NL2005944C2

NL2005944C2 - Solar panel, solar cell converter and method of manufacturing a solar panel.

Info

Publication number: NL2005944C2
Application number: NL2005944A
Authority: NL
Inventors: Walter Knulst; Michiel Herman Mensink
Original assignee: M H Mensink Beheer B V
Priority date: 2010-12-31
Filing date: 2010-12-31
Publication date: 2012-07-03

Description

P30429NL00/HSE

Solar panel, solar cell converter and method of manufacturing a solar panel 5 The invention relates to a solar panel, to a solar cell converter comprising such solar panel and to methods of manufacturing such a solar panel.

In solar panel technology, a focus has been on increasing solar energy conversion efficiency and on reducing cost price. Most present solutions provide an adequate performance by either optimizing efficiency for flat panels in which a total surface is covered by solar cells, 10 or by focusing the sunlight to highly intense spots and using high efficiency and costly solar cells to convert the radiation into electrical energy. The latter solution provides an economically feasible solution where a high solar intensity is commonly provided. For the first solution a trade off needs to be made: using higher efficiency solar cells, such as crystal silicon, that are more expensive, or using lower efficiency solar cells, such as thin film, that have low 15 costs.

A further development has been the introduction of so-called back contact configurations, allow (part of) the electrical conductors to be positioned at a backside, hence allowing wide, low resistance conductive traces and reducing shadowing losses, however at the cost of an increased manufacturing complexity and cost. Nevertheless, applying the above solu-20 tions in flat panels requires that large areas would have to be covered and as a consequence large amounts of semiconductor material, e.g. crystal silicon based materials provided with specific doping, would be required.

An object of the invention is to provide a solar conversion that may be manufactured with a low amount of semiconductor material and that exhibits a potential to be efficient even 25 in geographical areas with lower solar intensity.

This object may be achieved by a solar panel comprising a plurality of photoelectric cells and a concentrator to project incident radiation onto the photoelectric cells, wherein the photoelectric cells are elongate cells each comprising at least one fiber.

Thereby, a solar panel may be produced that allows photoelectric cells to be pro-30 duced at a low cost - namely in the form of fibers that only require a relatively low amount of semiconductor material and which may be produced at large lengths and cut to a desired dimension as required. By using optical concentrators, the photoelectric cells may be spaced apart from each other. As a result, a relatively large panel area can collect sunlight, while only a low amount of semiconductor material for the placed apart photoelectric cells is required to 35 convert the radiation into electrical energy. The focal properties of the concentrator may be chosen so the sunlight is imaged to narrow lines that have a width that is small enough (e.g.

2 smaller than a diameter of the photoelectric cells) so that the front electrodes, such as grid fingers, may be moved to a side of the photoelectric cell, as to eliminate shadowing. Furthermore, due to the spacing between the photoelectric cells, wide electrical conductors may be placed between the photoelectric cells, so as to reduce electrical losses and to function as 5 heat sink, thereby lowering the temperature and increasing the solar panel efficiency. Furthermore, the concentrator provides for a converging of the incident light towards an image line, which results in the light to reach the photoelectric cell at a large range on angles of incidence. In case the photoelectric cell would be flat, large angles of incidence would result in large reflection losses, hence reducing an efficiency of the solar cell. The photoelectric cell 10 may comprise a single fiber which may result in the converged solar radiation to reach an outer surface of the photoelectric cell at a smaller angle of incidence (i.e. more perpendicular to the outer surface of the photoelectric cell) due to its circular cross section, so that reflection losses may be inherently low. The solar cells may be spaced apart, the concentrator may comprise a repetitive structure matching the spacing of the solar cells, and arranged for con-15 centrating the incident solar radiation on the solar cells. The concentrator may thereto project the incident radiation for example on repetitive lines or strips at locations where the solar cells are to be placed. The concentrator may be formed by a single unit or a plurality of individual elements (i.e. lenses). The concentrator may comprise refractive and/or reflective optical elements (i.e. refractive and/or reflective lenses).

20 In an embodiment, a focal length of the concentrator is chosen in a range of 10 to 100 times, preferably 10 to 50 times a width of the photoelectric cells. As a result, a full image line may be projected within a width of the photoelectric cell. To achieve a very large reduction of semiconductor material in a solar panel, a width of the photoelectric cell is chosen to be larger than a image line by a factor that is slightly larger than unity. Using low-cost manufacturing 25 methods a concentrator may be manufactured in the preferred range. Between 50-100 times more advanced technology has to be applied to achieve very thin image lines. Additionally, photoelectric cells may have very small width of about 0.5 mm, so that a total panel thickness is limited when choosing a focal length of 20 mm, which is a factor 40.

Furthermore, a lens width of the concentrator is chosen in a range of 10 to 100 times, 30 preferably 10 to 50 times a width of the photoelectric cells. This ratio may determine directly the amount of semiconductor material that is saved per solar panel, therefore higher values which may result in larger cost reduction. Between 50 - 100 times more advanced technology may be applied to achieve a very thin image lines and a high concentration ratio.

35 The term fiber should be understood as any elongate structure having a length that is at least a factor 10 larger than its width, preferably more than 100 times larger. The fiber may 3 be round, elliptical or have any other suitable cross sectional shape. Preferably, although not necessarily, a diameter of the fiber is substantially constant over the length of the fiber.

In an embodiment, an optical concentration factor of the concentrator is larger than 5, preferably larger than 10, more preferably larger than 20, so that incident solar radiation is 5 concentrated to a small surface part, thus allowing narrow photoelectric cells and wide openings between the photoelectric cells, so that large, low electrical resistance conductors may be provided in between the photoelectric cells. Also, a good thermal dissipation may be provided by such conductors so as to keep a temperature of the photoelectric cells to a low level, thereby allowing them to operate at a temperature at which an efficiency thereof is high.

10 In an embodiment, the concentrator comprises a plurality of cylindrical lenses, each cylindrical lens preferably having a plano-convex shape, wherein a convex side of a respective one of the plano-convex lenses faces a respective one of the photoelectric cells so that easy cleaning or self cleaning properties may be provided due to a substantially flat front face.

15 In an embodiment, the concentrator comprises a plurality of linear Fresnel lenses, each linear lens having a plane and Fresnel facets side, wherein the Fresnel facets of a respective one of the Fresnel lens for example faces a respective one of the photoelectric cells so that easy cleaning or self cleaning properties may be provided due to a substantially flat front face. The Fresnel lenses may be manufactured from glass, PMMA such a plexiglass or 20 Perspex, silicone on glass or any other suitable material.

In an embodiment, each of the photoelectric cells comprises a core and a first layer around the core wherein a first contact electrode being connected to the first layer, the first contact electrode extending along a length of the photoelectric cells. Thereby, a structure may be obtained that allows a low ohmic contacting: as the first contact electrode extends along 25 the length of the photoelectric cells, so that electrical charge generated by a photoelectric effect only have to travel a short distance through the layer before being reaching the first contact electrode. The core may be formed by the fiber or a center of the fiber. The first layer, i.e. the layer around the core may extend around an entire circumference thereof, or around a part of the circumference. The first layer around the core may be a layer generated by diffu-30 sion, a thin film technology layer, a thick film technology layer, or any other suitable layer. The layer may form a part of a p-n junction providing a photodiode, together with the core or other layer as will be described in more detail below.

In an embodiment, each photoelectric cell further comprises an at least partly transparent electrically conductive outer layer that connects the first contact electrode to the first 35 layer, i.e. the layer around the core. The at least partly transparent, electrically conductive layer may allow to further reduce an electrical resistance, as it allows electrical charge gener- 4 ated by the photoelectric effect to travel to the first contact electrode via the electrically conductive layer.

Each photoelectric cell may further comprise a second contact electrode connected to the core. The second contact electrode may be provided at one or both of the ends of core, or 5 the second contact electrode may be provided so as to extend along a length of the core. The former allows to contact the core at minimum intrusion, hence avoiding additional processing steps that might complicate the manufacturing, and may be applied for example in configurations wherein an electrical resistance of the core is low. The latter may be applied so as to allow to establish a low resistance electrical contact and reduce a path to be travelled by elec-10 trical charge towards the electrode.

Each photoelectric cell may further comprise a second layer located between the first layer and the core, the second contact electrode being connected to the second layer. The first and second layer may together form a p-n junction providing a photodiode. In order to provide a low resistance path towards the second contact electrode, each photoelectric cell 15 may further comprise an electrically conductive material layer below the second layer to electrically connect the second contact electrode to the second layer.

The core of the photoelectric cells (which is formed by the fiber or by a center of the fiber) may comprise at least one of glass, polymer, carbon, silicon carbide, and metal. First, these fibers may be fabricated at very long lengths and small diameters at low-costs. Addi-20 tionally, fibers of glass, carbon and specific metals, for instance one of tungsten or molybdenum, may withstand very high temperatures that may be required during fabrication of the photoelectric cell. Additional, a metal fiber may have other functionalities for the photoelectric cell, namely being the back contact for photovoltaic semiconductor layer and being a heat conductive medium to conduct heat to heat sinks.

25 In an embodiment, the first contact electrode extends (lengthwise along the photoelec tric cells) along two sides of the photoelectric cells and contacts the photoelectric cells from two sides so that a good heat conductivity, i.e. a good heat sinking, may be provided to guide heat (e.g. from the incident radiation and the electrical current) away from the photoelectric cells. An efficiency of the photoelectric cells depends on temperature. Generally, at a higher 30 temperature, an efficiency may deteriorate. Hence, keeping the temperature of the photoelectric cells to a lower level may enhance an efficiency of the photoelectric cells.

In order to minimize or avoid a shading effect by the contacts on the photoelectric cells, the first and second contact electrodes may be located at a side of the photoelectric cell that faces a substrate of the solar panel, so that incident solar radiation is not impeded from 35 reaching the photoelectric cells. To provide a large surface of the first contact electrode and 5 thereby allow a good heat sinking, the first contact electrode may extend substantially to a center line between adjacent photoelectric cells.

In order to further improve heat sinking, a thermally conductive layer may be provided 5 between the substrate and the first electrode, preferably comprising a graphite.

Each photoelectric cell may comprise a single fiber so that per optical concentration by the concentrator, one fiber is provided. Since fibers have in general diameters smaller than 1 mm, it fits very well with the narrow image lines of the concentrator lenses. During fabrication 10 the complete cell structure is fully around the fiber it does not have a top and bottom and therefore twisting of the fiber may be ignored. Additionally, the incoming light beam to the fiber is converging and hit the surface of a fiber having a circular cross section much more perpendicular than a flat solar cell (as explained above). Alternatively, the photoelectric cells each comprise a plurality of parallel fibers thereby being arranged as multicore photoelectric 15 strips whereby each following lens of the concentrator is configured to project incident radiation on a following photoelectric strip. The photoelectric cell comprising two or many more fibers may recapture an initially reflected sunray from one fiber at the following fiber, as the angle of incidence at the following fiber may be closer to perpendicular, so that reflection losses may be inherently lower at the following fiber. Furthermore, the photoelectric cell con-20 sisting of two or many more fibers is constructed from fibers with smaller diameter and with the front electrode on the backside. As a result, very short paths may be created for the charges to travel from the point of photovoltaic conversion of the sunlight on the front side along the outer radius of an individual fiber to front electrode on the backside. Due to this short path length resistance losses may be minimized and the photoelectric cell efficiency 25 may be maximized, while the manufacturing may be simple and low cost.

In case of the multicore strip, an additional degree of freedom in the design of the solar panel is obtained, as a width of the photoelectric cell may differ from a diameter of the fiber, the photoelectric cell comprising two or more fibers arranged in a strip. Furthermore, this configuration, as will be discussed in some more detail below, a metallisation may be pro-30 vided below the strip, which allows to carry high currents, to minimize a shading so as to avoid optical losses by shading as much as possible, and to decrease a distance from the photoelectric material where the photoelectric effect occurs, to the electrodes, to approximately a half of a diameter of the fibers or less, so as to reduce series resistance.

An interdistance between the fibers of the multicore photoelectric strip may be smaller 35 than a diameter of the fibers, preferably zero so that solar radiation that is reflected by one of 6 the fibers of the photoelectric strip, is directed to a next one of the fibers of the photoelectric strip, so as to reduce losses due to reflection.

The invention further comprises a solar energy converter comprising the solar panel according to the invention and a single axis tracking system. The single axis tracking system 5 allows to follow a solar position along its daily orbital so as to provide an optimum angle of incidence of the solar irradiation. The fiber shape of the photoelectric cells in combination with the optical concentrator that concentrates the incident solar irradiation on the photoelectric cells, may make the solar energy converter less sensitive to the seasonal declination of the sun (in particular when the photoelectric cells extend from a top side of the panel to a bottom 10 side). A commonly used dual axis tracking system (more complex) may thereby be avoided.

According to an aspect of the invention, there is provided a method of manufacturing a solar panel, comprising: a) proving a fiber; b) creating a photoelectric cell from the fiber; and 15 c) mounting the photoelectric cell on a substrate.

A photoelectric cell may created from the fiber by forming a photodiode junction along a surface of at least part of the photoelectric cell. The forming of the photodiode junction will be described in more detail below. By using a fiber as a basis, a photoelectric cells may be created using a low amount of semiconductor materials, and using relatively compact and 20 simple machinery, with which the fiber shaped photoelectric cells may be produced efficiently at long lengths. At least one electrical contact electrode may be provided along a length of the fiber so as to provide a low loss electrical connection, a short path length for charge to reach the contact electrode and allow effective heat sinking. The method may further comprise mounting an optical concentrator so as to concentrate incident radiation (e.g. solar radiation) 25 on the photoelectric cells. The concentrator may be arranged to image the incident radiation to lines, the lines e.g. having a width smaller than or equal to a width or diameter of the photodiodes.

In a first version of the above method of manufacturing a solar panel, use is made of a fiber of a semiconductor material, such as a silicon fiber, a p-n junction being created in the fiber. In 30 accordance with this version, the above method of the invention may further be characterized in that a) comprises providing a semiconductor fiber having one of a p-doping and an n-doping; and b) comprises doping an outer layer of the semiconductor fiber by an opposite one of the p-doping and the n-doping so as to form a first layer on or in at least part of an outside surface of the fiber.

35 In alternative wording, this first version of the method of manufacturing a solar panel as described above, may be formulated as a method of manufacturing a solar panel, comprising: 7 a) providing a semiconductor fiber having one of a p-doping and an n-doping; b) doping an outer layer of the semiconductor fiber by an opposite one of the p-doping and the n-doping, so as to provide a p-n junction; c) mounting the semiconductor fiber on a substrate; the method preferably further comprising: 5 d) connecting a first contact electrode to the outer semiconductor layer; and e) connecting a second contact electrode to a core of the semiconductor fiber.

By this method of manufacturing, a relatively simple process may be applied to fibers having a long length (e.g. meters or kilometers), such as silicon fibers, which may be doped by means of well-known processes. Thereby, the photoelectric cells may be produced and 10 e.g. cut to a desired length before being mounted onto the substrate. The method may further comprise mounting an optical concentrator so as to project the incident radiation onto the photoelectric cells. Silicon single crystal fibers may be used, which may be produced using a micro-pulling down technique. Such fibers may have a diameter of for example 0.5 millimeters and a length of several tens of centimeters. The fibers may have different shapes, such as 15 round, D-shaped or arc shaped, the shape for example being determined by a shape of an opening through which extrusion is performed, for example extrusion of molten silicon. The shape may be optimized in regard of an incidence of the solar radiation so that the solar radiation converged by the concentrator is incident on the surface of the photoelectric cell at angles optimized for minimum reflection. In order to provide low resistance contacting, a short 20 path length for charge to reach the contact electrode and allow effective heat sinking, the method may further comprise d) connecting a first contact electrode to the first layer; and e) connecting a second contact electrode to a core of the semiconductor fiber. The first (and optionally the second) contact electrode may extend along a length of the photoelectric cell, e.g. substantially parallel to a length thereof. In an embodiment, the method may further com-25 prise removing a part of the outer semiconductor layer along a length of the semiconductor fiber so as to lay open a core of the semiconductor fiber (e.g. by etching or any mechanical removal process), and wherein e) comprises: connecting the second contact electrode to the layed-open core. As a result, a good, low resistance electrical contact may be established, so as to allow electrical charge, generated by the photoelectric effect, to flow to the electrical 30 contact with low losses. Alternatively, the method may further comprise providing a laser grooved buried contact along a length of the semiconductor fiber so as to contact the core of the semiconductor fiber; and wherein e) comprises: connecting the second contact electrode to the laser grooved buried contact. Again, a good, low resistance electrical contact may be established. Furthermore, a narrow segment of the photoelectric cell needs to be removed 35 thereby - preferably at a side of the photoelectric cell that faces the substrate, so as to avoid the second contact to interfere with incident solar irradiation. As a further alternative, b) may 8 be performed on a cylinder segment shaped surface part of the semiconductor fiber, whereby e) comprises connecting the second electrode to a surface part not doped in b). The laying open of the core, the providing of a laser grooved buried contact or similar may be performed before mounting the photoelectric cell on the substrate.

5 The fibers when mounted on the substrate may be interconnected, for example by a suitable conductor pattern on the substrate. The fibers may be connected in parallel, in series or a combination thereof. The fibers may be divided in sections, and diodes may be provided to interconnect the sections. Shaded section of the solar panel may be bypassed by means of the diodes.

10 In order to reduce reflection losses, b) may further comprise: b2) coating on top of the outer layer or treating the outer layer so that an antireflection layer is formed to enhance anti-reflective properties.

It is noted that in any version of the method according to the invention, the steps may be performed in any suitable order. It is thus not per se necessary that the steps are per-15 formed in the same order as in which they have been written down in this document. For example, an anti reflective coating may be applied before mounting the photoelectric cell on the substrate, or thereafter.

In a second version of the above method of manufacturing a solar panel, use is made of a 20 fiber such as a glass fiber that is coated with silicon, preferably polysilicon, a p-n junction be ing created in the polysilicon. In accordance with this version, the above method of the invention may further be characterized in that b) comprises coating the fiber by a semiconductor material having one of a p-doping and an n-doping; and doping an outer layer of the semiconductor material by an opposite one of the p-doping and 25 the n-doping so as to form a first layer, a remainder of the semiconductor material to form a second layer between the first layer and the fiber.

In alternative wording, this second version of the method of manufacturing a solar panel as described above, may be formulated as a method of manufacturing a solar panel, comprising: 30 a) coating a fiber (such as a glass fiber) by a semiconductor material (such as polysilicon) having one of a p-doping and an n-doping; b) doping an outer layer of the semiconductor material by an opposite one of the p-doping and the n-doping; c) mounting the fiber on a substrate, the method preferably further comprising: 35 d) connecting a first contact electrode to the outer layer of the semiconductor material; and e) connecting a second contact electrode to an inner layer of the semiconductor material.

9

Again, a relatively simple process may be applied to fibers having a long length (e.g. meters or kilometers). The fiber may be coated using chemical vapor deposition technology. At high temperatures, the deposed silicon will convert into poly-silicon. The photoelectric cells may be produced and e.g. cut to a desired length before being mounted onto the substrate. The 5 method may further comprise mounting an optical concentrator so as to project the incident radiation onto the photoelectric cells. The fibers may have different shapes, such as round, D-shaped or arc shaped, the shape for example being determined by a shape of an opening through which extrusion is performed, for example extrusion of molten silicon. The shape may be optimized in regard of an incidence of the solar radiation so that the solar radiation con-10 verged by the concentrator is incident on the surface of the photoelectric cell at angles optimized for minimum reflection.

In order to provide low resistance contacting, a short path length for charge to reach the contact electrode and allow effective heat sinking, the method may further comprise d) connecting a first contact electrode to the first layer; and e) connecting a second contact elec-15 trade to the second layer. The first (and optionally the second) contact electrode may extend along a length of the photoelectric cell, e.g. substantially parallel to a length thereof.

In an embodiment, the further comprises removing a part of the outer layer along a length of the fiber so as to lay open the inner layer of the semiconductor material, and wherein e) comprises: connecting the second contact electrode to the layed-open inner layer. 20 As a result, a good, low resistance electrical contact may be established, so as to allow electrical charge, generated by the photoelectric effect, to flow to the electrical contact with low losses. Alternatively, a laser grooved buried contact Is provided along a length of the fiber so as to contact the inner layer of the semiconductor material; whereby e) comprises: connecting the second contact electrode to the laser grooved buried contact. Again, a good, low resis-25 tance electrical contact may be established. Furthermore, a narrow segment of the photoelectric cell needs to be removed thereby - preferably at a side of the photoelectric cell that faces the substrate, so as to avoid the second contact to interfere with incident solar irradiation. As a further alternative, b) may be performed on a cylinder segment shaped surface part of the semiconductor fiber, whereby e) comprises connecting the second contact electrode to a sur-30 face part not doped in c). The laying open of the inner layer, the providing of a laser grooved buried contact or similar may be performed before mounting the photoelectric cell on the substrate.

In an embodiment, prior to b), an electrical contact layer is coated on the fiber so as to provide an internal electrode, thereby e) comprising connecting the second contact electrode 35 to the electrical contact layer. The electrical contact layer may comprise molybdenum, carbon, wolfram or other metal coating, so as to be able to withstand high temperatures to which 10 the fiber will be subjected in one or more of the successive steps. Electrical charge may thereby be conducted away via the internal electrode so as to provide a low loss conductive path. The second contact electrode may be connect along the length of the fiber, thereby using techniques as described above, however it is also possible that the second contact elec-5 trode contacts the internal electrode at an the end of the fiber, thereby to simplify a manufacturing as a laying open of the internal electrode may be omitted, and due to the fact that the electrical contact electrode realizes a low resistance conductive path, a low resistance contacting may be established nevertheless to conduct high current that may be generated at the high solar irradiation levels provided as a result of the solar energy concentration by the con-10 centrator. In order to establish a good connection to the internal electrode, a thin, semiconductor layer with a high doping level may prior to b) be deposited on the electrical contact layer.

The fibers when mounted on the substrate may be interconnected, for example by a suitable conductor pattern on the substrate. The fibers may be connected in parallel, in series 15 or a combination thereof. The fibers may be divided in sections, and diodes may be provided to interconnect the sections. Shaded section of the solar panel may be bypassed by means of the diodes.

In order to reduce reflection losses, b) may further comprise: b2) coating on top of the outer layer or treating the outer layer so that an antireflection layer is formed to enhance anti-20 reflective properties.

According to in a third version of the above method of manufacturing a solar panel, so-called thin film technology (such as thin film PV technology, i.e. thin film photovoltaic technology) may be applied whereby a thin film is coated on a fiber, such as a glass fiber, polymer fiber, carbon fiber or a metal wire.

25 In accordance with this third version, the above method of the invention may further be characterized in that b) comprises coating the fiber by an inner photoelectric semiconductor layer so as to form an absorber layer of a photocell; and providing an outer photoelectric semiconductor layer on at least part of the inner photoelectric semiconductor layer so as to form a junction between the outer and inner photoelectric semiconductor layers, the outer 30 photoelectric semiconductor layer forming a first layer, the inner photoelectric semiconductor layer forming a second layer between the first layer and the fiber.

In alternative wording, this third version of the method of manufacturing a solar panel as described above, may be formulated as a method of manufacturing a solar panel, comprising: 35 a) coating a fiber by an inner photoelectric semiconductor layer so as to form an absorber layer of a photocell; 11 b) providing an outer photoelectric semiconductor layer of a different material composition than in a) so as to form a junction; c) mounting the fiber on a substrate with an optional heat conductive layer in between; the method preferably further comprising: 5 d) connecting a first electrode to the outer photoelectric semiconductor layer; and e) connecting a second electrode to the inner photoelectric semiconductor layer.

By this method of manufacturing, again a relatively simple process may be applied to fibers having a long length (e.g. meters or kilometers). The photoelectric cells may be produced and e.g. cut to a desired length before being mounted onto the substrate. The method may further 10 comprise mounting an optical concentrator so as to project the incident radiation onto the photoelectric cells. Thin film silicon (single junction or multi junctions of amorphous silicon, CdTe (ll-VI semiconductor), and CI(G)S (l-lll-VI compound semiconductor with calcophyrite-crystal structure) may be used in steps a) and b). Also, a thin film layer of a nanostructure materials may be applied. The thin film materials may require a sequential deposition of thin 15 layers: for example, in case of CdTe, a very thin CdS layer may be required to create a p-n junction. In case of CI(G)S different fabrication methods may be used: as an example, one or more precursor layers may be deposited after which a selenisation process is applied in order to form the CI(G)S layer. A single double or triple junction may be created. The thin film layers may have a thickness of for example 2-5 micrometers. The fibers may have a diameter of 20 typically larger than 50 micrometers, for example 0.5 millimeters and a length of several tens of centimeters. The fibers may have different shapes, such as round, rectangular, D-shaped or arc shaped, the shape for example being determined by a shape of an opening through which extrusion is performed. When using the optical concentrator, the shape may be optimized in regard of an incidence of the solar radiation so that the solar radiation converged by 25 the concentrator is incident on the surface of the photoelectric cell at angles optimized for minimum reflection. Reflection losses may be reduced thereby. Optionally, a heat conductive layer may be provided between the fiber and the substrate so as to allow the fiber the sink heat towards the substrate, thereby allowing to reduce a temperature of the fiber, hence allowing an efficiency of the photoelectric solar energy conversion to be at a high level.

30 In order to provide low resistance contacting, a short path length for charge to reach the contact electrode and allow effective heat sinking, the method may further comprise d) connecting a first contact electrode to the first layer; and e) connecting a second contact electrode to the second layer. The first (and optionally the second) contact electrode may extend along a length of the photoelectric cell, e.g. substantially parallel to a length thereof. In 35 case a nonconductive fiber is applied, such as glass or polymer, the fiber may be coated with a layer with a conductive materials so as to form an inner conductor and back contact for the 12 photoelectric semiconductor. The layer of conductive material, such as molybdenum, wolfram of carbon, will be able to withstand high temperatures of the following steps and allows to carry the high electrical currents that may occur as a result of the optical concentration by the concentrator. In case of lower temperatures in the following steps, metals such as copper or 5 aluminum may be applied also. A front electrode may be formed in that b) further comprises: b2) coating the fiber with a conductive, transparent layer (such as a TCO layer comprising Ti02 or ZnO) so as to form a transparent conductive front electrode, and optionally b3) coating on top of the outer layer or treating the outer layer to enhance an anti-reflective property thereof.

10 In case the fiber comprises a metal wire, it may for example comprise molybdenum, tungsten or carbon will be able to withstand high temperatures as may be applied during the application of the thin film layers. Good electrical conductivity is provided to carry the high electrical currents that may occur as a result of the optical concentration by the concentrator. In case of thin film layers that may be applied at lower temperatures, metals such as copper, 15 steel or aluminum may be applied also.

In an embodiment, the method further comprises removing a part of the outer layer along a length of the fiber so as to lay open the inner layer, whereby e) comprises: connecting the second electrode to the layed open inner layer. As a result, a good, low resistance electrical contact may be established, so as to allow electrical charge, generated by the photoelec-20 trie effect, to flow to the electrical contact with low losses. Alternatively, the method may further comprise providing a laser grooved buried contact along a length of the fiber so as to contact the inner layer; whereby e) comprises: connecting the second contact electrode to the laser grooved buried contact. Again, a good, low resistance electrical contact may be established. Furthermore, a narrow segment of the photoelectric cell needs to be removed thereby 25 - preferably at a side of the photoelectric cell that faces the substrate, so as to avoid the sec ond contact to interfere with incident solar irradiation. As a further alternative, b) may be performed on a cylinder segment shaped surface part of the fiber, wherein e) comprises connecting the second contact electrode to a surface part not covered in b).

The first and second semiconductor layers may each respectively comprise one of 30 - thin film CIGS, compromising a composition Copper, Indium, Galium and Selinium in any configuration, and CdS, - thin film silicon, and - thin film CdTe and CdS,

The fibers when mounted on the substrate may be interconnected, for example by a suitable 35 conductor pattern on the substrate. The fibers may be connected in parallel, in series or a combination thereof. The fibers may be divided in sections, and diodes may be provided to 13 interconnect the sections. Shaded section of the solar panel may be bypassed by means of the diodes.

In each of the above methods and various versions and embodiments thereof, in order to avoid shading, an electrical contact with the first and/or second electrode is provided along 5 a side of the fiber facing the substrate, i.e. along a side of the fiber facing away from the incident solar radiation, so that obstructing the incident solar radiation by the first and or second contact may be avoided.

In each of the above methods and various versions and embodiments thereof, the fibers, i.e. the photoelectric cells, may be assembled as multicore photoelectric strips before 10 being mounted on the substrate. Hence, each concentrator element projects radiation on a multicore solar cell strip comprising at least two fibers. Hence, an additional degree of freedom in the design of the solar panel is obtained, as a width of the photoelectric cell may differ from a diameter of the fiber, the photoelectric cell comprising two or more photoelectric cells arranged in a strip. Furthermore, this configuration, as will be discussed in some more detail 15 below, a metallisation may be provided below the strip, which allows to carry high currents, to minimize a shading so as to avoid optical losses by shading as much as possible, and to decrease a distance from the photoelectric material where the photoelectric effect occurs, to the electrodes, to approximately a half of a diameter of the fibers or less, so as to reduce series resistance.

20 In an embodiment, the individual fibers are arranged in a strip at a desired interdistance using a molt; wherein an adhesive on top being provided to fix the fibers into the strip, preferably a transparent polymer; and wherein a backside of the strip is coated with a conductive metal so to form a front electrode. Due to the fact that the outer conductive layer of the fibers (which is the top layer or just beneath the antireflection coating) is fully around the fiber, there is a con-25 ductive path from the front (light receiving side) surface to the back surface of the strip at each fiber. Starting with very small diameters of fiber, for instance 50 micrometers, very short paths are realized from the front to the back surface of the strip just by putting the fibers in parallel without any additional technology to make this connection. This embodiment may be very suitable for fibers having a thin film semiconductor of amorphous silicon, CdTe or CI(G)S 30 layer.

In an embodiment, from a backside a layer with a thickness large enough so as to lay open a substantial part of the cores is removed, thereby for example removing a layer with a thickness approximately equal to a 1Λ of the radius of the photoelectric fiber, and wherein on a backside isolated lines of front and backside electrode compromising of conductive material 35 are provided, wherein the back electrode is centered at the vertical center line of the photoelectric fiber and connected to the inner photoelectric layer (e.g. the second layer) or core, 14 and wherein the front electrode is centered in between two following back electrodes and connected to the outer photoelectric semiconductor layer (e.g. the first layer). This embodiment may be very suitable for fibers having a silicon core and fibers having a polysilicon layer, since an inner conductor having a very good electrical conductance is omitted due very 5 high process temperatures. By putting the fibers in parallel in a strip a conductive path is introduced from the front to the back surface without any additional technology to make this connection. By processing the strip from the backside electrode connections may be made with the photovoltaic layer.

The photoelectric cells connected in any configuration, e.g. photovoltaic, photocurrent, 10 or any other configuration.

It will be understood that all subject matter disclosed with reference to the method according to the invention, is also applicable to the solar panel according to the invention, and vice versa.

Further advantages, features and effects of the invention will become apparent from 15 the appended drawing, showing non limiting embodiments of the invention, in which:

Figure 1A - 1D depict schematic views of a solar panel according to embodiments of the invention;

Figure 2A- 2F depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention; 20 - Figure 3A- 3F depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention;

Figure 4A- 4D depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention; - Figure 5A- 5F depict cross sectional views of fiber shaped solar cells as applied in 25 embodiments of the invention;

Figure 6A- 6F depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention;

Figure 7A- 7D depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention; 30 - Figure 8 depict in embodiments of the invention;

Figure 9A- 9F depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention; - Figure 10A-10C depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention; 35 Figure 11 A-11E depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention; 15

Figure 12A-12C depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention; and

Figure 13A and 13B depict cross sectional views of fiber shaped solar cells as applied in embodiments of the invention.

5 A solar panel will be described that may be arranged for low-to-middle concentration of sunlight. The Solar Panel (as schematically depicted in Figure 1A) comprises of a plate TRC comprising a glass or other at least partially transparent material with integrated lenses, such as cylinder lenses CLC that each form a concentrator. These lenses CLC focus the 10 sunlight on underlying line-shaped solar cells LSP, i.e. photoelectric cells. The solar cells are mounted on a base plate BPL, also referred to as a substrate BPL, which may serve as passive cooling element. The photoelectric cells LSP are shaped as a fiber (line, wire, or any other extended structure etc) and extend substantially parallel to each other on, over or in a surface of the substrate BPL. Likewise, the concentrator lenses CLC of the plate TRC extend 15 substantially parallel to each other. For each photoelectric cell LSP, a corresponding concentrator lens CLC is provided to project incident radiation on the respective photoelectric cell. Although the fiber shaped photoelectric cells are depicted equidistantly and parallel, other configurations are possible also.

A schematic side view is depicted in figure 1B: Each concentrator CLC concentrates 20 incident solar radiation SUN on a respective photoelectric cell LSP. The photoelectric cells extend in a direction perpendicular to the plane of drawing of Figure 1B.

Figure 1C depicts a cross sectional, somewhat more detailed view of a single one of the concentrator lens CLC and photoelectric cells SCP of the arrangement depicted in figure 1B. Concentrator lens CLC (also briefly referred to in this document as concentrator CLC) con-25 centrates incident solar radiation SUN onto the elongate photoelectric cell SCP. A line of focus of the concentrator is substantially parallel, preferably substantially coinciding with a length axis of the respective photoelectric cell SCP. Due to the convergence of the radiation SUN by the concentrator, an angle of incidence of the converged radiation SUN varies in respect of the surface of the substrate BPL. In order to reduce reflection losses and make an 30 antireflection coating that may be provided on an outside surface of the photoelectric cell, more effective, a substantially constant angle of incidence may be desired. The fiber shape of the photoelectric cell may help to provide, due to the for example curved surface of the photoelectric cell (in this example a round fiber), that an angle of incidence is kept more constant, and in this example more close to perpendicular to the surface of the photoelectric cell, so 35 that reflection is reduced and consequently an efficiency of the solar cell (in terms of output power versus optically radiated input power) may be improved. The photoelectric cell may be 16 embedded in an arrangement that provides for a good thermal conductivity so as to sink generated heat, and that provides (preferably highly electrically conductive) electrical connections to the photoelectric cell so as to conduct the generated electrical energy.

Another embodiment is depicted in figure 1D, which largely corresponds to the ar-5 rangement depicted in figure 1C, however the solar cell MCP, instead of comprising a single fiber, comprises a plurality of parallel arranged fibers. Apart from other potential advantages of this configuration that may be explained elsewhere in this document, incoming radiation that is reflected by one of the parallel fibers as its angle of incidence for example substantially deviates from perpendicular, may be reflected towards an adjacent one of the parallel fibers 10 of the same solar cell MCP, and may arrive at a surface of that solar cell substantially perpendicular, so as to be adsorbed. Hence, reflection losses may be reduced in this configuration also.

The following dimensions are given as an example: The focal length of the lenses CLC of the concentrator is set in such a way that the inter-distance between the lenses and the base 15 plate BPL is 25 mm. This enables that a total thickness of the solar panel is about 35 mm, which is about the same as a standard flat solar panel. Typically, the cylindrical lenses CLC are 10 mm in width and the photoelectric cells LSP (also referred to as solar cells LSP) are 0.5 mm in width. In this way, a concentration factor of 20 may be achieved, which means that in total 20 panels may be made using a same amount of photovoltaic materials as for a flat 20 panel. Due to the narrow line shape of the solar cells, such solar panels are sometimes referred to as MicroLine solar panels.

Some examples of a shape of the fibers are depicted in figures 2A - 2F which each depict a cross sectional view, namely round, for example having a diameter of 500 microme-25 ters (figure 2A), half round for example having a diameter of 500 micrometers (figure 2B), rectangular for example having a width of 500 micrometers and a height of 200 micrometers (figure 2C), annular for example having an outer diameter of 500 micrometers and an inner diameter of 200 micrometers (figure 2D), arc shaped over 180 degrees for example having an outer diameter of 500 micrometers and an inner diameter of 200 micrometers (figure 2E), arc 30 shaped over less than 180 degrees having similar dimensions as in the previous example (figure 2F). The cross sections other than round mainly may reduce the amount of semiconductor material, for instance crystal silicon per fiber, while keeping the optical absorption of the sunlight optimal, which requires about 200 micrometers of crystal silicon thickness. In case of the D-shaped configurations (figures 2B and 2E) removes the inactive half below or in 35 case of the hollow fibers (figures 2D and 2E) removes the inactive core or in case of the strip configurations (figures 2C and 2F) reduces the cross sectional area.

17

Existing solar cells for low-to-middle concentration conditions are in general fabricated from mono-crystalline silicon wafers. Relatively high efficiencies can be obtained by applying special techniques, such as “back contact” in which all electrical contacts are on the back side 5 of the wafer. Additionally, when one would cut the silicon wafer into many small strips the material loss would be huge that in return would increase the price of cells. The present development provides novel wafer-free embodiments having the shape of wires or fibers to decrease material loss. Individual wire- and fiber-based solar cells can be combined in strips, forming a solar cell that has special features especially suited for concentrator applications.

10 A first embodiment is based on crystal silicon fibers. The solar cells may have typical dimensions of 0.5 mm in width and several tens of centimeters in length. Since these cells are applied in a concentrator solar panel, the efficiency may be optimized for concentrated light conditions. This may be done by tuning all layer thicknesses and adjusting the resistivity 15 value of the used materials, for example by a suitable doping concentration.

The embodiments can be divided into several groups, such as solar cells based on silicon crystal fibers of different shapes, solar cells based on silicon (e.g. polysilicon) coated glass fibers, solar cells based on thin film coated glass or metal fibers, etc.

20

The line-shaped solar cells can be applied as single elements in the linear focus of cylinder lenses. For instance, the width of the solar cell can be 0.5 mm to cover the full image of the sun. Electrodes can be put underneath and next to the line-shaped solar cell, so that there is no negative effect of shading. Fabrication of these line-shaped solar cells is in princi-25 pie cylindrical symmetric. Due to its 1-dimensional nature, small and compact machinery can be used through which the very long fiber- or wire-base material is transported.

When using optics to concentrate the sunlight on the solar cell, the sunrays do not incident collimated, but are converging to an image point. This may cause great angles of inci-30 dence when using large numerical aperture optics. In case the solar cell would have a flat surface the reflection would increase severely at larger angles of incidence and thereby increasing the optical loss. Introducing wire- or fiber-based solar cells may at least partly eliminate this problem, because the converging rays may incident substantially perpendicular on the spherical surface of the wire or fiber. Therefore, reflection losses are much less in this 35 case.

18

As depicted in fig. 1D, and as will be described in more detail below, the e.g. lineshaped solar cells can also be applied in a multicore configuration forming a strip of fibers. This may provide a very modular concept, as by tuning the diameter of the wires or fibers and the number of elements, any width of the strip can be made. This configuration may provide 5 great advantages when used under concentrated light conditions. For concentrated solar cell it is advantageous to increase the metallization (to carry higher currents), to minimize the shading (to reduce the optical loss) and to decrease distance to the electrodes (to minimize the serial resistance). In these embodiments all electrodes are internal and/or on the backside, which may eliminate the shading effect, and the distance the charge carriers have to 10 travel to the electrodes is equal to half the circumference of the wire or fiber, which can be very small when using small diameters.

In an embodiment, crystal silicon fibers CSC are used as a basis. Silicon single crystal fibers can be made using a so-called micro-pulling down technique. Typically, diameter as 15 small as 500 pm and length of several tens of centimeters can be fabricated. Below the production steps are summarized, thereby referring to Figure 3A-3F.

Step 1: Fibers that can have different shapes of the cross section (as explained before with reference to figure 2A-2F), such as D-shape, arc-shape, are fabricated. The fiber 20 shape may be determined by the shape of the opening through which the molted sili con is extruded. The silicon fiber can be intrinsic p- or n-doped from the melt. Figure 3A-3F depicts an example of the steps for a fiber CSC having a round cross section). Step 2: Then an outer layer SEL of the silicon fiber CSC will be doped by the opposite doping compared to the fiber core. A result being depicted in Figure 3B. For instance, 25 when the silicon fiber is p-type, the outer layer SEL will be n-doped to create a pn- junction over the complete surface of the silicon fiber. This layer SEL is usually called the emitter layer and carriers the solar current to the negative electrode. In another configuration, the opposite doping can be introduced not over the complete surface, but rather over a light-receiving surface SEL (Figure 4A and 4B) i.e. sub-30 stantially circumferentially half the surface.

Step 3: Surface passivation is performed and anti-reflection coatings ARC are added (Figure 3C).

Step 4: To be able to make the connection between the electrode and the fiber core in the case the surface is fully covered with the opposite doping, first the core material has 35 to be layed open by using etching RSF (Figure 3D).

19

Step 5: Connecting the core of the fiber to the electrode material FCE, for instance when the core is p-type it is connected to the positive electrode and visa versa. Another solution might be to make a laser grooved buried contact SCE (Figure 4D). The connection is made at the backside so that the electrode does not obstruct the incident 5 sunlight on the line-shaped solar cell (Figure 3E).

Step 6: Connecting the surface of the fiber to the electrode material SCE, for instance when the surface is n-type it is connected to the negative electrode and visa versa. The connection is made at the sides so that the electrode does not obstruct the incident sunlight on the line-shaped solar cell (Figure 3F).

10

After manufacturing, the line-shaped solar cells can be cut at certain length to fit into a solar panel. If necessary the cut solar cell strip may be further divided into solar cells by making isolated section along the length of the strip, for instance by laser scribing. By inserting bypass diodes, the sections can be bypassed when it is shaded (an example being depicted 15 in Figure 8).

In another embodiment, polysilicon coated glass fibers are applied. Glass fiber are coated by silicon to form a layer of polysilicon. In general, glass fibers may have a circular cross section, but fibers with other cross section like the ones in described with reference to 20 Figure 2B-2F may also be applied. First, a configuration will be described wherein polysilicon is coated directly on the glass fiber, then a configuration will be described wherein an internal coaxial electrode is provided between glass fiber and polysilicon coating.

The configuration wherein polysilicon is coated directly on the glass fiber will be de-25 scribed with reference to Figure 5A-5F

Step 1: A glass fiber FIC will be coated by a silicon PSL using for instance the CVD (chemical vapour deposition) technology (Figure 5A). When using very high substrate temperatures or annealing temperatures, the deposited silicon will be converted into polysilicon. The polysilicon may be either p- or n-type. The silicon layer may have a 30 thickness typically between 20 and 200 pm.

Step 2: Then, the outer layer of the silicon fiber SEL will be doped by the opposite doping compared to the fiber core (Figure 5B). For instance, when the silicon fiber is p-type, the outer layer will be n-doped to create a pn-junction over the complete surface of the silicon fiber. This layer is usually called the emitter layer and carriers the solar 35 current to the negative electrode. In another configuration, the opposite doping can 20 be introduced not over the complete surface, but rather over a light-receiving surface SEL (Figure 4A and 4B) i.e. substantially circumferentially half the surface.

Step 3: Surface passivation is performed and anti-reflection coatings ARC are added (Figure 5C).

5 Step 4: To be able to make a connection between an electrode and the core coating in the case the surface is fully covered with the opposite doping, the core material has to be layed open RSF by using etching ((Figure 5D).

Step 5: Connecting the core of the fiber to the electrode material SCE, for instance when the core coating is p-type it is connected to the positive electrode and visa versa (Figure 10 5E). Another solution might be to make a laser grooved buried contact SCE (alike

Figure 4D). The connection may be made on the backside facing the substrate so that the electrode does not obstruct the incident sunlight on the line-shaped solar cell.

Step 6: Connecting the surface of the fiber to the electrode material FCE, for instance when 15 the surface is n-type it is connected to the negative electrode and visa versa (Figure 5F). The connection may be made at the sides so that the electrode does not obstruct the incident sunlight on the line-shaped solar cell.

The configuration wherein an internal, e.g. coaxial, electrode is provided between 20 glass fiber and polysilicon coating will be described below with reference to Figure 6A-6F:

Step 1: Coating the glass fiber FIC with metal coating ECL that will form the inner electrode of the solar cell (Figure 6A). A thickness of the metal coating should be large enough to carry high currents that are typically required for concentrator solar cells. The metal (e.g. molybdenum, carbon or tungsten) is chosen so as to withstand the high 25 temperature treatments that may be required to produce the silicon coating.

Step 2: A very thin silicon layer HDL is deposited with high doping levels to make a good connection to the electrode (Figure 6B).

Steps 3, 4 and 5 essentially correspond to steps 3, 4 and 5 of the above described configuration wherein polysilicon is coated directly on the glass fiber, as depicted successively 30 in Figure 6C-6E).

Step 6: An opposite electrode FCE to the inner electrode is connected to the outer surface of the silicon fiber solar cell (Figure 6F). The electrode is placed at sides of the fiber so that the electrode does not obstruct the incident sunlight on the line-shaped solar cell.

35 21

After manufacturing, the line-shaped solar cells can be cut at certain length to fit into a solar panel. If necessary the cut solar cell strip may be further divided into solar cells by making isolated section along the length of the strip, for instance by laser scribing. By inserting bypass diodes, the sections can be bypassed when it is shaded (an example being schemati-5 cally depicted in Figure 8).

Figure 8 depicts a section of fiber shaped photoelectric cells. An anode of one photoelectric cell is electrically connected with a cathode of an adjacent photoelectric cell, so that the photoelectric cells are electrically connected in series. Each cell may be bypassed by a 10 respective bypass diode.

The above described solar cells may be configured as single core solar cell, whereby each photoelectric cell comprises a single fiber SCP, as depicted and described with reference to Figure 1A and 1C. Alternatively, each photoelectric cell may comprise a plurality of optical fibers together forming a strip MCP, as depicted in and described with reference to 15 Figure 1D).

The latter, so-called multicore (i.e. multi fiber) solar cell strips are manufactured from the line-shaped solar cells based on crystal silicon fibers or polysilicon coated glass fibers, a manufacturing of which has been described above. The fibers are arranged next to each 20 other, for example touching each other, although some space in between the fibers may be provided. A zero distance is preferred, as thereby no optical loss is caused by the gaps and as thereby solar irradiation that is reflected by one of the fibers may likely be directed to an adjacent one of the fibers, so that at least part of the initially reflected radiation may be caught in. All electrodes may be connected at the bottom of the multicore solar cell strip, i.e. the side 25 facing the substrate. Due to the construction of the solar cell strip the sunlight can illuminate the strip from the front side without being blocked by metal electrodes, which are on the backside. In a specific configuration, one of the electrodes is an internal electrode, that is connected at the end points of the line-shaped solar cells rather than at the bottom.

30 An example of the manufacturing steps is described below with reference to Figure 7.

The below steps start from a plurality of solar cells based on a silicon fiber (CSP) or a glass fiber (PSP or SPI), as obtained in accordance with the above described method steps.

Step 1: Putting the single line-shaped solar cell side-to-side at the desired interdistance using a molt and fix them using a layer of adhesive (TPM), for instance a transparent 35 polymer. The other side of the film is coated with the electrode material (FCE) to 22 connect to the outer layer of the single line-shaped solar cells, for instance by a conducting metal (Figure 7A, 7B, 7C and 7D, top). The material should be added on the backside of the strip, so that the incident sunlight cannot be blocked.

Step 2: Etch the multicore solar cell strip (RSF) from the backside to a point that the core 5 silicon material (Figure 7A and 7B, middle) or the internal electrode (Figure 7C, mid dle) is layed open. When there is an internal electrode, this etching step is skipped and the backside can be covered by a single electrode material (Figure 7D).

Step 3: Add lines of positive (SCE) and negative (FCE) electrode materials to connect the corresponding p- and n-type material (Figure 7A and 7B, bottom) or the correspond- 10 ing p- or n-type material and internal electrode (Figure 7C, bottom). By adding isola tion material (ISO) the electrode should be electrical isolated. In the case of an internal electrode (Figure 7D), this electrode can be connected at the end of the multicore solar cell strip and isolated lines on the backside are omitted.

15 After manufacturing, the line-shaped solar cells can be cut at certain length to fit into a solar panel. If necessary the cut solar cell strip may be further divided into solar cells by making isolated section along the length of the strip, for instance by laser scribing. By inserting bypass diodes, the sections can be bypassed when it is shaded as described above.

20 Below, a further embodiment will be described wherein the thin film technology is ap plied. The solar cells may be based on thin film photovoltaic (PV) coated fibers, e.g. glass, carbon, polymer or silicon carbide, with internal electrode that may be omitted. Alternatively, the solar cells may be based on thin film photovoltaic (PV) coated metal wires of different shapes.

25

Thin film PV material such as thin film silicon (single or multijunctions of amorphous silicon), CdTe (ll-VI semiconductor) and CI(G)S (l-lll-VI compound semiconductor with chal-copyrite crystal structure) may be applied. Such line-shaped solar cells can be applied as single elements in the linear focus of cylinder lenses. For instance, the width of the solar cell 30 can be 0.5 mm to cover the full image of the sun. Electrodes may be put underneath and next to the line-shaped solar cell, so that there is no negative effect of shading. Fabrication of these line-shaped solar cells is in principle cylindrical symmetric. Due to its 1-dimensional nature, small and compact machinery may be used through which the very long fiber- or wire-base material is transported.

35 23

In the embodiments using thin film technology, when using optics to concentrate the sunlight on the solar cell, the sunrays do not incident collimated, but are converging to the image point. This causes great angles of incident when using large numerical aperture optics. When the solar cell would have a flat surface the reflection would increase severely at large 5 angles of incidence and thereby increasing the optical loss. Introducing wire- or fiber-based solar cells may alleviate this problem, as the converging rays incident substantially perpendicular (or at least more perpendicular than they would have in case of a flat surface) on the spherical surface of the wire or fiber. Therefore, again reflection losses may be significantly reduced in this case.

10

The focal length of the lenses of the concentrator may be set in such a way that the inter distance between the lenses and the base plate (i.e. the substrate) is 25 mm. This enables that the total thickness of the solar panel is about 35 mm, which is about the same as a standard flat panel. Typically, cylinder lenses are used, for example being 10 mm in width and the 15 solar cells may be 0.5 mm in width (therefore called MicroLine). In this way, a concentration factor of 20 may be achieved, which means that in total 20 panels may be made using the same amount of photovoltaic materials as would be required for a flat panel.

Similarly to the above described embodiments using silicon fiber or silicon coated 20 glass fiber, these thin film line-shaped solar cells may also be applied in multicore configuration forming a strip of wires or fibers. Again, a modular concept may be provided, as by tuning the diameter of the wires or fibers and the number of elements, any width of the strip can be made. This configuration may provide advantages when used under concentrated light conditions. For concentrated solar cells it is important to increase the metalization (to carry higher 25 currents), to minimize the shading (to reduce the optical loss) and to decrease distance to the electrodes (to minimize the serial resistance). In the embodiment described here, all electrodes are internal and/or on the backside, which eliminates the shading effect, and the distance the charge carriers have to travel to the electrodes is equal to half the circumference of the wire or fiber, which may be very small.

30

Below, a manufacturing of the thin film solar cells in according with an embodiment of the invention will be discussed in more detail. First, a manufacturing of solar cells based on thin film PV coated glass fibers is described. Then, a manufacturing of solar cells based on thin film PV coated metal wires. Finally, combining the line-shaped solar cells into multicore 35 solar cell strips is described.

24 A manufacturing of solar cells based on thin film PV coated fibers is described below.

Fibers may have very small diameters. As an example, diameters larger than the typical layer thickness of thin film PV, typically 5 pm, are considered. Fiber diameters may for 5 instance be equal and larger than 50 pm. A length may be scaled easily upto several kilometers. On the fiber practically any thin film solar cell may be applied, such as thin film silicon (single or multijunctions of amorphous silicon), CdTe (ll-VI semiconductor) and CI(G)S (l-lll-VI compound semiconductor with chalcopyrite crystal structure) or any future thin film coating utilizing nanostructures materials. A glass fiber may be used as base material. Instead of 10 glass also polymer, carbon or silicon carbide fiber may be used. Below the production steps are summarized referring to Figures 9A-9F:

Step 1: Coating the glass fiber (FIC) with metal coating (ECL) so as to form an inner electrode of the solar cell (Figure 9A and 9B). A thickness thereof should be large 15 enough to carry high currents that are typically required for concentrator solar cells.

Also, the metal (such as molybdenum, carbon or wolfram) is chosen so as to withstand high temperature treatments that may necessary to make the thin film PV coating. In some cases the temperature treatments may be at lower temperatures and then other metals may be used as well, such as copper and aluminum. When apply-20 ing CI(G)S it is desired to use sodium glass fibers and copper mixed with indium or gallium may be used as electrode material.

Step 2: The metal coated glass fiber will then be coated by the thin film PV materials, such as thin film silicon, CdTe, CI(G)S or any suitable thin film coating utilizing nanostructures materials (Figure 9C and 9D). Such thin film PV materials may require a se-25 quence of layer depositions, for instance in case of CdTe were a very thin layer of

CdS may be required to make the pn-junction. In the case of CI(G)S different fabrication methods can be used. For instance, one or more precursor layers may be deposited after which a selenization process is applied to form the CI(G)S PV layer. For the deposition of thin film silicon, different configuration may be chosen of, for in-30 stance, a single, double or triple junction.

Step 3: An outer surface of the thin film PV materials will then be covered by a TCO layer (TCO), such as T1O2 or ZnO, that acts as an electrode (Figure 9E). The TCO layer should have enough conductivity to carry the concentrator current to the metal electrodes at the side of the line-shaped solar cell. Additionally the surface may be 35 coated or threaded (ARC) to enhance the anti-reflection properties (Figure 9F).

25

In Figure 10A-10C, three examples are depicted that illustrate a general construction of a thin film silicon, CdTe and CI(G)S glass-fiber based solar cell.

After manufacturing, the line-shaped solar cells may be cut at certain length to fit into 5 a solar panel. If desired the cut solar cell strip may be further divided into solar cells by making isolated section along the length of the strip, for instance by laser scribing. By inserting bypass diodes, the sections can be bypassed when it is shaded as described above.

Next, a manufacturing of solar cells based on thin film PV coated metal wires is de-10 scribed.

Metal wires may have very small diameters (widths) and may have different cross sections, such as circular or rectangular. In this example, diameters much larger than the typical layer thickness of thin film PV, typically 5 pm, are considered. Wire diameters may for in-15 stance be equal and larger than 50 pm. The length can be scaled easily upto several kilometers. On the wires practical any thin film solar cell can be applied, such as thin film silicon, CdTe (ll-VI semiconductor), CI(G)S (l-lll-VI compound semiconductor with chalcopyrite crystal structure) or any future thin film coating utilizing nanostructures materials. The choice of metal material for the wire depends on the temperature treatments of the deposition of PV 20 layers. For instance, for very high temperatures metals such as molybdenum, carbon or tungsten may be preferred. When lower temperatures are applied, metals such as copper, steel or aluminum may be used. Below the production steps are summarized with reference to Figure 11A-11E): 25 Step 1: The metal wire (MWC) will be coated by the thin film PV materials (TFL), such as thin film silicon, CdTe, CI(G)S or any future thin film coating utilizing nanostructures materials (Figure 11A and 11B). These thin film PV materials may require a sequence of layer depositions, for instance in case of CdTe were a very thin layer of CdS is required to make the pn-junction. In the case of CI(G)S different fabrication methods 30 may be used. For instance, one or more precursor layers may be deposited after which a selenization process is applied to form the CI(G)S PV layer. For the deposition of thin film silicon different configuration may be chosen of, for instance, a single, double or triple junction.

Step 2: An outer surface of the thin film PV materials will be covered by a TCO layer (TCO), 35 such as Ti02 or ZnO that acts as the electrode (Figure 11C). This layer should have enough conductivity to carry the current to the metal electrodes at the sides of the 26 line-shaped solar cell. Additionally the surface may be coated or threaded (ARC) to enhance the anti-reflection properties (Figure 11D and 11E).

In Figures 12A-12C, three examples are placed that show the general construction of 5 a thin film silicon, CdTe and CI(G)S wire-based solar cell.

After manufacturing, the line-shaped solar cells may be cut at certain length to fit into a solar panel. If necessary the cut solar cell strip may be further divided into solar cells by making isolated section along the length of the strip, for instance by laser scribing. By insert-10 ing bypass diodes, the sections can be bypassed when it is shaded, as described above.

The above described solar cells may be configured as single core solar cell, whereby each photoelectric cell comprises a single fiber, as depicted and described above. Alternatively, each photoelectric cell may comprise a plurality of optical fibers together forming a strip.

15

Multicore (i.e. multi fiber) solar cell strips are manufactured from the line-shaped solar cells based on thin film coated fibers (both glass/polymer/carbon/silicon carbide as well as metal fibers), a manufacturing of which has been described above. The fibers are arranged next to each other, for example touching each other, although some space in between the 20 fibers may be provided. A zero distance is preferred, as thereby no optical loss is caused by the gaps and as thereby solar irradiation that is reflected by one of the fibers may likely be directed to an adjacent one of the fibers, so that at least part of the initially reflected radiation may be caught in. All electrodes may be connected at the bottom of the multicore solar cell strip, i.e. the side facing the substrate.

25

The multicore solar cell strips are manufactured from the single line-shaped solar cells based on thin film PV coated glass (or polymer, carbon, silicon carbide) fibers or metal wires. Due to the construction the sunlight may illuminate the solar cell strip without being blocked by metal electrodes. One type of the electrode may internal and the other type of electrode 30 may be connected at the bottom of the multicore solar cell strip.

Referring to Figure 13A and 13B, manufacturing steps are described below. Figure 13A depicts an example wherein isolated lines are provided, while figure 13B depicts an example where connected lines are provided. Figure 13A and 13B depicts below each other 35 multicore solar cell strips based on thin film metal rectangular wire solar cell (TWP, top), thin 27 film metal round wire solar cell (TSP, middle) and thin film fiber solar cell (TFP, below) respectively.

Step 1: Putting the single line-shaped solar cell side-to-side at the desired interdistance using a molt and fix them using a layer of adhesive (TPM), for instance a transparent 5 polymer.

Step 2: The other side of the film, i.e. the side facing the substrate, is covered by isolated lines of negative electrode materials to connect the outer TCO layer of the lineshaped solar cell (Figure 13A). When isolation is used between each line, the separated lines can be connected in series or parallel. Alternatively, the other side of the 10 film can be completely covered by the negative electrode materials (Figure 13B).

The internal positive electrode can be connected at the end of the multicore solar cell strip.

After manufacturing, the solar cell strips may be cut at certain length to fit into a solar 15 panel. If necessary the cut solar cell strip may be further divided into solar cells by making isolated section along the length of the strip, for instance by laser scribing. By inserting bypass diodes, the sections may be bypassed when it is shaded.

It is remarked that the invention also comprises a solar panel manufactured according 20 to any of the methods described herein.

A list of symbols applied above is provided below.

ARC Antireflection Coating ASL Amorphous Silicon Photovoltaic Layers BPD Bypass Diode 25 BPL Base Plate of Solar Panel CIL CIGS Photovoltaic Layers CLC Cylinder Lens of Concentrator CSC Crystal Silicon Core CSP Crystal Silicon Fiber Photovoltaic Cell 30 CTL Cadmium Telluride Photovoltaic Layers ECL Electric Conductive Layer FCE First Contact Electrode FIC Fiber Core HDL Highly Doped Layer 35 ISO Isolation Material LSP Line-shaped Photovoltaic Cell 28 MCP Multicore Photoelectric Cell MSC Metal Strip Core MWC Metal Wire Core PCI Photovoltaic Cell with Inner Conductor 5 PSL Polysilicon Layer PSP Polysilicon coated Fiber Photovoltaic Cell RSF Removed Part of Silicon Fiber SCE Second Contact Electrode SCP Single Core Photoelectric Cell 10 SEL Silicon Emitter Layer SPI Polysilicon coated Fiber Photovoltaic Cell with Inner Conductor SUN Sunlight Rays TCO Transparent Conducting Oxide TFL Thin Film Photovoltaic Layers 15 TFP Thin Film Fiber Photovoltaic Cell with Inner Conductor TPM Transparent Polymer Matrix TSP Thin Film Strip Photovoltaic Cell TRC Transparent Concentrator TWP Thin Film Metal Wire Photovoltaic Cell 20 The following numbered clauses form part of the description: 20. A method of manufacturing a solar panel, comprising: a) providing a semiconductor fiber having one of a p-doping and an n-doping; b) doping an outer layer of the semiconductor fiber by an opposite one of the p-doping and the n-doping; 25 c) mounting the semiconductor fiber on a substrate; d) connecting a first contact electrode to the outer semiconductor layer; and e) connecting a second contact electrode to a core of the semiconductor fiber.

21. The method according to clause 20, further comprising removing a part of the outer semiconductor layer along a length of the semiconductor fiber so as to lay open a core of the 30 semiconductor fiber, and wherein e) comprises: connecting the second contact electrode to the layed open core.

22. The method according to clause 20, further comprising providing a laser grooved buried contact along a length of the semiconductor fiber so as to contact the core of the semiconductor fiber; 35 and wherein e) comprises: connecting the second contact electrode to the laser grooved buried contact.

29 23. The method according to clause 20, wherein b) is performed on a cylinder segment shaped surface part of the semiconductor fiber, and wherein e) comprises connecting the second electrode to a surface part not doped in b).

24. The method according to any of clauses 20 - 23, wherein b) further comprises: 5 b2) coating on top of the outer layer or treating the outer layer so that an antireflection layer is formed to enhance anti-reflective properties.

25. A method of manufacturing a solar panel, comprising: a) coating a fiber by a semiconductor material having one of a p-doping and an n-doping; b) doping an outer layer of the semiconductor material by an opposite one of the p-doping 10 and the n-doping; c) mounting the fiber on a substrate; d) connecting a first contact electrode to the outer layer of the semiconductor material; and e) connecting a second contact electrode to an inner layer of the semiconductor material.

26. The method according to clause 25, further comprising removing a part of the outer layer 15 along a length of the fiber so as to lay open the inner layer of the semiconductor material, and wherein e) comprises: connecting the second contact electrode to the layed open inner layer.

27. The method according to clause 25, further comprising providing a laser grooved buried contact along a length of the fiber so as to contact the inner layer of the semiconductor material; 20 and wherein e) comprises: connecting the second contact electrode to the laser grooved buried contact.

28. The method according to clause 25, wherein b) is performed on a cylinder segment shaped surface part of the semiconductor fiber, and wherein e) comprises connecting the second contact electrode to a surface part not doped in 25 c).

29. The method according to clause 25, wherein prior to b), an electrical contact layer is coated on the fiber, and wherein e) comprises connecting the second contact electrode to the electrical contact layer, preferably at the end of the fiber.

30. The method according to any of clauses 25 - 29, wherein the semiconductor material ap-30 plied for coating in a) is polysilicon.

31. The method according to any of clauses 25 - 30, wherein b) further comprises: b2) coating on top of the outer layer or treating the outer layer to enhance an anti-reflective property of the outer photoelectric semiconductor layer.

32. A method of manufacturing a solar panel, comprising: 35 a) coating a fiber by an inner photoelectric semiconductor layer so as to form an absorber layer of a photocell; 30 b) providing an outer photoelectric semiconductor layer of a different material composition than in a) so as to form a heterojunction; c) mounting the fiber on a substrate with an optional heat conductive layer in between; d) connecting a first electrode to the outer photoelectric semiconductor layer; and 5 e) connecting a second electrode to the inner photoelectric semiconductor layer.

33. The method according to clause 32, wherein prior to b), an electrical contact layer is provided on the fiber, and wherein e) comprises connecting the second contact electrode to the electrical contact layer.

34. The method according to clause 32 or 33, wherein b) further comprises:: 10 b2) coating the fiber with a conductive, transparent layer so as to form a transparent conduc tive front electrode, and b3) coating on top of the outer layer or treating the outer layer to enhance an anti-reflective property thereof.

38. The method according to any of clauses 32 - 34, wherein the first and second semicon-15 ductor layers respectively comprise one of - thin film CIGS, compromising a composition Copper, Indium, Galium and Selinium in any configuration, and CdS, - thin film silicon, and - thin film CdTe and CdS, 20 39. The method according to any of clauses 32 - 38, wherein the fiber comprises one of a glass fiber, polymer fiber, carbon fiber, SiC fiber and a metal wire.

40. The method according to any of clauses 20 - 39, wherein an electrical contact with the first and/or second electrode is provided along a side of the photoelectric cell facing the substrate.

25 41. The method according to any of clauses 20 - 40, wherein the photoelectric cells are as sembled as multicore photoelectric strips before being mounted on the substrate.

42. The method according to clause 41, wherein the individual fibers are arranged in a strip at a desired interdistance using a molt; wherein an adhesive on top being provided to fix the fibers into the strip, preferably a trans-30 parent polymer; and wherein a backside of the strip is coated with a conductive metal so to form a front electrode.

43. The method according to clause 41 or 42, wherein from a backside a layer with a thickness large enough so as to lay open a substantial part of the cores is removed, thereby removing a layer with a thickness approximately equal 35 to a 1/4 of the radius of the photoelectric fiber, and wherein 31 on a backside isolated lines of front and backside electrode compromising of conductive material are provided, wherein the back electrode is centered at the vertical center line of the photoelectric fiber and connected to the inner photoelectric layer or core, and wherein the front electrode is centered in between two following back electrodes and connected to the 5 outer photoelectric semiconductor layer.

44. The method according to any of clauses 20 - 43, further comprising mounting an optical concentrator so as to allow solar irradiation to be projected onto the or each photoelectric cell.

Claims

A solar panel comprising a plurality of photoelectric cells and a concentrator for projecting incident radiation onto the photoelectric cells, the photoelectric cells being elongated cells each comprising at least one fiber.

The solar panel of claim 1, wherein each of the photoelectric cells comprises a core and a first layer around the core with a first contact electrode connected to the first layer, and the first contact electrode extending along a length of the photo -electric cells.

The solar panel of claim 2, wherein each photoelectric cell further comprises a second contact electrode connected to the core.

4. Solar panel according to claim 2, wherein each photoelectric cell further comprises the second contact electrode and a second layer arranged between the first layer and the core, the second contact electrode being connected to the second layer.

The solar panel of claim 4, wherein each photoelectric cell further comprises a layer of an electrically conductive material beneath the second layer for electrically connecting the second contact electrode to the second layer. 20

The solar panel according to claim 4 or 5, wherein each photoelectric cell further comprises a transparent electrically conductive outer layer which connects the first contact electrode to the first layer.

The solar panel according to any of claims 2-6, wherein the core of the photoelectric cells comprises at least one of glass, polymer, carbon, silicon carbide, and metal.

8. Solar panel according to any of claims 2-7, wherein the first contact electrode extends along two sides of the photoelectric cells and the photoelectric cells 30 contacts from two sides. -33-

The solar panel according to any of claims 2-8, wherein the first and second contact electrodes are provided on a side of the photoelectric cell that faces a substrate of the solar panel.

10. Solar panel according to any of claims 2-9, wherein the first contact electrode extends substantially to a center line between neighboring photoelectric cells.

11. Solar panel according to any of claims 2-10, further comprising a thermally conductive layer between the substrate and the first contact electrode, preferably comprising a graphite.

12. Solar panel as claimed in any of the foregoing claims, wherein the photoelectric cells each comprise a plurality of parallel fibers which are arranged as multi-core photoelectric strips, wherein each subsequent lens of the concentrator is arranged for projecting incident radiation onto a following photograph -electric strip.

Solar panel according to claim 12, wherein a distance between the fibers of the multi-core photoelectric strip is smaller than a diameter of the fibers, preferably zero.

A solar panel according to any one of the preceding claims, wherein a focal length of the concentrator is selected in a range of 10 to 100 times, preferably 10 to 50 times a width of the photoelectric cells.

15. Solar panel as claimed in any of the foregoing claims, wherein a lens width of the concentrator is selected in a range of 10 to 100 times, preferably 10 to 50 times a width of the photoelectric cells.

16. Solar panel as claimed in any of the foregoing claims, wherein an optical concentration factor of the concentrator is greater than 5, preferably greater than 10, more preferably greater than 20.

17. Solar panel as claimed in any of the foregoing claims, wherein the concentrator comprises several cylindrical lenses, wherein each cylindrical lens preferably has a plano-convex shape, wherein a convex side of a respective plano-convex lens 35 faces a respective photo electric cell. -34-

18. Solar panel according to one of the preceding claims, wherein the concentrator comprises several linear Fresnel lenses.

A solar energy converter comprising the solar panel according to any one of the preceding claims and a single axis tracking system.

A method for manufacturing a solar panel, comprising: a) providing a fiber; B) creating a photoelectric cell from the fiber; and c) mounting the photoelectric cell on a substrate.

The method of claim 20, wherein a) comprises providing a semiconductor fiber with one from a p-doping and an n-doping; and wherein b) comprises doping an outer layer of the semiconductor fiber with an opposite of the p-doping and the n-doping to form a first layer on or in at least a portion of an outer surface of the fiber.

The method of claim 21, further comprising: d) connecting a first contact electrode to the first layer e) connecting a second contact electrode to a core of the semiconductor fiber.

The method of claim 20, wherein b) comprises coating the fiber with a semiconductor material having one of a p-doping and an n-doping; and doping an outer layer of the semiconductor material with an opposite of the p-doping and the n-doping to form a first layer, wherein a remaining part of the semiconductor material forms a second layer between the first layer and the fiber.

The method of claim 23, further comprising: d) connecting a first contact electrode to the first layer; and e) connecting a second contact electrode to the second layer.

25. A method according to claim 23 or 24, wherein the semiconductor material provided in b) is for coating polysilicon. -35-

The method of claim 20, wherein b) comprises coating the fiber through an inner photoelectric semiconductor layer to form an absorbent layer of a photocell; and providing an outer photoelectric semiconductor layer on at least a portion of the inner photoelectric semiconductor layer to form a junction between the outer and inner photoelectric semiconductor layers, the outer photoelectric semiconductor layer forms a first layer, the inner photoelectric semiconductor layer forms a second layer between the first layer and the fiber. 10

The method of claim 26, further comprising: d) connecting a first contact electrode to the first layer; and e) connecting a second contact electrode to the second layer.

The method of claim 26 or 27, wherein b) further comprises: coating the fiber with a conductive transparent layer, to form a transparent conductive electrode and b3) coating the outer photoelectric semiconductor layer or the treating the outer photoelectric semiconductor layer to improve its anti-reflective property.

29. A method according to any of claims 26-28, wherein the first and second semiconductor layers respectively comprise one of: - thin film CIGS, comprising a composition Copper, Indium, Galium and Selenium in any configuration and CdS, - thin film silicon, and - thin film CdTe and Cds,

30. A method according to any of claims 26-29, wherein the fiber comprises one of a glass fiber, polymer fiber, carbon fiber, silicon carbide fiber and a metal wire.

The method of any of claims 20-30, further comprising removing a portion of the first layer along a length of the fiber to open the second layer or the fiber, and wherein e) comprises connecting the second contact electrode 35 with the exposed second layer or fiber. -36-

The method of any of claims 20-30, further comprising providing a laser-grooved buried contact along a length of the fiber for contacting the second layer or the fiber, and wherein e) comprises: connecting the second contact electrode with the laser grooved buried contact.

The method of any of claims 20-30, wherein the first layer is provided around a cylinder segment-shaped portion of the surface of the fiber, and wherein e) comprises connecting the second contact electrode to a portion of the surface that not covered in b).

The method of any one of claims 20-33, wherein b) further comprises: coating on top of the first layer or treating the first layer to form an anti-reflection layer 15 to improve anti-reflective properties.

35. A method according to any of claims 20-34, wherein prior to b) an electrical contact layer is coated on the fiber, and wherein e) comprises connecting the second contact electrode to the electrical contact layer preferably at the end of the fiber .

The method of any of claims 20-35, wherein b) further comprises: coating on the first layer or treating the first layer to improve an anti-reflective property thereof. 25

The method of any one of claims 20 to 36, wherein an electrical contact with the first and / or second electrode is provided along a side of the photoelectric cell facing the substrate.

The method of any one of claims 20-37, wherein the photoelectric cells are assembled as multi-core photoelectric strips, each comprising a plurality of fibers, before being mounted on the substrate.

39. Method according to claim 38, wherein the individual fibers are arranged in a strip with a desired mutual distance, using a molt; Wherein an adhesive is provided at the top for fixing the fibers in the strip, preferably a transparent polymer; and wherein a back side of the strip is coated with a conductive metal to form a front electrode. 5

A method according to claim 38 or 39, wherein from a rear side a layer of a thickness large enough for the opening of a substantial part of the cores of the fibers is removed, and wherein on a rear side isolated lines of front and rear electrodes consisting of 10, conductive material is provided, the back electrode being centered with the vertical center line of the photoelectric fiber and connected to the second layer or core of the fiber, and the front electrodes being centered between two subsequent back electrodes and connected to the first layer.

A method according to any of claims 20-40, further comprising mounting an optical concentrator to allow solar radiation to be projected onto the or each photoelectric cell.