WO2008141878A1

WO2008141878A1 - Method of contacting photovoltaic modules

Info

Publication number: WO2008141878A1
Application number: PCT/EP2008/054637
Authority: WO
Inventors: Rainer Klaus Krause
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 2007-05-24
Filing date: 2008-04-17
Publication date: 2008-11-27
Anticipated expiration: 2009-11-24
Also published as: TW200903825A

Abstract

A method of contacting photovoltaic modules is provided. The method comprises the steps of : - providing photovoltaic cells with backside contacts; - placing said cells onto a glass substrate, thus forming a module; - including the desired wiring of the cells into a backside covering foil used to encapsulate the module; - placing said backside covering foil onto said module, whereby the wiring of the foil is matched to the contact points of the cells; - securing said contact points; and encapsulating said module by means of said covering foil.

Description

D E S C R I P T I O N

Method of Contacting Photovoltaic Modules

Field of the Invention

The present invention relates in general to a method for the manufacture of solar modules. More particularly, the present invention relates to a method for contacting the individual cells (Si and thin film technology) on such modules.

Background of the Invention

A solar cell or photovoltaic cell is a semiconductor device consisting of a large-area p-n junction diode, which in the presence of sunlight is capable of generating usable electrical energy. This conversion is called the photovoltaic effect .

Solar cells have many applications. They are particularly well suited to, and historically used in, situations where electrical power from the grid is unavailable, such as in remote area power systems, handheld calculators, remote radiotelephones and water pumping applications. Solar cells (in the form of modules or solar panels) on building roofs can be connected through an inverter to the electricity grid in a net metering arrangement.

A solar module or panel is a flat collection of solar cells or solar thermal collectors used for converting solar energy into electricity or heat. The term "solar module" can be applied to either solar hot water modules (usually used for providing domestic hot water) or solar photovoltaic modules (providing electricity) . In the following the main focus will be on solar photovoltaic modules.

Solar cells that are to be in operation for a long time need to be protected from environmental factors such as dampness. To achieve this, the upper side of the solar cells is covered with a transparent covering layer. This can be glass or plastic sheet. The covering layer is glued to the surface of the solar cells with a plastic that networks when heated.

Encapsulation takes place in a vacuum laminator. The solar cell is placed face up inside it on a flat heater plate. EVA (ethyl vinyl acetate) foil is laid on it and, on top of that, the transparent protective covering (glass or plastic sheet) .

The lid of the laminator is then closed. In this lid, there is a membrane, which now rests on the solar cell, dividing the laminator chamber into two sealed parts. At the beginning of the process, both of these spaces are evacuated and at the same time, the solar cell is heated up. On reaching a predetermined temperature (e.g. 80⁰C), air is let in to the space above the membrane. This presses the membrane onto the stack consisting of solar cell, EVA foil and covering layer, creating a continuous contact between the individual layers over the entire surface. Upon increasing the temperature further, the EVA foil polymerizes, at about 150⁰C, becoming a transparent, thermally stable film and creating a strong bond between the surface of the solar cells and the covering layer.

The individual cells on solar modules are contacted using contact wires and a certain soldering technique. This is a difficult and complex process concerning cell handling and proper contacting. The mono- and poly-crystalline silicon cells are fairly thin (200 - 330 μm) and therefore highly exposed to break during the process. Each process step which can be saved increases the process and product yield.

Summary of the Invention

It is therefore an object of the present invention to provide a method for contacting photovoltaic modules that simplifies handling, reduces costs and improves lead time significantly.

This and other objects and advantages are achieved by the process disclosed in claim 1.

Advantageous embodiments of the invention are disclosed in the dependent claims.

Brief Description of the Drawings

The invention will be described in more detail below in connection with the accompanying drawings, in which

Fig. 1 depicts a generic cell example layout with backside contacts; the contacts are either pads in the corner or could be contact stripes along the edge;

Fig. 2 schematically shows an EVA foil used to pack and encapsulate the solar module with low voltage; the foil contains already the finished contact wiring as well as contact pads fitting the cell contact pads/stripes; the contact wiring is arranged to have the cells in one row in parallel and the rows serialized;

Fig. 3 schematically shows a solar module with finished contact wiring on the EVA foil for low voltage; the set up is made to have the cells per row serialized and the rows in parallel mode;

Fig. 4 schematically depicts an EVA foil used to pack and encapsulate the solar module with high voltage while the EVA foil contains already the contact wiring; the set up is made to have all cells in serial mode, to achieve the highest possible voltage;

Figs. 5A to 5D schematically depict the encapsulation process using a wired EVA foil;

Fig. 6A schematically shows a solder concept using a tip heated stamp; and

Fig. 6B schematically depicts a glue contact concept using a UV light stamp.

Detailed Description of the Preferred Embodiment

The inventive method starts with cells having backside contacts 2, as shown in Fig. 1. In this example, the cell has 3,26 V and 2,33 A.

A backside covering foil 4 (e.g., an EVA foil) normally used for module encapsulation can be used to connect individual cells on the glass substrate. The required wiring can be included into the foil. The wiring pattern on the foil determines the module's parameters like output voltage and output current, examples for different wiring patterns, low, medium and high voltage applications are shown in Figs. 2 to 4. The final voltage/current is really dependent on the cell setup (patterning spaces) and on how many cells are linked parallel and/or serial on module level. The inventive method allows any range from lowest cell voltage, highest current (all parallelized) to highest cell voltage, lowest current (all serialized) .

Thus, Fig. 2 shows an example using an EVA foil with contact stripes for low voltage application (3 rows in serial mode with each 6 cell in parallel mode - cells are all positioned the same way, see polarity pattern) . For this example, an individual cell would have 3,25 V and 2,33 A, the power for 18 cells per module would be at 136,31 W. For the cell/module example, any range is possible between 3,25 V/41,94 A and 58,5 V/2,33 A, with other cell parameters the range would look different - e.g., 8 cells in parallel mode deliver a 3,25 V/41,94 A module performance and all 18 cells in serial mode deliver a 58,5 V/2,33 A module performance. The application of Fig. 2 would have the following parameters:

Voltage: 9,75 V

Current: 13, 98 A

Power: 136,31 W

In Fig. 3, there is shown an example using an EVA foil with contact stripes for medium voltage application (3 rows in parallel mode with each 6 cell in serial mode - cells are all positioned the same way, see polarity pattern) . The application of Fig. 3 would have the following parameters:

Voltage: 19,5 V

Current: 6, 99 A

Power: 136,31 W

Fig. 4 depicts an example using an EVA foil with contact stripes for high voltage application (3 rows in serial mode with each 6 cell in parallel mode - cells in one row are placed alternating, see polarity pattern) . The application of Fig. 4 would have the following parameters: Voltage : 58,5 V Current : 6, 99 A Power : 136,31 W

The possible module configurations for this cell example are shown in the following table 1:

Table 1

The different examples demonstrate the flexibility of the inventive wiring approach. In case a constant cell design is used, the approach gives maximum flexibility to customize the module performance. In the case of the listed cell performance, any voltages and currents between 3,25 V - 58,5 V and 2,33 A - 41,94 A can be realized, using the module technique described here. It is clear for the skilled worker that, if the cell is designed differently, other numbers will result. Varying the cell design allows even a wider range of module performance. The wiring on the foil can be a conductive polymer, metallic wires (like copper) , which are glued or printed on the foil surface, and build the final module wiring ending in the exit connector to the converter. The wire and contact pattern depends on the application and the cell size (see table above) .

Table 2 below gives various cell performances at a specific patterning width for different cell sizes. Table 2

Cell setup at certain patterning

This means that the module performance can easily be customized by the wiring pattern on the backside covering foil only.

The known encapsulation process can, according to the present invention, not only be used to cover and seal the module, but also to connect the contact pads of the cell having backside contact pads .

The connection between the contact pads on the cells and the pads and wires on the foil can be either realized through contact gluing or soldering, as shown in Fig. 5.

First, solar cells 10 are placed, e.g., by a pick-and-place process, on a glass substrate 12, which might be of a size of 60 x 120 cm². The cells, in this case, have a size of 20 x 20 cm². However, other sizes are possible.

In case of the contact glueing method, the contact paste is placed on the backside of the EVA foil, on the contact pads 2, using a mask. The same technique is used in case of soldering, by placing the solder paste through a mask, like in a regular SMT process. On top of the assembled cells 14, the EVA foil 16 is placed with matching contact pads 18. At the positions of the arrows 20, metallic stamps 22 (cf. Figs. 6A, 6B) are placed during the encapsulation process, putting pressure on the contacts during curing. In case of soldering, the metallic stamps 22 are heated at their lower ends (arrows 24) to realize local soldering between the contact pads.

The cell set up, as basic layout, remains the same and does not get changed. This allows a maximum flexibility in customization at very low effort and cost impact. The foil 16 is placed on the backside using video imaging technique, to secure exact positioning of the cell contacts vs. the foil contacts and wires. The contacts can be reliably secured using either a contact glue 26 or the foil contacts get solder paste 28, through a SMT like process step. The soldering is achieved during a vacuum and furnace process using heated stamp tips for the individual solder joints (see Fig. 5d) during encapsulation the foil is in a vacuum process attached to the module backside, during this process the pin tip heated stamps are pressed on the solder joints, this enables a local soldering of the contact pads (see Fig. 6a) . In case of the glueing the contact glue is also put onto the foil 16 using the SMT technology, during the encapsulation process the local stamps press on the contact pads applying UV for curing (arrows 30), while the light can be provided through the stamp directly, using a quartz glass type of stamp (see Fig. 6b) .

In the examples shown, the cells are once placed either always the same direction or in the second case in alternative direction. Again, the cell layout itself remains the same and is generic. This means that any technology can be used, like mono- and poly-crystalline cells as well as cells based on thin film technology, like CIGS and CdTe, etc. As long as the contacts are located in the corners of the cells, any set up can be achieved using the generic wiring technique on modules.

Claims

C L A I M S

1. Method of contacting photovoltaic modules, comprising the steps of:

providing photovoltaic cells (10) with backside contacts (2) ; placing said cells (10) onto a glass substrate (12), thus forming a module; including the desired wiring of the cells into a backside covering foil (16) used to encapsulate the module; placing said backside covering foil (16) onto said module, whereby the wiring of the foil is matched to the contact points (18) of the cells (10); securing said contact points (18); and encapsulating said module by means of said covering foil (16) .

2. Method according to claim 1, wherein said step of securing is performed by contact gluing, thereby placing a contact paste on the backside covering foil's backside.

3. Method according to claim 1, wherein said step of securing is performed by soldering.

4. Method according to any one of claims 1 to 3, wherein during the encapsulation process metallic stamps are placed on the assembly consisting of the backside covering foil and said module to put pressure on the contacts.

5. Method according to claim 3 and 4, wherein said metallic stamps are heated at their lower ends.

6. Photovoltaic module, consisting of a plurality of photovoltaic cells (10) with backside contacts (2), wherein a backside covering foil (16) comprising the desired wiring of said cells is placed onto said module, the wiring of the foil being matched to the contact points (18) of said cells (10) .

7. Photovoltaic module according to claim 6, wherein said contact points (18) are secured by contact glueing.

8. Photovoltaic module according to claim 6, wherein said contact points (18) are secured by soldering.