GB2564123A

GB2564123A - Multi-purpose off-grid PV module design

Info

Publication number: GB2564123A
Application number: GB1710690.7A
Authority: GB
Inventors: Rando Tarrosa Loyd; Gauri Sridhara Shankar
Original assignee: REC Solar Pte Ltd
Current assignee: REC Solar Pte Ltd
Priority date: 2017-07-04
Filing date: 2017-07-04
Publication date: 2019-01-09
Also published as: GB201710690D0

Abstract

A photovoltaic module 1 has strings 5 of solar cells 3. The solar cells 3 are connected in series, and the strings 5 are electrically isolated from each other. A junction box 17 is electrically connected to each string 5. Each junction box 17 provides an external output for electricity generated by the connected string 5. Each junction box 17 may have a bypass diode 9, a cable 19 and connector pair 21. Electronic appliances or components, such as batteries, may be connected to each junction box 17, for off-grid (off-the-grid, OTG) power supply or charging. The solar cells 3 may be wafer based silicon cells, spaced apart but connected with metallic interconnectors 7 or wires. A housing encloses all of the strings 5, and may be a glass-backsheet or glass-glass superstrate.

Description

TECHNICAL BACKGROUND

A solar cell is a photovoltaic device which may directly convert light energy into electric energy.

Typically, a plural number of solar cells is electrically connected in series in order to form strings of solar cells having an overall output voltage corresponding to a sum of the output voltages of the individual solar cells. Additionally, solar cells or strings of solar cells may be connected in parallel such that an overall output current corresponds to a sum of the output currents of the individual solar cells or strings, respectively.

The solar cells electrically interconnected in such manner are then generally included in a module. Such module typically comprises a superstrate construction with a front substrate and a rear substrate including the solar cells in between. Generally, the front substrate is arranged on a front side of the solar cells to be directed towards incoming sunlight. It is optically highly transparent and may be formed for example by a glass plate. The rear substrate is arranged at a rear side of the solar cells and may or may not be transparent. A frame such as a metal frame may enclose the front and rear substrate at their lateral edges.

The front and rear substrate and, optionally, the frame form a housing enclosing the solar cells and thereby protecting them from both, mechanical and chemical, environmental influences.

In most cases, solar modules are used to supply the electric power generated by the solar cells to a large electricity grid, for example to a national electricity grid. In such appliances, typically a large number of solar modules is electrically interconnected and is connected to a converter which converts their electricity to a level such as to comply with electric requirements of the grid. Today, a typical solar module for grid applications provides a peak electric power of between 200 and 300 W_p.

However, there are specific appliances in which solar modules shall not be connected to a larger electricity grid but shall provide their electricity locally. For example, such off-grid or micro-grid solar modules may be used in remote areas not being connected to a public electricity grid. Other applications are in marine and RV solar systems. Therein, the off-grid solar modules are generally used for charging batteries or other electricity storage means or for supplying their electricity directly to consumer devices.

It is to be noted that the term off-grid solar module shall refer herein to both, single solar modules not being connected to other solar modules (i.e. real off-grid solar modules) as well as solar modules to be interconnected with small numbers (e.g. less than 100) of other solar modules such as to form a micro-grid.

Conventionally, off-grid solar modules are specifically designed and configured for special appliances or purposes. For example, an off-grid solar module today in many cases comprises 36 solar cells connected in series such as to provide output voltages of about 18 to 22 V, such voltages being usable for example for charging conventional lead batteries.

However, designing and adapting off-grid solar modules to each of a variety of specific appliances and purposes generally requires substantial efforts and causes increased designing, manufacturing and material costs. Furthermore, a specifically designed off-grid solar module may in most cases not be easily modified such as to serve for other appliances and purposes.

SUMMARY OF THE INVENTION

Accordingly, there may be a need for an alternative solar module, particularly an alternative off-grid solar module, which may be produced at low costs and/or which may easily be adapted to various appliances and purposes.

Such needs may be met with the subject-matter of the independent claim. Advantageous embodiments are defined in the dependent claims and in the following specification.

According to an aspect of the present invention, a solar module comprising a plural number of strings of solar cells, a plural number of junction boxes and a common housing is proposed. Each string comprises a multiplicity of solar cells being electrically connected in series. Therein, each string is electrically separated from each of the other strings of solar cells comprised in the solar module. The plural number of junction boxes corresponds to the plural number of strings of solar cells. Each junction box is electrically connected to exactly one of the strings of solar cells and provides for an external output for electricity generated by this string of solar cells. The common housing encloses all of the plural number of strings of solar cells.

Principles relating to embodiments of the present invention may be understood as being based, inter alia and without restricting a scope of the invention, on the following ideas and recognitions:

As briefly indicated above, it has been found that specifically configuring off-grid solar modules for each of a variety of possible appliances and purposes may cause substantive costs. For example, a number of solar cells to be included in the off-grid solar module has to be specifically selected and a geometry of the housing, i.e. the substrates forming the superstrate and the frame, enclosing the solar cells has to be specifically designed.

It has been found that manufacturing costs and material costs for an off-grid solar module may be substantially lowered by providing the off-grid solar module with a same geometry and/or with same components as used for standard solar modules to be connected to the grid.

However, a standard solar module generates electric power exceeding typical requirements to be fulfilled by off-grid solar modules. Inter-alia, standard solar modules typically provide voltages which substantially exceed the voltages necessary for charging e.g. standard batteries. On the other hand, it has been observed that in many off-grid applications, it may be helpful to enable various types of electricity output configurations.

It is therefore proposed to provide an off-grid solar module which, on the one hand, has a geometry and/or uses components similar or same to those of standard grid-connected solar modules. On the other hand, the off-grid solar module proposed herein comprises a plural number of strings of solar cells, each string being connected to a junction box associated only to this string such that the electricity generated by the solar cells of this string may be output externally via the junction box. Therein, each string of solar cells shall be electrically independent and isolated from other solar cell strings of this off-grid solar module and shall be connected to its own associated junction box. Accordingly, electricity from each one of the strings of solar cells may be output independently via its associated junction box.

For example, if necessary for a specific application, two or more junction boxes of the off-grid solar module may be interconnected in series or in parallel, thereby suitably summing the voltages or the currents, respectively, in order to adapt the off-grid solar module's electrical output configurations or characteristics to fulfil specific requirements of one or various appliances.

For example, in some cases it might be desired to charge multiple batteries at the same time but independently from each other, i.e. a charging process for a first battery may be started and finished at other points in time then for another battery. For such purpose, each battery may be connected to one of the junction boxes of the off-grid solar module and may be charged via its associated solar cell string. In another configuration, higher electric voltages may be required, for example for operating a specific electric device, and in such situation, two or more of the junction boxes of the off-grid solar module may be connected in series.

Accordingly, on the one hand, by including two or more strings of solar cells in a same solar module and independently connecting them each to one of a plurality of junction boxes, the off-grid solar module proposed herein may be adapted to a variety of requirements and purposes. On the other hand, by including the multiplicity of solar cell strings in a common housing and, preferably, providing the housing with dimensions and/or components as typical for standard grid-connected modules, a manufacturing process may be significantly simplified. Particularly, same or similar machines and/or processes may be used for manufacturing both, standard modules as well as off-grid solar modules. Accordingly, for example in large-scale production environments, no significant modifications have to be implemented when for example temporarily manufacturing off-grid solar modules instead of manufacturing standard grid-connected modules. Thus, downtimes may be reduced and production yield may be increased.

According to an embodiment, each of the junction boxes of the proposed off-grid solar module is electrically separate from each of the other junction boxes of the module and each junction box comprises individual cable and connector pairs.

In other words, each of the multiple junction boxes provided at the module is connected to exactly one of the strings of solar cells included in this module and comprises its individual cable and connector pairs via which electricity generated in the respective string may be output through the junction box to an external electric grid including an electric consumer such as a battery to be charged. Therein, the entire circuitry comprising the junction box and its connected solar cell string is electrically completely independent of other circuitries comprising another junction box and another solar cell string comprised in the same off-grid solar module. Due to such electric isolation between neighbouring solar cell string circuitries, electricity may be dissipated from each of the junction boxes independently. Alternatively, the junction boxes may be electrically interconnected in a variety of manners such as to provide suitable series connections or parallel connections adapted for specific applications.

According to an embodiment, each of the junction boxes comprises a bypass diode for electrically bypassing the string of solar cells connected to this junction box.

In other words, at least one bypass diode is provided for and electrically included into an electric circuit created by a solar cell string and its associated junction box. Therein, a bypass diode is a diode preferably electrically connected between both end terminals of a solar cell string, i.e. generally interconnected between the connector pair of a junction box, but oriented in a reverse configuration compared to the configuration of the diodes formed by the solar cells. As such, the bypass diode is inoperative as long as the associated solar cell string is operating normally, i.e. is generating electricity upon being correctly illuminated. However, in case a solar cell string is e.g. defective or is temporarily shaded and therefore does not generate electricity, the bypass diode may short-circuit the end terminals of the string or the connector pair of the junction box, respectively. Thereby, the bypass diode may avoid that the defective or shaded solar cell string may block electricity generation of the entire solar module, i.e. may block also electricity generation from other ones of the solar cell strings of this solar module in cases where several junction boxes are e.g. connected in series with each other.

According to an embodiment, the plural number of strings of solar cells is three, i.e. the proposed off-grid solar module comprises exactly three strings of solar cells.

It has been found that in a solar module of standard dimensions, three independent circuitries each comprising its own solar cell string connected to its own associated junction box may be included in a manner such that each circuitry may provide for electric characteristics which are suitable for a large variety of electric applications. However, in principle, the off-grid solar module proposed herein may have any other plural number of solar cells strings such as two, four, five or even more solar cell strings.

Independent of the number of solar cell strings comprised in a module, it may be beneficial that each solar cell string is provided with a same number of solar cells and/or a same type of solar cells. This may simplify a manufacturing process as for example only one type of solar cell has to be provided and/or only one type of cables, connector pairs and junction boxes has to be provided and/or interconnection schemes and processes may be standardized.

However, it is also possible to provide each of the solar cell strings comprised in a common housing with a different number of solar cells and/or different type of solar cells. Therein, the number and/or type of solar cells may be adapted for providing specific electric characteristics. For example, a first string may comprise a larger number of solar cells thereby providing a higher output voltage whereas a second string may comprise fewer solar cells for providing a lower output voltage.

According to an embodiment, each of the strings of solar cells comprises at least 36 solar cells. Preferably, each strings of solar cells may comprise 40 solar cells. With each single solar cell typically having an output voltage at its maximum power point V_mpp of between 0.5 and 0.6 V, such number of solar cells in a string has been found to provide for an output voltage of typically more than 18 V, preferably more than 20 V. Such output voltage is assumed to be suitable for many typical appliances of off-grid solar modules.

According to an embodiment, each solar cell has a rectangular non-square geometry. In such rectangular non-square geometry, a dimension in a first direction is longer than a dimension in a second direction perpendicular to the first direction. Therein, the term rectangular may be interpreted broadly as substantially rectangular, including for example slight deviations from a purely rectangular geometry; for example, edges of a rectangle may be chamfered or rounded, as it is often the case for example in solar cells made from Cz silicon wafers.

Preferably, a width dimension of each solar cell is double the size of a length dimension of the solar cell. Therein, the length dimension may be the length in a longitudinal direction of the solar cell substrate parallel to a busbar and the width dimension is measured in a direction rectangular to the longitudinal direction. Such solar cells are also referred to as half-cut cells as they may be produced by initially producing cells based on square substrates and then cutting the substrates into halves. Accordingly, while the initial square substrates may effectively be produced with standard machinery configured for standard square substrate sizes, the final solar cells after being half-cut may have a reduced series resistances due to shorter busbars, thereby increasing their efficiency.

Particularly, each solar cell may have dimensions with a width of up to 160mm and a length of up to 80mm. Specifically, preferably each solar cell may have dimensions of 156mm x 78mm. In other words, the off-grid solar module proposed herein may advantageously be provided with half-cut solar cells made from substrates which, according to a present industry standard, have dimensions of approximately 156 mm x 156 mm.

It shall be mentioned that all dimensions indicated herein with respect to e.g. cell sizes may be subject to standard manufacturing tolerances. Such tolerances may be for example up to ± 1% relative. A solar wafer of present industry standard may have e.g.

156.75 mm x 156.75 mm

According to an embodiment, spacings between neighbouring solar cells are between 2mm and 7mm. In other words, in the off-grid solar module, the solar cells may be arranged such that they are neighbouring each other but not necessarily mechanically adjoining each other. Instead, there may be a gap or spacing between neighbouring solar cells. This spacing may be dimensioned such that, for example, metallic interconnectors or wires may extend through such spacing for electrically interconnecting front side contacts of a solar cell with rear side contacts of a neighbouring solar cell. Spacings of between 2 mm and 7 mm may be substantially same as those applied in standard grid-connected solar modules.

According to an embodiment, the solar module has a length of up to 2005mm and a width of up to 1011mm. Preferably the module has a length of 2005mm and a width of 1011mm. Such dimensions correspond to dimensions typically realised in some standard grid-connected solar modules.

The solar cells comprised in the off-grid solar module may be wafer-based silicon solar cells. Currently, such wafer-based silicon solar cells are used for a major part of all industrially produced solar modules and have been proven to be highly efficient and long-term reliable. The wafers may consist of mono-crystalline, multi-crystal line or poly-crystalline silicon and may have a typical thickness of between 100 and 500pm, preferably between 130 and 300pm.

According to an embodiment, each string of solar cells is adapted to provide an output voltage V_mpp at a maximum power point of between 12 V and 32 V, preferably of between 18 V and 26 V and more preferably between 20 V and 23 V. Such output voltages have been found to be suitable for a large variety of solar applications.

According to an embodiment, the housing comprises a superstrate construction with one of a glass-backsheet construction and a glass-glass construction. In other words, while a front substrate forming a front side cover of the solar module shall typically be highly transparent for incoming sunlight and may therefore be made with transparent material such as glass sheets and/or some glass-like highly transparent plastic materials (therefore herein also referred to a glass substrate), a back substrate forming a back side cover of the solar module may or may not be highly transparent for incoming sunlight, depending on whether the solar module shall be monofacial, i.e. shall receive light only from the front side, or bifacial, i.e. shall receive light from both sides. For a monofacial module, the back substrate may be opaque and may therefore be made with an intransparent backsheet.

It may be noted that possible features and/or benefits of embodiments of the present invention are described herein with respect to various embodiments of a solar module. One skilled in the art will understand that features of various embodiments may be combined with or replaced by features of other embodiments and/or may be modified in order to come to further embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the following, embodiments of the invention will be described herein with reference to the enclosed drawings. However, neither the drawings nor the description shall be interpreted as limiting the invention.

Fig. 1 shows a top view onto a standard solar module for grid connection.

Fig. 2 shows a top view onto an off-grid solar module according to an embodiment of the present invention.

The figures are only schematic representations and not to scale. Same or similar reference numerals refer to same or similar features throughout the figures.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 schematically shows a configuration of a standard solar module 101 as it is currently produced by the applicant under the name TwinPeak. The solar module 101 comprises 120 solar cells 103. The solar cells 103 may be made from multi-crystalline silicon wafers and are half-cut with lateral dimensions of 156 x 78 mm². The solar cells 103 are grouped into six groups of 20 solar cells 103. The solar cells 103 of each group are connected in series via interconnectors 107 such as to form a string 105. Two of such strings 105 are connected in parallel and are connected to an associated bypass diode 109. Accordingly, such standard solar module comprises two matrices of the three strings 105 in parallel connected in series. Such standard solar module 101 may provide a maximum power P_mpp of about 290 W_p with a nominal voltage V_mpp of between 30 and 33 V and a nominal current I_mpp of between 8 and 9 A.

The solar cells 103 are embedded in a common housing 111. The housing 111 comprises a superstrate 113 with a front cover of glass and a rear cover of highly resistant polyester. Furthermore, an aluminium frame 115 is provided and surrounds edges of the superstrate 113.

The standard solar module 101 comprises a single junction box 117 schematically illustrated in the figure by a dotted box. The junction box 117 includes the three bypass diodes 109 and is connected to each of the solar strings 105 via cables 119. Opposing ends of these cables 119 are connected to connector pairs 121. Electricity generated by the solar module 101 may be output via these connector pairs 121. It may be noted that, while in the schematic figure, a plus-connector and a minus-connector of the connector pair 121 are illustrated at opposing sides of the solar module 101, such connector pair 121 may also be provided with both connectors at a same side of the solar module 101.

Fig. 2 shows an off-grid solar module 1 according to an embodiment of the present invention. Such off-grid solar module 1 may have a very similar appearance as the standard solar module 101 as it may be made with similar or same main components such as the solar cells 3 and the housing 11.

Particularly, the off-grid solar module 1 may comprise 120 solar cells 3, preferably being of the same type as used in the standard solar module 101. Furthermore, the off-grid solar module 1 may have a common housing 11 which is made of the same components for the superstrate 13 and the frame 15 as described above for the standard solar module 101. Particularly, outer dimensions of the housing 11 may be the same as for the housing 111 of the standard solar module 101. Accordingly, upon a front side view, the off-grid solar module 1 and the standard solar module 101 may hardly be distinguished from each other.

However, an internal wiring of the off-grid solar module 1 may significantly differ from the wiring applied in the standard solar module 101.

Particularly, instead of grouping the 120 cells 103 into six strings 105 and suitably electrically interconnecting all these six strings 105, as is the case for the standard solar module 101, the 120 solar cells 3 of the off-grid solar module 1 are grouped into three groups of 40 solar cells 3 only, thereby forming three strings 5 of solar cells 3 which are serially connected via interconnectors 7.

In further contrast to the standard solar module 101, the three strings 5 of solar cells 3 are electrically not connected with each other internally within the off-grid solar module 1. Instead, each string 5 of solar cells 3 is connected to exactly one out of three junction boxes 17', 17, 17'. Each of the junction boxes 17', 17, 17' is electrically separate from each of the other junction boxes 17', 17, 17' and comprises its individual cables 19 and connector pairs

21. Furthermore, each of the junction boxes 17', 17, 17' comprises a bypass diode 9 for electrically bypassing the associated string 5 of solar cells 3 connected to this junction box 17', 17, 17', respectively.

Accordingly, the off-grid solar module 1 with its solar cells 3 comprised in a common housing 11 may act like three independent energy sources, each providing the electric energy generated by one of the solar cell strings 5 via its associated junction box 17', 17, 17'. Therein, each string 5 may have a maximum power output which is determined, inter-alia, by a number and quality of solar cells 3 comprised therein. For example, with 40 half-cut multicrystalline solar cells 3 of a dimension of 156.75 mm x 78.375 mm, each string 5 may provide an maximum power output of about 96 W with a maximum current output of about 4.5 A and a maximum voltage output of about 24 V.

While the strings 5 and the associated junction boxes 17', 17, 17' are not internally electrically connected within the off-grid solar module 1, a user can connect them using the provided junction boxes 17', 17, 17' and connect them with each other via external connectors (not shown) in any arbitrary configuration. For example, with all junction boxes 17', 17, 17' connected in series, an output voltage of about 72 V with an output current of about 4.5 A may be obtained whereas with all junction boxes 17', 17, 17' connected in parallel, an output voltage of 24 V with an output current of about 13.5 A may be obtained. Such flexibility may enable the user to configure the off-grid solar module 1 based on system design requirements e.g. for a battery type and charging method used. For example, each individual string 5 of the off-grid solar module 1 may be able to charge one 12 V battery with a charge controller at 4.5 A peak charge current.

The off-grid solar module 1 and the standard solar module 101 may be produced mainly using the same components and utilising same automated machines for example for cell and string placement as well as EVA and backsheet placement, and module assembly and testing. Accordingly, with the off-grid solar module 1 proposed herein, a module assembly production process will hardly be adversely affected by a design change and it may be possible to implement manufacturing with minimal loss to production output and minimal downtime. In principle, no material changes are needed except for the junction boxes 17', 17, 17'.

Finally, it should be noted that terms such as comprising do not exclude other elements or steps and the a or an does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

LIST OF REFERENCE SIGNS

I off-grid solar module solar cells strings interconnectors bypass diodes

II housing superstrate frame junction boxes cables connector pairs

101 standard solar module

103 solar cells

105 strings

107 interconnectors

109 bypass diodes

III housing

113 superstrate

115 frame

117 junction boxes

119 cables

121 connector pairs

Claims

1. A solar module (1) comprising:

a plural number of strings (5) of solar cells (3), each string (5) comprising a multiplicity of solar cells (3) being electrically connected in series and each string (5) being electrically separated from each of the other strings (5) of solar cells (3) comprised in the solar module (1);

a plural number of junction boxes (17', 17, 17'), the plural number corresponding to the plural number of strings (5) of solar cells (3), each junction box (17', 17, 17') being electrically connected to exactly one of the strings (5) of solar cells (3) and providing for an external output for electricity generated by this string (5) of solar cells (3);

a common housing (11) enclosing all of the plural number of strings (5) of solar cells (3).

2. The solar module of claim 1, wherein each of the junction boxes (17', 17, 17 j is electrically separate from each of the other junction boxes (17', 17, 17 j of the solar module (1) and wherein each junction box (17', 17, 17') comprises individual cable (19) and connector pairs (21).

3. The solar module of one of the preceding claims, wherein each of the junction boxes (17', 17, 17') comprises a bypass diode (9) for electrically bypassing the string (5) of solar cells (3) connected to this junction box (17', 17, 17').

4. The solar module of one of the preceding claims, wherein the plural number of strings (5) of solar cells (3) is three.

5. The solar module of one of the preceding claims, wherein each of the strings (5) of solar cells (3) comprises at least 36 solar cells (3), preferably wherein each strings (5) of solar cells (3) comprises 40 solar cells (3).

6. The solar module of one of the preceding claims, wherein each solar cell (3) has a rectangular non-square geometry.

7. The solar module of claim 6, wherein a width dimension of each solar cell (3) is double the size of a length dimension of the solar cell (3).

8. The solar module of one of the preceding claims, wherein each solar cell (3) has dimensions with a width of up to 160mm and a length of up to 80mm, preferably wherein each solar cell has dimensions of 156mm x 78mm.

9. The solar module of one of the preceding claims, wherein spacings between neighbouring solar cells (3) are between 2mm and 7mm.

10. The solar module of one of the preceding claims, wherein the solar module (1) has a length of up to 2005mm and a width of up to 1011mm, preferably wherein the solar module (1) has a length of 2005mm and a width of 1011mm.

11. The solar module of one of the preceding claims, wherein the solar cells (3) are waferbased silicon solar cells (3).

12. The solar module of one of the preceding claims, wherein each string (5) of solar cells (3) is adapted to provide an output voltage Vmpp at maximum power point of between 12 V and 32 V, preferably of between 18 V and 26 V.

13. The solar module of one of the preceding claims, wherein the housing (11) comprises a superstrate (13) construction with one of a glass-backsheet construction and a glass-glass construction.

14. The solar module (1) of claim 1, comprising:

- three strings (5) of solar cells (3), each string (5) comprising a multiplicity of wafer-based silicon solar cells (3) being electrically connected in series, and each string (5) being electrically separated from each of the other strings (5) of solar cells (3) comprised in the solar module (1);

wherein each of the strings (5) of solar cells (3) comprises at least 36 solar cells (3) and each solar cells (3) has a rectangular non-square geometry;

wherein each string (5) of solar cells (3) is adapted to provide an output voltage Vmpp at maximum power output of between 12V and 32V;

- a three junction boxes (17', 17, 17'), each junction box (17', 17, 17') being electrically connected to exactly one of the strings (5) of solar cells (3) und providing for an external output for electricity generated by this string (5) of solar cells (3);

wherein each of the junction boxes (17', 17, 17') is electrically separate from each of the other junction boxes (17', 17, 17') of the solar module (1) and wherein each junction box (17', 17, 17') comprises individual cable (19) and connector pairs (21);

- a common housing (11) enclosing all of the three strings (5) of solar cells (3).

Intellectual Property Office