WO2019134736A1

WO2019134736A1 - Solar panel cleaning apparatus and method

Info

Publication number: WO2019134736A1
Application number: PCT/EP2018/050053
Authority: WO
Inventors: Prathamesh TERNIKAR; Miska HIRVELÄ
Original assignee: Fortum Oyj
Priority date: 2018-01-02
Filing date: 2018-01-02
Publication date: 2019-07-11

Abstract

An apparatus (300) for cleaning a solar panel (10) comprises a longitudinal axis (302) parallel to the direction of movement of the apparatus (300) during cleaning operation, one or more electric power sources (310) for providing alternating (AC) or direct (DC) current and/or voltage, a first unit (100) and a second unit (200). An electric current for detaching particles from the solar panel (10) is transmitted into the one or more first conductors (110) of the first unit (100) comprising one or more first conductors (110) connected to the one or more electric power sources (310). The second unit (200) comprises a collector surface (220,222) and an elongated conductor (210) for conveying detached particles onto the collector surface (220,222) when an electric current is transmitted into the elongated conductor (210). The elongated conductor (210) is arranged substantially perpendicularly with respect to the longitudinal axis (302), whereas the first unit (100) and the second unit (200) are arranged on the longitudinal axis (302) with the first unit (100) positioned before the second unit (200) in the direction of movement of the apparatus (300) during cleaning operation.

Description

SOLAR PANEL CLEANING APPARATUS AND METHOD

FIELD

The present disclosure relates to cleaning solar pan els. In particular, the disclosure relates to water less and semi-automatic or automatic cleaning of solar panels .

BACKGROUND

Solar panels and their efficiency in particular are sensitive to build-up of small particles such as dust, dirt, organic matter and other particulate contami nants on the surface of the panel. Large solar panel installations involving thousands or even hundreds of thousands of solar panels may be built on locations such as desert regions, where the solar panels require frequent cleaning. While the panels in such panel farms have been previously cleaned manually, this is laborious, time consuming, expensive and includes oth er drawbacks as well such as excessive consumption of water .

To alleviate the problems mentioned above, various cleaning methods have been devised. These include at least partially automated methods and devices, which use techniques such as air flow, automated brushes or even electrostatic cleaning with electric field gener ation. These methods however, retain at least some of the previous drawbacks, such as possible damage caused by contact-based methods to the panel surface or an antireflective coating applied thereon, while at the same time introduce some of their own such as the add ed weight and other expenses of installing a compres sor for pressurized air. They may also not necessarily allow a construction suitable, at the same time, for autonomous operation and for cleaning large panel are as .

OBJECTIVE

An objective is to eliminate or alleviate at least some of the disadvantages mentioned above.

In particular, it is an objective to provide a con tactless and waterless apparatus and a method for electrostatic cleaning of solar panels utilizing com pact cleaning units, which may be automated.

SUMMARY

Many of the design parameters may depend on the par- ticular environment and operating conditions, under which the cleaning apparatus and method is used. In particular, the method and apparatus disclosed herein may be adapted for cleaning dust and/or sand from so lar panels. The noncontact cleaning apparatus and method disclosed herein may be particularly adapted for non-damaging cleaning of solar panels with coat ings such as an antireflective coating.

According to a first aspect, and apparatus for clean- ing a solar panel comprises a longitudinal axis paral lel to the direction of movement of the apparatus dur ing cleaning operation, one or more electric power sources for providing alternating (AC) and/or direct (DC) current and/or voltage, a first unit and a second unit. The first unit is arranged for detaching parti cles from the solar panel when an electric current for detaching particles from the solar panel is transmit ted into the one or more first conductors and it com prises one or more first. The second unit is for col lecting particles detached from the solar panel and it comprises a collector surface and an elongated conduc- tor for conveying detached particles onto the collec tor surface when an electric current is transmitted into the elongated conductor. The elongated conductor is arranged substantially perpendicularly with respect to the longitudinal axis, whereas the first unit and the second unit are arranged on the longitudinal axis with the first unit positioned before the second unit in the direction of movement of the apparatus during cleaning operation. The elongated conductor may be straight or arranged straight. When more than first conductors are used, they may be arranged in the same electric potential to prevent short-circuits between the first conductors. The construction allows electrostatic cleaning where the electric field may be adjusted specifically for detaching and collecting particles. The electric field generated by the first unit causes the particles at tached to the solar panel to detach, even forcibly so that they jump e.g. 4 centimeters upwards. As the par ticles float down or when they have landed on solar panel but not yet adhered, the second unit may be used to collect the particles using the electric field gen erated therein and a collector surface. The first unit thus generates the pull or torque necessary to detach the particles allowing cleaning with improved speed and reduced energy while the second unit generates the velocity for the particles to be conveyed for collec tion. The elongated shape of the conductor in the sec- ond unit allows resistance of the second conductor to be increased so that relatively small currents may be used to generate a large voltage across the conductor to facilitate conveying of particles on the collector surface. The construction allows the cleaning appa- ratus to be compact and it may be adjusted to various different types of installations. In an embodiment, the apparatus comprises a third unit, which comprises one or more conductors connected to the one or more electric power sources for detach ing particles from the solar panel when an electric current is transmitted into the one or more conduc tors. The third unit is arranged on the longitudinal axis and the second unit is positioned between the first unit and the third unit. This allows the appa ratus to operate in two opposite directions. The appa ratus may be arranged to move or be moved linearly along a line parallel to the longitudinal axis so that when the apparatus moves in first direction, the first unit is powered for detaching particles and when the apparatus moves in the opposite direction with respect to the first direction, the third unit is powered for detaching particles. This allows the cleaning appa ratus to be operated in to-and-fro motion across mul tiple solar panels, for example at solar panel farms having panel surfaces extending long distances e.g. more than 100 or 200 meters. The apparatus may be ar ranged to move from a first end of a line of solar panels with a second unit trailing a first unit having power on and, after reaching the other end of the line of solar panels, to reverse direction and return to the first end with the second unit trailing the third unit having power on. To conserve energy, the first unit or the third unit may be turned off when it is trailing the second unit. The third unit may comprise the same features as the first unit and it may even be substantially identical to the first unit. Consequent ly, any features described in relation to the first unit herein may be related to the third unit as well.

In an embodiment, the electric current transmitted in to the one or more first conductors is direct (DC) current. In particular when more than one elongated conductors are used, this allows increasing the elec- trie field strength and/or the charge generated while at the same time reducing the chance that the conduc tors short-circuit with each other. The electric cur rent transmitted into the elongated conductor may be alternating (AC) current to improve collecting effi ciency .

In an embodiment, the second unit comprises a first wall and a second wall arranged on opposite sides of the elongated conductor on the longitudinal axis. The first wall and the second wall of the second unit may be electrically grounded. This allows localizing the electric field within the second unit to improve the collecting efficiency of the apparatus. Since the walls are arranged before and after the elongated con ductor in the direction of movement, at least one of them or both may also function as the collector sur face. The first wall and the second wall of the second unit may also be connected to each other, for example by two side walls, which may also be electrically grounded. The second unit may thus comprise a two- dimensional enclosure, or a chamber, through which the elongated conductor is extended. In an embodiment, the first and/or the second wall of the second unit has a lower edge at a substantially same height as the elongated conductor. On one hand, this allows the elongated conductor to be arranged close to the surface of the solar panel. On the other hand, this allows the wall to be close to both affect the electric field and prevent particles from escaping the second unit.

In an embodiment, the elongated conductor is posi- tioned at a substantially equal distance from the first wall and the second wall of the second unit. This further allows shaping the electric field in a way which has been found out to improve the collecting efficiency of the second unit.

In an embodiment, the distance between the first wall and the second wall of the second unit is 20-100 mil limeters in a direction parallel to the longitudinal axis. In a further embodiment, the distance is 30-80 millimeters or 35-55 millimeters. Depending on the construction of the apparatus, this has been found out to improve the cleaning efficiency.

In an embodiment, the second unit comprises a roof of non-conductive material. The roof may extend from the first wall to the second wall. It may cover the second unit or the chamber formed in the second unit to pre vent particles from escaping the second unit in the upwards direction. It has been found that using a non- conductive cover may notably improve the collecting efficiency of the apparatus.

In an embodiment, the first unit comprises a first wall and a second wall arranged on opposite sides of the one or more first conductors on the longitudinal axis. The first wall and the second wall of the first unit may be non-conductive. This allows generating an electric field and/or charge and confining it into a small space to improve detaching efficiency of the first unit. The first wall and the second wall may be arranged to provide an electric neutral to the first unit. The first wall and the second wall of the first unit may further be electrically grounded, for example from a distance to prevent short circuit with the one or more first conductors.

In an embodiment, the first unit and the second unit are separated by a distance of 30-150 millimeters in a direction parallel to the longitudinal axis. In a fur- ther embodiment, the distance is 50-120 millimeters or 90-100 millimeters. While electric insulation might be used as an alternative, it has been found out that a gap between the units may be used to prevent the charges and/or electric fields of the first and the second units from overlapping and therefore also to prevent short-circuiting the apparatus. On the other hand, by not making the gap too large, e.g. by keeping the distance below 200 millimeters, it is possible to improve the collecting efficiency of the apparatus.

In an embodiment, the one or more first conductors comprise one or more elongated conductors arranged substantially perpendicularly with respect to the lon gitudinal axis.

In an embodiment, the one or more first conductors comprise at least six elongated conductors arranged substantially perpendicularly with respect to the lon gitudinal axis. The electric field and/or the charge generated may be increased by increasing the number of wires. It has been found that, at least for certain configurations, the detaching efficiency may be nota bly increased by using more than five conductors. The number of conductors may be eight but the optimal num ber may also depend on various factors, including bal ancing with the size and cost of the device. At least for certain configurations, it suffices to use at most ten such conductors in the first unit.

In an embodiment, the one or more first conductors comprise a grid of a first set of one or more elongat ed conductors arranged substantially perpendicularly with respect to a second set of one or more elongated conductors. The first set may be arranged substantial ly perpendicularly with the longitudinal axis so that the second set is substantially parallel to the longi tudinal axis .

In an embodiment, the first conductors and/or the elongated conductor are conductive wires. Wires being narrow conductors, the resistance of the conductors may be thus increased so that a relatively small cur rent in the wires can correspond to a large voltage across the wires. This allows generating an electric field and/or charge improving the detachment/or and collecting efficiency of the apparatus.

In an embodiment, the electric current transmitted in to the one or more first conductors and/or the elon gated conductor is alternating (AC) current. The al ternating current may have a frequency of 5-5000 Hz. In certain configurations, using alternating current may notably increase the collecting efficiency of the second unit. The apparatus has been found to work even with smaller frequencies such as 5-200 Hz, 5-100 Hz or 50-100 Hz allowing compact power sources and/or sup plies to be used.

In an embodiment, the electric current transmitted in to the one or more first conductors and/or the elon gated conductor is alternating single-phase current.

In an embodiment, the electric power source is ar ranged to provide a voltage of 5-40 kV across the one or more first conductors (110) and/or the elongated conductor. The number corresponds to the voltage across each individual conductor. For DC current, the voltage may be either positive or negative. It may further be 5-30 kV for DC voltage and/or 6-20 kV for AC voltage. A suitable voltage may notably improve the detachment and/or collecting efficiency of the appa ratus . In an embodiment, the apparatus has dimensions ar ranged so that one or more first conductors, the elon gated conductor or both are within one centimeter from the surface of the solar panel when the apparatus is positioned against the solar panel for cleaning opera tion. A suitable distance may notably improve the de tachment and/or collecting efficiency of the appa ratus. The apparatus may be arranged so that it has a substantially constant distance with the solar panel surface, for example by extensions coupling with the solar panel structures such as its support structure. In a further embodiment, one or more first conductors, the elongated conductor or both are within half a cen- timeter from the surface of the solar panel when the apparatus is positioned against the solar panel for cleaning operation. They may also be arranged at least three millimeters from the surface of the solar panel to prevent small obstacles on the panel surface from colliding with the conductors.

In an embodiment, the apparatus comprises one or more actuators for moving the apparatus along the solar panel in a direction parallel to the longitudinal ax- is. The actuator may be connected to the at least one electric power source for power. The actuator may fur ther be arranged for linear movement along either or both directions parallel to the longitudinal axis. Various means of actuation are possible as the appa- ratus may also be arranged on various manual, autono mous or semi-autonomous cleaning devices.

According to a second aspect, a method for cleaning a solar panel comprises generating alternating (AC) or direct (DC) current into one or more first conductors of a first unit for detaching particles from the solar panel and moving the first unit along the solar panel in a direction parallel to a longitudinal axis to de tach particles from the solar panel. The method also comprises generating alternating (AC) or direct (DC) current into an elongated conductor arranged substan tially perpendicularly with respect to the longitudi nal axis and moving a second unit for collecting par ticles detached from the solar panel behind the first unit along the longitudinal axis along the solar pan el. The second unit comprises at least a collector surface and the elongated conductor for conveying de tached particles onto the collector surface. Two or more or even all of the steps described above may be performed simultaneously. The first unit and/or the second unit may be moved across one or more solar pan els for cleaning the solar panels. The first and the second unit may be comprised in an apparatus according to the first aspect or any combination of its embodi ments. Also, any features or effects described in re lation to the apparatus may be used or applicable also in relation with the method including those related to any of the structure of the first unit, the structure of the second unit, the electric currents involved and the movement of the apparatus.

It is to be understood that the aspects and embodi ments described above may be used in any combination with each other. Several of the aspects and embodi ments may be combined together to form a further em bodiment .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to pro vide a further understanding and constitute a part of this specification, illustrate embodiments and togeth er with the description help to explain the principles of the invention. In the drawings: Fig. la illustrates a first unit according to an em bodiment from a perspective view.

Fig. lb illustrates a cross section of first unit ac cording to an embodiment and a solar panel from a side view .

Fig. lc illustrates a first unit according to another embodiment from a perspective view.

Fig. 2a illustrates a second unit according to an em bodiment from a perspective view.

Fig. 2b illustrates a cross section of second unit ac cording to an embodiment and a solar panel from a side view .

Figs. 3a-c illustrate an apparatus according to embod iments from a perspective view.

Fig. 4 illustrates a method according to an embodi ment .

Like references are used to designate equivalent or at least functionally equivalent parts in the accompany ing drawings .

DETAILED DESCRIPTION

The detailed description provided below in connection with the appended drawings is intended as a descrip tion of the embodiments and is not intended to repre sent the only forms in which the embodiment may be constructed or utilized. However, the same or equiva lent functions and structures may be accomplished by different embodiments. Figure la illustrates a first unit 100 for detaching particles from a solar panel according to an embodi ment. Any or all features described hereafter with re spect to a first unit may be comprised in any combina tion in one or more additional first units or in one or more third units.

The first unit 100 comprises a longitudinal axis 102 and one or more first conductors 110 for detaching particles from a solar panel when an electric current is transmitted into the conductors 110. The first unit 100 may comprise a first wall 120 and a second wall 122, which may be parallel. The first wall 120 and/or the second wall 122 may be facing a direction parallel to the longitudinal axis 102. The first wall 120 and/or the second wall 122 may be flat in the plane perpendicular to the longitudinal axis 102. The first wall 120 and/or the second wall 122 may be made of a non-conductive material, for example of a polymer ma terial such as nylon. The first wall 120 and/or the second wall 122 may be arranged to form an electric neutral to the first unit.

The first wall 120 and the second wall 122 may share any or all characteristics including shape, thickness, width (e.g. perpendicular to the longitudinal axis), height (e.g. perpendicular to the longitudinal axis) or material. The first wall 120 and/or the second wall 122 may be electrically grounded. The grounding may be arranged at a distance to the walls and/or the first unit to prevent short circuit with the one or more first conductors 110. The first unit 100 may further comprise one, two or more side walls 124, which may share any or all characteristics with the first wall 120 and/or the second wall 122 including shape, thick ness, width, height or material. They may be substan tially parallel with the longitudinal axis 102. The first wall 120 and the second wall 122 may be connect ed to form a monolithic body, for example through the side walls 124, which may be electrically grounded as a whole. The side walls 124 may comprise one or more openings to allow the one or more first conductors 110 to pass through the side walls 124. The first wall 120, the second wall 122 and, optionally, the side wall (s) 124 may together enclose the one or more first conductors 110, or at least a middle part the one or more first conductors 110, in a plane parallel to the longitudinal axis and the conductors 110. This forms a chamber for the conductors 110 which chamber may be used for confining the electric field created by the electric current transmitted into the conductors 110. In many cases, the width of the first unit 100 may be larger than the length. As an example of dimensions, the first wall 120 and/or the second wall 122 of the first unit 100 may have a width of 100-3000 millime ters. In an embodiment applicable for solar farms, the width may be 550 millimeters plus or minus 0-100 mil limeters. It is also possible to arrange several first units 100 side-by-side for cleaning operation. The length (parallel to the longitudinal axis 102) of any side walls 124 and/or the distance between the first wall 120 and the second wall 122 may be, for example, 30-300 millimeters or 90 millimeters plus or minus 0- 30 millimeters. The height of any or all of the walls 120, 122, 124 may be 10-50 millimeters or 25 millime ters plus or minus 0-10 millimeters. The thickness of any or all of the walls 120, 122, 124 may be, for ex ample, 5-80 millimeters or 32 millimeters plus or mi nus 0-10 millimeters

Figure lb illustrates a cross section of a first unit 100 for detaching particles from a solar panel 10 ac cording to an embodiment. The cross section has been taken along the longitudinal axis 102 in Fig. la. The solar panel 10 is illustrated in a simplified form and a person skilled in the art understands that the appa ratus and method described herein may be applied on various different types of solar panels and surfaces.

The first unit 100 may comprise a roof 130 which may be supported on any or all of the walls 120, 122, 124. The roof 130 may cover, fully or partially, the cham ber for the one or more first conductors 110. The roof 130 may be arranged to prevent detached particles from escaping from the first unit 100 in the direction per pendicular to the surface of the solar panel 10. The roof 130 may be made of non-conductive material, for example a polymer material such as acrylate polymer or acrylic glass. The roof 130 may be transparent. The dimensions of the first unit 100 may be controlled to improve the detaching efficiency of the unit. The first unit 100 may be arranged so that it has a sub stantially constant gap 140 between the one or more first conductors 110 and the surface of the solar pan el 10 during operation of the first unit 100. The gap 140 may be less than 10 millimeters, for example 5 millimeters or less. It may be larger than 1 millime ter, for example 3 millimeters or more so that colli sions of the conductors 110 due to small obstacles or changes in panel surface height may be prevented. The first wall 120 and/or the second wall 122 may have a lower edge arranged substantially at the same height as the one or more first conductors 110. The lower edge may be parallel with at least some of the one or more first conductors 110. A gap or free space 142 may be arranged in the first unit 100 or the chamber of the first unit 100 above (i.e. on the opposite side of the conductors 110 with respect to the solar panel 10 when the first unit 100 is positioned on the solar panel 10 for operation) the one or more first conduc tors 110. The gap or free space 142 may be, for exam- pie, 10-50 millimeters or 25 millimeters plus or minus 0-10 millimeters (in the direction perpendicular to the surface of the solar panel 10) . The gap or free space 142 may extend at least to a level corresponding substantially to the upper edge of the first wall 120 and/or the second wall 122. The gap or free space 142 may extend to the roof 130.

The one or more first conductors 110 may be arranged to be substantially parallel to the surface of the so lar panel 10 when the first unit 100 is positioned on the solar panel 10 for operation. Some or all of the one or more first conductors 110 may be parallel with respect to each other. Some or all of the one or more first conductors 110 may be arranged substantially perpendicularly to the longitudinal axis 102. The one or more first conductors 110 may be elongated conduc tors allowing also the resistance of a single conduc tor to be increased. The number of the first conduc tors 110 may be larger than one to increase the strength of the electric field and/or charge generated by a current transmitted into the conductors 110. The number may be larger than five, for example eight. In many applications, it may suffice to have ten first conductors or less, at least as a number of first con ductors arranged substantially perpendicularly to the longitudinal axis 102. Some or all of the one or more first conductors 110 may also be arranged parallel to the longitudinal axis 102.

Figure lc illustrates a first unit 100 for detaching particles from a solar panel according to an embodi ment, where the one or more first conductors 110 com prise a grid of a first set of one or more elongated conductors arranged substantially perpendicularly with respect to a second set of one or more elongated con ductors. The conductors in the first set are substan- tially parallel to each other and also the conductors in the second set are substantially parallel to each other. The conductors in the first set or the second set may be substantially parallel to the longitudinal axis 102.

Figure 2a illustrates a second unit 200 for collecting particles detached from a solar panel according to an embodiment. The second unit 200 comprises a longitudi nal axis 202, a collector surface and an elongated conductor 210 for conveying detaching particles onto the collector surface when an electric current is transmitted into the conductor 210. The collector sur face may be a planar surface for collecting detached particles when an electric current is transmitted into the conductor 210. The second unit 200 may comprise a first wall 220 and a second wall 222, which may be parallel. The first wall 220 and/or the second wall 222 may be arranged to function as the collector sur face. The first wall 220 and/or the second wall 222 may be facing a direction parallel to the longitudinal axis 202. The first wall 220 and/or the second wall 222 may be flat in the plane perpendicular to the lon gitudinal axis 202. The first wall 220 and/or the sec ond wall 222 may be made of a conductive material, for example metal. The first wall 220 and the second wall 222 may share any or all characteristics including shape, thickness, width (e.g. perpendicular to the longitudinal axis), height (e.g. perpendicular to the longitudinal axis) or material. The first wall 220 and/or the second wall 222 may be electrically ground ed. The second unit 200 may further comprise one, two or more side walls 224, which may share any or all characteristics with the first wall 220 and/or the second wall 222 including shape, thickness, width, height or material. They may be substantially parallel with the longitudinal axis 202. The first wall 220 and the second wall 222 may be connected to form a mono lithic body, for example through the side walls 224, which body may be electrically grounded as a whole. The side walls 224 may comprise one or more openings to allow the one or more first conductors 210 to pass through the side walls 224. The first wall 220, the second wall 222 and, optionally, the side wall (s) 224 may together enclose the elongated conductor 210, or at least a middle part the elongated conductor 210, in a plane parallel to the longitudinal axis and the con ductors 210. This forms a chamber for the elongated conductor 210 which chamber may be used for confining the electric field created by the electric current transmitted into the conductor 210. In many cases, the width of the second unit 200 may be larger than the length. As an example of dimensions, the first wall 220 and/or the second wall 222 of the second unit 200 may have a width of 100-3000 millimeters. In an embod iment applicable for solar farms, the width may be 550 millimeters plus or minus 0-100 millimeters. It is al so possible to arrange several second units 200 side- by-side for cleaning operation. The length (parallel to the longitudinal axis 202) of any side walls 224 and/or the distance between the first wall 220 and the second wall 222 may be, for example, 10-100 millime ters or 36 millimeters plus or minus 0-10 millimeters. The height of the any or all of the walls 220, 222, 224 may be 10-50 millimeters or 25 millimeters plus or minus 0-10 millimeters. Any or all of the walls 220, 222, 224 may be arranged as plates and their thickness may be less than 10 millimeters.

Figure 2b illustrates a cross section of a second unit 200 for collecting particles detached from a solar panel according to an embodiment. The cross section has been taken along the longitudinal axis 202 in Fig. 2a. The solar panel 10 is illustrated in a simplified form and a person skilled in the art understands that the apparatus and method described herein may be ap plied on various different types of solar panels and surfaces .

The second unit 200 may comprise a roof 230 which may be supported on any or all of the walls 220, 222, 224. The roof 230 may cover, fully or partially, the cham ber for the elongated conductors 210. The roof 230 may be arranged to prevent detached particles from escap ing from the second unit 200 in the direction perpen dicular to the surface of the solar panel 10. The roof 230 may be made of non-conductive material, for exam ple a polymer material such as acrylate polymer or acrylic glass. In particular for the second unit 200, the roof 230 may improve the confinement of the elec tric field to notably improve the collecting efficien cy of the second unit 200. The roof 230 may be trans parent .

The dimensions of the second unit 200 may be con trolled to improve the collecting efficiency of the unit. The second unit 200 may be arranged so that it has a substantially constant gap 240 between the elon gated conductor 210 and the surface of the solar panel 10 during operation of the second unit 200. The gap 240 may be less than 10 millimeters, for example 5 millimeters or less. It may be larger than 1 millime ter, for example 3 millimeters or more so that colli sions of the conductor 210 due to small obstacles or changes in panel surface height may be prevented. The elongated conductor 210 may be arranged substantially perpendicularly to the longitudinal axis 202 and/or substantially parallel to the surface of the solar panel 10 when the second unit 200 is positioned on the solar panel 10 for operation. The first wall 220 and/or the second wall 222 may be parallel to the elongated conductor 210. The elongated conductor 210 may be positioned at the middle line between the first wall 220 and the second wall 222 plus or minus 0-10 percent of the distance between the first wall 220 and the second wall 222. It has been found that to improve the collecting efficiency of the second unit 200, the elongated conductor 210 may be positioned at a sub stantially equal distance from the first wall 220 and the second wall 220. The first wall 220 and/or the second wall 222 may have a lower edge arranged sub stantially at the same height as the elongated conduc tor 210. The lower edge may be parallel with the elon gated conductor 210. A gap or free space 242 may be arranged in the second unit 200 or the chamber of the second unit 200 above (i.e. on the opposite side of the elongated conductor 210 with respect to the solar panel 10 when the second unit 200 is positioned on the solar panel 10 for operation) the elongated conductor 210. The gap or free space 242 may be, for example, 10-50 millimeters or 25 millimeters plus or minus 0-10 millimeters (in the direction perpendicular to the surface of the solar panel 10) . The gap or free space 242 may extend at least to a level corresponding sub stantially to the upper edge of the first wall 220 and/or the second wall 222. The gap or free space 242 may extend to the roof 230.

The second unit 200 may comprise exactly one elongated conductor 210 to avoid short-circuiting conductors, in particular when alternating current is transmitted in to the elongated conductor. However, it is possible to arrange two or more second units 200 in succession, for example along the longitudinal axis 202. In such a case, two successive second units may be arranged back-to-back with no gap between them, for example so that they share a first wall 220 or second wall 222 with each other. It is possible that any or all of the walls 220, 222, 224 of two or more second units are connected to form a monolithic body, for example through side walls 224. The monolithic body may be electrically grounded as a whole. For example, two, three or four second units may be joined in succession and, optionally, each two successive pairs may share a grounded wall 220, 222 in between. For certain config urations, it has been noted that already three second units 200 in succession may be used to collect over 90 percent of dust from the surface of a solar panel 10. For two or more successive second units 200, their longitudinal axes 202 may coincide. Also the elongated conductors 210 may be parallel with each other.

Regarding the conductors in either or both the first unit 100 and the second unit 200, the one or more first conductors 110 and/or the elongated conductor 210 may be of metal, such as copper or aluminum or steel. In particular, stainless steel has been found suitable as it allows making thin conductors which are strong enough for operating the apparatus 300. Some or all of the one or more first conductors 110 and/or the elongated conductor 210 may be conductive wires which allow reduction of electricity consumption and in crease of resistance. Some or all of the one or more first conductors 110 and/or the elongated conductor 210 may have submillimeter thickness, for example a thickness of 0.1-0.4 millimeters or 0.2 millimeters plus or minus 0-0.04 millimeters.

Figure 3a illustrates an apparatus 300 for cleaning solar panels according to an embodiment. The apparatus 300 comprises at least one first unit 100, at least one second unit 200 and a longitudinal axis 302. The longitudinal axis 302 may be parallel with the longi tudinal axis 102 of the first unit 100 and/or the lon gitudinal axis 202 of the second unit 200 and it may even coincide with the longitudinal axis 102 of the first unit 100 and/or the longitudinal axis 202 of the second unit 200. The longitudinal axis 302 is arranged parallel to the direction of movement of the apparatus 300 during cleaning operation. The apparatus may be arranged to move or moved in various ways, for example along a line parallel to the longitudinal axis 302 during cleaning operation. The apparatus 300 may com prise support structures such as extensions, arms and/or rails for supporting it on the solar panel. The support structures may be adapted for positioning the apparatus 300 with respect to the solar panel for cleaning operation of the apparatus 300.

The apparatus 300 comprises one or more electric power sources 310 for providing electric power to the appa ratus 300. In particular, the one or more electric power sources 310 allow providing alternating (AC) and/or direct (DC) current and/or voltage for the first unit 100 and the second unit 200 and, optional ly, also to additional first, second and/or third units. The power source 310 may be rechargeable power source such as a battery but other power sources may be applicable depending on how and where the apparatus 300 is operated. The power source 310 is comprised in a power supply for providing electric current and/or voltage for the one or more first units 100 and/or one or more second units 200. As understood by a person skilled in the art, the power supply may comprise one or more components such as transformers, rectifiers and/or inverters for adjusting the current and/or voltage transmitted into any of the first units 100 and second units 200. Additionally, frequency of the current and/or voltage may be adjusted.

The electric current transmitted into the one or more first conductors 110 may be direct (DC) current. This has been found to provide efficient detaching perfor mance by overcoming electrostatic or van der Waal forces attaching the particles to the solar panel and forcing the particles to jump upwards even several centimeters, while at the same time allowing the num ber of conductors 110 to be increased without short- circuiting them with each other. The electric current may be positive or negative DC current. The one or more first conductors 110 may be arranged in the same electric potential to prevent short circuiting the conductors. In particular, a set of parallel conduc tors such as the first set and/or the second set as described above for a grid-like arrangement of first conductors may be arranged in the same electric poten tial. The electric current transmitted into the elon gated conductor 210 of the second unit 200 may be al ternating (AC) current. This has been found to allow efficiently collecting the particles detached by the first unit 100 by moving them along with the device so that they are conveyed on the collector surface 220, 222. In any case, an alternating (AC) current may have frequency of 5-5000 Hz, which has been found to im prove cleaning efficiency of the apparatus 300, par ticularly when such alternating current is applied in one or more second units 200 for collecting detached particles. Also sub-kilohertz frequencies may be used, for example 5-50 Hz and/or 50-100 Hz. The alternating current may be alternating single-phase current. The phase of the current may be same across all the one or more first conductors 110 and/or the elongated conduc tors 210. The electric power source 310 may be ar ranged to provide a voltage of 5-40 kV across the one or more first conductors 110 and/or the elongated con ductors 210 of the second units 200. When AC voltage is used, the voltage level may be for example 5-20 kV or 6-15 kV. When DC voltage is used, the voltage level may be for example 5-30 kV or 10-20 kV. The level of the voltage may be controlled by the power supply. The voltage may be same across all the one or more first conductors 110 and/or the elongated conductors 210 of the second units 200.

The first unit 100 and the second unit 200 are ar ranged on the longitudinal axis 302 with the first unit 100 positioned before the second unit 200 in the direction of movement of the apparatus 300 during cleaning operation. The first unit 100 and the second unit 200 may be arranged in the same plane. The first unit 100 and the second unit 200 may be arranged to have substantially the same distance to the solar pan el during cleaning operation. The first unit 100 and the second unit 200 may be arranged to have a distance 340 with respect to each other during cleaning opera tion, which distance may be a minimum or a substan tially constant distance. This may be provided by the first unit 100 and the second unit being connected to each other, for example by a direct connection but other alternatives exist as well, for example, if the first unit 100 and the second unit 200 are arranged as separate mobile units, which may have their own sepa rate power sources for movement and/or electric cur rent generation. The first unit 100 and the second unit 200 may be connected by one or more connecting bodies 320, which may be for example extensions of any of the walls of the first unit 100 and or the second unit 200. The connecting bodies 320 may form a mono lithic body with any combination of a first unit 100 or a wall thereof and/or a second unit 200 or a wall thereof. The connecting bodies 320 may comprise hold ers extending from the first unit 100 and/or the sec ond unit 200 and connected to each other and/or di rectly to the first unit 100 and/or the second unit 200. The holders may extend substantially perpendicu larly upwards from the apparatus 300 (i.e., in a di- rection perpendicular to the longitudinal axis 302 and the elongated conductor 220 and away from the solar panel when the apparatus 300 is positioned on the so lar panel for cleaning operation) . In an example em bodiment, it has been found that a distance 340 of 30- 150 millimeters between the first unit 100 and the second unit 200 in a direction parallel to the longi tudinal axis 302 may be used to provide improved cleaning efficiency for the apparatus 300. This may be applied for example for movement speeds of 0.5-10 feet/minute (or 15-300 cm/minute) of the apparatus 300. The distance 340 may also be 50-120 millimeters or 90-100 millimeters. The distance 340 may be filled, partially or fully with material such as electrically insulating material but it has been found that for many practical arrangements of the apparatus 300 it is also possible to simply arrange a gap, e.g. an air gap, between the first unit 100 and the second unit 200. The distance 340 between the first unit 100 and the second unit 200 may be measured from the front wall 220 of a second unit 200 to the rear wall 122 of a first unit 100 or between corresponding positions.

The apparatus 300 may comprise an actuator 330 for moving the apparatus 300 along the solar panel in a direction parallel to the longitudinal axis 302. The actuator 330 may be a drive system comprising, for ex ample, one or more wheels, rail assemblies and/or track assemblies such as a chain track. The actuator 330 may be arranged to support the apparatus 300 on the support structure of the solar panel. It may also be arranged to couple to the support structure to pro vide the friction for moving the apparatus 300. The actuator 330 may be arranged for linear movement and even be confined to linear movement along the longitu dinal axis 302. It may naturally be possible to ar range the apparatus 300 as a part of various manually, autonomously or semi-autonomously operated devices in cluding even flying vehicles such as drones. The appa ratus 300 may be arranged, for example, for movement speeds of 0.5-10 feet/minute (or 15-300 cm/minute). The actuator may be powered by the one or more elec tric power sources 310.

Figure 3b illustrates an apparatus 300 for cleaning solar panels according to an embodiment. The apparatus 300 may comprise two sets of one or more first units 100 for detaching particles from a solar panel, the two sets located on separate sides of one or more sec ond units 200 along the longitudinal axis 302. Here, the other set of first units 100 is also called a set of third units 100' but it should be understood that the properties described in relation to the first units 100 may be directly applied also to the third units 100'. Arranging first units 100, 100' on both sides of the one or more second units 200 allows the apparatus 300 to be used for cleaning operation in both directions along the longitudinal axis 302. When the one or more first units 100 are located before the one or more third units 100' in the direction of move ment, the one or more electric power sources 310 may be used to transmit electric current into the one or more first conductors 110 of the first units 100 for detaching particles. Conversely, when the one or more third units 100' are located before the one or more first units 100 in the direction of movement, the one or more electric power sources 310 may be used to transmit electric current into the one or more first conductors 110' of the third units 100' for detaching particles. In either or both cases, the unit 100, 100' trailing the other unit may be powered off so that no current is transmitted into its conductors. Figure 3c illustrates an apparatus 300 for cleaning solar panels according to yet another embodiment. The apparatus 300 here comprises at least two consecutive second units 200. As illustrated, the units 200 may share a side wall 224, which may be a conductive plate, e.g. a metal plate. This embodiment may be com bined with other embodiments, including that of Fig. 3b so that the apparatus 300 comprises at least two first units 100 and at least two second units 200. While it is possible to arrange the first units 100 and the second units 200 to alternate in various al ternative manners, an example embodiment involves a set of two or three second units 200 in the middle and one first unit 100, 100' at the front and one at the rear along the longitudinal axis 302.

The apparatus 300 may be arranged to perform cleaning automatically or semi-automatically . For this purpose, the apparatus 300 may comprise at least one processor, at least one memory and program instructions on the memory, the at least one memory and the computer pro gram code configured to, with the at least one proces sor, cause the apparatus to at least perform some of the procedures described herein including, for exam ple, the movement control of the apparatus 300. The apparatus 300 may comprise a receiver such as an an tenna e.g. for radio waves to allow remote control, which may involve adding and/or updating the program instructions. The apparatus 300 may be arranged to re peat cleaning operations periodically, for example once a day, once in two days or once a week. This may involve, for example through program instructions on a memory, to move across a row of one or more solar pan els in one direction during one period. It may addi tionally involve, at the end of the row, reversing di rection and returning to the opposite end of the row during the same period. The apparatus 300 may be ar- ranged for connecting into a docking station for charging. It may comprise, for example, a connector, a socket or a plug for this purpose. The apparatus 300 may be arranged, for example through program instruc tions on a memory, to move across a row of one or more solar panels in one direction and, at the end of the row, connect into a docking station and recharge it self. The apparatus 300 may also be arranged, for ex ample through program instructions on a memory, to move across a row of one or more solar panels in one direction and, at the end of the row, reverse direc tion, return to the opposite end of the row and then connect into a docking station and recharge itself. Naturally, the apparatus 300 may also be arranged for various other charging schemes as well, for example recharging on as-needed basis or recharging whenever a docking station is available. The apparatus 300 may be arranged, for example through program instructions on a memory, to perform cleaning of solar panels at night and recharge during daytime.

Figure 4 illustrates a method of cleaning a solar pan el according to an embodiment. The method comprises generating 402 alternating (AC) or direct (DC) current into one or more first conductors 110 of a first unit 100 for detaching particles from the solar panel 10 and moving 404 the first unit 100 along the solar pan el 10 in a direction parallel to a longitudinal axis 302 to detach particles from the solar panel 10. The method further comprises generating 406 alternating (AC) or direct (DC) current into an elongated conduc tor arranged substantially perpendicularly with re spect to the longitudinal axis 302 and moving 408 a second unit 200 for collecting particles detached from the solar panel 10 behind the first unit 100 along the longitudinal axis 302 along the solar panel 10, the second unit 200 comprising a collector surface 220, 222 and the elongated conductor 210 for conveying de tached particles on the collector surface (220, 222) . Both the generating and moving for both the first unit 100 and the second unit 200 may be performed simulta neously. The first unit 100 and the second unit 200 may be comprised in an apparatus 300 as described hereinabove .

At least parts of the apparatus may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The ap plication logic, software or instruction set may be maintained on any one of various conventional comput er-readable media. A "computer-readable medium" may be any media or means that can contain, store, communi cate, propagate or transport the instructions for use by or in connection with an instruction execution sys tem, apparatus, or device, such as a computer. A com puter-readable medium may comprise a computer-readable storage medium that may be any media or means that can contain or store the instructions for use by or in connection with an instruction execution system, appa ratus, or device, such as a computer. The exemplary embodiments can store information relating to various processes described herein. This information can be stored in one or more memories, such as a hard disk, optical disk, magneto-optical disk, RAM, and the like. One or more databases can store the information used to implement the exemplary embodiments of the present inventions. The databases can be organized using data structures (e.g., records, tables, arrays, fields, graphs, trees, lists, and the like) included in one or more memories or storage devices listed herein. The databases may be located on one or more devices com prising local and/or remote devices such as servers. The processes described with respect to the exemplary embodiments can include appropriate data structures for storing data collected and/or generated by the processes of the devices and subsystems of the exem plary embodiments in one or more databases. All or a portion of the exemplary embodiments can be implement ed using one or more general purpose processors, mi croprocessors, digital signal processors, micro controllers, and the like, programmed according to the teachings of the exemplary embodiments, as will be ap preciated by those skilled in the computer and/or software art(s) . Appropriate software can be readily prepared by programmers of ordinary skill based on the teachings of the exemplary embodiments, as will be ap preciated by those skilled in the software art. In ad dition, the exemplary embodiments can be implemented by the preparation of application-specific integrated circuits or by interconnecting an appropriate network of conventional component circuits, as will be appre ciated by those skilled in the electrical art(s) . Thus, the exemplary embodiments are not limited to any specific combination of hardware and/or software

The different functions discussed herein may be per formed in a different order and/or concurrently with each other.

Any range or device value given herein may be extended or altered without losing the effect sought. Also any embodiment may be combined with another embodiment un less explicitly disallowed.

Although the subject matter has been described in lan guage specific to structural features and/or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are dis closed as examples of implementing the claims and oth- er equivalent features and acts are intended to be within the scope of the claims.

It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item may refer to one or more of those items.

The term 'comprising' is used herein to mean including the method, blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

It will be understood that the above description is given by way of example only and that various modifi cations may be made by those skilled in the art. The above specification, examples and data provide a com plete description of the structure and use of exempla ry embodiments. Although various embodiments have been described above with a certain degree of particu larity, or with reference to one or more individual embodiments, those skilled in the art could make nu merous alterations to the disclosed embodiments with out departing from the spirit or scope of this speci fication .

Claims

1. Apparatus (300) for cleaning a solar panel (10), the apparatus (300) comprising:

a longitudinal axis (302) parallel to the di rection of movement of the apparatus (300) during cleaning operation;

one or more electric power sources (310) for providing alternating (AC) and/or direct (DC) current and/or voltage;

a first unit (100) comprising one or more first conductors (110) for detaching particles from the solar panel when an electric current is transmit ted into the one or more first conductors (110); and a second unit (200) for collecting particles detached from the solar panel (10) comprising a col lector surface (220, 222) and an elongated conductor (210) for conveying detached particles onto the col lector surface when an electric current is transmitted into the elongated conductor (210) , the elongated con ductor (210) being arranged substantially perpendicu larly with respect to the longitudinal axis (302);

wherein the first unit (100) and the second unit (200) are arranged on the longitudinal axis (302) with the first unit (100) positioned before the second unit (200) in the direction of movement of the appa ratus (300) during cleaning operation.

2. Apparatus (300) according to claim 1, comprising a third unit (100') comprising one or more conductors (110') connected to the one or more electric power sources (310) for detaching particles from the solar panel (10) when an electric current is transmitted in to the one or more conductors (110'); wherein the third unit (100') is arranged on the longitudinal axis (302) and the second unit (200) is positioned between the first unit (100) and the third unit (100') .

3. Apparatus (300) according to any of the preced ing claims, wherein the electric current transmitted into the one or more first conductors (110) is direct (DC) current and the electric current transmitted into the elongated conductor (210) is alternating (AC) cur rent .

4. Apparatus (300) according to any of the preced- ing claims, wherein the second unit (200) comprises a first wall (220) and a second wall (222) arranged on opposite sides of the elongated conductor (210) on the longitudinal axis (302); and wherein the first wall (220) and the second wall (222) of the second unit (200) are electrically grounded.

5. Apparatus (300) according to claim 4, wherein the first (220) and/or the second wall (222) has a lower edge at a substantially same height as the elon- gated conductor.

6. Apparatus (300) according to claims 4 or 5, wherein the elongated conductor (210) is positioned at a substantially equal distance from the first wall (220) and the second wall (222) .

7. Apparatus (300) according to any of claims 4-6, wherein the distance between the first wall (220) and the second wall (222) of the second unit (200) is 20- 100 millimeters in a direction parallel to the longi tudinal axis (302) .

8. Apparatus (300) according to any of the preced ing claims, wherein the second unit (200) comprises a roof (230) of non-conductive material.

9. Apparatus (300) according to any of the preced ing claims, wherein the first unit (100) comprises a first wall (120) and a second wall (122) arranged on opposite sides of the one or more first conductors (110) on the longitudinal axis (302); and wherein the first wall (120) and the second wall (122) of the first unit (100) are non-conductive.

10. Apparatus (300) according to any of the preced ing claims, wherein the first unit (100) and the sec ond unit (200) are separated by a distance of 30-150 millimeters in a direction parallel to the longitudi nal axis (302) .

11. Apparatus (300) according to any of the preced ing claims, wherein the one or more first conductors

(110) comprise one or more elongated conductors ar ranged substantially perpendicularly with respect to the longitudinal axis (302) .

12. Apparatus (300) according to claim 11, wherein the one or more first conductors (110) comprise at least six elongated conductors arranged substantially perpendicularly with respect to the longitudinal axis (302) .

13. Apparatus (300) according to any of the preced ing claims, wherein the one or more first conductors

(110) comprise a grid of a first set of one or more elongated conductors arranged substantially perpendic ularly with respect to a second set of one or more elongated conductors.

14. Apparatus (300) according to any of the preced ing claims, wherein the first conductors (110) and/or the elongated conductor (210) are conductive wires.

15. Apparatus (300) according to any of the preced ing claims, wherein the electric current transmitted into the one or more first conductors (110) and/or the elongated conductor (210) is alternating (AC) current having frequency of 50-100 Hz.

16. Apparatus (300) according any of the preceding claims, wherein the electric current transmitted into the one or more first conductors (110) and/or the elongated conductor (210) is alternating single-phase current .

17. Apparatus (300) according to any of the preced ing claims, wherein the electric power source (310) is arranged to provide a voltage of 5-40 kV across the one or more first conductors (110) and/or the elongat ed conductor (210) .

18. Apparatus (300) according to any of the preced ing claims, wherein the apparatus (300) has dimensions arranged so that one or more first conductors (110), the elongated conductor (210) or both are within one centimeter from the surface of the solar panel (10) when the apparatus (300) is positioned against the so lar panel (10) for cleaning operation.

19. Apparatus (300) according to any of the preced ing claims comprising an actuator (330) for moving the apparatus (300) along the solar panel (10) in a direc tion parallel to the longitudinal axis (302) .

20. Method for cleaning a solar panel (10) compris ing :

generating (402) alternating (AC) or direct (DC) current into one or more first conductors (110) of a first unit (100) for detaching particles from the solar panel (10) ; moving (404) the first unit (100) along the solar panel (10) in a direction parallel to a longitu dinal axis (302) to detach particles from the solar panel (10) ;

generating (406) alternating (AC) or direct

(DC) current into an elongated conductor arranged sub stantially perpendicularly with respect to the longi tudinal axis (302); and

moving (408) a second unit (200) for collect- ing particles detached from the solar panel (10) be hind the first unit (100) along the longitudinal axis (302) along the solar panel (10), the second unit (200) comprising a collector surface (220, 222) and the elongated conductor (210) for conveying detached particles onto the collector surface (220, 222) .