Patent Application
20170018670
The present invention relates to a photovoltaic module comprising a back side conductive substrate and a plurality of PV-cells having back contacts and being arranged in an array on a top surface of the back side conductive substrate, wherein a circuit of series and/or parallel connected PV-cells is formed by connections between the back contacts and the back side conductive substrate.
International patent publication WO2006/027225 discloses a solar cell assembly and method for connecting a string of solar cells, including by-pass diodes having three contacts both on their upper and lower surface. This allows to contact a solar cell associated with the by-pass diode (in parallel), as well as provide a contact to a further solar cell (in series connection).
International patent publication WO2010/135801 discloses a photovoltaic module string arrangement having a shading protection implemented. Conductors and bypass diodes are provided on a perimeter margin of the photovoltaic module, and are connected to strings of cells.
International patent publication WO 2011/050367 discloses a PV module with a plurality of solar cells in the form of doped regions disposed on a single silicon substrate wherein backside contacts are provided. In an embodiment, subsets of the cells are provided connected in parallel, with one or more cells wired with its two connections in reverse of the other cells. These reverse cells then act as bypass diodes, and cannot contribute to energy generation (and lowering the effective surface of the PV module).
US patent publication US 2014/060610 discloses a PV module comprising back contact solar cells having an on-cell electronic component such as a bypass switch, which is also provided at the back side of the PV module. The publication discloses that the bypass switch may comprise e.g. a Schottky diode or pn-junction diode.
US patent publication U.S. Pat. No. 6,563,289 discloses a solar cell arrangement comprising a bypass diode disposed on an oblique side of a solar cell, within an area bound by projections of two mutually orthogonal sides of the solar cell. The diode is electrically connected across the associated cell by a front interconnect and a back interconnect.
The present invention seeks to provide a more efficient photovoltaic module, especially in the sense of shadow performance, use of the front surface of the photovoltaic module and in homogenous appearance of the photovoltaic module.
According to the present invention, a photovoltaic module according to the preamble defined above is provided, further comprising a plurality of by-pass diodes having back contacts in electrical contact with the circuit of series and/or parallel connected PV-cells wherein each by-pass diode is a wafer based diode and is connected in parallel with one or more of the plurality of photovoltaic cells and wherein the by-pass diodes are positioned on empty parts of the top surface of the back side conductive substrate, the empty parts being located near corners of adjacent ones of the plurality of PV-cells.
The present invention will be discussed in more detail below, using a number of exemplary embodiments, with reference to the attached drawings, in which
The present invention embodiments comprise an assembly of (semi-square) back-contact cells and back-contacted wafer-based by-pass diodes where the by-pass diodes are located in the diamond-shaped spaces in between semi-square solar cells, where cells and by-pass diodes are mounted on one or two conductive, patterned, foils where the conductive foils are isolated from each other. This is shown in the front view of an embodiment of a photovoltaic module according to the present invention as shown in
In alternative wording, a conductive foil based photovoltaic module is provided with semi-square (high efficiency) back-contacted solar cells, where the space in between the cells is used for wafer-based by-pass diodes. In this way, a module can be manufactured with a more homogeneous appearance and with enhanced shadow performance. All kind of tracks can be made in the conductive foil to create intricate electronic circuits, for the best possible response to shading.
In a first aspect, the present invention relates to a photovoltaic module comprising a back side conductive substrate 10 (in the form of a conductive layer or a (patterned) foil), a plurality of PV-cells 2 having back contacts and being arranged in an array on a top surface of the back side conductive substrate 10, wherein a circuit of series and/or parallel connected PV-cells 2 is formed by connections 8 between the back contacts and the back side conductive substrate 10, and a plurality of by-pass diodes 5 having back contacts 6a, 6b in electrical contact with the circuit of series and/or parallel connected PV-cells 2, wherein each by-pass diode 5 is a wafer based diode and is connected in parallel with one or more of the plurality of photovoltaic cells 2, and wherein the by-pass diodes 5 are positioned on empty parts 4 of the top surface of the back side conductive substrate 10, the empty parts 4 being located near corners of adjacent ones of the plurality of PV-cells 2.
As mentioned, the plurality of by-pass diodes 5 may comprises wafer based diodes. These have a flat shape with a thickness which can be chosen to be similar in thickness to a PV-cell 2, or even slightly thicker (allowing more current to flow through the by-pass diode 5). E.g. the by-pass diodes 5 may be obtained from a multi-crystalline wafer, allowing a process much alike that of providing a PV-cell 2. Multiple bypass diodes 5 may be cut from a processed 15.6×15.6 cm (standard size) cell. The by-pass diode 5 may be obtained using similar techniques as used for obtaining back contact PV-cells 2, such as Metal Wrap Through (MWT), Emitter Wrap Through (EWT),
Interdigitated Back Contact (IBC), or even Metal Wrap Around (MWA). Specific embodiments of by-pass diodes 5 usable in the present invention embodiments are discussed in more detail below, with reference to
In a further embodiment, use is made of dummy wafer-based by-pass diodes 5, which can be positioned in the empty parts 4 enclosed by the rounded corners of the PV-cells 2 to give a homogeneous appearance of the photovoltaic module.
As mentioned above, and described with reference to the embodiment shown in
A by-pass diode 5 may be present for each of the plurality of PV-cells 2, allowing a very efficient protection functionality.
In conventional modules a by-pass diode 5 is typically connected in parallel with twenty PV-cells 2. This implies that under unshaded conditions the by-pass diode 5 typically is subject to a negative bias of typically 20×−0.5=−10V. This puts stringent requirements to the by-pass diodes 5 IV characteristics. In forward bias (in case of shading) the by-pass diode 5 should be able to conduct 9 A at voltages typically lying between +0.5V and +1V. At the same time, in unshaded conditions the by-pass diodes 5 should not exhibit a significant leakage current at −10V. In that case the leakage current should typically be less than 0.1% of the PV module's short-circuit current of typically 9A. In conventional modules rather expensive by-pass diodes 5 are needed that fulfill this requirement. However, many solar cells 2 in the dark yield currents higher than this at the mentioned −10V and are therefore not suitable for by-passing twenty cells. However, the present invention embodiments enable circuits where every PV-cells 2 is by-passed by a wafer-based by-pass diode 5 and in these circumstance the negative bias, under unshaded conditions, is much smaller and the leakage current is sufficiently low. So, by applying more by-pass diodes 5 per solar cell 2 less stringent requirements for the by-pass diodes 5 are needed and one can resort to wafer-based solar cells that are made opaque and therefore can act as by-pass diodes 5. This implies that one can prevent the use of expensive, high-quality, by-pass diodes that are used in conventional modules, usually located in the by-pass diode box mounted on the rear side of the module. It also implies that one can manufacture wafer-based by-pass diodes by cutting it from a ‘mother’ solar cell. This results in by-pass diodes 5 with bare edges, adversely affected by the cutting process (e.g. using a laser). These bare, possibly damaged, edges results in enhanced recombination of carriers and therefore in higher I0 values, where we have the approximate equation I=I0*exp(V/n/vth) , where I is the current through the by-pass diode 5 as a function of its voltage V and where n is the ideality factor, typically between 1 and 2 and where with is the thermal voltage (vth=k_B*T/q), i.e. approximately 0.0257 V at room temperature. Higher I0 values imply higher leakage current at negative bias (unshaded module conditions) and also higher currents at (shaded conditions) forward bias. More by-pass diodes 5 per cell 2 allow higher I0 values and therefore enables wafer-based by-pass diodes 5 cut from ‘mother’ cells with bare edges. By applying an edge passivation (e.g. coatings of Al2O3, SiNx, SiO2) on the edges the I0 values can be further reduced and the wafer-based by-pass diodes 5 can be used for circuits where up to, typically, twenty four cells 2 can be connected in parallel. A trade-off exists between quality of the by-pass diode 5 (low Io) and the cost to manufacture them. The current invention embodiments allow many by-pass diode circuit solutions amongst which one can determine the most cost-effective solution for a preferred shading behavior.
By-pass diodes 5 and PV-cells 2 can be mounted on the back foil (back side conductive substrate 10) with the same pick-and-place tool in the manufacturing process. This allows easy manufacturing of the module and prevents issues with stress build up in module. It prevents mounting of a by-pass diode box on the rear side of the module, giving more flexibility in applications (flatter panels). E.g. a conductive adhesive may be used to position and attach the PV-cells 2, as well as the by-pass diodes 5 to the back side conductive substrate 10.
The invention results in a shade tolerant module both for small shade areas and bigger shade areas. Applications are e.g. advantageous in shade-rich environments. More dense positioning (shorter intra module distances) in a field or on a flat roof, will cause self-shading. These modules allow these dense packaging since they are more tolerant to shade. In the winter at low sun inclinations more self shade will occur, but the modules are more tolerant to these shades, whereas in the summer more power can be harvested from a flat roof per unit of area due to the closer packing.
As mentioned, the by-pass diodes 5 of the present invention embodiments can be mounted to the conductive foil (formed by, or part of the back side conductive substrate 10) in the same way as the PV-cells 2 are mounted. This is technically much easier than mounting different types of devices, such as solar cells and SMDs. The same or similar pick-and-place robot can be used in the same machine. The same contacting process (e.g. stencil printing conductive adhesive on a patterned copper foil) can be utilized.
Conventional modules have e.g. three strings of PV-cells connected in series, where each string has a by-pass diode. These modules have non-optimal shade behavior. Shading one cell will take down one entire string, i.e. one third of the photovoltaic panel. Horizontal shading of, say, 6 cells in a row distributed over three strings will take down the entire module. Moreover, the area that the string occupies is elongated which makes the module vulnerable to shades that have its elongation perpendicular to the elongated string-area.
Moreover, the bypass diodes are adding to the costs of the module. In addition, the by-pass diodes need to be accommodated in the by-pass diode box. This box is placed on the rear-side of the module which brings about limitations of module applications, e.g. flat, in-roof mounting is hampered by the size of the by-pass diode box, in particular for frameless modules.
Incorporating more than the conventional three by-pass diodes is an alternative solution. However, the difficulty here is that it is increasingly difficult to accommodate all these by-pass diodes in a by-pass diode box. This would require a vast amount of conductive leads (bussing) towards the by-pass diode box. Moreover the number of by-pass diodes is limited due to the topology of the bussing (cross-overs of bussing and tabbing is cumbersome and would require bus-tab isolation and bigger inter-cell spacings). More bypass diodes and more (complicated) tabbing and bussing is also a cost concern.
Alternatively, by-pass diodes can be laminated together with the photovoltaic cells. However due to the size of a conventional by-pass diode, that is able to carry 9 A, this brings about lamination difficulties (stress/tension). Moreover, by-pass diodes will add to the cost of the PV-panel (see e.g. the disclosure of WO2010/135801 discussed above).
The photovoltaic module embodiments of the present invention aims to be shade tolerant both for small and bigger shade areas. For small shade areas, typically up to 36 cm2, i.e. 15% opaqueness on a 15.6 cm high shunt resistance semi-square cell 2, it acts as a conventional module whereas for bigger shade areas the high number of by-pass diodes 5 takes care of good shade behavior by by-passing only small groups of shaded PV-cells 2 rather than big groups of shaded cells (e.g. twenty cell strings) in a conventional module.
It is noted that the empty part 4 or empty space between PV-cells 2 can have any form, depending on the outer circumferential shape of the PV-cell 2 (or sub-module of a plurality of smaller PV-cells), and may provide sufficient space for one, two (semi-diamond shaped) by-pass diodes 5, or even more. In an exemplary embodiment, the plurality of PV-cells 2 each have a semi-square form and by-pass diodes 5 are positioned in an open space 4 between the corners of adjacent PV-cells 2. In an alternative exemplary embodiment, the by-pass diodes have a triangular form. Two of such by-pass diodes 5 can then be positioned in a diamond shaped space 4 in between four adjacent PV-cells 2, or a single triangular shaped by-pass diode 5 fits into a space 4 between two adjacent PV-cells 2 at an edge of the photovoltaic module.
In an alternative embodiment, which is shown schematically in
The present invention embodiments make use of the semi-square nature of wafers that are used in some module technologies to place the by-pass diodes 5 in the spaces 4 between the PV-cells 2 or PV sub-modules, where anyhow it is very easy to let the conductive copper foil (of the back side conductive substrate 10) reach these space 4. In other concepts, square wafers (PV-cells 2) are used. In this case it might still be beneficial to integrate wafer-based by-pass diodes 5 in the electrical circuitry, to allow more by-pass diodes 5 than are generally used in a junction box. For this reason parts of the square wafers 2 can even be cut out (e.g. corners) to allow integration of wafer-based by-pass diodes 5 in the circuitry, or they are placed in additional spaces that are realized between the PV-cells 2 or at the edges of the module. In this case, the shape might be preferably rectangular (e.g. with the length of a full wafer) rather than square. The size of the wafer-based bypass diode 5 (and therefore the size of the cut-out) can e.g. be matched to the current that they need to be able to carry. To allow for the optimal current through the by-pass diode 5, the wafers that are used to process by-pass diodes 5 could be made thicker than standard wafers, as long as the thickness is tolerated in the laminate (encapsulant thickness) of the photovoltaic module.
Providing the by-pass diodes 5 as wafer based diodes this allows to have a sufficiently high current rating of the plurality of by-pass diodes 5, e.g. at least 6 A, e.g. 9 A. With a 2×2 cm wafer diode 5, this would result in a current density of 2.12 A/cm2, or 4.5 W dissipated power (when active in by-pass mode). Of course, if different circuits are used, using more or less by-pass diodes 5 per PV-cell 2, the requirements on current rating may be different. When smaller sized PV-cells 2 (or rather sub-modules 2) are used, the current rating of the associated by-pass diodes 5 may be lower, e.g. at least 2.25 A in the case of a quarter sized sub-module 2, or at least 4.5 A in the case of half-size sub-module 2.
In further alternative embodiments, it would also be possible to provide one, multiple or all of the plurality of by-pass diodes 5 in other empty parts 4 available in the photovoltaic module, e.g. at the outer edges thereof. When positioned near an edge of an associated PV-cell 2, e.g. having an elongate shape, by-pass diodes 5 may be efficiently positioned, even possible having better I-V characteristic for that specific part of the photovoltaic module.
In the embodiments described above, the term PV-cell 2 is used. However, this term is intended to also include sub-modules or groups of (smaller sized) PV-cells. E.g. in an embodiment the semi-square ‘mother’ PV-cell 2 of a standard size (5″×5″ or 6″×6″) is cut into m×n equal-area solar cells. This will reduce the current and to increase the voltage, and as an effect a lower current means less dissipation in the associated by-pass diode 5 as well.
In a specific embodiment, the plurality of PV-cells 2 are made from wafers of a semi-conductor material, e.g. mono-crystalline Czochralski (Cz) type material. This material is created by cutting off four edges from a cylindrical silicon rod, resulting in four straight sides and four rounded corners, where the diameter typically is 20 cm and the edge-to-edge distance typically is 15.6 cm. When combined this results in an open diamond shaped surface part between four adjacent PV-cells 2. In a further exemplary embodiment, semi-square photovoltaic cells 2 are used with a side-to-side distance of 15.6 cm and a corner-to-corner distance of 20 cm, including square by-pass diodes 5 of 2.06 cm×2.06 cm positioned in the spaces 4 between the photovoltaic cells 2. In an alternative embodiment, each wafer obtained would be divided in four equal parts, resulting in smaller PV-cells 2 each having only one oblique corner, as shown in the embodiment of
A careful choice of cutting lines in a 20 cm diameter wafer could even improve efficient use of the semiconductor ingot material. In the standard much used form, where the PV-cells would take a 15.6 cm as longest dimension, 76% if the wafer material is used.
When taking a slightly larger basic form of the PV-cell 2 (16.8 cm as largest dimension, when split in four resulting in a largest dimension of the PV-cell 2 of 8.4 cm), sufficient wafer material remains for cutting four by-pass diodes 5 (e.g. triangular shaped) with a sufficient dimension to provide high enough capacities to be utilized in the present invention embodiments. This would result in 86% of the wafer surface to be utilized, the by-pass diodes 5 then being obtained with no additional semiconductor material costs.
When assembling the PV module, the (smaller) PV-cells 2 can be individually positioned on the back side conductive substrate 10 (possibly using rotation for the proper positioning), or four smaller PV-cells 2 can be positioned simultaneously (as a regular larger sized PV-cell 2) with only the PV-cells 2 at the edges of the PV-module being positioned individually.
In further embodiments, the number of by-pass diodes 5 in relation to the number of PV-cells 2 may vary, depending on the type of circuit being formed in the photovoltaic module. The circuit may comprise serial groups of PV-cells 2 and by-pass diodes 5, staggered groups and/or multilevel groups.
An example of a multilevel circuit of PV-cells 2 and by-pass diodes 5 is shown in
Alternatively, tracks 8 can be made where a solar cell 2 and a by-pass diode 5 are connected in parallel, recursively. Here a solar cell 2 and a bypass diode 5 are connected in parallel, and this parallel connection is in its turn connected in parallel with again a solar cell 2 and a bypass diode 5. This newly formed circuit is then again connected in parallel with a solar cell 2 and a bypass diode 5. This can be repeated n times.
In
Such a staggered circuit is also used in the embodiment shown in
In
It is noted that the back side conductive substrate 10 is primarily used for providing contacts between PV-cells 2 and other components of the photovoltaic module. It may however also comprise material implementing a structural function, e.g. using a light-weight panel. The back side conductive substrate 10 in a further embodiment comprises one or more conductive sheets. These multiple sheets may be advantageous by allowing easier formation of interconnecting circuits as desired. The one or more conductive sheets are isolated from each other, and possibly provided with openings or apertures allowing to interconnect the conductive sheets where desired, to define an even more complex circuit of PV-cells 2.
In general the plurality of by-pass diodes 5 as used in the present invention implementations comprise a front surface 22 with a texture and color similar to a front surface of the PV-cells 2. E.g. a texture and SiNx top layer just like regular solar cells may be provided, to give the by-pass diode 5 the same appearance as the PV-cell 2. This provides for a similar appearance of the majority of components of the photovoltaic module visible during actual operation thereof, improving the aesthetic aspects and thus ease of integrating the photovoltaic module in buildings, etc.
Several types of (wafer based) by-pass diodes may be used, examples of which are shown in the cross sectional views of
As a further alternative embodiment to the opaque layer 22, an embodiment is provided where the by-pass diodes 5 have a structured top surface 22 (e.g. white paint with Lambertian reflection, TiO2 spheres coating or a grating structure) so that light is reflected or scattered by this layer 22 so that a big part of the light stays inside the photovoltaic module via internal reflectance (e.g. on a glass-air interface). In other words, the plurality of by-pass diodes 5 comprise a light diversion top layer arranged for directing light impinging on the front surface of the by-pass diode 5 towards the adjacent PV-cells 2.
The present invention embodiments have been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012556 | Apr 2014 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/057302 | 4/2/2015 | WO | 00 |
