Electricity: power supply or regulation systems – In shunt with source or load – Using diode
Reexamination Certificate
2000-04-07
2001-05-01
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using diode
C323S906000
Reexamination Certificate
active
06225793
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a circuit arrangement for power generation with solar cells connected in series and in strings of several solar cells, where the strings, to each of which a bypass diode is connected in parallel, are connected in series.
Photovoltaic systems for transforming solar energy into electrical energy comprise solar cells arranged in modules on which are arranged strings of solar cells connected in series and each jumpered by a bypass diode. The strings are also connected in series. The modules with the strings of solar cells are generally of plate-like design. The plates have thin-film solar cells in adjacent strips. The conditions at the installation location of the modules frequently do not allow identical radiation onto all strings of a module, and it may be that strings are in the shade of neighboring objects and hence cannot play any part in power generation.
2. Description of Related Art
To prevent the operation of shaded solar cells, which are for that reason polarized in the non-conducting direction, bypass diodes are used that revert to the conducting state when the strings are in shade. Since the bypass diodes have internal resistances during operation in the conducting direction, heat losses due to current occur in them, thereby reducing the efficiency of the photovoltaic system. The currents flowing via the bypass diodes must not heat up the diodes beyond permitted limit temperatures. Precautions must therefore be taken for heat dissipation by convection and/or radiation, for example by mounting the bypass diodes on heat sinks.
The strings are provided with connections for external lines. The lines from and to the strings are arranged with their one end in connection boxes in which the strings are connected to one another.
When numerous strings and possibly solar modules are connected in series, relatively high currents flow via the bypass diodes of individual strings when the latter are in shade. The number of strings in shade corresponds to the number of conducting bypass diodes. The energy yield of a photovoltaic system is therefore also reduced by the bypass diodes in an unwelcome way when the strings are in shade.
A solar generator is described in DE 88 15 963.9U1, in which each solar cell module is connected in parallel to a shunt diode and the latter to an LED, in order to rapidly detect a defective solar cell module by visual means.
SUMMARY OF THE INVENTION
The problem underlying the present invention is to develop a circuit arrangement with solar cells connected in series and in strings and provided with a bypass diode for each string, to the extent that the rise in the power loss proportional to the number of shaded and hence non-conducting strings, and resulting from currents in the bypass diodes when two and/or more strings in a series of strings are non-conducting, is substantially reduced.
The problem is, in a circuit arrangement with solar cells connected in series and in strings and with strings connected in series, each of which has a bypass diode, substantially solved in accordance with the invention in that in each case a diode is connected in parallel to two and/or more than two bypass diodes connected in series and connected in parallel to a string. If in the circuit in accordance with the invention those strings connected in series whose bypass diodes are jumpered by a parallel diode are polarized in the non-conducting direction, i.e. by shading, the current flows via the parallel diode, as a result of which the power loss only occurs in one diode. In each two bypass diodes jumpered by a parallel diode, only half as many diodes would be carrying current as bypass diodes are present, in the event that all strings consist of an even number and are polarized in the non-conducting direction.
This shows the considerable reduction of the power loss in the circuit in accordance with the invention. The power loss in diodes can be reduced even further by other diodes jumpering several bypass diodes.
In a convenient embodiment, the bypass diodes and the diodes parallel thereto for two or more strings are arranged on one side of the printed circuit board, and on the other side printed conductors with connection points for external lines and with plated-through holes for the connections of the bypass diodes are provided, with metal surfaces as contact faces for the bypass diodes and the diodes being provided on the surface of the printed circuit board. With this embodiment, a heat transfer takes place from the bypass diodes and the other diodes to the metal surfaces. Since only a few of the diodes arranged on the printed circuit board carry current even when there is a large number of non-conducting strings, the board with the metal surfaces is sufficient for dissipating the heat. The printed circuit board with the bypass diodes and the diodes jumpering these takes up very little space. The printed circuit board with the bypass diodes and further diodes for a large number of strings is preferably arranged in a connection box.
Schottky diodes are preferably used as bypass diodes and as diodes parallel to the bypass diodes. Schottky diodes have a low internal resistance in the conducting direction. The result is low voltage drops and heat losses.
Further details, advantages and features of the invention are shown not only in the claims and in the features they contain —singly and/or in combination —but also in the following description of a preferred embodiment shown in the drawing.
REFERENCES:
patent: 4513167 (1985-04-01), Brandstetter
patent: 4744430 (1988-05-01), McCoy
patent: 5235232 (1993-08-01), Conley et al.
patent: 5248931 (1993-09-01), Flesner et al.
patent: 5500052 (1996-03-01), Horivchi et al.
patent: 5677833 (1997-10-01), Bingley
patent: 88159639 (1989-04-01), None
Angewandte Solarenergie - ASE GmbH
Dennison, Scheiner Schultz & Wakeman
Sterrett Jeffrey
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