Economical Polar-Axis Solar Tracker for a Circular Reflective Dish

Abstract

The most urgent need in the field of solar energy is to lower the final cost per watt of all involved components. Some of the most expensive components within a solar tracker go into the precision drive system which accurately follows the motion of the sun. This invention reduces the complexity and the required number of drive components in a tracker optimized for reflective dishes. With this invention a single drive motor can keep 20 or more large reflective dishes accurately tracking the sun, whereas 40 drive motors with more complex control systems would typically be required for the same number of dishes. In addition this invention allows for complete inversion of the dishes, which helps reduce dust accumulation on the optical surfaces and lowers wind resistance during storms.

1 . A polar-axis solar tracker comprising:
 a) A strong and stable support base capable of aligning a tracker frame in a true North-South direction, and firmly holding it in that alignment.   b) A tracker frame in the shape of a letter “C”; substantially like a 180 degree arc, which owing to its shape can be mounted to the support base at any angle, particularly such that the endpoints of the arc are inclined from the horizontal at an angle equal to the geocentric latitude of the installation site, so that said endpoints are in parallel alignment with the earth's polar (rotational) axis.   c) A polar axle rotatably attached to said endpoints of said tracker frame, which is thereby positioned in parallel alignment with the polar axis of the earth, so that as the earth rotates the polar axle can be rotated in the opposite direction, and thus hold all things mounted on the polar axle in a substantially fixed orientation relative to the sun, despite the rotation of the earth.   d) A dish support member pivotally attached to the center of the polar axle so that it can pivot through declination angles of plus or minus 23.43 degrees (or more) towards said endpoints of the tracker frame, so that a circular reflective dish mounted on said dish support member can follow the sun's seasonal motion above and below the earth's equator.   e) A circular reflective dish supported on one end of said dish support member.   f) A solar energy receiver supported at the other end of said dish support member, positioned substantially at the focal point of said circular reflective dish.   g) A polar axle rotation means, capable of rotating the polar axle and all components attached to it at a rate of one revolution per day.   h) A declination adjustment means, capable of adjusting the pivot angle of the dish support member and all other components attached to it, so as to follow the seasonal motion of the sun.   
     
     
         2 . A polar-axis solar tracker, as defined in  claim 1 , in which said circular reflective dish is slotted or split so as to allow passage and clearance for said polar axle when said dish support member is pivoted through its full range of motion. 
     
     
         3 . A polar-axis solar tracker, as defined in  claim 1 , in which said circular reflective dish is sized and shaped so as not to collide with said tracker frame at any angle of the dish support member pivoting motion, nor any angle of the polar axle rotation. 
     
     
         4 . A polar-axis solar tracker, as defined in  claim 1 , in which said solar energy receiver is sized, shaped and positioned so as not to collide with said tracker frame at any angle of the dish support member pivoting motion, nor any angle of the polar axle rotation. 
     
     
         5 . A polar-axis solar tracker, as defined in  claim 1 , in which said solar energy receiver is positioned and/or weighted such that the pivot point of said dish support member is at or very near the center of mass of the dish assembly, comprising the solar energy receiver, the dish support member and the circular reflective dish, thus making it possible to pivot the dish assembly and rotate the polar axle with a minimum of torque. 
     
     
         6 . A polar-axis solar tracker, as defined in  claim 1 , in which said polar axle rotation means is capable of simultaneously rotating the polar axles of multiple solar trackers at the same time, thus eliminating the need for multiple polar axle rotation means, and thus significantly reducing the cost when installing multiple trackers. 
     
     
         7 . A polar-axis solar tracker, as defined in  claim 1 , in which said polar axle rotation means is a system of one or more cables and pulleys, and hence induces zero backlash, as is commonly caused by gears. 
     
     
         8 . A polar-axis solar tracker, as defined in  claim 1 , in which said polar axle rotation means is a system of cables and pulleys, with tensioning springs positioned periodically between said cables in such a way that the thermal expansion or contraction of said cables is absorbed by the springs, and causes minimal or zero misalignment in the driven polar axles. 
     
     
         9 . A polar-axis solar tracker, as defined in  claim 1 , with provisions for the following fine-tuning adjustments:
 a) fine-tuning adjustment(s) for bringing the support base precisely into level.   b) Horizontal fine-tuning adjustment(s) for bringing the polar axle into alignment with the North-South direction at the installation site.   c) Vertical fine-tuning adjustment(s) for bringing the inclination or slant of the polar axle into alignment with that of the earth's polar (rotational) axis.   d) Rotational fine-tuning mean adjustment(s) to fine-tune the rotational angle of the polar axle relative to that prescribed by said polar axle rotation means, so that when multiple trackers are driven by the same rotation means, each of them can be brought independently into alignment with the direction of the sun.   
     
     
         10 . A polar-axis solar tracker, as defined in  claim 1 , in which said declination adjustment means can optionally be a mechanism which is periodically and manually re-aligned with the sun, thus avoiding the costs of an automated adjustment means, and further reducing the overall costs of the system. 
     
     
         11 . A polar-axis solar tracker, as defined in  claim 1 , in which said polar axle rotation means can be driven so as to completely invert said dish assembly at night, or at other selected occasions, for reduced accumulation of dust on said circular reflective dish, or to better withstand high winds or other potentially harmful situations.