hole
pair and will contribute to the energy conversion
process. Thus, the spectral nature of sunlight is an
important consideration in the design of efficient solar
cells.
the understanding and modelling of PV cell is
necessary[6,7,8]. The ideal equivalent circuit of a solar
cell is a current source in parallel with a single-diode as
shown in fig 1.4a.
Types of PV cell:
Fig: 3 Ideal equivalent circuit diagram of PV cell
The current generated by the cell is given by eqn (2)
(2)
Where Io = diode reverse bias saturation current
q = electron charge
m = diode ideality factor
Fig.2 Types of PV Cells
k = Boltzmann’s constant
Based on the semiconductor material, the PV cells are
classified as crystalline and non crystalline (thin film)
PV cells.
T = cell temperature
The crystalline solar PV cells include single crystalline
silicon (c-Si) cells, poly-crystalline silicon (pc-Si) cells
and Gallium Arsenide (GaAs) cells. Non crystalline or
thin film PV cells mainly include the Amorphous
Silicon (a-Si) cells, Cadmium Telluride (CdTe) cells and
the Copper Indium Diselenide (CIS) cells. A PV cell has
a voltage of just 0.6V. To meet the voltage/current
demand according to a given application, several solar
cells are connected electrically in series or parallel to
realize a PV module. Several PV modules are connected
in series according to the voltage requirement of the
application to make a PV string. Several PV strings are
connected in parallel according to the current
requirement of the application to make a PV array.
The open circuit voltage Voc is the greatest value at the
cell terminals and it is given by Eqn (3) for I=0
Is= Short circuit current
(3)
So the output power is given by Eqn (4)
(4)
P-V characteristic of PV cell is shown in fig. 1.4b.
Again the power produced by a single module is not
sufficient to meet the power demands for most of the
practical purposes. PV arrays can use inverters to
convert the dc output into ac and use it for motors,
lighting and other loads. The modules are connected in
series for more voltage rating and then in parallel to
meet the current specifications.
One Diode Model:
As mentioned previously, the solar cells are
semiconductor with a p-n junction fabricated in a thin
wafer or layer of semiconductors. When exposed to light
a photo current proportional to the solar radiation is
generated, if the photon energy is greater than the band
gap. In the dark, the I-V characteristics of a solar cell
have an exponential characteristic similar to that of a
diode. In order to maximize the extracted output power
from a PV power plant with the help of MPPT control,
Fig: 4 P-V characteristics of PV cell
The practical equivalent circuit model of a solar cell
consists of a current generator and a diode plus series
and parallel resistance as shown in Fig.1.5
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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II. VARIOUS TOPOLOGIES
A. Parallel-connected PV modules:
fig .2.1 shows parallel connection of PV modules. In this
voltage of all PV cells are same but currents are
different which depends on solar radiation level [3].
Fig: 5 Practical equivalent circuit diagram of PV cell
More accuracy can be introduced to the model by adding
a series resistance and shunt resistance. The effect of
solar radiation, diode ideality factor and PV cell
temperature are also taking into consideration to get the
accurate result from the model. Figs 1.6a to 1.6c show
the I-V characteristics of PV cell for various parameters.
Fig .9 shows parallel connection of PV modules
Fig. 6 V-I char. of PV cell for various solar radiation.
Fig 2.2a shows the typical generation characteristics and
I–V curve for two parallel-connected PV modules that
have different generation conditions. In this figure, PV1
and PV2 represent shaded and non shaded modules,
respectively [9,10]. In parallel connection, the
generation voltage is the same for each PV module.
Thus, the operating point of each PV module is given by
the point of intersection of the operation line, which is
parallel to the y-axis. When the output current of the PV
system is increased from zero to the maximum current,
the operation point of each PV module moves as
indicated in Fig.2.2b for PV1 and for PV2.
Fig. 7 V-I char. of PV cell for various diode Ideality
factors.
Fig.10 I–V curve for two parallel-connected PV
modules
Fig. 8 V-I char. of PV cell for various temperatures.
As solar radiation increases, Isc increases but Voc is
almost constant compared to Isc as shown in fig. 1.6a.
As diode ideality factor increases, Isc remain constant
but Voc increases in fig. 1.6b. As temperature of PV cell
increases, Voc decreases as shown in fig.1.6c.
Hence, the total output power characteristic of these PV
modules is obtained as shown in Fig. 2.2b. Then, the
total output power is given by Eqn (5)
(5)
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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Fig. 13 I-V curve for PV modules
Fig.11 P–V curve for two parallel-connected PV
modules
This means that the shaded PV module cannot generate
any power and causes a power loss. On operation line,
the non shaded PV module, PV2 generates the
maximum power, but the shaded module, PV1 causes a
power loss. Hence, the output power is given by Eqn 6
B. Series-connected PV modules:
Fig. 2.4a shows the typical I-V curve for PV modules
connected in series for the same conditions shown in
Fig. 2.3 In series connection the generation current is the
same for each PV module[3]. Therefore, the operating
point of each PV module is given by the point of
intersection of the operation line, parallel to the x-axis
and the – curve of each PV module. When the output
current of the PV system is increased from zero to the
maximum current, the operation point of each PV
module moves as indicated in Fig. 2.4a, for PV1 and for
PV2.
(6)
Fig.14 P–V curve for two series-connected PV modules
The total output power characteristic of this PV system,
the P-V curve, is obtained in the same manner and is
shown in Fig.2.4b. Two peaks in power exist, but the
output powers at these peak points are much smaller
than that of the parallel connected condition shown in
Fig. 2.4b.
III. COMPARISON BETWEEN SERIES &
PARALLEL CONNECTION
1. When two identical cells are connected in series, the
short-circuit current of the system would remain same
but the open circuit voltage would be twice.
Fig .12 shows parallel connection of PV modules
On operation line, the shaded PV module, PV1
generates its maximum power, but the non shaded
module, PV2 does not generate its maximum power yet
[9,10]. When the operation line moves, the operation
points of each module PV1 and PV2 move respectively
and the generation power increases. However, the
operation point of PV moves to the negative voltage
region because the current generated from PV flows
through the bypass diode connected in anti-parallel with
PV and the resultant generation power on PV becomes
negative.
2. When two identical cells are connected in parallel, the
open circuit voltage of the system would remain same
but the short-circuit current would be twice
3. In series connection two peaks in power exist, but the
output powers at these peak points are much smaller
than parallel connected PV modules.
4. In parallel connection if voltage across each cell is not
equal then there is a possibility of circulating current.
5. In parallel connection, if the voltage at the maximum
power point is substantially different for one of the cells
then this will force all cells to operate for less maximum
power point.
6. In series connection, if one cell produces a
significantly lower current than the other cells, then the
string will operate at that lower current level and the
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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remaining cells will not be operating at their maximum
power points.
strategy for optimization of solar photovoltaics
array
under
Non-Uniform
Illumination
Conditions”, 37th IEEE Photovoltaic Specialists
Conference, Seattle, USA June 19-24, 2011
IV.CONCLUSION
This paper presents the series and parallel connection of
PV modules. To improve the performance of PV
module, power extraction from PV cell need to be
increased. In series connection, total power is sum of
power output of shaded and non shaded module. The
drawback of series connection is unequal current due to
partial shading. To improve the performance of PV
module in series connection, antiparallel diodes are
connected to bypass the shaded module but it degrades
the voltage output of that string. In parallel connection,
total power is the subtraction of power output of non
shaded and shaded module. The drawback of parallel
connection is circulating current due to unequal voltages
and antiparallel diode cannot used in partial shading
problem.
To overcome the drawbacks of series parallel topology,
reconfiguration approach is more effective. In this, PV
cells are rearranged to get maximum power and avoid
the use of antiparallel diode. This technology operates at
GP and avoids multiple peaks in the system. To
reconfigure the PV cell structure, automatic mechanism
will be most efficient approach. It will make the system
more efficient, fast. Optimum utilization of PV cells
may reduce the size and cost of solar energy application.
[4]
Toshihisa Shimizu, Member, IEEE, Masaki
Hirakata,
TomoyaKamezawa,
and
Hisao
Watanabe.“Generation Control Circuit for
Photovoltaic Modules.” IEEE transactions on
power electronics, vol. 16, no. 3,pp.293-300,
May 2001
[5]
Jeffery L. Gray, “The Physics of the Solar Cell.”
Purdue University, West Lafayette, Indiana,
USA, pp 1-52.
[6]
K. Kobayashi, I. Takano, and Y. Sawada, “A
study on a two stage maximum power point
tracking control of a photovoltaic system under
partially shaded insolation conditions,” Solar
energy Materials and Solar Cells, vol. 90, no. 18,
pp. 2975-2988, Nov. 2006
[7]
L. Kui-Jun and K. Rae-Young, “An adaptive
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systems,” IEEE Trans. Power Electron. vol. 27,
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[8]
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maximum-powerpoint tracking controller for
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Trans. Ind. Electron., vol. 48, no. 3, pp. 594-601,
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[9]
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[10]
A. bete, E. Barbisio, F. Cane, “A study of
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REFERENCES
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H. Patel, V. Agarwal “MATLAB-Based
Modeling to Study the Effects of Partial Shading
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