Various solar energy collection arrangements have been devised which employ collector panels or reflectors and which are directed at the sun in order to efficiently collect solar energy. Many of the applications of solar tracking systems have been implemented in connection with parabolic reflectors, since proper attitude of parabolic reflector troughs is more critical than is the orientation of flat solar collection panels. Parabolic reflector troughs are generally of uniform cross section and have a concave highly reflective parabolic surface which receives the rays of the sun and reflects this solar radiation into a longitudinally extending concentrator pipe conducting a heat transfer medium and located at the parabolic focus. The reflected solar energy is absorbed in the heat transfer medium, usually a liquid, which flows through the pipe to a heat exchanger.
In prior art systems employing parabolic reflectors, the desirablity of maintaining the trough in proper orientation relative to the position of the sun overhead has been recognized and considerable effort has been directed to implementing workable tracking systems. All conventional systems heretofore employed, however, have been significantly deficient in one or more respects. In the simplest arrangement, where manual orientation is contemplated, the solar collection panels are seldom properly oriented, with the result that energy collection is only occassionally conducted at maximum efficiency. Electromechanical systems have been implemented to maintain proper orientation, but these systems have all involved an inordinate consumption of energy in the process. For example, one and three quarter horsepower motors have been employed to rotate reflector dishes or troughs of conventional solar collection systems. The amount of energy necessary to effectuate rotation detracts significantly from the net energy output achieved using conventional solar collection systems of this type.
In all of the foregoing prior art systems, some positive drive system has been necessary to alter the orientation of the collector. That is, it has heretofore been necessary to drive some mass to effectuate rotation of the collector during the daylight hours in order to maintain proper collector orientation toward the sun. The energy expended in this manner has seriously detracted from the overall benefits to be gained by solar tracking. That is, such collector systems tend to utilize a significant portion of their increased energy output for their own operation, and hence do not significantly improve the net energy output as productive solar energy. The required energy consumption is aggravated with increased size of collector systems which are necessary in order to provide a sufficient energy output to justify the initial cost of maintenance of a solar energy collection system.
In the aforesaid U.S. Pat. Application Ser. No. 744,290, a system of much greater simplicity was implemented. The embodiment depicted in that application involves the lateral movement of a counterweight relative to the rotational axis of a solar collection device to tilt the collector to a controlled degree. That is prior to solar noon, the counterweight is laterally offset from the axis of rotation to tilt the collector toward the east. At solar noon the counterweight is positioned in a vertical plane passing through the center of gravity and the rotational axis of the collector. After solar noon the counterweight is offset from the axis of rotation to tilt the solar collector toward the west. While this arrangement is quite advantageous in overcoming the defects of the prior art, the present invention represents an even greater improvement.
It is an object of the present invention to provide a solar energy tracking arrangement which does not require the movement of a mass of a magnitude proportional to the mass of the solar collector. Rather, the present invention relies upon the force of gravity to effectuate rotation of the collector to maintain proper orientation toward the sun. Energy consumption during the daylight hours only occurs incident to the release of a locking system which opposes the force of gravity. The release mechanism, however, may be a very lightweight device and does not depend in any way upon the mass of the system to be controlled. Preferably, control of the tracking system is achieved by merely withdrawing a pawl from a ratchet gear for a short interval to allow the collector to rotate slightly. An alternative form of the invention involves momentarily disabling an electric brake which otherwise prevents rotation of the collector. In any form of the invention, rotation of the collector results the force of gravity acting upon it. After sunset when the collector no longer is able to receive solar energy, it may either be manually reset to an initial starting position from which it will begin progressing at sunrise, or it may be driven by a very low power motor through a high gear ration, since repositioning of the collector need not be completed before dawn.
A particularly advantageous feature of the invention is its application to flat plate collectors. Previously, tracking systems had not generally been applied to flat plate collectors because any increase in efficiency resulting from a tracking system applied to flat plate collectors could not be justified by the expense of the tracking system. However, it has been found that an overall increase in efficiency of 30 percent is to be expected by applying the present invention to a flat plate solar energy collection panel system. That is, by employing the tracking system of the present invention the number of flat plate solar collection panels that are required to produce a given energy output is decreased by 30 percent. Furthermore, because of the simplicity of the tracking system of the present invention, tracking with flat plate collectors can be achieved without modification of the collector panels themselves and with a minimal investment for a tracking system.
A further object of the invention, especially as applied to flat plate collectors, is to obtain an advantage in facilitating maintenance. In conventional systems, rectangular collectors are packed side by side in a fixed rectilinear array. Consequently, a defect in an interiorally located flat plate collector panel is extremely difficult to reach and service. Using the tracking and orientation system of the present invention, however, the panels need merely be tilted on edge to provide a passageway for access to service, repair and replace interiorally located panels.
A further feature of the invention is the tandem interconnection of collectors in which the rotation of one collector can be transmitted to induce a uniform rotation in all of the collectors using a single rotation restraint applied to a single collector.
A result of utilization of the invention is that the increase in efficiency in a flat plate solar energy collection system achieves a critical goal which is necessary for the application of solar energy to refrigeration. In order to be able to refrigerate to any commercially meaningful degree, temperatures of at least 212.degree. F. must be achieved for a significant refrigerating effect to occur. Conventional flat plate collector systems in stationary arrays are able to achieve consistent temperatures of only about 180.degree. F. However, by implementing the tracking system of the present invention, temperatures in excess of 212.degree. F. may be achieved using flat plate collector systems. This opens up the entire range of cooling applications to implementation by solar energy. This is especially significant since in those areas where the ground surface availability of solar energy is greatest, such as in desert areas, the requirement for air conditioning and other refrigeration is especially great. By increasing the energy collection of solar energy by thirty percent, as is possible using the present invention, the available output in refrigeration capacity of flat plate collector systems is increased by 50 percent during the solar cycle. Thus, not only does the present invention achieve a raw increase in efficiency in solar energy collection, it also expands the efficiency of energy utilization in refrigeration by an even greater percentage.
The effect of increased efficiency in solar energy collection achieved by the present invention utilizing flat plate collectors may be numerically determined by considering the amount of energy lost in flat plate solar panels that are oriented at other than perpendicular incidence to solar radiation. At an angle of 10.degree. relative to normal incidence, there is an energy collection loss of 1 1/2%. At 15.degree. this loss increases to 3 1/2% while at 20.degree. and 25.degree. the losses are 6% and 9 1/2% respectively. It can thus be seen that in conventional flat plate collector systems the efficiency of solar energy collection is less than 90% throughout the greater portion of the solar day with the exception of that time period between 10 am and 4 pm. Since this maximum efficiency period encompasses only four hours out of a 10 hour solar day, and since the present invention increases collection efficiency to over 90% throughout the entire solar day, the magnitude of the advance achieved through the present invention may be appreciated.