Abstract:
A device consisting of solar photovoltaic cells, a solar activated dc motor, contact brushes and wiring to transfer the electric current to the applied load. The cells are mounted on vanes attached to a central shaft that is made to rotate by the dc motor. The electrical output of the photovoltaic cells is transferred by means of brushes to a stationary contact points wired to the applied load. The device exhibits phase behavior and produces a varying electrical output. By wiring the stationary contact points opposite each other, the output produced is AC electricity. When both ends are wired in the same direction the output is fluctuating do current similar to pulsating DC. The electricity generated can be put through a transformer.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention is directed to a compact device for generating alternating current using solar energy.  
         BACKGROUND OF THE INVENTION  
         [0002]    Present solar generators employ photovoltaic cells that are connected to generate direct current (DC) electricity. For example, U.S. Pat. No. 4,614,879 describes a photovoltaic panel for converting solar energy into electrical energy output having a desired voltage and current and which is connected to a load. Typically, as described in U.S. Pat. No. 4,321,416 solar generator systems comprise an array of photovoltaic cells or modules that are connected in particular series-parallel circuited arrangements to achieved the desired outputs. The DC output can be converted into alternating current (AC) by passing the DC through an inverter such as in the apparatus described in U.S. Pat. No. 4,217,633. Other AC solar generators employ pairs of PN junction solar cells that are connected in antiparallel and a means for directing light alternatively to the PN junctions. (See U.S. Pat. No. 4,577,052.)  
           [0003]    Despite the many advances in AC solar generators such prior art systems exhibit a number of limitations. For one thing, a typical panel produces only approximately 5 to 6 watts per square foot of coverage, which means that extensive surface areas are required to generate enough power for many applications. In addition, standard DC electrical outputs cannot be transformed and therefore cannot be transmitted long distances from the place of generation. Rather, the DC output must first be converted to AC before being put through a transformer to be transported long distances or to be put into the existing electric grid. Finally, a photovoltaic cell&#39;s energy generating capacity depends on its orientation to the sun.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention is directed to a portable device that generates AC electric energy. The device includes a plurality of solar panels that are attached to vanes that are mounted on a rotating shaft that is actuated by a DC motor. As the panels rotate a fluctuating, or alternating, voltage is developed. The output voltage and current vary in a sinusoidal waveform of the light intensity incident on each panel. Specifically, by rotating each vane, the intensity of incident radiation on the panel varies sinusoidally, thereby developing a sinusoidal electrical voltage and current output. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a schematic of the solar electric AC generator;  
         [0006]    [0006]FIG. 2 illustrates the attachment of the vanes to the shaft of the generator;  
         [0007]    [0007]FIGS. 3 and 4 illustrate the attachment of the rotating plates, which include electric contact brushes, onto the edges of the vanes;  
         [0008]    [0008]FIGS. 5 and 6 illustrate stationary contact plates; and  
         [0009]    [0009]FIG. 7 is a cross sectional view of an electric contact device with a point contact. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]    Referring to FIG. 1, the solar alternating current generator  100  includes an actuator  10  which is typically a DC motor that is powered by a battery  12  which in turn can be charged by a solar panel  14 . Motor  10  is attached to shaft  20  onto unto which a set of vanes  22 ,  24 ,  26 , and  28  is attached. The number and configuration of the vanes in each set can vary from one to five or more; two to four vanes are preferred. The configuration of each vane is not critical. The other end of the shaft  20  is connected to a roller bearing ring  16  of shaft support  30 . As is apparent, additional shaft supports with roller bearing rings can be employed if the shaft is very long and/or additional sets of vanes are employed. FIG. 1 illustrates an embodiment in which only one set of vanes is employed, however, it is understood that multiple sets that are preferably positioned in tandem, can be employed. For example, in one embodiment, multiple sets of vanes each set apart from the next and positioned in tandem along a shaft are employed. In this design, intermediate shaft supports with roller bearing rings can be positioned between adjacent sets of vanes to minimize friction and to support the weight of the shaft and vanes.  
         [0011]    Each vane preferably comprises a flat member that is made of a durable, light weight material such as, for example, aluminum, carbon fiber, fiberglass, or plastic. FIG. 1 illustrates an embodiment with 4 vanes that are 90 degrees apart and the vanes are secured to a solid shaft. Although more than 4 vanes can be used, expanding the number of vanes increases the likelihood that solar radiation will be partially or fully intercepted by an adjacent vane before the radiation reaches photovoltaic cells that are attached to a particular vane surface.  
         [0012]    [0012]FIG. 2 is a partial cross sectional view showing two vanes  40  and  46  that are clamped onto solid shaft  44 . Clamp collars  32 ,  42  are positioned on opposite sides of shaft  44 ; the curved contour of the inner surface of each collar matches the round outer surface of the shaft. The collars are secured to the shaft by nuts  33 ,  34  and bolt  43 . Vane  40  is secured between collars  32  and  42  by nuts  50 ,  51 , and bolt  48 ; similarly, vane  46  is secured between the collars by nuts  52 ,  53  and bolt  38 . One or more solar or photovoltaic cells  56  are attached to the outer surfaces of the vanes.  
         [0013]    The term “solar cell” or “photovoltaic cell” is meant to encompass any photovoltaic device or photoelectric transducer that converts solar light energy into DC. Typical solar cells are semiconductor devices. Solar cells are commercially available and are typically packaged as an array or panel of solar cells that are electrically coupled to provide a specified current and voltage outputs depending on the solar radiation intensity. Suitable solar cells are available from ASE Americas, Inc. (Billerica, Mass.). Flexible solar modules that comprise photovoltaic cells adhered onto polymer substrates are available from Iowa Thin Film Technologies, Inc. (Boone, Iowa).  
         [0014]    [0014]FIG. 3 is a partial side view of the right edges of the vanes wherein vanes  22 ,  24 , and  26  are shown. Vane  28  of FIG. 1 (not shown) is positioned opposite vane  24 . As shown, a positive rotating plate  70  is attached to the edges of the vanes. The rotating plate  70  is made of a non-electrically conducting material (i.e. insulative) such as plastic and the rotating plate  70  rotates as shaft  20  is rotated. Mounted on the outer surface of the rotating plate  70  are four contact electric brushes  72 ,  74 ,  76 , and  78 .  
         [0015]    Similarly, FIG. 4 is a partial side view of the left edges of the vanes wherein vanes  22 ,  24 , and  26  are shown; vane  28  of FIG. 1 (not shown) is positioned opposite vane  24 . In addition, a negative rotating plate  90  is attached to the edges of the vanes. The rotating negative plate  90  is made of an electrically insulative material and it rotates as shaft  20  is rotated. Mounted on the outer surface of the rotating plate  90  are four contact electric brushes  92 ,  94 ,  96 , and  98 .  
         [0016]    Instead of using brushes, each electric contact can comprise a spring loaded electric contact point device to electrically connect the photovoltaic cells on the vanes to metal strips located on contacts plates. As shown in FIG. 7, attached to rotating plate  130  is a metal spring  132  that has a metal sphere  134  within the spiral at the distal end of the spring. The proximal end  140  of the spring functions as an electric connector to the photovoltaic cell input (positive or negative terminal), which is further described herein. Both the spring and sphere are constructed of electrically conductive metals or alloys such as steel. Spring  132  is secured in place with sleeve  136  with is made of an electrically insulating material such as hard plastic. The metal sphere is in contact with metal rail or strip  138  which is attached to stationary contact plate  142 , which are further described herein. The metal sphere will rotate about its own axis as the rotating plate turns; the movement of the sphere will reduce the static friction load on the motor shaft. The spring acts as a shock absorber and helps maintain a constant pressure on the sphere thereby facilitating continuous electrical contact to the strip.  
         [0017]    Each of the solar panels on vanes  22 ,  24 ,  26 , and  28  has a positive terminal and a negative terminal that are electrically connected to a contact electric brush or point on the positive and negative rotating plates, respectively. Thus, each of the four solar panels corresponding to the four vanes is electrically connected to individual positive and negative brushes. As an example, the positive and negative terminals of the array of solar cells on vane  22  can be connected to contact electric brushes  72  and  92 , respectively. The positive and negative terminals for the other three arrays on vanes  24 ,  26 , and  28  are similarly connected to the appropriate brushes.  
         [0018]    As further shown in FIG. 1, the solar AC generator also includes frames  60  and  62  which border the right and left edges of the vanes. Mounted on the inner side of frame  60  that faces the vanes is stationary contact plate  64  and mounted on the side of the frame  62  that faces the vanes is stationary contact plate  66 . FIGS. 5 and 6 depict the inner surfaces (facing the vanes) of plates  64  and  66 , respectively. As shown in FIG. 5, the inner surface of contact plate  64  is embedded with four arc-shaped metal strips labeled A+, B+, A− and B−. Similarly, as shown in FIG. 5, the inner surface of contact plate  66  is embedded with four sets arc-shaped metal strips labeled C+, D+, C− and D−.  
         [0019]    Designating the four vanes  22 ,  24 ,  26 , and  28  as vanes A, B, C, and D, respectively, in a preferred embodiment the positive terminal and negative terminal of the array of solar cells attached to vane A are connected to metal strips A+ and A−, respectively. The positive and negative terminals of the arrays attached to vanes B, C, and D are also similarly connected to the appropriate metal strips. As shown in FIG. 5, the positive metal strips and negative metal strips in turn are connected to leads  110  and  112 , respectively. Similarly, as shown in FIG. 6, the positive metal strips and negative metal strips in turn are connected to leads  114  and  116 , respectively. As depicted in FIG. 1, positive leads  110  and  114  are connected to form terminal  122  and negative leads  112  and  116  are connected to form terminal  124 . Terminals  122  and  124  can be connected directly to any device or load that operates on AC.  
         [0020]    To provide protection from the elements, e.g., wind and rain, the solar electric AC generator  100  is preferably enclosed within a transparent protective housing  102  as shown in FIG. 1. Rigid plastic such as acrylic can be used. In addition, a reflective material or mirror  104  can be positioned on the base of the housing under the vane. The reflected radiation is captured by solar cells of the AC generator thereby increasing the efficiency of the AC generator. Because the position of the sun relative to the AC generator changes during the course of the day, the intensity of incident radiation on the panels will also fluctuate. However, the mirror will decrease the level of fluctuation.  
         [0021]    In operation, motor  10  is initially activated with battery  12  to rotate the vanes of the solar AC generating device as shown in FIG. 1. As the array of solar cells in the vanes convert radiation initially into DC, the device provides a current and voltage with a phase behavior which when put through a transformer allows for the generation of the required magnetic flux necessary to transform input current and voltage. Typically, the frequency and magnitude of the power generated are directly proportional to the rotating or angular velocity of the vane. In a preferred embodiment, the solar cells that are mounted on the vanes generated a current (I) output that is in accordance with the following expressions:  
           I=CdV/dt,  where  dV/dt=V ω cos ω  t  and  C =capacitance; and   (i)  
         P=NIV, where P=power, N=number of cells, V=generated voltage, and ω=rotating (angular) velocity of the vane.   (ii)  
         [0022]    As is apparent, the rotating vanes produce a current that fluctuates at a certain frequency. The current is transmitted from the positive contact of the array of cells at the edge of a vane to its corresponding brush on the rotating plate. The current is transmitted from the brush to the metal strips.  
         [0023]    The generated AC electricity can also be fed directly to a transformer or into the power grid. Since the power grid is a 60 Hz system, the solar AC generating device has to generate 60 Hz electricity. In order to do so, the shaft speed of the device would have to be 60 Hz/N, wherein N is the number of panels. Since the number of panels that can be packed onto the shaft in any axial portion is limited, the shaft speed would need to be relatively high. For example, if N is 4, then the shaft would need to rotate 15 times per second. Furthermore, a solar panel may need to be illuminated under a steady state condition prior to its developing its full output, i.e., a rise time. A fast rotation may exceed this rise time. This would result in a steady phase shift of the output waveform during the day. The power grid must be frequency stable, requiring very low tolerance for frequency and phase shifts. Because the solar cells are rotating the orientation to the sun rays will hit a maximum at the point where the sun rays fall at 90 degrees (zenith for device) and a minimum at the opposite side (nadir for the device).  
         [0024]    The device can preferably be wired in two different configurations: (i) one to provide fluctuating (sinusoidal current and voltage) DC, with current going in one direction only and (ii) a second configuration to provide AC, with current cycling in opposite directions.  
         [0025]    Although only preferred embodiments of the invention are specifically disclosed and described above, it will be appreciated that many modifications and variations of the present invention are possible in light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.