Photovoltaic module with an electronic device laminated in a stack

0001The invention relates to a photovoltaic module which serves in particular to transform solar energy into electrical energy.

0002Such photovoltaic modules are currently designed to provide an electrical power of between 12 and 230 W. They are used in many terrestrial applications to provide direct current or alternating current. For example, they are used in isolated sites or connected to the distribution network:<ul id="ul0001" list-style="dash" compact="compact"><li>in the EDF type public power network;</li><li>in private homes: lighting, radio, television, small appliances;</li><li>for public lighting: advertising signs, bus shelters;</li><li>for rural electrification;</li><li>for pumping;</li><li>for telecommunications: infrastructure, GSM relay, isolated subscriber station;</li><li>for signage: road, sea, radio, television. Generally a photovoltaic module comprises N photovoltaic cells, for example thirty-six, mounted in series and connected to each other by means of tin-plated copper flat ribbons. More particularly, the photovoltaic cells are single-junction photovoltaic cells made of multi-crystalline silicon doped "P" with boron during the melting of the silicon and doped "N" with pho sphore on their illuminated surface. These cells are put in place in a laminated stack. The laminated stack may consist of EVA (Ethyl Vinyl Acetate) coating the photovoltaic cells to protect the constituent silicon, oxidation and moisture, said photovoltaic cells being further nested between a tempered glass plate and a sheet of polymer, for example Tedlar® which is a polyvinyl fluoride manufactured by the company DuPont. This structure allows the photovoltaic module to withstand the most severe atmospheric and environmental conditions such as in tropical, polar or maritime environments. The current Im supplied by the photovoltaic module is equal to the current Ic produced by each photovoltaic cell of the module. The current Ic depends mainly on the illumination and the physical characteristics of the cell such as its size and the quality of the silicon constituting it. The voltage Vm supplied by the module is the sum of the voltages Vc of all the photovoltaic cells of the module subjected to illumination and is given by the relation:<maths id="math0001"><math display="block"><mrow><msub><mrow><mtext>Vm = S</mtext></mrow><mrow><mtext>i = 1</mtext></mrow></msub><msub><mrow><mtext> at </mtext></mrow><mrow><mtext>NOT</mtext></mrow></msub><msub><mrow><mtext>(Vc</mtext></mrow><mrow><mtext>i</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1544922A1_D0001.tif" /></maths>    <b>S</b> designating the algebraic sum function. In the case where a photovoltaic cell of the module is shaded, that is to say that it does not receive the light because of a deterioration or because it is covered with an opaque material, a sheet of tree for example, the cell no longer provides electrical energy. On the other hand, it can become resistant and receive the electrical energy that is produced by the other cells to which it is connected in series. As a result, the voltage Vo across the shaded cell is reversed and can reach a voltage equivalent to the sum of the voltages of all the other cells of the module, this equivalent voltage being calculated by the following relationship:<maths id="math0002"><math display="block"><mrow><msub><mrow><mtext>Vo = -S</mtext></mrow><mrow><mtext>i = 1 to N-1</mtext></mrow></msub><msub><mrow><mtext> (Vc</mtext></mrow><mrow><mtext>i</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1544922A1_D0002.tif" /></maths>The power Wo received by the shaded cell can reach the maximum power produced by all the other cells of the module so that this shaded cell will heat which can cause its destruction, as well as the degradation of the laminated stack and the module. This power received by the shaded cell is expressed by the following relation:<maths id="math0003"><math display="block"><mrow><msup><mrow><mtext>Wo = Im </mtext></mrow><mrow><mtext>*</mtext></mrow></msup><mtext> Vo</mtext></mrow></math><img file="EP1544922A1_D0003.tif" /></maths>To reduce the heating of the shaded cells and the energy loss that this generates in a photovoltaic module, a "bypass" diode is used which is connected in parallel with a number of photovoltaic cells in series, for example eight. A module may contain several "bypass" diodes connected in parallel to several groups of cells respectively. In this way, a shaded cell is protected because the bypass diode starts conducting the current and limits the power received by the shaded cell. The latter heats very little but it is now the bypass diode that heats up. The power dissipated by the diode is equal to the product of the direct voltage of the diode by the current flowing through it, the latter being the difference between the current of the external circuit and the current flowing through the shaded cell. Furthermore, the shaded cell receives only the power supplied by the other photovoltaic cells of the group of cells that are protected by the same bypass diode in the module, which limits its heating and reduces the energy loss of the module. The smaller the number of cells in a group of cells protected by a bypass diode, the more the heating will be limited and the energy loss low. In known photovoltaic modules, the bypass diodes are arranged in a junction box separate from the laminated stack of the module. The heat dissipation of the bypass diodes in the junction boxes may be insufficient. In addition, the very soon implementation of a new qualification standard IEC61215 Ed.2 considerably strengthens the test criteria of protection bypass diodes. Increasing the values ​​of the tests imposes the increase of the level of heat dissipation of the bypass diodes. The temperature of the bypass diodes placed in the junction box amounts to values ​​that go well beyond the permissible limit values. In the current state of achievements it is not possible to meet this new standard without using power bypass diodes or without installing radiators on the bypass diodes, as is presented in the patent US6225793, this which greatly increases the cost of the module. In addition the implantation in the junction boxes of other semiconductor circuits used for the control and control of the module of the type "MOSFET" (Metal-Oxide-Silicon Field Effect Transistor), thyristor or "GTO thyristor" (" Gate Turn Off thyristor "), increases the complexity of the wiring between the junction box and the photovoltaic cells. In the patent document WO99 / ​​62125, the bypass diodes are mounted in the laminated stack on the photovoltaic cells so that the photovoltaic cells dissipate the heat produced by the bypass diode but this heat dissipation is insufficient. The object of the invention is to overcome the disadvantages set out above by proposing a photovoltaic module in which the heat dissipation of the bypass diodes is improved at a lower cost. For this purpose, the subject of the invention is a photovoltaic module comprising one or more photovoltaic cells connected in series and arranged inside a laminated stack of glass and polymer and an electronic protection device, for example a bypass diode, arranged to derive the electrical current flowing through at least one photovoltaic cell, the electronic protection device being a semiconductor circuit which is arranged inside the laminated stack, characterized in that the semiconductor circuit is electrically connected to the module cells by at least one flat metal ribbon disposed in the laminated stack to dissipate thermal energy released by the semiconductor circuit. This arrangement of the photovoltaic cells and bypass diodes in the photovoltaic module makes it possible to eliminate part of the wiring. It is no longer necessary to remove the flat copper ribbons from the laminated stack to protect the photovoltaic module with the bypass diodes. The flat metal ribbons make it possible to improve the heat dissipation of the semiconductor circuit by establishing a large heat exchange surface with the surrounding elements and thus with the outside of the module. According to a preferred embodiment of the invention, the semiconductor circuit is connected to the photovoltaic cells by means of two flat copper ribbons. According to another preferred embodiment of the invention, the semiconductor circuit is an electronic chip soldered to a photovoltaic cell. According to another preferred embodiment of the invention, each photovoltaic cell is inserted between a glass plate and a polymer layer, the protective semiconductor circuit being arranged between a cell and the polymer layer. The bypass diode can then dissipate thermal energy through the polymer layer and the photovoltaic cell which has good thermal conductivity. According to another preferred embodiment of the invention, the semiconductor circuit is arranged between two adjacent photovoltaic cells. According to another preferred embodiment of the invention, the semiconductor circuit comprises a multi-crystalline support. The performances of the bypass diodes do not need to be very high and can very well be realized with a lower cost with a multi-crystalline support. According to another preferred embodiment of the invention, the semiconductor circuit is mounted on a metal plate having good thermal conductivity, said plate serving as a radiator for dissipating thermal energy. According to another preferred embodiment of the invention, the semiconductor circuit is integrated in the photovoltaic cell, thus eliminating any wiring between cells for the protection of the module. According to another preferred embodiment of the invention, each photovoltaic cell is provided with a semiconductor protection circuit. The implementation of a bypass diode in parallel on each photovoltaic cell limits the problems related to the shaded cells, because the shaded cell and the corresponding bypass diode are then isolated and do not dissipate the power provided by other cells. . In addition, there is no need to create cabling to put multiple cells in parallel with a diode. According to another preferred embodiment of the invention, the photovoltaic module further comprises circuits for controlling and / or controlling photovoltaic cells, and wherein these control and / or control circuits are semiconductor circuits arranged inside the laminated stack. The semiconductor control and / or control circuits can be implanted in the laminated stack to protect the photovoltaic modules against theft or to manage the right of access to the current produced. According to another preferred embodiment of the invention, the control and / or control circuits are semiconductor circuits of the thyristor, MOSFET or GTO type. Several embodiments of a photovoltaic module according to the invention will now be described in more detail and illustrated in the accompanying drawings.</li><li>Figure 1 is a schematic representation of a laminated stack of a photovoltaic module according to the invention.</li><li>FIG. 2 is a very schematic cross-sectional view of part of a laminated stack of a photovoltaic module according to the invention.</li><li>FIG. 3 is a very schematic representation of a semiconductor circuit for protecting a photovoltaic module according to the invention.</li><li>FIG. 4 is a very schematic representation of a semiconductor protection circuit arranged on a plate of a photovoltaic module according to the invention.</li><li>FIG. 5 is a very schematic representation of a semiconductor circuit for controlling and / or controlling a photovoltaic module according to the invention</li><li>Figure 6 is a very schematic representation of the rear face of a photovoltaic module according to the invention.</li><li>FIG. 7 is a very schematic representation of two photovoltaic cells mounted in series and individually protected by a semiconductor circuit of a photovoltaic module according to the invention.</li><li>FIG. 8 very schematically shows a semiconductor circuit integrated in the rear face of a photovoltaic cell of a photovoltaic module according to the invention.</li></ul>

0003FIG. 1 schematically shows a laminated stack of a photovoltaic module 1 according to the invention having different parallel layers stacked one on the other. The back of the photovoltaic module 1 is formed by a layer 2 of resistant polymer which is for example a Tedlar® sheet, on which is disposed an encapsulating polymer 3, for example EVA. Inside the encapsulating polymer are arranged photovoltaic cells 4 in the same plane and ordered according to a grid with their rear faces facing the layer 2, as well as semiconductor circuits 5 placed under certain photovoltaic cells 4. Finally on the encapsulating polymer 3 is disposed a glass plate 6 forming the front of the photovoltaic module.

0004The crosslinking of the encapsulating polymer 3 to fix the photovoltaic cells 4 and the semiconductor circuits 5 can be carried out under vacuum at a temperature, approximately 150 ° C for the EVA. The layer 2 of resistant polymer ensures the sealing and protection against mechanical damage from the rear of the module, while minimizing its mass.

0005FIG. 2 shows the disposition of a flat semiconductor circuit 5 in the laminated stack according to the invention. The semiconductor circuit 5 is in the encapsulating polymer 3, very close to the layer 2 of resistant polymer.

0006The semiconductor circuit 5 which may be a semiconductor protective circuit (bypass diode) may conduct the current when it protects a shaded cell. It derives the current from the external circuit which can not cross the shaded cell. The semiconductor circuit then receives power, heats up and dissipates thermal energy. The heat dissipation is facilitated by the photovoltaic cell 4 and the glass plate 6 which have good thermal conductivity and act as radiators. The thermal energy of the semiconductor circuit 5 is dissipated in the photovoltaic cell 4 which exchanges this thermal energy over its entire surface with the encapsulant 3 and the glass plate 6. In addition, the encapsulating polymer 3 and the resistant polymer layer 2 also facilitate the heat dissipation of the semiconductor circuit 5. The semiconductor circuit 5 placed in the laminated stack according to the invention heats up much less than a similar semiconductor circuit placed in a junction box.

0007In FIG. 3, a flat protective semiconductor circuit 5a (an electronic chip) is shown which is a bypass diode for protecting the photovoltaic module against heating of shaded photovoltaic cells. Two ribbons 7a, 7b metal plates, for example tinned copper, or composed of materials having a very good thermal and electrical conductivity, are connected (welded) on the input and the output of the bypass diode 5a. A copper ribbon 7a of thickness 220 micrometers and width 3 mm constitutes the anode and is connected to a not shown photovoltaic cell having a higher potential than that of the cell. A copper ribbon 7b with a thickness of 220 microns and a width of 5 mm constitutes the cathode and is connected to another photovoltaic cell (not shown) with a potential lower than that connected to the anode. These ribbons 7a, 7b do not have the same width to undo the connections. When ribbons or cables cross, they are isolated from each other by insulating parts or films, for example EVA-Tedlar.

0008The two flat copper strips 7a, 7b arranged in the laminated stack have a very large contact area with the bypass diode 5a and a very good thermal conductivity. They therefore make it possible to improve the heat dissipation of the bypass diode. The heat of the diode is transmitted to the ribbons 7a, 7b which, by virtue of their wide flat shape, offer a very large surface area for the exchange of thermal energy with the surrounding elements such as the photovoltaic cells 4 to which they are connected, the encapsulant 3 or the layer of resistant polymer 2. This better diffusion and distribution of the heat improves the heat dissipation of the semiconductor circuit 5.

0009The flat shape of the ribbons 7a, 7b also allows their better insertion and integration into the rolled stack of the module which must remain as thin as possible.

0010The diode can also be connected directly between a photovoltaic cell and a flat copper ribbon. It will then dissipate its thermal energy in the cell and in the copper ribbon.

0011Tests performed in the laboratory show that the temperature rise of a bypass diode arranged according to the invention is reduced by about 55% compared to its current value. The tests consist in applying on the bypass diode in an environment at 75 ° C a current equivalent to 1.25 times the maximum operating intensity of the module 1 and measuring its temperature. The temperature is then compared to a limit temperature of use for the component and materials located in the vicinity fixed by a qualification standard to validate the use of said bypass diode with this maximum intensity. Given the current state of the art, it will be impossible, after the implementation of the new IEC61215 Ed.2 standard, to exceed a maximum current of 6A, whereas currently there is a need for bypass diodes operating, for example with a maximum intensity of 10A to protect photovoltaic cells from 150mm to 150mm. The bypass diodes 5 arranged in the laminated stack according to the invention meet the electrical and thermal technical characteristics of the new standard and give the possibility of reaching maximum intensities of 15A and thus meet current needs.

0012FIG. 4 shows a protective semiconductor circuit 5a arranged on a thin metal plate 9 composed of a very good electrical and thermal conductor, for example copper. The input or output of the bypass diode 5a is soldered to the copper plate 9 which serves as a connection to one of the flat copper strips 7b. The other terminal of the diode is directly connected to another ribbon 7a of copper.

0013This copper plate 9 serves as a radiator and further improves the heat dissipation of the bypass diode 5a by increasing the exchange surface of the thermal energy with the surrounding elements and thus with the outside of the photovoltaic module 1 .

0014FIG. 5 shows a control and / or control semiconductor circuit 5b having a wired, optical or electromagnetic connection with the outside of the module. The semiconductor 5b is for example a thyristor, a MOSFET or a GTO. The user of the module controls and controls the operation of the photovoltaic module via one or more semiconductors such as 5b which are in the laminated stack of the module. This arrangement makes it possible to protect the photovoltaic module against theft. Indeed, to reach the semiconductor control and / or control circuit 5b which can serve as a switch or circuit breaker, it is necessary to open the laminated stack of the module which is a delicate operation. The control and / or control semiconductor circuit 5b also makes it possible to effectively manage the right of access to the power produced when the photovoltaic module is in toll lease.

0015Figure 6 shows the back of a photovoltaic module and shows an arrangement of twelve photovoltaic cells 4₁, 4₂, 4₃, 4₄, ..., 4₁₂ mounted in series. The rear face of each photovoltaic cell is electrically connected to the front face of the next photovoltaic cell. Between the back of cell 4₄ and the back side of cell 4₉ is connected a protective semiconductor circuit such as 5a of Figure 3 by means respectively of copper strips 7b and 7a. The semiconductor circuit 5a is then connected in parallel with a group of cells comprising the photovoltaic cells 4₅ - 4₉. The semiconductor circuit 5a then makes it possible to protect the photovoltaic cells 4₅ - 4₉ photovoltaic module.

0016Since the semiconductor circuit 5a is placed in the laminated stack of the module, it is not necessary to pull some cables out of the laminated stack of the module. This reduces the length of the cables and therefore their cost, and simplifies the wiring and therefore the wiring operation, because fewer cables must cross.

0017In FIG. 6, it can be seen that the electrical connections, for example the connections between photovoltaic cells belonging to different rows, such as the connection between the cell 43 and the cell 44, have portions that extend beyond the edge. lateral cells. It is also possible to design a photovoltaic module in which these portions of electrical connections are folded at the edge of the cells on the rear face of the module so as to reduce the size of the photovoltaic module. An insulating film, for example made of EVA-Tedlar, makes it possible to avoid any electrical interconnection between connections and between connections and cells.

0018According to the invention, each cell of the module 1 may be provided with a bypass diode 5c as shown in FIG. 7. Thus, each cell is independently protected against heating due to shaded cells. This allows a better protection of the photovoltaic module and avoids the energy losses of the module by the heating of a cell or the semiconductor. If a cell is shaded the current will pass through the bypass diode paralleled but very little energy will be consumed. The power received by the semiconductor 5c will remain limited, which will prevent degradation of the cell and therefore the degradation of the module.

0019Moreover, no cabling between the different cells is necessary for the protection of the module, which further reduces the density of the wiring.

0020The bypass diodes 5c necessary for the protection of the photovoltaic modules do not need to have a very good performance (low reverse voltage and low leakage current acceptable). Thus it is sufficient to use semiconductor protective circuits 5c produced on a multi-crystalline support, of the same type as that constituting the photovoltaic cells 4. These semiconductor circuits 5c are of lower quality than electronic chips but especially much cheaper and can be easily manufactured by the manufacturer of photovoltaic cells. It is then possible by using multi-crystalline semiconductor circuits 5c to implant a semiconductor circuit 5c per photovoltaic cell 4 at a reasonable cost.

0021It can be seen in FIG. 7 that the semiconductor circuit 5c is soldered directly to the rear face of the photovoltaic cell 4. This embodiment also makes it possible to eliminate cables.

0022The soldering of a semiconductor circuit 5c on each photovoltaic cell 4 can be carried out on an industrial scale automatically by cold welding or reflow soldering of the CMS (Surface Mounted Component) type.

0023In FIG. 8, an integrated 5d semiconductor circuit (etched) is seen directly on the rear face of the photovoltaic cell 4, in the component material, that is, multi-crystalline silicon. A semiconductor circuit 5d of sufficient quality is previously integrated on the photovoltaic cell 4, which reduces the manufacturing operations of the photovoltaic module by eliminating welds.

0024The invention makes it possible to reduce the cost of the wiring of the module, since 30 to 50% of the cabling can thus be eliminated. The space saving generated by the removal of wiring reduces the size of the module.

0025The invention also makes it possible to improve the heat dissipation of the semiconductor circuits and thus to meet the requirements of the new IEC61215 Ed.2 standard.