Optical: systems and elements – Mirror – Plural mirrors or reflecting surfaces
Reexamination Certificate
2000-03-20
2001-05-15
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Mirror
Plural mirrors or reflecting surfaces
C359S850000, C359S851000, C126S569000, C126S571000, C126S572000
Reexamination Certificate
active
06231197
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a heliostat used for a sunlight collecting system that utilizes sunlight as energy.
2. Prior Art
For the global environment, the CO
2
problem is so serious that the present social system relying heavily on petroleum energy is a great concern for every country. In this context, as clean energy not affecting the environment, solar energy has attracted much attention. Particularly in countries in desert areas, projects for collecting solar energy to obtain huge energy have proceeded.
Those projects, however, have not gotten good results in performance and costs. The reason is that in order to utilize sunlight as energy, it is required to concentrate sunlight into a point to convert it into thermal energy and then to convert the thermal energy into electricity, in which there is difficulty in controlling heliostats for concentrating the sunlight into the point. The heliostats are arranged in large numbers around a light-collecting point for collecting the sunlight, and their individual concave mirrors are each rotated in both azimuth and altitude directions to reflect and converge the sunlight into the point. Since the above projects have attempted controlling the concave mirror of each heliostat by computer, the controlling is complex and difficult. More specifically, the movement of the sun changes in both azimuth and altitude with time, which fact causes difficulty in controlling the concave mirrors of the heliostats in large numbers simultaneously, pursuing the movement of the sun. Moreover, since the concave mirror of the heliostat has a diameter as large as ten-odd meters, the concave mirror can deform largely in such an area as a desert where the difference in temperature between day and night is large. As a result, the precision of information on a position sent from the concave mirror to the computer is likely to be lowered, which fact also causes difficulty in computer controlling.
The present invention directs its attention to the above prior art technique and provides a heliostat for a sunlight collecting system, a convex mirror of which can be controlled without computer.
SUMMARY OF THE INVENTION
The present invention relates to a heliostat for a sunlight collecting system comprising a concave mirror rotating in both an azimuth direction and an altitude direction to constantly reflect and converge sunlight into a fixed light-collecting point, a driving mechanism for rotating the concave mirror in the azimuth direction and the altitude direction and an azimuth sensor unit and an altitude sensor unit each outputting signals related to the amounts of rotations in the azimuth direction and the altitude direction, respectively, to the driving mechanism wherein, each of the azimuth sensor unit and the altitude sensor unit has a pair of optical sensors disposed along its direction, which pair of optical sensors being disposed toward the sun in the form of a tapered section narrower to the front end and broader to the rear end with their light-receiving surfaces outward, and the azimuth sensor unit and the altitude sensor unit themselves rotate so as to balance the light-receiving amounts of their respective pairs of optical sensors and output signals for rotating the concave mirror in the same directions by half the amounts of the rotations of the azimuth sensor unit and the altitude sensor unit to the drive mechanism.
According to the present invention, each of the azimuth sensor unit and the altitude sensor unit has the pair of optical sensors disposed toward the sun in the form of the tapered section narrower to the front end and broader to the rear end, thereby having a broader sunlight receiving angle and easily detecting the difference in the light-receiving amounts of the pair of optical sensors. The azimuth sensor unit and the altitude sensor unit each constantly rotate so as to face to the direction of the sun, so that the amounts of their rotations agree with the amount of rotation of the sun in diurnal motion. Since the concave mirror reflecting sunlight rotates by half the amounts of the rotations of the azimuth sensor unit and the altitude sensor unit (the amount of the rotation of the sun in diurnal motion) in the same directions, reflected sunlight is constantly directed to the same point. Accordingly, the concave mirror can reflect and converge sunlight constantly into a fixed light-collecting point. Thus, balancing the light-receiving amounts of the pair of optical sensors provides the controlling of the concave mirrors, which is simpler than the computer controlling, causing few errors.
A preferable angle of each optical sensor with respect to the direction of sunlight radiation is 5 to 10 degrees.
It should be noted that the present invention is not limited to the above explanation. The objects, advantages, features and uses of the present invention will be more apparent from the following detailed description in reference to the accompanying drawings. It should be understood that suitable modifications not departing from the spirit of the invention all reside in the scope of the present invention.
REFERENCES:
patent: 5979438 (1999-11-01), Nakamura
patent: 52-10931 (1975-07-01), None
patent: 56-102645 (1981-08-01), None
patent: 56-102646 (1981-08-01), None
patent: 57-63504 (1982-04-01), None
patent: 57-120809 (1982-07-01), None
patent: 59-74460 (1984-04-01), None
McWilliams Matthew P.
Mitaka Kohkico., Ltd.
Pepper Hamilton LLP
Sikder Mohammad
Villacorta Gilberto M.
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