Inexpensive bi-axial sun tracker for solar concentrators

Abstract

A relatively simple, inexpensive, and easily manufactured device for accurately tracking the daily and seasonal movement of the sun anywhere, and in any climate, without the need for human and/or computer intervention. This sun tracker can be made to any size, out of common materials, and using standard assembly line techniques. Said sun tracker can be installed for any application by an unskilled person. Once installed, it will use a simple electro-mechanical configuration instead of a complex mechanical or costly computer control, as all prior art required.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

PPA filed Sep. 18, 2009 Ser. No. 61/277,014

FEDERALLY SPONSORED RESEARCH

NONE

SEQUENCE LISTING

NONE

BACKGROUND

This application relates to sun trackers, which are used to increase the output of solar cells. The idea of producing electricity from the sun has been around for over one hundred years. While the efficiencies of solar cells continue to rise, they remain costly to produce. Recently, an attempt has been made to lower the cost of solar power by concentrating the sun's rays onto a solar collector. This concentrated sunlight can then be either converted directly into electricity by a solar cell, or be used to boil water and drive a turbine. This, however, presents a new challenge. For solar concentrators to work, some means of accurately tracking the sun must be employed. Unfortunately, all known methods compromise cost, accuracy, and complexity.

For example, U.S. Pat. No. 4,027,651 to Ronald W. Robbins, Jr. (1977) uses an opaque divider between two sets of liquid-filled coils. Whichever set received more radiation gets hotter, the liquid boils, and the solar cells move in that direction. Although simple, it could not deliver a high degree of accuracy because of the large temperature difference needed. Also, it could not be used in extreme climates. Other methods provide more accuracy, but tend to me complex and costly. U.S. Pat. No. 5,600,124 to Alexander Berger (1997) was able to bypass air temperature problems, but needed a complex mechanical drive to operate. For large scale energy production, fields of mirrors have been used to concentrate sunlight onto a solar tower. The concentrated light boiled water and drove a turbine. However, every individual mirror needed its own precise path, which was controlled by a complex and costly computer program.

The cost of fossil fuels continues to rise, and easy sources are becoming harder to find. We are already running out of options other than to extract them from environmentally and politically sensitive areas. Unless a practical alternative is found and utilized soon, widespread habitat destruction and political confrontations(wars) are likely in these areas. Every day, enough sunlight strikes the earth's surface to supply mankind's energy needs for hundreds of years. Clearly, an effective means of harnessing the sun's extreme power is needed.

SUMMARY

A simple, portable, low-cost, and user-friendly device for accurately tracking the sun. It uses no exotic materials, and can be used anywhere. It can be made to a wide range of sizes, suiting virtually any demand.

The daily movement of the sun is sensed by individual cells which are arranged in a semi-circular pattern. Each cell contains a simple device that senses the temperature difference between sun and shade. When a cell is activated by sunlight, it closes an electrical circuit to rotate a solar concentrator from east to west. The seasonal movement of the sun from high to low in the sky is sensed by a separate device on the same unit. This sensor operate on the same principle as the beforementioned cells, except that it rotates up and down with the seasonal sun and keeps the solar concentrator at the same angle

The sun tracker uses a simple electro-mechanical system of rotating wheels and electrical contacts, eliminating the need for an operator or computer system while providing a high degree of accuracy. This sun tracker can also be made on an assembly line using common materials and techniques, making it available to the general population.

DRAWINGS

FIG. 1A is a side cross-section view of a Solar Responsive Cell, which is used to track the sun on its daily movement from east to west.

FIG. 1B is a top view of an SRC

FIG. 1C is a top view of the inner workings of an SRC

FIG. 1D is a front cross-section view of an SRC

FIG. 2A is a side cross-section view of a Sun Angle Sensor, showing its inner workings and outside electrical contacts

FIG. 2B is a front cross-section view of the SAS

FIG. 2C is a side view of an SRC adjacent to the SAS, showing metal plates

FIG. 3 shows entire tracking unit, with SRC mounts and SAS in place

FIG. 4A is a side view of concentrator assembly

FIG. 4B is a top view of concentrator assembly base, showing electrical contacts and motor

FIG. 4C is a bottom view of heavy-duty wheel to which solar concentrator is mounted

FIG. 4D is a top view of concentrator assembly

FIG. 4E is an enlarged top view of seasonal motor, seasonal gear, and control rod

FIG. 4F is a view of seasonal motor without seasonal gear, showing its electrical contact

FIG. 5 shows the electrical diagram for sun tracker

DRAWINGS

Reference Numerals

10	solar responsive cell	11	SRC black strip	12	SRC bare strip
13	SRC electrical contact	14	SRC housing	15	slit
16	SRC supports	17	shading shelf	18	rails
200	sun angle sensor	201	SAS black strips	202	SAS bare strips
203	SAS strip contacts	204	SAS housing	205	lens
206	SAS supports	207	axle stud	208	gear
209	SAS motor	210	SAS contacts	211	adjacent SRC plates
30	disk	31	rod	32	column
33	hex nut	34	SRC mounts	401	base
402	base contacts	403	base motor	404	wheel
405	wheel plates	407	hinge	408	solar concentrator
409	seasonal motor	410	seasonal gear	411	control rod
412	seasonal gear contacts	413	seasonal motor contact
50a, b, c, d	rechargeable batteries

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1A shows two identical bi-metallic strips placed side by side. Both are bent to form a long U-shape. The top half of one is painted black(11), and the other is left bare(12). Said bare strip has an electrical contact(13) that extends toward and just below the end of said black strip.

These two bi-metallic strips are encased inside of a housing(14) that completely encases them, except for a slit(15) in the top(FIG. 1B). Said slit is parallel to said black strip and runs across the top of said housing. Both said strips are attached to supports(16) underneath them so that the tops of said strips are immobilized, while their bottoms are free to move up and down. Said slit is covered by a transparent material, such as glass or plastic.

FIG. 1C shows a shelf(17) that extends from the side of said housing that completely shades said bare strip so that it cannot be seen through the slit at any angle. The entire top half of said black strip can be seen through slit. Said housing has two long rails(18, FIG. 1D) extending along either side of the bottom so that it can be attached to a mount(34) on a tracking unit. Said housing containing said black and bare strips shall be referred to as a Solar Responsive Cell, or SRC(10).

FIG. 2A shows a modified SRC. Four bi-metallic strips are bent into a U-shape and set side by side in the same way as the beforementioned SRC strips. The middle two said strips(201) are painted black, while the outside two(202) are bare. Each bare strip has an electrical contact(203) extending toward and just below adjacent black strip. There is a housing(204) around these four strips, just like in said SRC. The top of said housing has a lens(205) positioned so that the focal point is in the space between the tops of said black strips. The width of the area of concentrated sunlight in the space between said black strips is no greater that the width of the space itself. As in said SRC, all said strips have a support(206) underneath their top halves. This unit shall be referred to as a Sun Angle Sensor, or SAS(200).

At the center of each side of SAS housing perpendicular to SAS strips there is an axle stud(207) which sticks out from unit. Underneath SAS is a toothed gear(208) which covers no less that 47 degrees of arc, and centers on a line drawn between said axle studs. Said gear is perpendicular to direction of said SAS strips. There is a motor(209) underneath said gear which rotates very slowly.

On one side of the SAS that has an axle stud, there is a series of electrical contacts(210) which are arranged in a semicircle. Said semicircle takes up 47 degrees of arc and all contacts are equidistant from said axle stud. FIG. 2C shows the side of an SRC which shall be adjacent to said SAS on the side with the contacts. There are two metal plates(211) that are identical to each other and take up the same arc as the beforementioned SAS contacts. There is a gap between said plates which is equal to the width of two SAS contacts.

FIG. 3 shows the complete tracking unit. There are many SRC mounts arranged in a semicircle on the outside of a disk(30). Said disk is bisected vertically and the SAS is placed between the two halves, facing up. Said SAS rotates on its axle studs. At the center of each of the inside surfaces, there is a hole. A rod(31) runs between said disk halves and into both holes. Said rod is supported by a column(32) which goes into the ground. Said rod is fixed to column so that it cannot rotate in relation to the column. Between said column and said disk halves, said rod is threaded and a hexagonal nut(33) is placed on both sides of the rod.

FIG. 4A shows the concentrator assembly. The assembly begins with a circular base(401). In the center of said base there is a hole into which a slowly rotating motor(403) is placed. This motor shall be referred to as the base motor. Its axle is perpendicular to the base and points upward. A heavy-duty wheel(404) is mounted on the axle of said base motor. Heavy-duty wheel shall be referred to simply as the wheel. There is a hinge(407) attached to the outside of said wheel which rotates on an axis tangent to said wheel. Solar concentrator(408) is attached to said hinge so that it can rotate no less that 23.5 degrees in both directions. There is another motor(409) which sits on its side on top of wheel this motor shall be referred to as the seasonal motor. The axle of said seasonal motor is parallel to solar concentrator. There is a seasonal gear(410) which is set vertically, perpendicular to solar concentrator, and intersects with a small gear on the axle of seasonal motor. At the top of seasonal gear there is a hole into which a control rod(411) is riveted. Said rod is then attached to a point on solar concentrator so that rod is parallel to wheel. Said rod is not fixed at either end and remains parallel to wheel when concentrator and seasonal gear are rotated back and forth. There are electrical contacts(412) along 23.5 degrees of seasonal gear on either side of the point which is in contact with seasonal motor axle when the solar concentrator is perpendicular to wheel. There is one electrical contact(413) on seasonal motor which is the same width as each seasonal gear contact.

FIG. 4B shows the top of said base. There is a series of electrical contacts(402) arranged in a complete circle around said base. There are as many contacts as the maximum number of SRC's the tracking unit can accommodate. FIG. 4C shows the underside of said wheel. There are two identical metal plates(405) which completely encircle wheel except for a gap between them on both ends. These gaps are slightly wider than one base contact, and a line drawn through the center of the wheel and the centers of the gaps is parallel to beforementioned rod.

FIG. 5 shows the electrical wiring of the preferred embodiment. Four rechargeable batteries(50a,b,c,d) supply the power for the system. Said batteries shall be labeled A, B, C, and D. the positive terminal on battery A is wired to one terminal on base motor. The negative terminal on battery A is wired to each SRC bare strip. The positive terminal on battery B is wired to the base motor terminal not beforementioned. The negative terminal on battery B is wired to the negative terminal on battery A. Each SRC black strip is wired to one contact on base of solar concentrator. The next SRC black strip going west is wired to the next base contact going counterclockwise (clockwise if unit is being used in southern hemisphere), and so on. One wheel plate is wired to terminal on base motor; the other wheel plate is wired to the other base motor terminal.

The positive terminal on battery C is wired to one bare strip on SAS and one terminal on seasonal motor. The negative terminal on battery C is wired to one terminal on SAS motor an done plate on adjacent SRC. The positive terminal on battery D is wired to SAS bare strip not beforementioned. The negative terminal on battery D is wired to positive terminal on battery C and SAS motor terminal not beforementioned. Each SAS contact is wired to a corresponding contact on seasonal gear seasonal motor contact is wired to seasonal motor terminal not beforementioned.

OPERATION OF THE PREFERRED EMBODIMENT

Tracking unit is placed with the SAS pointing directly upward, and SAS studs point due east/west. Entire unit is then rotated, with SAS moving towards the earth's equator, the number of degrees as the latitude unit is being used at. For example, let's assume the sun tracker is being used in the District of Columbia, latitude 38.85° N. Looking east, tracking unit will be rotated clockwise from vertical just short of 39 degrees. Unit is then locked in place by tightening the hex nuts on supporting rod. Then SRC's are placed onto the unit so that they cover at least as much as fifteen degrees for every hour of sunlight on the summer solstice. Thus, in D.C., enough SRC's will be placed on the unit to cover 255 degrees for fifteen hours of daylight. SAS is then adjusted so that light beam falls between SAS black strips.

Concentrator assembly is then mounted so that the plane of the wheel is at the same angle to the ground as the tracking unit. A line drawn from the center of said wheel through the center of a wheel contact would point to the same point in space as a line drawn from the center of tracking unit through the center of said wheel contact's corresponding SRC. Concentrator assembly is mounted far enough off of the ground or other supporting structure so that concentrator assembly can rotate 360 degrees and solar concentrator can rotate 23.5 degrees up and down without hitting any solid object. Electrical wiring is then completed to the batteries. As this is done, electricity will run through SAS circuit and move concentrator so that it is at the same angle as the sun. If the sun is not shining already, when it does so next, it will shine on the black strip in one SRC. The strip will absorb radiation, heat up, and bend due to its bi-metallic nature. When it has bent enough to tough the contact on the bare strip beside it, an electrical circuit is completed through the SRC, its corresponding base contact, wheel plate, and base motor. Concentrator assembly then rotates until the gap between the two plates is centered above the energized base contact. Circuit is broken, and the solar concentrator is now pointed directly at the sun.

As the sun moves from east to west, its light will move off of the black strip it was before shining on. The sun will now be in direct alignment with the next SRC black strip going west, and an electrical circuit is completed through the next base contact. Concentrator assembly rotates until gap between plates is aligned with the newly energized base contact and stops. If the sun has not been shining for at least twelve hours, as is the case with a winter night or a considerably cloudy summer day, the energized base contact will then be touching the other wheel plate. The circuit through this plate is wired so that electricity flows the opposite way through base motor. Concentrator assembly will then move from west to east because that would be the shorter path to realignment with the sun. as the weeks go by, the sun will change its angle with the horizon. As the noon sun gets lower or higher in the sky, the beam shining through the lens in the SAS will move onto one of the black strips. When enough light is shining on this black strip, it will heat up and tough the contact on the bare strip beside it. An electrical current is completed through the SAS motor, and SAS slowly rotates in the direction of the sun. As SAS rotates, sunlight moves off of the strip it was shining on. Strip cools down, breaks the circuit, and SAS stops. As SAS rotates, its contacts move along the adjacent SRC strips. When SAS has moved enough so that the SAS contact which corresponds to the seasonal gear contact touching the seasonal motor contact now touches an SRC plate, an electrical circuit is completed through the seasonal motor. Concentrator will move vertically until the newly energized seasonal gear contact moves off of the seasonal motor contact. Circuit is broken, and solar concentrator is now seasonally adjusted.

When the sun reaches a solstice and moves in the opposite seasonal direction, the SAS black strip not beforementioned will receive the radiation, heat up, and close a circuit in which electricity flows in the opposite direction through the SAS motor. SAS moves in opposite direction, as does the concentrator.

CONCLUSION, RAMIFICATIONS, AND SCOPE

As can be seen, at least one embodiment of this sun tracker provides accurate tracking of the sun on a daily as well as a seasonal basis without the need for an operator, complex mechanical, or costly computer control. No device currently in existence can accomplish this. It can be used in any climate, anywhere on Earth. With simple modifications to the lengths of the tops of the SRC's, this sun tracker can even be used on extra-terrestrial surfaces. Also, one tracking unit can be wired in parallel to a virtually unlimited number of concentrators, further simplifying use.

Although my description and drawings contain many things, many are irrelevant to the specific technology I have invented. They only show one way of using it, and therefore should not be used to limit the scope. My invention should be defined by the following claims, and not by the preceding description. For example, contained fluids may be used instead of bi-metallic strips. The tracking unit may be immobilized by clips instead of nuts. Concentrating lenses may be used in the SRC gaps to further increase accuracy.

Claims

1. A device containing pairs of temperature sensors, one shaded and the other exposed to light, arranged in a circular pattern to track the sun for a solar collector by:

a. Detecting a temperature difference between said sensors and inducing an electrical current which moves said solar collector, and

b. Stopping said electrical current when said solar collector is pointing directly at said sun.