Abstract:
A method and system include a plurality of solar cells and a plurality of voltage controllers. Each of the plurality of solar cells is directly coupled to a dedicated one of the plurality of voltage controllers to form unique pairs of solar cells and voltage controllers. Each of a plurality of panels contain a plurality of unique pairs.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/003,091, filed Nov. 14, 2007, which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Typically, solar panels may have a string of cells connected in series. As shown in  FIG. 1 , panel  100  has a string of cells  101   ab - 101   nn  connected in series. As illustrated, panel  100  is a 9×4 series of cells or slices. Two leads  102   a,b  deliver the series voltage of all the cells together. If one of the cells is defective, shaded, dirty, or otherwise degraded, it can reduce the output performance of the whole panel. 
         [0003]      FIG. 2  shows a typical setup for a solar array system  201 , in which a number of parallel strings of serial panels P 11  to Pnn are used. If some of these panels are in a shaded area, as delineated by line  203   a . . . n,  the performance of the whole array  202   ab - 202   nn  may be undesirably affected. The strings are connected in parallel by lines  204 , which may typically connect to an inverter. 
         [0004]      FIG. 3  shows a solar array system  301  having panels  302   a . . . n,  with each panel having an attached management unit  304   a - n.  Each panel  302   a . . . n  and its associated management unit  304   a - n  are connected in parallel. Each of the management units  304   a - n  converts the voltage of the associated panel to high voltage for transmission on a bus. If a particular panel is shaded or if its performance is degraded by any other factors, this approach can help to limit the undesirable impact to the particular panel that is affected Degradation of the performance of the string, of which the affected panel is a part, can be reduced to some degree. 
         [0005]    Improved efficiency of panels, both by themselves as well as in larger groups, is needed. 
       SUMMARY 
       [0006]    In one of many embodiments of the present invention, a method and system include a plurality of solar cells and a plurality of voltage controllers. Each of the plurality of solar cells is directly coupled to a dedicated one of the plurality of voltage controllers to form unique pairs of solar cells and voltage controllers. Each of a plurality of panels contain a plurality of unique pairs. 
         [0007]    Other features and embodiments of the present invention will be apparent from the accompanying drawings and from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present disclosure is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
           [0009]      FIG. 1  illustrates a conventional panel in accordance with the prior art. 
           [0010]      FIG. 2  illustrates a conventional solar array in accordance with the prior art. 
           [0011]      FIG. 3  illustrates a conventional solar array with panels having associated management units in accordance with the prior art. 
           [0012]      FIG. 4  illustrates a panel in accordance with one embodiment of the present invention. 
           [0013]      FIG. 5   a  illustrates a voltage controller/converter in accordance with one embodiment of the present invention. 
           [0014]      FIG. 5   b  illustrates a voltage controller/converter in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the description. It will be apparent, however, to one skilled in the art that embodiments of the disclosure can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the description. 
         [0016]    Reference in this specification to “one embodiment”, “an embodiment”, “other embodiments”, or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. The appearances of, for example, the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments. 
         [0017]      FIG. 4  shows an exemplary panel  400  in accordance with one embodiment of the present invention. The panel  400  is a 4×9 array of solar cells or slices  401   a . . . n.  Each cell or slice  401   a . . . n  has its own voltage controller/converter (VCC)  402   a . . . n  to provide dc voltage, so each of the cells has power over the whole panel. In one embodiment, the output of the voltage controller/converter (VCC)  402   a . . . n  may be provided as a current source. In another embodiment, the output of the voltage controller/converter (VCC)  402   a . . . n  may be provided as a voltage source. In the case of a current source output, all the panels would provide the same current, but the voltage would vary according to the solar power available to each panel. In the case of a voltage source output, all the panels would provide the same voltage, but the current source would depend on the energy available. In some embodiments, rather than a single cell, two, four, or any other suitable low number of cells can be connected together to one voltage controller/converter (VCC)  402   a . . . n.  The cell to VCC ratio is a tradeoff between cost, efficiency of conversion, and efficiency of the panel. Different slices (cells) and different VCCs can result in a different optimal number of cell to VCC ratio. 
         [0018]      FIGS. 5   a  and  5   b  show two exemplary embodiments of voltage controllers/converters (VCC)  402   a - n  in  FIG. 4  as controller  402   x  and controller  402   y,  respectively. As shown in  FIG. 5   a,  the controller  402   x  is connected with a cell or slice  501 . The controller  402   x  includes an external rectifier  502 , a single chip regulator  503 , a capacitor  504 , and a Schottky diode  505 . Voltage is switched by the single chip regulator  503 , using the external rectifier  502  and the capacitor  504 . The Schottky diode  505  avoids back-flow current. While the Schottky diode  505  is used in one embodiment to improve efficiency, in other embodiments Schottky diode  505  is not used. The single chip regulator  503  and a controller chip  508 , which is discussed below, may be implemented as an integrated chip available from companies such as Maxim, Fairchild, Analog Devices, AnalogicTech, and other vendors who manufacture suitable components. 
         [0019]    As shown in  FIG. 5   b,  the controller  402   y  is connected with a cell or slice  511 . The controller  402   y  includes a rectifier  513 , a transistor  510 , the controller chip  508 , a capacitor  509 , a transistor  507 , a Schottky diode  506 , a capacitor  515 , a resistor  517 , and a resistor  519 . In one embodiment, the transistor  507  and the transistor  510  are p-channel MOSFETs. The controller  402   y  uses synchronous rectification and bucking (switching of a buck converter) with the transistors  507  and  510 , respectively, and the Schottky diode  506 . The controller chip  508  has a sense pin S connected to the input side of the circuit at the inductor  502  allowing it to sense how much current is delivered during the “on” phase of the transistor  510  and therefore to calculate the optimal timing. The capacitor  509  may be used for bootstrapping the chip when started with very low voltage until the output voltage is available and stable. Feedback pin FB can source current from the output side. It can also be used to measure the output voltage and in some cases synchronous rectification. The resistors  517  and  519  act as a voltage divider to set the nominal output voltage. 
         [0020]    Gate control lines G 1  and G 2  control the gate of transistor  510  and the gate of transistor  507 , respectively. They are used to drive the synchronously bucking gate (of transistor  510 ) and rectifier gate controls. Output capacitor  515  is used to keep the voltage stable during bucking. In one embodiment, all of the voltage controllers/converters (VCC)  402   a . . . n  can push a fixed voltage, and the current source could depend on the current of each solar cell available. 
         [0021]    Currently, single chip regulator  503 , as an integrated chip, has been available for very low currents that are measured in the hundreds of milliamps. However, single chip regulator  503  can be used not only for personal electronic devices but also for power generation solar panels. Likewise, in one embodiment, an approach such as that described for the operation of controller chip  508  could be integrated into a full chip, where chopping and synchronous rectifying transistors are integrated as well. 
         [0022]    In one embodiment, rather than a parallel wiring system, a converter, or controller, may be used to generate a preset, given current, and all the converters, or controllers, will be wired in series, as to create a current source, rather than a voltage source. Based on the maximum output power of each cell or group of cells, a open load voltage limit may be applied, as to avoid run-away voltages at low loads. 
         [0023]    In one embodiment, bootstrap charge pumps could be used to increase initial voltage during startup operations. Some precautions can be taken to avoid flow-back current during startup by waiting for stabilization of the bootstrap voltage before turning the main buck converter. In one embodiment, use of push-pull switching or other useful topology for the converter may be used. 
         [0024]    In various embodiments of the present invention, hardwired circuitry may be used in combination with software instructions to implement the techniques. Thus, the techniques are neither limited to any specific combination of hardware circuitry and software nor to any particular source for the instructions executed by the data processing system. 
         [0025]    In the foregoing specification the invention has been described with reference to specific exemplary embodiments thereof. It is clear that many modifications and variations of these embodiments may be made by one skilled in the art without departing from the spirit of the disclosure of the invention. These modifications and variations do not depart from the broader spirit and scope of the invention, and the examples cited here are to be regarded in an illustrative rather than a restrictive sense.