Patent Application
20070089774
The present invention relates to a bypass diode for a photovoltaic cell, of particular but by no means exclusive application in photovoltaic cell modules for use in solar concentrators of solar photovoltaic power systems.
Multijunction solar cells are used in solar concentrator photovoltaic power systems for generating power owing to their high efficiency. Although such solar cells are expensive, these efficiencies are sufficiently high to render such arrangements economically feasible. However, to maintain the reliability of such arrangements in which multiple cells are arranged in series, it is desirable to have a bypass diode for each cell in a series. The bypass diode prevents overloading of its corresponding cell when that cell has a reduced power output owing to poor illumination or performance, or some other malfunction. This allows the series of cells constituting a module to continue operating.
The number of cells in series, which determines the bus voltage, is usually greater than a hundred, so the bypassing of a single, failed cell will result in a power loss of 1% or less. The bypass diodes thus allow the system to keep operating with minimal loss of output.
One existing system is illustrated in U.S. Pat. No. 6,020,555, in which each cell is connected in parallel with its corresponding bypass diode resulting in a series of diodes in parallel with a series of cells.
However, in existing arrangements, where the bypass diodes are essentially adjacent to the cells, are unsuitable for systems with closely packed cells, such as dish concentrator or central receiver systems.
Accordingly, the present invention in a first aspect provides a photovoltaic power module. In this aspect, the module comprises:
a substrate provided with a circuit;
one or more photovoltaic cells mounted to said substrate and electrically connected to said circuit; and
one or more bypass diodes, each corresponding to a respective one or more of said cells;
wherein each of said diodes is located between said substrate and said cells and at least in part between conducting portions of said circuit.
Preferably said circuit takes the form of a printed or laminated circuit and each of said diodes is located between neighbouring metallised zones of said circuit. Preferably each of said diodes has a thickness that is substantially equal to or less than the thickness of said metallised zones. Thus, because the diodes are located (along with the circuit) between the substrate and the cells, the diodes do not prevent the solar cells from being packed as closely as previously.
Alternatively, however, if it is not possible to obtain or employ diodes that are sufficiently thin to be accommodated by one of the metallised zones (which may have a thickness of only 0.3 mm) the substrate may include one or more recesses for at least partially (though conceivably wholly) accommodating the diodes (preferably one diode per recess). Thus, in this embodiment the diodes are also between the substrate and the cells (their still being substrate material on the side of the diodes opposite the cells), but the diodes are also at least to some extent surrounded by substrate material.
Preferably the conducting portions of the circuit (in one embodiment the metallised zones) are contoured to fit or accommodate said diodes. Preferably the terminals of each of said diodes are metallised to complement the shape of said conducting portions.
The present invention provides in a further aspect a method of bypassing one or more photovoltaic cells in a photovoltaic power module, comprising:
locating one or more bypass diodes, each corresponding to a respective one or more of said cells, between said cells and the substrate of said module;
electrically coupling said bypass diodes to circuitry provided on said substrate to bypass the corresponding one or more cells if the voltage across said one or more cells drops below a predetermined level or is reversed.
Preferably the circuit is a printed or laminated circuit. Preferably each of said diodes is located between neighbouring metallised zones of said circuit.
Preferably each of said diodes has a thickness that is substantially equal to or less than the thickness of said metallised zones.
Preferably the method includes contouring portions of the circuit (in one embodiment the metallised zones) to fit said diodes. Preferably the terminals of each of said diodes are metallised to complement the shape of said conducting portions.
In one embodiment, the method includes providing one or more recesses in said substrate for at least partially (and in some cases wholly) accommodating the diodes (preferably one diode per recess). Thus, in this embodiment the diodes are located between the cells and the substrate (their still being substrate material on the side of the diodes opposite the cells), but the diodes are also at least to some extent surrounded by substrate material.
In order that the present invention may be more clearly ascertained, embodiments will now be described by way of example, with reference to the accompanying drawing, in which:
A representative detail of a photovoltaic module according to an embodiment of the present invention is shown in cross-section at 10 in
Each of a plurality of photovoltaic cells 16 is soldered to the metallised zones 14 by means of solder 18 (shown hashed in the figure). For each solar cell 16, a bypass diode 20 with terminals 22a and 22b is provided between that cell 16 and the substrate 12. Each cell 16 is connected in parallel across its respective bypass diode 20.
The diode 20 is electrically coupled to the appropriate portions of the metallised zones 14 of the circuit board by solder 18, so that it is in parallel with the corresponding cell 16.
In an alternative embodiment, the photovoltaic module includes a plurality of groups of cells. Each group of cells is then provided with a bypass diode 20, and the group of cells is connected in parallel with its corresponding bypass diode 20.
Each bypass diode 20 has a thickness approximately equal to or somewhat less than that of the metallised zones 14, hence also approximately equal to or somewhat less than 0.3 mm. The bypass diodes 20 thus do not increase the thickness of the module 10 and, being beneath the cells 16, do not restrict how closely the cells 16 can be packed in the module 10.
It is envisaged that, during manufacture, the diodes 20 would be positioned on the solder paste printed substrate 12, after which the solar photovoltaic cells 16 would be placed over the diodes 20 onto the metallised zones 14. In this manner the diode is integrated into the closely packed module 10 without requiring additional diode space around the photovoltaic cells 16.
The device is shown schematically for the sake of clarity. In reality, the diode 20 is smaller than it appears compared with the metallised zones 14. Thus, the gap between the metallised zones 14 would typically be about 0.7 mm, widening to about 1.5 mm to accommodate the diode 20. Thus, the area without metal for the cells to be soldered to is small.
The width (from left to right in this view) of the metallised zones 14 would typically be about 15 mm, while the width (from top to bottom in this view) of cell 16 would typically be about 10 mm. Neighbouring solar cells (16, 16′, 16″) are thus very close.
As in the embodiment of
This embodiment allows the use of diodes with a somewhat greater thickness than in the embodiment shown in
Thus, the bypass diode arrangement of this invention allows one to minimize the impedance of thermal transfer between the cell and the substrate. Such impedance—particularly in high intensity or high power applications—could otherwise seriously compromise performance or even render the device impractical.
Modifications within the scope of the invention may be readily effected by those skilled in the art. It is to be understood, therefore, that this invention is not limited to the particular embodiments described by way of example here and above.
In the claims that follow and in the preceding description of the invention, except where the context requires otherwise owing 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.
Further, any reference herein to prior art is not intended to imply that such prior art forms or formed a part of the common general knowledge.
This application is based on and claims the benefit of the filing date of U.S. provisional application Ser. No. 60/471,342 filed 19 May 2003, the contents of which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AU04/00667 | 5/19/2004 | WO | 11/13/2006 |
| Number | Date | Country | |
|---|---|---|---|
| 60471342 | May 2003 | US |
