Article D'Psa

Electrotehnica, Electronica, Automatica (EEA), vol. 71 (2023), nr. 1, pp.01-12
https://doi.org/10.46904/eea.23.71.1.1108001
1
Importance of Preventive Maintenance in Solar Energy Systems
and Fault Detection for Solar Panels based on Thermal Images
Alexandru-Ionel CONSTANTIN1, Gabriela IOSIF1, Rareș-Andrei CHIHAIA1, Dorian MARIN*1,
Gafireh Umut ABU SHEHADEH2, Mehmet KARAHAN3, Bilgin GERIKOGLU3, Stefan STAVREV4
1 Institutul Național de Cercetare-Dezvoltare pentru Inginerie Electrică (INCDIE) ICPE-CA, Splaiul Unirii, Nr. 313,
Sector 3, 030138, Bucharest, Romania,
2 Atahan Arge Turizm, Ehlibeyt Mahallesi, Tekstilciler Cad. Bayraktar İş Merkezi. 17/A Kat: 9, No.:33 Balgat,
06520, Çankaya, Ankara, Türkiye
3 Susurluk Mesleki ve Teknik Anadolu Lisesi, Sultaniye Mahallesi Yeni Sanayi 1. Sok. No 2/B 10600 Susurluk/
Balıkesir, Türkiye
4 EGLA Consulting Oy, Juuritie 7, 03100 NUMMELA, Finland
* Corresponding author
Abstract
The article presents the importance of renewable energy in reducing the potential dangers of global warming and
climate crises, related to a proper maintenance in solar energy systems in the context of increase in global energy
consumption which generates an excess of greenhouse gases. The operation and maintenance activities of
photovoltaic systems represent key aspects for obtaining the profitability of investments and ensuring their
viability and reliability. Currently, the procedures applied mainly refer to simple techniques such as visual
inspection and scheduled maintenance strategies. Also, the types of faults that can occur in photovoltaic panels
can be detected by thermography (single hot spot, multiple hot spots, activation of the bypass diode and a higher
temperature of the junction box) and are therefore presented with their characteristics and consequences. In the
last part of the article, a thermal imaging processing software based on artificial intelligence technology is
proposed for use for the preventive maintenance, in order to detect the photovoltaic (solar) panels with faults to
be repaired or changed to increase the efficiency of the system. The software will be used to develop an
innovative maintenance and repair curricula for the departments related to solar energy in vocational and
technical education schools in order to better predict and prevent malfunctions in solar energy systems.
Keywords: Solar Energy, Photovoltaic system, Preventive maintenance, Thermography, Fault detection
Received: 2 March 2023
How to cite this paper:
CONSTANTIN A-I., IOSIF G., CHIHAIA R-A., MARIN D., ABU SHEHADEH G. U., KARAHAN M., GERIKOGLU B., STAVREV
S., “Importance of Preventive Maintenance in Solar Energy Systems, Fault Detection for Solar Panels based on
Thermal Images”, in Electrotehnica, Electronica, Automatica (EEA), 2023, vol. 71, no. 1, pp. 01-12, ISSN 1582-
5175.
1. Introduction
Energy is among the most important components
of economic activities, production processes and
daily life. Being determinant in both the economic
growth and development indicators of countries,
energy is a scarce resource. World resources have
been consumed to obtain energy and the damaged
natural environment in the last two centuries [1].
A great part of the energy produced in the world
is obtained from fossil fuels such as oil, coal and
natural gas. The damage to the natural environment
is not limited to the production of energy from fossil
fuels. Use of these resources also results in high
carbon emission rates in the atmosphere, which is
the primary cause of climate crisis.
Threat caused by the production and use of fossil
resources is getting closer to an irreversible point,
which threatens all the gains of humanity. For this
reason, it becomes very critical to turn to renewable
resources.
The energy needs of the rapidly increasing
population and developing industry cannot be met
with limited resources, and the gap between energy
production and consumption is increasing. It is
estimated that global energy consumption will be
twice the amount of energy consumed in 1998 by
2035 and three times in 2055 [2].
This has led the world to seek alternative energy
sources. The search for alternative energy has
gained great momentum and studies on renewable
energy have begun to increase.

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Renewable energy sources are mainly grouped as
“solar”, “wind”, “geothermal”, “hydraulic”,
“biomass”, “wave” and “hydrogen” energies. It can
be said that the sun is the main source of most of
these types of energy and has a direct or indirect
effect on them. The 1950s were a turning point in
terms of search for renewable energy resources.
In 1954, Bell Labs demonstrated the first
practical silicon solar cell [3], and the New York
Times reported on a breakthrough in solar
photovoltaic (PV) technology that “may mark the
beginning of a new era, leading eventually to the
realization of one of mankind’s most cherished
dreams–the harnessing of the almost limitless energy
of the sun for the uses of civilization” [4].
Researchers discovered that silicon transistors,
the building blocks of computers, can generate
electricity when exposed to sunlight. However, in
the same year, nuclear power generation costs
began to decline, and throughout the 1950s,
extensive R&D support for nuclear energy emerged
in the United States. Solar energy has therefore
been overshadowed by nuclear energy since its
inception.
With the increase in the world population, the
demand for clean and cheap energy increased
steadily in the last decades.
The negative consequences of nuclear energy
and the high investment costs also caused the
popularity of this energy source to decrease.
The damage caused by fossil fuels to the
environment and the depletion of this resource have
led people to seek alternative energy sources (solar,
wind, hydraulic, geothermal, wave, biomass).
Solar energy is among the important clean energy
sources and has great growth potential. With the
development of technology and the decrease in
investment costs [5], solar energy has become one
of the most prominent sources among alternative
energy sources in recent years.
1.1. Use of solar energy in the World
The current situation of energy consumption
worldwide is given in [6]. The Global energy
consumption, which was approximately
156 Exajoules in 1965, increased by approximately
3.75 times to 584 Exajoules in 2019.
The share of renewable energy in total energy,
which followed a nearly constant course from 1965
to the beginning of the 2000s, was around 6% in the
mentioned period.
A serious upward trend has started since 2003,
and in parallel with this upward trend, the share of
renewable energy has increased to approximately
11.4 % in 2019. The amount of installed capacity
from 2000 to 2019 has increased more than 3 times
for total renewable energy sources. This increase is
approximately 500 times in the installed capacity of
solar energy.
This increase is also an indication that solar
energy has come to the fore as a serious option [7].
In the last 20 years, the installed solar power in
the world has increased with an annual growth rate
of 33.2 % and reached 710 GW installed power by
the end of 2020.
While the global solar energy installed power was
recorded as 940 GW at the end of 2021 with the
record installations added last year, it increased to
the "TW" level as of May 2022 [8]. For a sustainable
future, it is predicted that the installed solar power
will exceed 9 TW in 2050.
Solar energy can be converted into different
forms of energy with a wide range of applications.
For example, thermal energy is produced with
the help of collectors made of materials that absorb
heat.
Photovoltaic electricity is obtained by capturing
solar radiation by a photovoltaic cell system and
converting it directly into electricity. This electricity
is either used directly or stored in special batteries
or fed into the national grid [9].
1.2. Role in fight against climate change
In the past two centuries, primary energy uses
have undergone a long-term shift from conventional
fuels to coal, from coal to oil and natural gas.
Currently, 80 % of the available primary energy
supply is based on liquid fossil fuels [10].
Energy use, which still relies heavily on fossil
fuels, will continue to increase significantly in the
coming decades. It is estimated that the use of
crude oil and natural gas will increase by 30% and
53.2 %, respectively, and global energy consumption
will grow by 48 % in 2040. This trend has the
potential to cause more greenhouse gases and then
serious environmental problems with its effects on
the climate [11].
The goal of reducing the potential dangers of
global warming and climate crises and making
tomorrow more “sustainable” has become one of the
priorities of world economies. An unprecedented
effort is being made to control the emission of
carbon dioxide gas, the number one cause of global
warming. Countries are increasing their
commitments to move towards the common net zero
target and to eliminate their carbon footprints, and
they support this with various plans.
The diffusion and transfer of climate-friendly
energy technologies has become a constant topic in
international climate negotiations and major
conferences.
Developed countries, especially the European
Union (EU), are trying to take concrete steps to use
renewable energy sources more.
Starting from the late 1980s, studies have been
carried out under the leadership of the United
Nations and international organizations to reduce
the negative impact and pressure of people on the
climate system.
As a result of these studies, the United Nations
Framework Convention on Climate Change (UNFCCC)
was established in 1992 and the Kyoto Protocol (KP)
was established in 1997 with wide participation.
While the UNFCCC and KP brought legal regulations
to limit and reduce anthropogenic greenhouse gas
emissions, on the other hand, they have become

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increasingly active in international emission trade,
technology, and capital movements.
The comprehensive report published in October
2018 by the Intergovernmental Panel on Climate
Change (IPCC), the world's leading organization in
the assessment of the effects of climate change,
made it clear that the climate crisis should be
addressed urgently. The IPCC warns that if we do
not want climate change to have even more
devastating consequences on people and the world,
we should not rise above or at least 1.5 °C above
preindustrial levels.
The report reveals the enormous differences
between the 1.5 °C and 2 °C scenarios. We should
try to limit the global average temperature increase
to 1.5 °C (Paris United Nations (UN) Climate Change
Conference (21st Conference of Parties - COP21)).
The IPCC states that the only way to keep
warming below 2 degrees is that the world is
completely carbon-free by the end of this century,
without consuming any coal, oil, gas. This increases
the importance of solar energy, which is a more
stable, sustainable, and environmentally friendly
energy source.
Since the rays coming from the sun do not emit
any harmful gas, they create a healthy and safe
energy potential. In this direction, sun rays are
absorbed today with special systems; can be stored
and used directly.
2. The importance of preventive maintenance and
repair
There is a major downside to renewable energy
sources, which are gaining more attention as a
result of environmental concerns, demands for
security in energy supply, and the need for greater
independence in fuel imports.
The cost of energy produced from renewable
sources is still higher than the cost of energy from
conventional plants. Although the importance of
solar energy systems in combating climate change is
known, it has not yet become widespread in the
world at the desired level.
The economic life of Solar Power Plants is
considered to be over 25 years. The efficiency of a
facility that will produce energy for 25 years will
change over time. Solar panels can be damaged over
time, due to weather conditions, temperature
changes, pollutants, and UV rays.
The main factors affecting the efficiency of Solar
Energy Systems are the materials used, labour and
maintenance / repair services. In order for Solar
Power Plants to reach the promised operating
performances, to be long-lasting and to avoid vital
and financial losses, maintenance and repairs should
be done professionally.
The maintenance and repair of solar panels
should be carried out by experts in their fields, using
professional measuring devices calibrated in
accordance with international standards.
The equipment to be used during the controls
must comply with the standards, and the personnel
must have the necessary qualifications. Developing
innovative approaches in the training of personnel
who will work in the maintenance and repair of solar
energy systems will contribute to the protection of
the environment and the fight against climate
change.
Solar energy systems are long-lasting but highly
costly investments.
Malfunctions that may occur not only reduce the
service life of the systems, but also cause revenue
losses during the recovery process. Therefore, it is
extremely important to prevent the occurrence of
the malfunction as well as to eliminate the
malfunction in a short time. However, such an early
warning system has not yet been developed.
The energy demand in the world continues to
increase every year. Therefore, energy efficiency
and the ability to use renewable energy sources are
one of the ways to meet the increasing energy
needs.
Carrying out the maintenance and repairs of solar
energy systems without malfunctions will both
reduce maintenance costs and eliminate the energy
loss caused by the failure of the systems, thus
contributing to energy supply. Thanks to preventive
maintenance and repair services, the maintenance
and repair costs of the facilities will also be
reduced.
Recently, there is an increased interest regarding
how to evaluate the quality and performance of
photovoltaic modules and their service lifetime.
Thus, the reference definition of the defective PV
panel was considered from Subtask 3.2: Review of
Failures of Photovoltaic Modules [12]. A PV panel is
considered defective if its power has irreversibly
degraded under normal operating conditions or
creates a safety problem. A purely cosmetic problem
that has no effect on the power or safety in
operation is not considered a defect of the PV
module.
A defect of the photovoltaic module is relevant
to warranty terms only when it occurs under normal
operating conditions. A problem that is caused by
the misuse of the module or generated by the local
environment in which the module operates, is not
considered to be a defect.
Dirt on the module or faults caused by lightning
strikes are not considered defects. The dirt problem
has to be treated by the operator, and lightning
strike is considered a natural phenomenon which can
occur if the solar park is not suitably protected and
for which the module is not designed to withstand.
However, defects due to heavy snow load are
considered defects of the module, if stated in the
technical specification that the product can operate
under these conditions.
On their entire service life, photovoltaic modules
are subjected to mechanical stresses, solar
radiation, humidity, heat, snow, hail, salt fog, acid
rains, dust, wind, abrasive particles, etc.
All these external causes, when acting on PV
modules made with incompatible materials, produce
defects and/or accelerated degradation of their
output power. It is absolutely normal that these
causes affect all photovoltaic modules, but the
degradation of power, for those manufactured with

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compliant materials, must be under 0.7 %/year. The
main phenomena that occur in photovoltaic modules
and which lead to their failure and/or premature
aging are listed below [13]:
— Power degradation;
— Corrosion of electrical contacts;
— Cells breaking;
— Interrupting cell connections;
— Delamination of encapsulation;
— Air bubbles formation inside the encap-
sulation;
— Changing the colour of the encapsulated foil
and/or the back sheet;
— Snail trails (dark cell traces due to cell
cracking);
— Back sheet deformation;
— Degradation of ribbon welding on the PV cell;
— Burning encapsulation and film due to electric
arc or hot spot;
— Bypass diode failure;
— Breaking the glass;
— Degradation of the anti-reflex layer of the
glass;
— Degradation of the adhesive that secures the
connection box.
Maintenance deficiencies can be easily identified
in old photovoltaic parks. One of the common
shortcomings is related to the growing vegetation in
the immediate vicinity of the panels. The most
common situations encountered is due to the plants
that grow under the panels and seeking the sunlight,
come out above the PV panels generating hot spots.
The hot spot phenomenon produces not only a
decrease in the string power of the shaded panel but
also its irreversible degradation by changing the
colour of the EVA film and destroying the structure
of the silicon crystal [14].
The hot spot generated by the plant that grew
under the panel can reach 107 oC and will destroy
the PV cell eventually. Hot-spot heating occurs when
there is one low current solar cell in a string of at
least several high short-circuit current solar cells. If
the operating current of the overall series string
approaches the short-circuit current of the "bad"
cell, the overall current becomes limited by the bad
cell.
The extra current produced by the good cells
then forward biases the good solar cells. If the series
string is short circuited, then the forward bias across
all of these cells reverses biases the shaded cell.
Hot-spot heating occurs when a large number of
series connected cells cause a large reverse bias
across the shaded cell, leading to large dissipation
of power in the poor cell. Essentially, the entire
generating capacity of all the good cells is dissipated
by the bad cell. The enormous power dissipation
occurring in a small area results in local
overheating, or "hot spots", which in turn leads to
destructive effects, such as cell or glass cracking,
melting of solder or degradation of the solar
cell [15].
A photovoltaic (PV) plant is essentially an
electrical power system with very few elements
impacted by regular ageing and damage. However,
overstraining due to high temperatures and
electrical overloads may be substantial in the case
of inverters, switches and other system components.
In addition, the components exposed to weather
fluctuations require continuous supervision in order
to avoid premature damage.
Preventive Maintenance (PM)
It represents the service which, by scheduled
system interventions, avoids the accidental fall of
the essential components related to the
photovoltaic system. Constant monitoring,
associated to a Condition-based maintenance (CBM)
program, is indispensable to providing a high-
Performance Ratio (PR).
In the frame of maintenance contracts, intensive
monitoring of the operating parameters and
technical conditions regarding the photovoltaic
installation is carried out. All the gathered data is
stored in the monitored system database and is used
as a constant resource for periodic reports on the
performance of the photovoltaic system. Each
maintenance activity is recorded in the operating
and maintenance report of the supervised PV plant
and transmitted to the customer monthly. All the
activities focus on cost efficiency and safety
regarding the operation of photovoltaic installations.
Preventive (or planned) maintenance (PM)
It includes routine inspections and equipment
maintenance, defined by technical specifications,
with a fixed frequency established by equipment
type, environmental conditions, and warranty
terms. The purpose of PM maintenance is to prevent
unnecessary damage and production losses (power
losses).
This approach is becoming increasingly popular
due to the fact that it significantly reduces the
probability of unplanned withdrawing from service
of the PV power plant. Optimization and moderate
costs associated to PM activity comparing to the
total cost will always be considered, thus avoiding
unnecessary activities.
The intervention usually begins with the visual
inspection of the equipment, in particular of the PV
modules. Some hotspots, like the ones caused by
bird droppings or glass breakage can be visible to
the naked eye. Still, there are some defects which
are visible only by using the thermal camera, such as
the poor connection between the cells, the
activation of the bypass diode in the panel junction
box, broken PV cell or damaged encapsulation film.
Corrective maintenance
It is the intervention that is typically performed
following Preventive Maintenance (PM) finding when
an inappropriate operation of an inverter is
detected (for example, entering limiting /protection
mode, with or without real justification, or entering
thermal protection due to inadequate ventilation) or
when relatively low power produced by a series of

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modules is encountered (one of the string’s modules
is provided by power losses). It is usually solved by
adjusting/repairing (in case of inverters) or
replacing/repairing the faulty module.
The Corrective Maintenance is different from
Reactive Maintenance. The latter involves
interfering with a PV system or equipment when it is
already out of service.
In general, preventive maintenance (scheduled
according to the contract) associated with the
corrective maintenance which is described above
apply where the monitoring equipment does not
provide sufficient information to allow a Condition-
based maintenance program.
Condition-based maintenance (CBM)
It uses real-time data from PV power plants in
order to anticipate faults and/or lower performance
and prioritize activities maintenance and resource
allocation. Intervention is performed if one or more
indicators show that the equipment will fail, or the
performance of the equipment deteriorates.
For the most part, PV power plants are equipped
with hardware and software equipment which offer
real-time data on the state of the PV system such
as: DC and AC (active and reactive) power, electric
current and voltage at the inverters’ input and
output of, PR (Performance Ratio), weather data
(temperature, humidity, wind speed and solar
irradiation) and other data depending on the
complexity of the monitoring equipment. Such a
system determines the state of a PV power plant (PV
panels, inverters, connection boxes, cables,
connectors, etc.), intervening when necessary (i.e,
decrease of PR, the current /power of an inverter
drops inappropriately compared to the other
inverters, etc.).
The intervention consists in performing specific
parameter measurements in the area where a
disturbance has been identified, on the DC side
comprising the area of PV panels along with cables,
connectors and Stringer Boxes or the alternating AC
side with inverters, cables, and connection boxes.
Both universal instruments (voltmeter, ammeter,
and ohmmeter) as well as equipment specific to PV
system measurements are used.
The measurements that determine the status of
PV panels must be performed according to the SR EN
61829:2016 – “Photovoltaic (PV) array. On-site
measurement of current-voltage (IV)
characteristics”, according to the SR EN 60904-1,
Art. 5 –“Measurement of the current-voltage of
photovoltaic devices in natural light” and according
to SR EN 60904-1, Art. 7 – “Measuring the current-
voltage of photovoltaic devices in pulsed solar
light”.
The Current-Voltage curve diagram is presented
in Figure 1 under typical faults.
Figure 1. I-V curve diagram under typical faults
Figure 1 shows the I-V curve diagram that
changes when specific defects are encountered.
The interpretation of the IV characteristics, can
determine the degradation state of a PV panel (by
comparison to the initial parameters), the failure of
a cell, an interrupted or degraded connection of the
connectors or cables, or, more seriously, the effect
of Potential Degradation Induced (PID).
A complete analysis of a PV module also involves
electroluminescence (field test) for crack detection
or PID effect.
Reactive maintenance
It is performed after the equipment has ceased
to work. It is opposed to the Preventive Maintenance
(PM), which faces a pre-established program.
Reactive Maintenance (also known as
"Maintenance of Malfunction") is limited to bringing
the equipment to its normal operating condition
after being defective. Faulty equipment is replaced
or repaired by replacing defective parts/components
in accordance with the service contract
specifications.
Emergency repairs cost 3 times to 9 times more
than the planed repair, so maintenance plans that
are based on Reactive Maintenance are generally the
most expensive. This type of maintenance is
expensive due to the fact that failures occur
accidentally during production (instead of pre-
programmed maintenance interruptions) while the
period and cost of spare parts supply is relatively
high. Special transport is needed and also the
maintenance personnel are often needed to work
overtime in order to complete the equipment repair.
3. Fault detection with the thermographic method
The biggest disadvantage of photovoltaic systems
is their high installation costs and low efficiency.
This affects the return time of the investment cost.
If the installed power of the plant is not obtained as
scheduled for the entire operation life, then the
expected efficiency is not met, causing financial
losses.
In order to prevent these efficiency losses,
installations must be made and monitored regularly
in accordance with international standards without
compromising system security.