Abstract:
An active tracking solar assembly includes a main actuator cable and a secondary cable having a first end and a second end. The first end is connected to the main actuator cable and the second end is connected to a roof weight. An actuator bar has a counter weight attached to a first end and a first pulley attached to a second end, and the secondary cable engages the first pulley.

Description:
This application claims priority under 35 U.S.C. §119 to Provisional Patent Application No. 60/031,868 entitled: “Counterweighted Active Tracking Solar Panel Rack,” filed on Feb. 27, 2008, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the present invention relate generally to methods and systems for active tracking solar panel racks. 
     DESCRIPTION OF RELATED ART 
     One obstacle in roof-top tracking of solar panels involves the uneven distribution of wind forces inherent to the rigidly connected actuator design. 
     The description herein of disadvantages and deleterious properties associated with known compositions, methods, and systems is in no way intended to limit the scope of the invention to their exclusion. Indeed, embodiments of the invention may include portions of, or one or more known compositions, methods, and systems without suffering from the disadvantages and deleterious properties. 
     SUMMARY OF THE EMBODIMENTS 
     One embodiment of the invention encompasses a counterweighted active tracking solar panel rack. 
     Other objects, features, and characteristics of the present invention will become apparent upon consideration of the following description and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a single row embodiment. 
         FIG. 2  shows a side view of the embodiment shown in  FIG. 1 ). 
         FIG. 3  shows a close up of the mechanical lock assembly of the embodiment shown in  FIG. 1 . 
         FIG. 4  shows a close up of the dampener assembly of the embodiment shown in  FIG. 1 . 
         FIG. 5  shows a close up of the actuator bar of the embodiment shown in  FIG. 1 . 
         FIG. 6  shows a close up of the actuator bar and the two pulleys that link it to the main cable of the embodiment shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of this invention include an apparatus that completely decouples the tilt actuator from the wind design constraints and allows the rack  100  to be designed in very much the same way as a fixed rack. Another embodiment of this invention is a method of decoupling tracker mechanism  104  from wind forces on an array  106 . In addition, each driven row is actuated independently through a common drive unit. Embodiments of the invention use ballasts  605  to guarantee an upper load on an actuator system as depicted in the figures. Wind tunnel data is used to provide moments on each row as a function of row panel area, windspeed, and wind direction. The ballast loads are then tuned to provide positive tracking control up to a chosen wind speed at which point the rack  100  is allowed to blow to a mechanically limited stop position. By designing the actuator  102  in this manner, the wind loads are evenly distributed among the array  106  rather than channeled through the actuator system  102 . The actuator system  102  may be designed to 20 mph wind speeds in a 70 mph wind zone for example. This allows design for a force of about 8% which is 20^2/70^2. 
       FIG. 1  shows a single row model rack  100 . One set up has a spacing of ˜10 feet between adjacent rows and the axis down the center of the square tube runs N-S. The “mechanical lock assembly”  104  and “actuator bar”  108  are seen in the center of the picture and the “dampener assembly” is seen on the right. 
       FIG. 2  shows a side view of the rack  100 . 
       FIG. 3  shows a close-up of the mechanical lock assembly  104 . The mechanical lock assembly  104  is a type of four-bar linkage. Since this rack  100  is designed to “let go” under higher wind speeds (the specific let-go speed is determined in conjunction with the counterweight size), the rack needs a method to constrain the rotation bounds. This unit  104  then transmits all additional force into the local structure providing a distributed roof loading which is very important in a roof-top tracker. It also allows the user to guarantee an upper limit on the actuator loading  102 . 
       FIG. 4  shows the “dampener assembly”  110 . An embodiment uses a modified truck shock  112  that has equal dampening in both extension and compression. However, since this design only uses extension, any standard car shock, or other shock absorber, without gas pre-load would work. 
       FIG. 5  shows the “actuator bar”  108 . The counterweight  605  on one end provides a constant torque around the rack  100  which will tend to always tilt it to one side. This tendency is countered by the actuator  102  setup that will be described later. An important difference between this approach and a “passive tracker” is that the passive tracker relies on a balanced center of gravity, usually refrigerant that is exposed to the sun. This system  100  is positively controlled and will always have a restoring force equal to the counterweight  605  chosen. 
       FIG. 6  shows the actuator bar  108  and the two pulleys  114 ,  116  that link it to the main cable  601 . The way this rack  100  functions is to use a system of two cable types. A main cable  601  runs linearly down the Z channel  118  shown in the photo. This cable  601  will transmit the actuator drive force to each row independently through secondary cables  603  that run through the pulley  114  shown on the end of the actuator bar  108  opposite the counter weight  605 . This cable  603  is then attached to a weight  607  resting on the roof (or protective surface or wear pad). This weight  607  is 2× the counter weight  605  (assuming equal moment arms). The drive of the rack  100  is therefore to always have that weight  607  resting on the roof, but with a tension in the secondary cable  603  equal to that of the counter weight  605 . 
     Under higher winds, one of two things may happen. 1) With a wind blowing into the page, the rack  100  may pick up this weight  607  sitting on the roof until it reaches a mechanically locked position through the “mechanical lock assembly”  104 . 2) With the wind blowing out from the page, the rack  100  may rotate the rack the other way and introduce some slack into the secondary cable  603  attaching the weight  607  on the roof to the main drive cable  601 , until it becomes locked through the mechanical lock assembly  104 . 
     In either of these two conditions, the maximum pull introduced to the main drive cable  601  from the secondary cable  603  of one row is that of the counterweight  605 . Therefore, if there are 50 rows driven by one actuator and each row has a 25 pound counterweight, then an actuator capable of withstanding at least 1250 pounds will be necessary. Since the main cable  601  is the only cable subjected to this force and it is in a straight line down the array  106 , very little structure is required to deal with this loading. The secondary cables  603  in this example would be subjected to no more than roughly 25 pounds. 
     Another important aspect mentioned is that this array  106  is driven independently. All rows will tend to keep the weight on the roof sitting there with 25 pounds tension in their own secondary cables  603 , but each of these rows is driven independently of each other in terms of when they “let go”. It is possible, therefore, to drive each row with a common actuator unit and single main cable  601 , but it is not necessary to design the secondary cables  603  and rack structure for a compounding loading due to the actuator. 
     Finally, the rows are highly dampened to prevent high intermittent winds from interfering with the tracking. The dampener  110  also removes the possibility of the weights  605 ,  607  slamming into the roof or of the rack  100  rotating quickly and breaking when the mechanical lock assembly  104  locks out. 
     The module clamps shown and the square tube to circular housing bushings are parts that are known. The 4″ steep tube is standard. The Z channel  118  and connection posts  120  to attach to the roof are borrowed from a “standard rack” design.