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A brief history and future aspects in automatic

cleaning systems for solar photovoltaic panels
a a
Amit Kumar Mondal & Kamal Bansal
a
Electronics and Instrumentation Department, University of Petroleum and Energy Studies ,
Dehradun, India
Published online: 23 Apr 2015.

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To cite this article: Amit Kumar Mondal & Kamal Bansal (2015) A brief history and future aspects in automatic cleaning
systems for solar photovoltaic panels, Advanced Robotics, 29:8, 515-524, DOI: 10.1080/01691864.2014.996602

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 Advanced Robotics, 2015
Vol. 29, No. 8, 515–524, http://dx.doi.org/10.1080/01691864.2014.996602

SURVEY PAPER
A brief history and future aspects in automatic cleaning systems for solar photovoltaic panels
Amit Kumar Mondal* and Kamal Bansal
Electronics and Instrumentation Department, University of Petroleum and Energy Studies, Dehradun, India
(Received 9 March 2014; revised 22 September 2014; accepted 26 November 2014)

The energy or efficiency produced by solar photovoltaic modules is related with the Sun’s available irradiance and spec-
tral content, as well as other factors like environmental, climatic, component performance and inherent system. These
dust, dirt and bird droppings are the major reasons for the solar photovoltaic system underperformance. This paper dis-
cusses a comprehensive overview of dust problem and the recent developments made on automated cleaning system for
solar photovoltaic modules which give brief overview on techniques like electrical, mechanical, chemical and electro-
static. The main objective of the study is to review the literature on solar photovoltaic module automated cleaning tech-
niques for identifying research gaps in the automated cleaning systems.
Downloaded by [New York University] at 08:53 22 May 2015

Keywords: solar photovoltaics (SPV); dust; electrodynamic screening (EDS); automated cleaning process

Introduction an array reduces their efficiency in energy generation

The global energy requirements have increased considerably and emphasizes the need to keep the panel
significantly in the past several decades and are predicted surface as clean as possible.[3,4] Due to humidity, when
to rise more than 50% by 2030.[1] Present world energy light hits water droplets, it may be refracted, reflected or
requirements are met mostly from the conventional diffracted, which affects the reception levels. High con-
sources of energy like coal, gas and oil, which are being tent of water vapour in the air causes encapsulation.[19]
exploited in an unregulated manner resulting in exhaust- Because of the water content of the humidity, failure
ing world reserves of fossil fuels in the near future. With at cell interconnections or cracked cells happens in crys-
increasing cost of electricity and concern for the environ- talline silicon cells, and failure at scribe lines is the
mental impact of fossil fuels, implementation of renew- dominant cause of cell thin film modules degradation.
able energy sources like solar power are rising. The The impact of sedimentation (i.e. dust and dirt particles)
main method for harnessing solar power is with arrays on exposed surfaces of SPV panels. Dust prevents the
made up of photovoltaic (PV) cells. Electricity generated incident light in reaching to the SPV, causing reduced
using solar photovoltaic (SPV) technology can only be power output and efficiency. Dust accumulation occurs
economical if the PV modules operates reliably for 25– at different rates in different parts of the world; also, it
30 years under field conditions.[2] The main limiting fac- depends upon the panel orientation,[20] direction of
tors which reduce extensive use of PV applications wind,[21] and nature of dust [22]: dust composition, size
include the high initial investment cost [5] and the rela- distribution, deposition density as shown in Figure 3–6.
tively low conversion efficiency of PV cells due to heat- Apart from the above natural factors, even the
ing of PV panels.[6,7,10] Module temperature is always manufacturing technology also plays a role, as different
higher than the ambient temperature.[9] Higher tempera- type of PV technologies having different amount of
ture of the module is because of the glass cover over it, efficiencies as listed in the Table 1.
which traps the infrared radiation. Overall, power output Orientation and tilt angle of the PV module plays an
and efficiency of the PV cells decrease with the increase important role for the efficiency of SPV as performance
in its operating temperature as shown in Figure 1. Dust of SPV module depends on the amount of solar radiation
collection on PV panel surface also reduces its efficiency received by a PV module which in turn depends on the
[8,9], and the output power of the PV module strongly orientation and tilt angle.[17,18] Orientation of modules
depends upon the solar irradiation falling on it.[9] The is generally north in southern hemisphere and south in
power output of a module increases linearly with the northern hemisphere. Tilt angle is site dependent and has
increase in the incident solar radiation shown in Figure 2. to be optimized to maximize the incident solar radiation
Accumulation of dust and debris on even one panel in on the PV module surface.

*Corresponding author. Email: akmondal1603@gmail.com

© 2015 Taylor & Francis and The Robotics Society of Japan

 516 A.K. Mondal and K. Bansal

Figure 1. Effect of temperature on the I–V curve of the PV

module.[9]
Figure 4. Power output for various particle sizes as a function
of dust deposition density.[22]
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Figure 2. Effect of Solar irradiance on the I–V curve of the

PV module.[9]
Figure 5. Reduction in solar intensity for various particle
sizes as a function of dust deposition density.[22]

Figure 6. Reduction in fill factor for various particle sizes as

Figure 3. Short circuit current for various particle sizes as a a function of dust deposition density.[22]
function of dust deposition density.[22]

electrostatic methods. The paper also reviews various

The review includes the detailed description on dif- successful electrical, mechanical, chemical and electro-
ferent automated solar panel cleaning systems, a brief static methods developed in the recent years for various
overview about electrical, mechanical, chemical and applications.
 Advanced Robotics 517

Table 1. SPV technologies.

PV technology Efficiency (%)

Carbon nanotubes (CNT) [52] 3–4
Amorphous silicon [13] 5–7
Poly crystalline silicon [12] 8–12
Dye synthesized [51] 11.1
Mono crystalline silicon [11] 15–18
Other thin film (CdTe, CIS, etc.) [14, 15] 16–20
Triple junction under concentrated Sun [16] Up to 37.4
Hot carrier solar cell [53] 66

Automated cleaning solutions

There are several existing methods available in industrial
grade and is been used in real time. Solutions are not
only limited to using them on Earth but also in Mars.
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Existing solutions are also dependent on:

Figure 7(b). Real-time operation of PV cleaner.[23]
(1) Geographical terrain
(2) Area of application

Depending on the above factors, existing solutions

can be further compared on the basis of cost, ease of
use, performance rate, etc. One of these solutions is a
solar panel cleaning robot,[23] its design comprises two
motorized trolleys at the edges of panels which provide
horizontal motion, and a cleaning head driven by a belt
and pulley system for vertical motion. Cleaning head
comprises rotating cylindrical brushes to scrub the PV
panel and a scraper to remove the dirt solution as shown
in Figures 7(a) and 7(b).
In addition, robotic cleaning mechanisms such as
‘Gekko Solar’ [24] and ‘Gekko Solar Farm’ [25] from
Serbot Swiss Innovations developed for mobile deploy-
ment onto SPV panels as shown in Figure 8. Its cleaning
is through a rotating brush and demineralized water. Its Figure 8. Cleaning of Solar PV module using Gekko
movement is based on feet, with vacuum technology, Solar.[24]

Figure 7(a). Simulated operation of PV cleaner.[23] Figure 9(a). Wash panel cleaning over SPV.[26]
 518 A.K. Mondal and K. Bansal

which are rotating on two trapezoid-shaped geared belt possible supervision and management from remote site.
drives, enabling the robot to astonishing flexible move- It doesn’t require any extra frame, support and additional
ment in every chosen direction. guides. It can be installed on ground systems, buildings,
It can be radio controlled with a joystick. For larger peaked roof or shed roof. For continuous monitoring, it
application, ‘Gekko Solar Farm’ has been used. Another sends text messages to mobiles, allowing command con-
product available is ‘solar panel cleaning robot’ [26] trol from remote sites as shown in Figures 9(a) and 9(b).
from wash panel. Wash panel’s system is fully autono- ‘HECTOR’ [27] is a robotic cleaning system for
mous, it has a double programmable functioning through Heliostat’s, which can be used for Solar PV panel clean-
a rain sensor and by use of water jets. It provides a con- ing also, as shown in Figure 10. It is wireless, recharge-
stant and uniform cleaning. This system is modular, with able and carries water solution tank with itself. It is
fused with various sensors which permit it to navigate
autonomously without any human supervision. It requires
no external power or water supply for its operation; it
carries its own batteries and water tank. HECTOR is
designed for night and day operation. Its performance is
very slow and the weight of HECTOR is over the panel.
‘Solar brush’,[28] is a robotic cleaning system for SPV
panels. The robot ‘solarbrush’ walks over the solar PV
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Figure 9(b). Wash panel placing over the SPV.[26]

Figure 12. Greenbotics solar PV cleaning robot in action.[29]

Figure 10. HECTOR robot cleaning SPV module.[27]

Figure 13. PIC microcontroller-based mechanical design for

Figure 11. Solar brush cleaning SPV module.[28] cleaning.[40]
 Advanced Robotics 519

panel as shown in Figure 11. It can function up to an It automatically washes and rinses the solar panels. It
inclination of 35 degrees. It is wireless and rechargeable. attaches nozzles to the solar panels as shown in
It is having a cleaning brush which swipes the dust. Figure 15. It comprises a reservoir for soap concentrate.
Solarbrush is light weight of 2.5 kg. ‘GB1’ [29] from There is also a sediment filter that contains water soft-
Greenbotic’s is a robotic cleaning system for SPV panels ener media. It is also having an anti-siphon valve to pre-
as shown in Figure 12. It is wireless and rechargeable. It vent backwashing into the system. System consists of a
comprises rotating cleaning brushes perpendicular to the controller which automatically provides wash and rinse
axis of panel and a wiper system, such that not only cycles, the controller programming can be changed as
does it clean the panel, but also clear the dirty water. per seasonal requirements. Tuff Fab [30] is manufacturer
Hence, effective for all types dust and bird droppings. of special type of a coating solution which is easy to
Also, effective for one-axis tracking solar PV panels. apply. Once applied, it makes the glass surface non-stick,
‘GB1’ is moving at the edges of the frame of solar PV easy to clean and look new for years. User no longer
panel as shown in Figure 12. Few other researches have needs to use harsh chemicals and scrub clean your glass
been done in demo-based purpose where PIC [40]-based any more. Just a wash with clean water or mild detergent
microcontroller and PLC [39] have been used for con- and a wipe with a soft towel will clean the panels. In
trolling the cleaning purposes, as shown in Figures 13 this method cleaning has to be done, only advantage is
and 14. cleaning process would be easy. Similar to Tuff Fab’s
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Apart from the automated cleaning system, there are product, few other researches have been done on coating
few other types of systems also available like the particles [32] and its structure like fishnet meta-struc-
Heliotex’s ‘Automatic Solar panel Cleaning System’.[29] ture.[33]
Up till now, solutions which were discussed needs
pressurized water/water as a potential source of cleaning.
SPV panels installed in the dry areas like Saudi Arabia
or places where there is no water like Mars require elec-
trostatic techniques for cleaning. Electrostatic charge
concept for lifting and transporting charged particles of
insulating materials has been used for providing standing
wave-type electric curtain.[31,50] Shown in Figure 16
are two comb type-electrodes, one being ground and the
other being supplied with AC voltage.
In this case, we have a standing wave, and at any
point, the electric field has a definite direction and ampli-
tude oscillating at the imposed frequency. A single
charged particle oscillates along the field line.
For a horizontal set-up, it experiences an uprising
vertical resulting force which can lift it, and part of it
escapes the stressed zone. The main constraint of this
technique is, it requires dry state of the surface and for
Figure 14. PLC-based mechanical design for cleaning.[39] this reason it has been suggested for Mars climatic

Figure 16. Single-phase electric curtain with the two ‘combs’

Figure 15. Heliotex automatic solar panel cleaning system.[29] of parallel electrode.[50]
 520 A.K. Mondal and K. Bansal

by polarization of a charge or through induction,

allowing it to also be cleared from the surface.

Discussion
The existing solutions are not universally applicable for
all situations; details have been provided in Table 2 with
their limitations.
The developments in automated cleaning systems
have emerged in recent years i.e. after 2000, which
include EDS system developed for Mars mission. Later
on the developments focused on electromechanical
automatic cleaning systems and further research is going
Figure 17. Block diagram of EDS/PV array system.[35] on till date. Further advancements are implemented after
the development of surface coatings technology as the
earlier systems were dependent on the availability of
power, water, mobility, etc. The structural and chemi-
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cal properties of the surface coatings have unique

advantages like:

(1) Increases the contact angle between the surface

and water droplets, leading the water droplet to
quickly roll off, carrying dust and other particles
with them.[55]
Figure 18(a). Surface electrodes energized by phased voltages (2) Increases the anti-reflectiveness.[57]
produce an electrostatic travelling wave for lifting and trans-
porting dust particles.[37] Although both the techniques i.e. electromechanically
cleaning and SPV coating are available, yet, to make
both the techniques more effective, research is still
going on.
In order to reduce the frequency and cleaning cost, it
is advisable to find a solution to minimize dirt deposition
over the PV modules. This can be achieved by the
following ways:

(1) By over sizing, the initial PV array installation to

ensure any power reduction would not affect the
Figure 18(b). Simulation model for calculated particle trajec- expected system performance.
tory.[37]
(2) By discouraging birds from nesting and landing
on PV panels, this can be achieved by frighten-
conditions. An electro-dynamic screen (EDS) [34,35,38] ing the birds using scare crow.
or multi-phase electric curtain-based system requires a (3) By deterrence [42,43,49] and surface modifica-
high-voltage external power source for its operation, but tion [42,43,45–48] (treatments, coatings and
the EDS can be made self-sustainable with the power films), so that dirt will not be settled or not been
output from the PV cell itself. It incorporates a transpar- able to form strong bonding with the surface.
ent EDS with a PV array as its power source to make (4) By Electrostatic biasing,[42] in which thousands
itself sustainable. The block diagram of the system is of volts with normal electric field reject the
shown below in Figure 17. The three-phase high volt- particles.
ages create a travelling wave with a strong translational (5) By stowing (inverting) [42] the PV modules.
energy that can move the triboelectrically charged dust (6) By aerodynamic streamlining, a turbulent flow
particles from one end of the substrate to another,[36] boundary layer is induced by aerodynamic spoil-
the same has been shown and modelled in the Figures ers that are specially designed and positioned on
18(a) and 18(b).[37] Uncharged particles that may the PV panel, in order to sweep out the dust
become deposited on the screen soon become charged from the surface.
 Advanced Robotics 521

Table 2. Various types of cleaning systems.[41]

Cleaning system Advantage Shortcomings

EDS for standing wave
electric curtain [31] (1) Highly efficient at high gas (1) Removal is difficult when gas (atmospheric)
pressure. pressure is below a certain limit.
(2) No mechanical movement to (2) Dust removal capability depends on the size of
scratch the protective surface. the particles deposited.
(3) Requires high voltage.

EDS for multi-phase electric

curtain [34,35,38] (1) Efficient and can be used to (1) Requires digital signal controller which is
remove dust from a variety of costly.
surfaces (2) Requires switching devices for converters hence
(2) No mechanical movement to more maintenance is required.
scratch the protective surface. (3) Requires high voltage.
(3) Efficient with and without use of
external power supply.

Heliotex’s ‘Automatic Solar

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panel Cleaning System’ (1) Water reaches to every part of (1) Treated water required.
[29] solar PV modules. (2) Filter has to be changed periodically.
(2) Helps in cooling of solar PV (3) Huge wastage of water.
modules, which increases the
efficiency.

Gekko solar [24]

(1) Self-regulating and flexible un (1) Limitation of inclination up to 45 degrees.
interrupted cleaning operations (2) Additional stresses on the surface due to gear,
belt and vacuum system

Gekko solar farm [25]

(1) Self-regulating and flexible un (1) Limitation of inclination up to 30 degrees.
interrupted cleaning operations. (2) Complex gear, belt system.

Solar brush [28]

(1) Automated robot (1) Heavy weight
(2) Works up to an inclination of 35 (2) Initial cost is high.
degrees (3) Requires human intervention
(3) Wireless controlled (4) Performance speed is very slow
(4) Rechargeable

PIC microcontroller [40] and

PLC based cleaning [39] (1) Self-regulating and flexible un (1) Complex chain, sprocket-based structure.
interrupted cleaning operations (2) Single panel-based design

Hector [27]
(1) Compatible, integrated with all (1) Performance is slow.
supplies. (2) Feeding has to be done regularly
(2) Operational day and night

Solar panel cleaning robot

[23] (1) Washing and wiping both process (1) Horizontal shifting of the robot over the PV
are present module results in skidding.
(2) Stress on the surface of the panel due to its
weight.

Wash panel’s solar panel

cleaning robot [26] (1) Able to clean dust and Bird (1) Human intervention is required to start the
droppings. operation and while moving from one row to
another.
(Continued)
 522 A.K. Mondal and K. Bansal

Table 2. (Continued).
Cleaning system Advantage Shortcomings
Sunpower-greenbotic’s GB1
[54] (1) Able to clean dust and Bird (1) Human intervention is required to start the
droppings. operation and while moving from one row to
another.

Tuff Fab’s nano clear [30]

(1) Long lasting (1) Cleaning is still required, but with less effort.

Asahi kasei corporation’s SPV

coating [56] (1) High Transmittance Capability. (1) Cleaning is still required, but with less effort.

(7) By vibrating [43,44] the surface, the free parti- technologies and need further modification to be
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cles from the PV panel surface can be removed used in practice. In coatings, recent developments
using electromechanical instrumentation, which with super hydrophilic and super hydrophobic
also helps in preventing the dust to accumulate materials, which can work in both dry and wet
at a single place. dust conditions, has come up. While the charged
dust repelling technology is being used in space
industry.[50]
(5) The frequency of cleaning must be taken into
Summary and observations account considering:
This review summarizes the developments achieved and (a) the area, for example, in commercial zones,
challenges faced due to the dust issues on PV panels. where dust deposition due to pollution is
The research review provided observations on perfor- more compared to residential zone.
mance of various automated cleaning techniques and (b) SPV surface, where most of the panels avail-
approaches developed. able in the market is coated, therefore, the
The following are the observations in brief: cleaning must be done keeping in view that
the coated layer must not be affected.
(1) Dust and dirt remains a problem, especially in (6) Several techniques have shown their effective-
desert areas, where solar energy potential is in ness and are being analysed technically as well
abundant as well as of sand also. Few reasons as economically for better results.
for it are: (7) It is recommended that electromechanical clean-
(a) Lack of natural cleaning by rain and shortage ing solution should be implemented in the small
of indigenous water resources. utilities, where the power generation through
(b) Sandy storms and dry climate. SPV is up to 100 kW, whereas hybrid system
(2) Dust and dirt degrades the energy output of SPV (coating + electromechanical) should be imple-
module by: mented in the larger utilities, where the power
(a) Reduction in solar intensity in the range of production is more than 1 MW.
20–50% or more.
(b) Reduction in output power of SPV system in In the recent literature and from experience in the
the range of 15–30% for moderate dust field, it is clear that a universal solution for dust cleaning
condition. is not possible, as its working and suitability depends on
(3) Till 1990s, much of the cleaning process has various factors. So, the optimum solution will be choos-
focused on restorative approach that is primarily ing the solution as per the surrounding factors.
on washing with water or detergent solutions.
After the 1990s automated cleaning techniques
started developing, that too initially with vehicle- Acknowledgement
mounted system with forced water jets. The authors would like to thank Mr. Venkateswaran PS,
(4) Dust preventive approaches like coatings and Research Scientist, University of Petroleum and Energy Studies
charged dust repelling, both are high-end for his assistance in reviewing the paper.
 Advanced Robotics 523

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