WO2009149504A1

WO2009149504A1 - A substrate for photovoltaic devices

Info

Publication number: WO2009149504A1
Application number: PCT/AU2009/000734
Authority: WO
Inventors: John Beavis Lasich; Pierre Jacques Verlinden
Original assignee: Solar Systems Pty Ltd
Priority date: 2008-06-11
Filing date: 2009-06-11
Publication date: 2009-12-17

Abstract

A substrate for a photovoltaic module comprising a substantially planar surface having therein a plurality of channels arranged to divide the surface into a plurality of sections to enable photovoltaic devices placed thereon to be connected in an electrical circuit, at least one channel adapted to receive at least one bypass diode such that at least one photovoltaic device can be electrically bypassed across the sides of the channels, at least portions of the at least one channel adapted to receive a bypass diode having channel sides following a non-linear path so as to define inwardly extending diode connection portions on opposite sides of the channel such that the lateral distance between opposing diode connection portions is less than a width of the channel in the regions where the bypass diode is to be connected.

Description

A SUBSTRATE FOR PHOTOVOLTAIC DEVICES

Related Application

This application claims priority and benefit to US application 61/060739 filed 11 June 2008 entitled ^WA SUBSTRATE FOR PHOTOVOLTAIC DEVICES", the disclosure of which is incorporated herein by reference.

Field

The invention relates to a substrate for photovoltaic devices as well as to a photovoltaic module incorporating a plurality of photovoltaic devices and the substrate, and a receiver comprising a plurality of photovoltaic modules.

Background to the Invention

Power systems where photovoltaic devices in the form of solar cells providing a receiver are reliant on high number of photovoltaic devices remaining operational or they lose efficiency. To this end, it has been proposed to incorporate bypass diodes to protect individual cells from reverse bias and enable individual cells to be bypassed if they fail.

The photovoltaic devices sit on a substrate which connects that electrical devices into an electrical circuit and in a system receiving light from mirror concentrators the substrate is also arranged to efficiently allow transfer of heat to a heat sink to cool the photovoltaic devices. We have previously proposed a technique for incorporating bypass diodes into the substrate.

There is a need for techniques which allow bypass diodes to be incorporated into the substrate effectively.

Summary of the Invention

The invention provides a substrate for a photovoltaic module comprising a substantially planar surface having therein a plurality of channels arranged to divide the surface into a plurality of sections to enable photovoltaic devices placed thereon to be connected in an electrical circuit, at least one channel adapted to receive at least one bypass diode such that at least one photovoltaic device can be electrically bypassed across the sides of the channels, at least portions of the at least one channel adapted to receive a bypass diode having channel sides following a non-linear path so as to define inwardly extending diode connection portions on opposite sides of the channel such that the lateral distance between opposing diode connection portions is less than a width of the channel in the regions where the bypass diode is to be connected.

In an embodiment, the width of the channel in the region where bypass diodes are connected is 1.5 to 3.0 times the lateral width between opposing diode connections.

In an embodiment, the width of the channel in the region where bypass diodes are connected is 2.25 to 2.75 times the lateral width between opposing diode connections.

In an embodiment, the width of the channel in the region is in the range of 400-600 microns.

In an embodiment, the width of the channel in the region where bypass diodes are connected is about 500 microns.

In an embodiment, the opposing diode connections are adapted to receive a diode having a width of 150-250 microns .

In an embodiment, the opposing diode connections are adapted to receive a diode having a width of about 200 microns .

In an embodiment, the plurality of channel portions having channel sides following a non-linear path are parallel to one another .

In an embodiment, some of the channels run transversely to the channel portions having channel sides following a nonlinear path.

In an embodiment, the connecting portions are trapezoidal.

In an embodiment, the connecting portions are rectangular.

In an embodiment, the connecting portions of the channel are sinusoidal.

In an embodiment, the substrate comprises a plurality of channel portions adapted to receive a bypass diode, each channel portion having channel sides following a non- linear path, whereby the substrate is adapted to receive a plurality of bypass diodes.

The invention also provides a photovoltaic module comprising: a substrate; a plurality of photovoltaic devices; and at least one bypass diode, the substrate comprising a substantially planar surface having therein a plurality of channels arranged to divide the surface into a plurality of sections with the photovoltaic devices placed thereon and connected in an electrical circuit, at least one channel adapted to receive the at least one bypass diode such that at least one of the photovoltaic devices can be electrically bypassed across the sides of the channels, at least portions of the at least one channel adapted to receive the bypass diode having channel sides following a nonlinear path so as to define inwardly extending diode connection portions on opposite sides of the channel such that the lateral distance between opposing diode connection portions is less than a width of the channel in the regions where the bypass diode is connected.

In an embodiment, the width of the channel in the region where bypass diodes are connected is 2.25 to 2.75 times the lateral width between opposing diode connections .

In an embodiment, the plurality of channel portions having channel sides following a non-linear path are parallel to one another . In an embodiment, some of the channels run transversely to the channel portions having channel sides following a nonlinear path.

In an embodiment, the connecting portions are trapezoidal.

In an embodiment, the connecting portions are rectangular.

In an embodiment, the connecting portions of the channel are sinusoidal.

In an embodiment, the photovoltaic module further comprises a cooling circuit in thermal contact with the substrate.

In an embodiment, the photovoltaic module comprises a plurality of bypass diodes and the substrate comprises a plurality of channel portions adapted to receive a bypass diode, each channel portion having channel sides following a non-linear path.

The invention also provides a receiver comprising a plurality of the above photovoltaic modules .

The invention also provides method of producing electricity comprising concentrating sunlight onto the above receiver.

Brief Description of the Drawings;

The present invention is described further by way of example with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of an exemplary system for generating electrical power from solar radiation; Figure 2 is a front view of the receiver of the system shown in Figure 1 which illustrates the exposed surface area of the photovoltaic cells of the receiver;

Figure 3 is a partially cut-away perspective view of the receiver with components removed to illustrate more clearly the coolant circuit that forms part of the receiver;

Figure 4 is an enlarged view of the section of Figure 3 that is described by a rectangle;

Figure 5 is an exploded perspective view of a photovoltaic cell module that forms part of the receiver;

Figure 6 is a top plan view of the substrate on which the photovoltaic devices sit showing a plurality of channels in the substrate;

Figure 7 shows detail G of Figure 6;

Figure 8 is a split cross-sectional view through one of the channels; and

Figure 9 is plan view showing a diode in one of the channels .

Detailed Description

The embodiment provides a substrate for a closely packed array of photovoltaic devices as well as a photovoltaic module incorporating the substrate and a plurality of photovoltaic devices, and a receiver comprising a plurality of photovoltaic modules. The embodiment is of particular use in solar power generation systems which employ a concentrator and a receiver. For example, systems which employ a parabolic mirror concentrator or a heliostat field as a concentrator. However, the embodiment can be employed in other closely packed arrays, for example, in trough reflectors. The substrate advantageously includes some channels with non-linear channel sides (defining a winding path) which provide connection portions for bypass diodes that are laterally closer together than the width of the channels. Thus, diodes substantially thinner than the channel width can be incorporated. Advantageously this reduces the power loss due to resistance from the bypass diodes.

An exemplary solar radiation-based electric power generating system shown in Figure 1 includes a concentrator 3 in the form of a parabolic array of mirrors that reflects solar radiation that is incident on the mirrors towards a plurality of photovoltaic cells 5.

The cells 5 form part of a solar radiation receiver 7 that includes an integrated coolant circuit. The surface area of the concentrator 3 that is exposed to solar radiation is substantially greater than the surface area of the photovoltaic cells 5 that is exposed to reflected solar radiation. The photovoltaic cells 5 convert reflected solar radiation into DC electrical energy. The receiver 7 includes an electrical circuit (not shown) for the electrical energy output of the photovoltaic cells.

The concentrator 3 is mounted to a framework 9. A series of arms 11 extend from the framework 9 to the receiver 7 and locate the receiver as shown in Figure 1. The system further includes: (a) a support assembly 13 that supports the concentrator and the receiver in relation to a ground surface and for movement to track the sun; and (b) a tracking system (not shown) that moves the concentrator 3 and the receiver 7 as required to track the sun.

As described in further detail in WO 02/080286 which is owned by the present applicant, Solar Systems Pty Ltd., the amount of heat generated by the concentrated light can lead to problems with the operating temperature and performance of the cells 5. To this end, the receiver 7 includes a coolant circuit such as described in WO

02/080286 which can be applied to a wide range of solar cells, including multi- junction solar cells, single junction solar cells, quantum well solar cells, quantum dot solar cells, monolithically integrated modules (MIM) , and inverted metamorphiσ solar cells.

The coolant circuit cools the photovoltaic cells 5 of the receiver 7 with a coolant, preferably water, in order to minimise the operating temperature and to maximise the performance (including operating life) of the photovoltaic cells 5.

Figures 3 and 4 illustrate components of the receiver that are relevant to an exemplary coolant circuit. Other cooling arrangements may also be employed. A number of other components of the receiver 7, such as components that make up the electrical circuit of the receiver 7, are not included in the Figures 1 to 5 for clarity.

With reference to Figures 3 and 4, the receiver 7 has a generally box-like structure that is defined by an assembly of hollow posts 15. The receiver 7 also includes a solar flux modifier, generally identified by the numeral 19, which extends from a lower wall 99 (as viewed in Figure 3) of the box-like structure. The solar flux modifier 19 includes four panels 21 that extend from the lower wall 99 and converge toward each other. The solar flux modifier 19 also includes mirrors 91 mounted to the inwardly facing sides of the panels 21.

The receiver 7 also includes a dense array of 1536 closely packed rectangular photovoltaic cells 5 which are mounted to 64 square modules 23. The array of cells 5 can best be seen in Figure 2. In the example, each module includes 24 photovoltaic cells 5. The photovoltaic cells 5 are mounted on each module 23 so that the exposed surface of the cell array is a continuous surface. The modules 23 are mounted to the lower wall 99 of the box-like structure of the receiver 7 so that, in this example, the exposed surface of the combined array of photovoltaic cells 5 is in a single plane.

The modules 23 are mounted to the lower wall 99 so that lateral movement between the modules 23 and the remainder of the receiver 7 is possible. The permitted lateral movement assists in accommodating different thermal expansion of components of the receiver 7.

Each module 23 includes a coolant flow path. The coolant flow path is an integrated part of each module 23. The coolant flow path allows coolant to be in thermal contact with the photovoltaic cells 5 and extract heat from the cells 5 so that the cells 5 are maintained at a temperature of no more than 80⁰C, preferably no more than 60⁰C, more preferably no more than 40⁰C.

The coolant flow path of the modules 23 forms part of the coolant circuit. The coolant circuit also includes the above described hollow posts 15. In addition, the coolant circuit includes a series of parallel coolant channels 17 that form part of the lower wall 99 of the box-like structure. The ends of the channels 17 are connected to the opposed pair of lower horizontal posts 15 respectively shown in Figure 3. The lower posts 15 define an upstream header that distributes coolant to the channels 17 and a downstream header that collects coolant from the channels 17. The modules 23 are mounted to the lower surface of the channels 17 and are in fluid communication with the channels so that coolant flows via the channels 17 into and through the coolant flow paths of the modules 23 and back into the channels 17 and thereby cools the photovoltaic cells 5.

The coolant circuit also includes a coolant inlet 61 and a coolant outlet 63. The inlet 61 and the outlet 63 are located in an upper wall of the box-like structure. The inlet 61 is connected to the adjacent upper horizontal post 15 and the outlet 63 is connected to the adjacent upper horizontal post 15 as shown in Figure 3.

In use, coolant that is supplied from a source (not shown) flows via the inlet 61 into the upper horizontal post 15 connected to the inlet 61 and then down the vertical posts 15 connected to the upper horizontal post 15. The coolant then flows into the upstream lower header 15 and, as is described above, along the channels 17 and the coolant flow paths of the modules 23 and into the downstream lower header 15. The coolant then flows upwardly through the vertical posts 15 that are connected to the downstream lower header 15 and into the upper horizontal post 15. The coolant is then discharged from the receiver 7 via the outlet 63. The above-described coolant flow is illustrated by the arrows in Figures 3 and 4. Alternative embodiments are envisaged. For example, the coolant flow paths provided by the vertical posts of the above described embodiment may be replaced by pipes supported by the box- like structure. All possible alternative arrangements are envisaged for providing coolant flow paths to and from the modules 23.

Figures 5 illustrates the basic construction of each module 23. As is indicated above, each module 23 includes an array of 24 closely packed photovoltaic cells 5.

Each module 23 includes a substrate 27, on which the cells 5 are mounted. Each module 23 also includes a glass cover 37 that is mounted on the exposed surface of the array of photovoltaic cells 5. The glass cover 37 may be formed to optimise transmission of useful wavelengths of solar radiation and minimise transmission of un-wanted wavelengths of solar radiation.

Each module 23 also includes a coolant member 35 that is mounted to the surface of the substrate 27 that is opposite to the array of photovoltaic cells 5.

The size of the coolant member 35 and the material from which it is made are selected so that the coolant member 35 acts as a heat sink. An exemplary material for the coolant member is copper. However, other materials having high thermal transfer properties may also be used.

Furthermore, the coolant member 35 is formed to define a series of flow paths for coolant for cooling the photovoltaic cells 5.

Each module 23 also includes electrical connections 81 that form part of the electrical circuit of the receiver 7 and electrically connect the photovoltaic cells 5 into the electrical circuit. The electrical connections 81 extend from a metallised layer of substrate 27 through the coolant member 35. The electrical connections 81 are housed within sleeves 83 that electrically isolate the electrical connections.

The coolant member 35 includes a base 39 and a side wall

41 that extends from the base 39. The upper edge 43 of the side wall 41 is physically bonded to the substrate 27. It can be appreciated from Figure 5 that the base 35 and the substrate 27 define an enclosed chamber. The base 39 includes a coolant inlet 45 and a coolant outlet 46 located in diagonally opposed corner regions of the base 39. The coolant member 35 further includes a series of parallel lands 47 which extend upwardly from the base 39 and occupy a substantial part of the chamber.

The upper surfaces of the lands 47 are physically bonded to the substrate 27. The lands 47 do not extend to the ends of the chamber and these opposed end regions of the chamber define a coolant inlet manifold 49 and a coolant outlet manifold 51. The lands 47 extend side by side substantially across the width of the chamber. The gaps between adjacent lands 47 define coolant flow channels 53.

It is evident from the above that the coolant inlet 45, the coolant manifold 49, the flow channels 53, the coolant outlet manifold 49, and the coolant outlet 46 define the coolant flow path of each module 23.

Figure 4 illustrates the position of one module 23 on the lower wall of the receiver 7. The coolant inlet 45 opens into one coolant channel 17 of the coolant circuit and the diagonally opposed coolant outlet 46 opens into an adjacent coolant channel 17 of the coolant circuit.

In use, as indicated by the arrows in Figure 4, coolant flows from one supply channel 17 into the inlet manifold 49 via the coolant inlet 45 and then flows from the coolant manifold 49 into and along the length of the channels 53 to the outlet manifold 51. Thereafter, coolant flows from the chamber via the coolant outlet 46 into the adjacent channel 17.

Further details of a receiver are found in WO 02/080286 the disclosure of which is incorporated herein. A further cooling arrangement is described in WO 2005/022652 and can be adapted for use with this embodiment. Figure 6 shows the substrate 27 in more detail. The substrate 27 has a base portion made of a ceramic material covered with metallized zones. The ceramic material is chosen to be a material with a low thermal expansion coefficient, such as aluminium oxide (alumina) or silicon nitride, or aluminium nitride because this material has a high thermal conductivity. Other ceramic material with low thermal expansion and high thermal conductivity could be used such as boron nitride or beryllium oxide. In the embodiment, the substrate is covered with metallized zones made of copper for its high electrical and thermal conductivity, and suitability for soldering process. The copper metallized zones could be laid down by different techniques. For example, copper could be directly bonded to the alumina to form Direct Bonded Copper (DBC) substrates . The same technique of direct bonding of copper could be used on aluminium nitride ceramic substrates. Also, the metallized zones could be formed by depositing by vacuum evaporation, sputtering or screen printing a thin adhesion metallic layer, for example such as titanium or chromium or other metal, onto the ceramic substrate then by plating a thick layer of copper. The copper layer could also be brazed to the thin adhesion metallic layer.

Electrical connections are located below connection regions 601,602. The substrate 27 has six horizontal channels 611,612,613,614,615,616 and three vertical channels 622,623,624 which enable the array 5 of twenty- four cells to be connected in a series between connections 83 which are advantageously located underneath the substrate 27. The channels are formed in the metallized zones of the substrate 27. While in one embodiment, the path is formed exclusively by the edges of the metalized zones. In other embodiments the path may also be formed partly in the substrate. For example, by etching the substrate. The area marked G in Figure 6 is shown in more detail in Figure 7 from which it will be appreciated that each horizontal channel 611/612,613/614,615,616 (as exemplified by channel 614 has a plurality of winding portions provided by non-linear channel sides which define diode connection portions 701,702 on opposite sides of the channel 604. The average channel width is about 500 microns whereas the connection portions are set apart by a lateral width of only 250 microns (i.e. distance x-x is 750 micron and distance y-y is 500 micron) . That is, there are alternating, inwardly projecting connection portions 701,702 on opposite sides of the channel. In the embodiment, each connecting portion is generally trapezoidal in shape, being about 1.0mm long at its narrowest portion and having two sloped portions about

0.25mm long. Neighbouring connection portions on the same side of the channel 614 are separated by a straight portion of channel such that the pattern of connection portions and straight portions repeats approximately every 3.00mm, such that there is room for four connection portions 701,702 on each side of the channel between each vertical channel.

These winding portions allow the bypass diode's width to be about 200 microns , the remaining 50 microns being taken up by solder connecting the diode to the diode connecting portions.

Figure 8 is a schematic split cross-section viewed generally from the direction of arrow M in Figure 7 - i.e. the section to the left of line Z-Z is set back from the section to the right of line Z-Z so that the ends of diode 810 can be shown connected to the connection portions 701,702 by solder 818. Figure 8 shows schematically that a cell 816 is mounted on metallised zones 814 of substrate 812 with diode 810 disposed within channel 614 to form photovoltaic module 800. Figure 9 is a schematic plan view showing that diode 810 extends the length of the portion of the channel having non-linear sides - i.e. the diode 810 is connected to four connecting portions 701,702 on each side of the channel by- solder 818.

An advantage of this arrangement is that a smaller bypass diode than the desired channel width is incorporated in the circuit while maintaining a constant channel width, thus reducing the power loss due to resistance from the bypass diodes. In an embodiment, this allows a smaller bypass diode than the practically achievable channel width to be incorporated in the circuit. That is an advantage of the serpentine path is that it enables a smaller bypass diode to be used than can be used if the path is straight, as it allows the size of the bypass diode to be smaller that the channel width the manufacturing equipment is capable of achieving.

The amount of heat generated by the bypass diodes is also reduced, reducing the impact on the operating temperature of the modules and the individual photovoltaic device.

For example, a typical photogenerated current at 500X solar concentration for a 1.5 cm2 triple- junction cell is 10 Amps. If one cell is being bypassed, the current in the bypass diode is 10 amps. The voltage drop across the diode at that current is 0.7V plus the voltage drop across the base of the diode due to the (non-zero) resistivity. For example, between IV and 5V. If for example, the cross section of the diode is 13 mm x 0.3mm = 3.9 mm2 = 0.039 cm2, then the thickness of the base of the diode is 0.02 cm. The resistivity of the material is typically 0.5 ohm. cm. The resistance due to the base of the diode is typically 0.5 ohm. cm x 0.02 cm/0.039 cm2 = 0.25 ohm. At 10 Amps, this corresponds to a voltage drop of 2.5V + 0.7V = 3.2V, and a power dissipation of 32 W per diode in bypass mode. If the diodes were twice as thick, 400 microns, this would be doubled.

Further details on the use of bypass diodes and how they may be connected may be found in WO 2004/102678, the disclosure of which is incorporated herein by reference.

A further advantage of embodiments of the invention is that the winding path results in an increased path length compared to a straight path. The increased path length means that forces resulting from expansion and contraction of the substrate due to the temperature cycle are distributed over a longer path resulting in comparatively less stress and strain in this region. This is advantageous as these forces can cause electrical connections or the cells themselves to breakdown over time, e.g. due to solder cracking or damage to the cell structure caused by strain.

In the above embodiment, the width of the channel is about 2.5 times the width of the diode and 2 times the lateral distance between the opposing connection portions. Persons skilled in the art will appreciate that other embodiments are possible, for example where the width of the channel in the region where bypass diodes are connected is 1.5 to 3.0 times the lateral width between opposing diode connections or more particularly, where the width of the channel in the region where bypass diodes are connected is 2.25 to 2.75 times the lateral width between opposing diode connections.

In exemplary embodiments, the width of the channels in the region of the winding portion is in the range of 400-600 microns. Put another way, the opposing diode connections of exemplary embodiments may be adapted to receive a diode having a width of 150-250 microns (the term "width" being used in this context to indicate the dimension extends in the same direction as the width of the channel) .

Persons skilled in the art will appreciate that the shape of the winding portions of the channel could take a number of different forms, for example the non-linear channel sides could define a sinusoidal channel, a ziz-zag shaped channel, or a stepped channel with square or rectangular steps (like a square or rectangular wave form) . An advantage of embodiments that employ smoothed path edges or curved paths such as a sinusoidal channel is that they are easier to manufacture and more reliably reproduced thereby reducing costs.

Further, while the above embodiment describes an arrangement where a bypass diode is provided for each photovoltaic device, in other embodiments there may be one bypass diode for several cells. For example, there may be one bypass diode for two cells. If the cells are more robust, it might be possible to have one bypass diode for

3, 4, 5, 6, etc. cells and even one bypass diode for one module of 24 cells.

In other applications, the substrate may be used for solar cells in an array for use in a hybrid photovoltaic/thermal receiver or in a photovoltaic receiver where the array of photovoltaic cells receives radiation from a source other than (or in addition to direct sunlight) , such as infrared radiation radiated from a heated body or light from a source other than the sun.

Many other variations may be made without departing from the scope of the invention. In particular, features of the above embodiments may be employed to form further embodiments.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be understood that, the reference to any prior art publications herein does not constitute an admission that the publication forms a part of the common general knowledge in the art.

Claims

CLAIMS :

1. A substrate for a photovoltaic module comprising a substantially planar surface having therein a plurality of channels arranged to divide the surface into a plurality of sections to enable photovoltaic devices placed thereon to be connected in an electrical circuit, at least one channel adapted to receive at least one bypass diode such that at least one photovoltaic device can be electrically bypassed across the sides of the channels, at least portions of the at least one channel adapted to receive a bypass diode having channel sides following a non-linear path so as to define inwardly extending diode connection portions on opposite sides of the channel such that the lateral distance between opposing diode connection portions is less than a width of the channel in the regions where the bypass diode is to be connected.

2. A substrate as claimed in claim 1, wherein the width of the channel in the region where bypass diodes are connected is 1.5 to 3.0 times the lateral width between opposing diode connections.

3. A substrate as claimed in claim 1, wherein the width of the channel in the region where bypass diodes are connected is 2.25 to 2.75 times the lateral width between opposing diode connections.

4. A substrate as claimed in claim 1, wherein the width of the channel in the region is in the range of 400-600 microns .

5. A substrate as claimed in claim 1, wherein the width of the channel in the region where bypass diodes are connected is about 500 microns.

6. A substrate as claimed in claim 1, wherein the opposing diode connections are adapted to receive a diode having a width of 150-250 microns.

7. A substrate as claimed in claim 1, wherein the opposing diode connections are adapted to receive a diode having a width of about 200 microns.

8. A substrate as claimed in any one of claims 1 to 6, wherein the plurality of channel portions having channel sides following a non-linear path are parallel to one another.

9. A substrate as claimed in claim 8, wherein some of the channels run transversely to the channel portions having channel sides following a non-linear path.

10. A substrate as claimed in any one of claims 1 to 9, wherein the connecting portions are trapezoidal .

11. A substrate as claimed any one of claims 1 to 9, wherein the connecting portions are rectangular.

12. A substrate as claimed any one of claims 1 to 9, wherein the connecting portions of the channel are sinusoidal.

13. A substrate as claimed in any one of claims 1 to 12 comprising a plurality of channel portions adapted to receive a bypass diode, each channel portion having channel sides following a non-linear path, whereby the substrate is adapted to receive a plurality of bypass diodes .

14. A photovoltaic module comprising: a substrate; a plurality of photovoltaic devices; and at least one bypass diode, the substrate comprising a substantially planar surface having therein a plurality of channels arranged to divide the surface into a plurality of sections with the photovoltaic devices placed thereon and connected in an electrical circuit, at least one channel adapted to receive the at least one bypass diode such that at least one of the photovoltaic devices can be electrically bypassed across the sides of the channels, at least portions of the at least one channel adapted to receive the bypass diode having channel sides following a nonlinear path so as to define inwardly extending diode connection portions on opposite sides of the channel such that the lateral distance between opposing diode connection portions is less than a width of the channel in the regions where the bypass diode is connected.

15. A photovoltaic module as claimed in claim 14, wherein the width of the channel in the region where bypass diodes are connected is 1.5 to 3.0 times the lateral width between opposing diode connections.

16. A photovoltaic module as claimed in claim 14, wherein the width of the channel in the region where bypass diodes are connected is 2.25 to 2.75 times the lateral width between opposing diode connections.

17. A photovoltaic module as claimed in claim 14, wherein the width of the channel in the region is in the range of 400-600 microns.

18. A photovoltaic module as claimed in claim 14, wherein the width of the channel in the region where bypass diodes are connected is about 500 microns.

19. A photovoltaic module as claimed in claim 14, wherein the opposing diode connections are adapted to receive a diode having a width of 150-250 microns.

20. A photovoltaic module as claimed in claim 14, wherein the opposing diode connections are adapted to receive a diode having a width of about 200 microns.

21. A photovoltaic module as claimed in any one of claims 14 to 20, wherein the plurality of channel portions having channel sides following a non-linear path are parallel to one another .

22. A photovoltaic module as claimed in claim 21, wherein some of the channels run transversely to the channel portions having channel sides following a non-linear path.

23. A photovoltaic module as claimed in any one of claims 14 to 22, wherein the connecting portions are trapezoidal.

24. A photovoltaic module as claimed any one of claims 14 to 22, wherein the connecting portions are rectangular.

25. A photovoltaic module as claimed any one of claims 14 to 22, wherein the connecting portions of the channel are sinusoidal .

26. A photovoltaic module as claimed in any one of claims 14 to 25, further comprising a cooling circuit in thermal contact with the substrate.

27. A photovoltaic module as claimed in any one of claims 14 to 26, comprising a plurality of bypass diodes and wherein the substrate comprises a plurality of channel portions adapted to receive a bypass diode, each channel portion having channel sides following a non-linear path.

28. A receiver comprising a plurality of photovoltaic modules as claimed in any one of claims 14 to 27.

29. A method of producing electricity comprising concentrating sunlight onto the receiver of claim 28.