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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 03, March 2019, pp. 994-1000. Article ID: IJMET_10_03_100
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
EFFECT OF HOT-SPOTTED CELL ON PV
MODULE PERFORMANCE
Najib Hamisu Umar*
Sharda University, Greater Noida (NCR, Delhi) - 201306, India
Birinchi Bora and Chandan Banerjee
National Institute of Solar Energy, Gurugram, India
*corresponding author
ABSTRACT
In this paper, the effects of the hot-spotted cell on PV module were evaluated. The
experimental observation was based on 100 kW PV array composed of 20 PV modules.
It was found that an increasing number of hot-spotted solar cells in a PV module would
likely increase its output power loss. It was also noticed that most of the PV modules
affected by hot-spotted PV string are relatively affected by high-temperature levels,
dust, and Partial shading due to trees or tall vegetation. Furthermore, the average
performance ratio (PR) and degradation rate (DR) of all examined PV modules were
analyzed. PR was observed to have a higher value of 0.78 in a non-hot-spotted PV array,
whereas low PR of 0.65 was observed in a hot-spotted PV array. High DR of 3.13/year
was observed in hot-spotted PV array; while low DR of 1.48/year was found in a module
with no hot-spot. It was evident that the mean PR is significantly reduced due to the
existence of hot-spots in the PV modules. DR was also increased due to hot-spot in the
PV array. Hence, it is important to select materials that have the highest thermal
stability to avoid mild hot spot situations that will lead to immediate damage of the
panel. Hot-spot study analysis will help increase PV lifetime power output by detecting
and preventing hot spotting before it permanently damages the PV panel.
Keyword: Photovoltaic system, Hot-spot, Performance ratio, Degradation rate,
Module defects, PV module
Cite this Article Najib Hamisu Umar, Birinchi Bora and Chandan Banerjee, Effect of
Hot-Spotted Cell on Pv Module Performance, International Journal of Mechanical
Engineering and Technology, 10(3), 2019, pp. 994-1000.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3
1. INTRODUCTION
In recent years, the deployment of photovoltaic (PV) system has increased significantly due to
its availability and cleanliness. Hence it is essential to conduct accurate studies on degradation
Najib Hamisu Umar, Birinchi Bora and Chandan Banerjee
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and performance analysis of the PV system. The aging and degradation of PV modules
significantly depend on climatic and environmental conditions such as ambient temperature,
relative humidity, solar radiation and dust [1-4]. Hot-spot heating occurs when a cell in a string
of series connected cells is negatively biased and dissipates power in the form of heat instead
of producing electrical power. This happens when the current generated by a given cell is lower
than the string current [5, 6].
Hot-spots may occur in a PV module when the solar cells are mismatched or have certain
defects, or when one or more cells in the module are partially shaded or damage [7-9]. The
concept of current mismatch refers to any mechanism that can cause a reduction in the short-
circuit current of a cell compared to other cells in the series string [10]. The power dissipation
for any given faulty or shaded cell depends on the series-parallel configuration of cells in a
module. In general, increasing the number of cells in series increases the power dissipation and
increasing the number of cells in parallel decreases the power dissipation of the faulty cell [9,
11]. The main aim of this paper is to analyze the impact of hot-spots on the performance of PV
modules.
2. METHODOLOGY
In In this paper, 100kW PV array composed of 20 solar modules underwent inspection to
identify modules with hot-spot. The Infra-red (IR) images were used to enable us to detect hot-
spot in the module. The module terminals were short-circuited, and the IR image is taken from
the back site. The FLIR E-60 IR camera was used to take the IR images. The temperature at
different points of each PV modules is extracted from IR images. The FLIR E-60 IR camera
and module with hot-spot are presented in Fig. 1 and 2 respectively. The temperatures were
normalized to the reference condition of 1000 W/m2 and 40°C, using the relation [11, 12]:
𝑇𝑛𝑜𝑟𝑚𝑎𝑙𝑖𝑧𝑒𝑑 =40 +(𝑇𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 − 𝑇𝑎𝑚𝑏𝑖𝑒𝑛𝑡)× 1000
𝐼𝑟𝑟𝑎𝑑𝑖𝑎𝑛𝑐𝑒
Where
𝑇𝑛𝑜𝑟𝑚𝑎𝑙𝑖𝑧𝑒𝑑 = 𝑛𝑜𝑟𝑚𝑎𝑙𝑖𝑧𝑒𝑑 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 (℃)
𝑇𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 = 𝑚𝑜𝑑𝑢𝑙𝑒 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 𝑓𝑟𝑜𝑚 𝐼𝑅 𝑖𝑚𝑎𝑔𝑒(℃)
𝑇𝑎𝑚𝑏𝑖𝑒𝑛𝑡 = 𝑎𝑚𝑏𝑖𝑒𝑛𝑡 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑎𝑡 𝑠𝑖𝑡𝑒 (℃)
Also
𝑀𝑜𝑑𝑢𝑙𝑒 ∆𝑇 = (𝑇max 𝑐𝑒𝑙𝑙,𝑛𝑜𝑟𝑚 − 𝑇𝑚𝑜𝑑𝑢𝑙𝑒,𝑛𝑜𝑟𝑚)
Where
𝑇max 𝑐𝑒𝑙𝑙,𝑛𝑜𝑟𝑚 = 𝑛𝑜𝑟𝑚𝑎𝑙𝑖𝑧𝑒𝑑 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑐𝑒𝑙𝑙 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑚𝑜𝑑𝑢𝑙𝑒𝑠
𝑇𝑚𝑜𝑑𝑢𝑙𝑒,𝑛𝑜𝑟𝑚 = 𝑛𝑜𝑟𝑚𝑎𝑙𝑖𝑧𝑒𝑑 𝑚𝑜𝑑𝑒𝑙 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑚𝑜𝑑𝑢𝑙𝑒
The mean monthly temperature of the site is greater than 27℃
Effect of Hot-Spotted Cell on Pv Module Performance
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Figure. 1: FLIR E-60 IR camera Figure. 2: Module IR image
The PV modules are allowed to operate for three months period (from February to April
2018). The daily electricity generation in kWh was extracted using a SCADA system.
Meanwhile, another 100kW PV array of the same number of modules but with no hot-spot ware
also analyzed. Average performance ratio (PR) and average degradation rate (DR) was
calculated for both hot-spot and non-hot-spot modules, using the following relations [13, 14]:
𝑃𝑅 = 𝑌
𝑓
𝑌
𝑟
Where
𝑌
𝑓=𝑓𝑖𝑛𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 𝑜𝑢𝑡𝑝𝑢𝑡 (𝑘𝑊ℎ)
𝑛𝑜𝑟𝑚𝑖𝑛𝑎𝑙 𝐷𝐶 𝑝𝑜𝑤𝑒𝑟 (𝑘𝑊)
𝑌
𝑟=𝑡𝑜𝑡𝑎𝑙 𝑖𝑛𝑝𝑙𝑎𝑛𝑒 𝑖𝑟𝑟𝑎𝑑𝑖𝑎𝑛𝑐𝑒 (𝑘𝑊ℎ/𝑚2)
𝑃𝑉 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑖𝑟𝑟𝑎𝑑𝑖𝑎𝑛𝑐𝑒 (𝑘𝑊/𝑚2)
𝐷𝑅=𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑃𝑅 − 𝑓𝑖𝑛𝑎𝑙 𝑃𝑅
𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑃𝑅 ×100
Furthermore, PR Comparison was made between hot-spot and non-hot-spot modules, and
lastly, DR for hot-spot modules and non-hot-spot was compared. The PV module and inverter
specifications were presented in Table 1 and 2 respectively.
Table 1: PV module specifications
1.2 kW Inverter Specifications
Maximum DC input voltage (Vmax)
600V
Rated DC input voltage (Vdcr)
185V
Rated DC input power (Pdcr)
1500W
Maximum input short circuit current
12.5A
Rated AC power (Pacr)
1200 W
Maximum AC output power (Pacmax)
1200 W
Rated AC grid voltage (Vac,r)
230V
AC voltage range
180..264 V
Rated output frequency (fr)
50 Hz / 60 Hz
Maximum efficiency (ηmax)
94.8%
Najib Hamisu Umar, Birinchi Bora and Chandan Banerjee
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Table 2: inverter specifications
Polycrystalline Module Specifications
Power output
Pmax
W
100
Module efficiency
ηm
%
13.09
Voltage at Pmax
Vmpp
V
29.5
Current at Pmax
Impp
A
7.20
Open-circuit voltage
Voc
V
36.0
Short-circuit current
Isc
A
7.80
Nominal operating cell temperature
NOCT
°C
46 +/- 2
Temperature coefficient of Pmax
γ
%/°C
-0.45
Temperature coefficient of Voc
βVoc
%/°C
-0.37
Temperature coefficient of Isc
αIsc
%/°C
0.06
3. RESULTS AND DISCUSSION
In this paper, the 100kW PV array composed of 20 PV modules was analyzed. The defectives
modules were identified by visual and IR inspection. The plant has been in operation since
2010.
3.1. PV array without hot-spot
The module cell temperature was found to be less than 80℃. The low temperature is due to the
absence of the defective module in the PV array. There is high energy production in the PV
array with no hot-spot defect. The average PR and DR was found to be 0.78 and 1.48/year
respectively.
3.2. PV array with hot-spot
It was observed that, out of 20 PV modules, only three modules were found to be defective with
hot-spot. The module cell temperature was found to be higher than 120℃. The sharp increase
in temperature of hot cells is attributable to the combined effect of the two parts, dissipated
power and heat converted from radiation. The average PR and DR was found to be 0.65 and
3.13/year respectively.
In general, the increasing number of hot-spots in PV modules, it is more likely to have a
more significant drop in output power. On the other hand, the PV modules with a whole hot-
spotted PV string are caused due to faulty bypass diodes. Therefore, there is more chance to
have less output power produced by these particular PV modules, since bypass diodes is used
to overcome the issue of the partial shading conditions which usually PV modules suffer from.
As presented in Fig. 3, high electricity generation is noticed in a module with no hot-spot,
whereas low electricity produced observed in a module with hot-spot. Performance ratio for
hot-spotted and non-hot-spotted PV module was presented in Fig. 4.
Performance ratio was observed to have a higher value of 0.78 in a non-hot-spotted PV
array, whereas a low-performance ratio of 0.65 was found in the hot-spotted PV array. The high
degradation rate of 3.13/year was seen in hot-spotted PV array; while PV array with no hot-
spot has the low degradation rate of 1.48/year. The analysis of the results exhibits that the hot-
spotted cell in PV module increases module temperature leading to accelerated aging of the PV
module, and gradually reduces the system efficiency.
Effect of Hot-Spotted Cell on Pv Module Performance
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Table 3: performance parameters for hot-spotted and non-hot-spotted PV module
Module without hot-spot
Module with hot-spot
0.78
0.65
1.48
3.13
13.3
33.4
74.6
126.2
Figure. 3: Electricity generation comparison
Figure. 4: Performance ratio comparison
4. CONCLUSION
In this paper, the effects of the hot-spotted cell on PV module performance were evaluated. The
experimental observation was based on 100 kW PV array composed of 20 PV modules. It was
found that an increasing number of hot-spotted solar cells in a PV module would likely increase
its output power loss. It was also noticed that most of the PV modules affected by hot-spotted
PV string are relatively affected by high-temperature levels, dust, and Partial shading due to
trees or tall vegetation. Furthermore, the PR and DR of all examined PV modules were